cannot execute any commands after executing git log. #1629
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FWIW I will address a part of this issue through resolving #1491, but in a way that you probably do not expect: Ctrl+C will no longer quit the pager. You will have to press q to quit the pager; pressing Ctrl+C will only terminate the Git process feeding the pager. |
dscho
added a commit
to git-for-windows/msys2-runtime
that referenced
this issue
Apr 23, 2018
This thing again... Background: when you hit Ctrl+C on Linux or macOS, a signal (SIGINT) is sent to the foreground process and its child processes. This signal can be intercepted by installing a signal handler for this specific signal. On Windows, there is no precise equivalent for this system. Instead, the Ctrl+C is translated by the current ConHost (i.e. the container running the Console processes) to a ConsoleCtrl event that is sent to all processes attached to that Console. If any of these processes installed a handler via SetConsoleCtrlHandler(), they can intercept that event (and avoid exiting or doing some cleanup work). On Linux and macOS (and every Unix flavor, really), processes can also be killed via the `kill` executable, which really just sends a signal to the process, typically SIGTERM. Processes can intercept that signal, too. To force processes to terminate, without giving them any chance to prevent that, SIGKILL can be sent. There is no equivalent for SIGTERM on Windows. To emulate SIGKILL on Windows, TerminateProcess() can be used, but it only kills one process (unlike SIGKILL, which is sent also to the child processes). In Git for Windows, we struggled with emulating SIGINT, SIGTERM and SIGKILL handling essentially since the beginning of the efforts to port Git to Windows. At least the SIGINT part of the problem becomes a lot worse when using a terminal window other than cmd.exe's: as long as using cmd.exe (AKA "ConHost"), Ctrl+C is handled entirely outside of our code. But with the big jump from v1.x to v2.x, Git for Windows not only switched from MSys to MSYS2, but also started using MinTTY as the default terminal window, which uses the MSYS2 runtime-provided pseudo terminals (inherited from Cygwin thanks to the MSYS2 runtime being a "friendly fork" of Cygwin). When Ctrl+C is pressed in MinTTY, all of the signaling has to be done by our code. The original code to handle Ctrl+C comes straight from Cygwin. It simply ignores the entire conundrum for non-Cygwin processes and simply calls TerminateProcess() on them, leaving spawned child processes running. The first attempt at fixing "the Ctrl+C problem" (with the symptom that interrupting `git clone ...` would not stop the actual download of the Git objects that was still running in a child process) was c4ba4e3357f. It simply enumerated all the processes' process IDs and parent process IDs and extracted the tree of (possibly transitive) child processes of the process to kill, then called TerminateProcess() on them. This solved the problem with interrupting `git clone`, but it did not address the problem that Git typically wants to "clean up" when being interrupted. In particular, Git installs atexit() and signal handlers to remove .lock files. The most common symptom was that a stale .git/index.lock file was still present after interrupting a Git process. Based on the idea presented in Dr Dobb's Journal in the article "A Safer Alternative to TerminateProcess()" by Andrew Tucker (July 1, 1999) http://www.drdobbs.com/a-safer-alternative-to-terminateprocess/184416547 we changed our handling to inject a remote thread calling ExitProcess() first, and fall back to TerminateProcess() the process tree instead: e9cb332976c This change was a little misguided in hindsight, as it only called TerminateProcess() on the process tree, but expected the atexit() handler of Git to take care of the child processes when killing the process via the remote ExitProcess() method. Therefore, we changed the strategy once again, to inject ExitProcess() threads into the child processes of the process to kill, too: 53e5c0313e1 (That commit also tries to handle Cygwin process among the child processes by sending Cygwin signals, but unfortunately that part of the commit was buggy.) This worked well for Git processes. However, Git Bash is used in all kinds of circumstances, including launching Maven, or node.js scripts that want to intercept SIGINT. Naturally, these callees have no idea that Git for Windows injects an ExitProcess() with exit code 130 (corresponding to 0x100 + SIGINT). Therefore, they never "got" the signal. So what is it that happens when ConHost generates a ConsoleCtrl event? This question was asked and answered in the excellent blog post at: http://stanislavs.org/stopping-command-line-applications-programatically-with-ctrl-c-events-from-net/#comment-2880 Essentially, the same happens as what we did with ExitProcess(): a remote thread gets injected, with the event type as parameter. Of course it is not ExitProcess() that is called, but CtrlRoutine(). This function lives in kernel32.dll, too, but it is not exported, i.e. GetProcAddress() won't find it. The trick proposed in the blog post (to send a test ConsoleCtrl event to the process itself, using a special handler that then inspects the stack trace to figure out the address of the caller) does not work for us, however: it would send a CTRL_BREAK_EVENT to *all* processes attached to the same Console, essentially killing MinTTY. But could we make this still work somehow? Yes, we could. We came up with yet another trick up our sleeves: instead of determining the address of kernel32!CtrlRoutine in our own process, we spawn a new one, with a new Console, to avoid killing MinTTY. To do that, we need a helper .exe, of course, which we put into /usr/libexec/. If this helper is not found, we fall back to the previous methods of injecting ExitProcess() or calling TerminateProcess(). This method (to spawn a helper .exe) has a further incidental benefit: by compiling 32-bit *and* 64-bit helpers and providing them as getprocaddr32.exe and getprocaddr64.exe, we can now also handle 32-bit processes in a 64-bit Git for Windows. Sadly not vice versa: calling CreateRemoteThread() on a 64-bit process from a 32-bit process seems to fail all the time (and require a lot of assembly hackery to fix that I am not really willing to include in Git for Windows' MSYS2 runtime). The current method was implemented in this commit: ca6188a7520 This is the hopeful final fix for git-for-windows/git#1491, git-for-windows/git#1470, git-for-windows/git#1248, git-for-windows/git#1239, git-for-windows/git#227, git-for-windows/git#1553, nodejs/node#16103, and plenty other tickets that petered out mostly due to a willingness of community members to leave all the hard work to a single, already overworked person. This fix also partially helps git-for-windows/git#1629 (only partially because the user wanted to quit the pager using Ctrl+C, which is not the intended consequence of a Ctrl+C: it should stop the Git process, but not the pager). Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
dscho
added a commit
to git-for-windows/MSYS2-packages
that referenced
this issue
Apr 23, 2018
This thing again... Background: when you hit Ctrl+C on Linux or macOS, a signal (SIGINT) is sent to the foreground process and its child processes. This signal can be intercepted by installing a signal handler for this specific signal. On Windows, there is no precise equivalent for this system. Instead, the Ctrl+C is translated by the current ConHost (i.e. the container running the Console processes) to a ConsoleCtrl event that is sent to all processes attached to that Console. If any of these processes installed a handler via SetConsoleCtrlHandler(), they can intercept that event (and avoid exiting or doing some cleanup work). On Linux and macOS (and every Unix flavor, really), processes can also be killed via the `kill` executable, which really just sends a signal to the process, typically SIGTERM. Processes can intercept that signal, too. To force processes to terminate, without giving them any chance to prevent that, SIGKILL can be sent. There is no equivalent for SIGTERM on Windows. To emulate SIGKILL on Windows, TerminateProcess() can be used, but it only kills one process (unlike SIGKILL, which is sent also to the child processes). In Git for Windows, we struggled with emulating SIGINT, SIGTERM and SIGKILL handling essentially since the beginning of the efforts to port Git to Windows. At least the SIGINT part of the problem becomes a lot worse when using a terminal window other than cmd.exe's: as long as using cmd.exe (AKA "ConHost"), Ctrl+C is handled entirely outside of our code. But with the big jump from v1.x to v2.x, Git for Windows not only switched from MSys to MSYS2, but also started using MinTTY as the default terminal window, which uses the MSYS2 runtime-provided pseudo terminals (inherited from Cygwin thanks to the MSYS2 runtime being a "friendly fork" of Cygwin). When Ctrl+C is pressed in MinTTY, all of the signaling has to be done by our code. The original code to handle Ctrl+C comes straight from Cygwin. It simply ignores the entire conundrum for non-Cygwin processes and simply calls TerminateProcess() on them, leaving spawned child processes running. The first attempt at fixing "the Ctrl+C problem" (with the symptom that interrupting `git clone ...` would not stop the actual download of the Git objects that was still running in a child process) was git-for-windows/msys2-runtime@c4ba4e3357f. It simply enumerated all the processes' process IDs and parent process IDs and extracted the tree of (possibly transitive) child processes of the process to kill, then called TerminateProcess() on them. This solved the problem with interrupting `git clone`, but it did not address the problem that Git typically wants to "clean up" when being interrupted. In particular, Git installs atexit() and signal handlers to remove .lock files. The most common symptom was that a stale .git/index.lock file was still present after interrupting a Git process. Based on the idea presented in Dr Dobb's Journal in the article "A Safer Alternative to TerminateProcess()" by Andrew Tucker (July 1, 1999) http://www.drdobbs.com/a-safer-alternative-to-terminateprocess/184416547 we changed our handling to inject a remote thread calling ExitProcess() first, and fall back to TerminateProcess() the process tree instead: git-for-windows/msys2-runtime@e9cb332976c This change was a little misguided in hindsight, as it only called TerminateProcess() on the process tree, but expected the atexit() handler of Git to take care of the child processes when killing the process via the remote ExitProcess() method. Therefore, we changed the strategy once again, to inject ExitProcess() threads into the child processes of the process to kill, too: git-for-windows/msys2-runtime@53e5c0313e1 (That commit also tries to handle Cygwin process among the child processes by sending Cygwin signals, but unfortunately that part of the commit was buggy.) This worked well for Git processes. However, Git Bash is used in all kinds of circumstances, including launching Maven, or node.js scripts that want to intercept SIGINT. Naturally, these callees have no idea that Git for Windows injects an ExitProcess() with exit code 130 (corresponding to 0x100 + SIGINT). Therefore, they never "got" the signal. So what is it that happens when ConHost generates a ConsoleCtrl event? This question was asked and answered in the excellent blog post at: http://stanislavs.org/stopping-command-line-applications-programatically-with-ctrl-c-events-from-net/#comment-2880 Essentially, the same happens as what we did with ExitProcess(): a remote thread gets injected, with the event type as parameter. Of course it is not ExitProcess() that is called, but CtrlRoutine(). This function lives in kernel32.dll, too, but it is not exported, i.e. GetProcAddress() won't find it. The trick proposed in the blog post (to send a test ConsoleCtrl event to the process itself, using a special handler that then inspects the stack trace to figure out the address of the caller) does not work for us, however: it would send a CTRL_BREAK_EVENT to *all* processes attached to the same Console, essentially killing MinTTY. But could we make this still work somehow? Yes, we could. We came up with yet another trick up our sleeves: instead of determining the address of kernel32!CtrlRoutine in our own process, we spawn a new one, with a new Console, to avoid killing MinTTY. To do that, we need a helper .exe, of course, which we put into /usr/libexec/. If this helper is not found, we fall back to the previous methods of injecting ExitProcess() or calling TerminateProcess(). This method (to spawn a helper .exe) has a further incidental benefit: by compiling 32-bit *and* 64-bit helpers and providing them as getprocaddr32.exe and getprocaddr64.exe, we can now also handle 32-bit processes in a 64-bit Git for Windows. Sadly not vice versa: calling CreateRemoteThread() on a 64-bit process from a 32-bit process seems to fail all the time (and require a lot of assembly hackery to fix that I am not really willing to include in Git for Windows' MSYS2 runtime). The current method was implemented in this commit: git-for-windows/msys2-runtime@ca6188a7520 This is the hopeful final fix for git-for-windows/git#1491, git-for-windows/git#1470, git-for-windows/git#1248, git-for-windows/git#1239, git-for-windows/git#227, git-for-windows/git#1553, nodejs/node#16103, and plenty other tickets that petered out mostly due to a willingness of community members to leave all the hard work to a single, already overworked person. This fix also partially helps git-for-windows/git#1629 (only partially because the user wanted to quit the pager using Ctrl+C, which is not the intended consequence of a Ctrl+C: it should stop the Git process, but not the pager). Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
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@vaibhavagrawal2912, As dscho noted, you do need to know that these unix/linux tools such as the pager, will need the special key combinations such as "q" to quit them, and that Ctrl-C means different things in the two (linux/Windows) environments. That said, the question is, How/where would you have found that out? It's a common problem, so if you are able to suggest how folks should be informed of the conventions, (ideally without annoying those who heve learnt them), that would be useful, as this issue does recur, and I'm always seeking ways of reducing these frictions. Any suggestions would be considered. |
dscho
added a commit
to git-for-windows/msys2-runtime
that referenced
this issue
Nov 9, 2018
This thing again... Background: when you hit Ctrl+C on Linux or macOS, a signal (SIGINT) is sent to the foreground process and its child processes. This signal can be intercepted by installing a signal handler for this specific signal. On Windows, there is no precise equivalent for this system. Instead, the Ctrl+C is translated by the current ConHost (i.e. the container running the Console processes) to a ConsoleCtrl event that is sent to all processes attached to that Console. If any of these processes installed a handler via SetConsoleCtrlHandler(), they can intercept that event (and avoid exiting or doing some cleanup work). On Linux and macOS (and every Unix flavor, really), processes can also be killed via the `kill` executable, which really just sends a signal to the process, typically SIGTERM. Processes can intercept that signal, too. To force processes to terminate, without giving them any chance to prevent that, SIGKILL can be sent. There is no equivalent for SIGTERM on Windows. To emulate SIGKILL on Windows, TerminateProcess() can be used, but it only kills one process (unlike SIGKILL, which is sent also to the child processes). In Git for Windows, we struggled with emulating SIGINT, SIGTERM and SIGKILL handling essentially since the beginning of the efforts to port Git to Windows. At least the SIGINT part of the problem becomes a lot worse when using a terminal window other than cmd.exe's: as long as using cmd.exe (AKA "ConHost"), Ctrl+C is handled entirely outside of our code. But with the big jump from v1.x to v2.x, Git for Windows not only switched from MSys to MSYS2, but also started using MinTTY as the default terminal window, which uses the MSYS2 runtime-provided pseudo terminals (inherited from Cygwin thanks to the MSYS2 runtime being a "friendly fork" of Cygwin). When Ctrl+C is pressed in MinTTY, all of the signaling has to be done by our code. The original code to handle Ctrl+C comes straight from Cygwin. It simply ignores the entire conundrum for non-Cygwin processes and simply calls TerminateProcess() on them, leaving spawned child processes running. The first attempt at fixing "the Ctrl+C problem" (with the symptom that interrupting `git clone ...` would not stop the actual download of the Git objects that was still running in a child process) was c4ba4e3357f. It simply enumerated all the processes' process IDs and parent process IDs and extracted the tree of (possibly transitive) child processes of the process to kill, then called TerminateProcess() on them. This solved the problem with interrupting `git clone`, but it did not address the problem that Git typically wants to "clean up" when being interrupted. In particular, Git installs atexit() and signal handlers to remove .lock files. The most common symptom was that a stale .git/index.lock file was still present after interrupting a Git process. Based on the idea presented in Dr Dobb's Journal in the article "A Safer Alternative to TerminateProcess()" by Andrew Tucker (July 1, 1999) http://www.drdobbs.com/a-safer-alternative-to-terminateprocess/184416547 we changed our handling to inject a remote thread calling ExitProcess() first, and fall back to TerminateProcess() the process tree instead: e9cb332976c This change was a little misguided in hindsight, as it only called TerminateProcess() on the process tree, but expected the atexit() handler of Git to take care of the child processes when killing the process via the remote ExitProcess() method. Therefore, we changed the strategy once again, to inject ExitProcess() threads into the child processes of the process to kill, too: 53e5c0313e1 (That commit also tries to handle Cygwin process among the child processes by sending Cygwin signals, but unfortunately that part of the commit was buggy.) This worked well for Git processes. However, Git Bash is used in all kinds of circumstances, including launching Maven, or node.js scripts that want to intercept SIGINT. Naturally, these callees have no idea that Git for Windows injects an ExitProcess() with exit code 130 (corresponding to 0x100 + SIGINT). Therefore, they never "got" the signal. So what is it that happens when ConHost generates a ConsoleCtrl event? This question was asked and answered in the excellent blog post at: http://stanislavs.org/stopping-command-line-applications-programatically-with-ctrl-c-events-from-net/#comment-2880 Essentially, the same happens as what we did with ExitProcess(): a remote thread gets injected, with the event type as parameter. Of course it is not ExitProcess() that is called, but CtrlRoutine(). This function lives in kernel32.dll, too, but it is not exported, i.e. GetProcAddress() won't find it. The trick proposed in the blog post (to send a test ConsoleCtrl event to the process itself, using a special handler that then inspects the stack trace to figure out the address of the caller) does not work for us, however: it would send a CTRL_BREAK_EVENT to *all* processes attached to the same Console, essentially killing MinTTY. But could we make this still work somehow? Yes, we could. We came up with yet another trick up our sleeves: instead of determining the address of kernel32!CtrlRoutine in our own process, we spawn a new one, with a new Console, to avoid killing MinTTY. To do that, we need a helper .exe, of course, which we put into /usr/libexec/. If this helper is not found, we fall back to the previous methods of injecting ExitProcess() or calling TerminateProcess(). This method (to spawn a helper .exe) has a further incidental benefit: by compiling 32-bit *and* 64-bit helpers and providing them as getprocaddr32.exe and getprocaddr64.exe, we can now also handle 32-bit processes in a 64-bit Git for Windows. Sadly not vice versa: calling CreateRemoteThread() on a 64-bit process from a 32-bit process seems to fail all the time (and require a lot of assembly hackery to fix that I am not really willing to include in Git for Windows' MSYS2 runtime). The current method was implemented in this commit: ca6188a7520 This is the hopeful final fix for git-for-windows/git#1491, git-for-windows/git#1470, git-for-windows/git#1248, git-for-windows/git#1239, git-for-windows/git#227, git-for-windows/git#1553, nodejs/node#16103, and plenty other tickets that petered out mostly due to a willingness of community members to leave all the hard work to a single, already overworked person. This fix also partially helps git-for-windows/git#1629 (only partially because the user wanted to quit the pager using Ctrl+C, which is not the intended consequence of a Ctrl+C: it should stop the Git process, but not the pager). Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
dscho
added a commit
to git-for-windows/msys2-runtime
that referenced
this issue
Feb 16, 2019
This thing again... Background: when you hit Ctrl+C on Linux or macOS, a signal (SIGINT) is sent to the foreground process and its child processes. This signal can be intercepted by installing a signal handler for this specific signal. On Windows, there is no precise equivalent for this system. Instead, the Ctrl+C is translated by the current ConHost (i.e. the container running the Console processes) to a ConsoleCtrl event that is sent to all processes attached to that Console. If any of these processes installed a handler via SetConsoleCtrlHandler(), they can intercept that event (and avoid exiting or doing some cleanup work). On Linux and macOS (and every Unix flavor, really), processes can also be killed via the `kill` executable, which really just sends a signal to the process, typically SIGTERM. Processes can intercept that signal, too. To force processes to terminate, without giving them any chance to prevent that, SIGKILL can be sent. There is no equivalent for SIGTERM on Windows. To emulate SIGKILL on Windows, TerminateProcess() can be used, but it only kills one process (unlike SIGKILL, which is sent also to the child processes). In Git for Windows, we struggled with emulating SIGINT, SIGTERM and SIGKILL handling essentially since the beginning of the efforts to port Git to Windows. At least the SIGINT part of the problem becomes a lot worse when using a terminal window other than cmd.exe's: as long as using cmd.exe (AKA "ConHost"), Ctrl+C is handled entirely outside of our code. But with the big jump from v1.x to v2.x, Git for Windows not only switched from MSys to MSYS2, but also started using MinTTY as the default terminal window, which uses the MSYS2 runtime-provided pseudo terminals (inherited from Cygwin thanks to the MSYS2 runtime being a "friendly fork" of Cygwin). When Ctrl+C is pressed in MinTTY, all of the signaling has to be done by our code. The original code to handle Ctrl+C comes straight from Cygwin. It simply ignores the entire conundrum for non-Cygwin processes and simply calls TerminateProcess() on them, leaving spawned child processes running. The first attempt at fixing "the Ctrl+C problem" (with the symptom that interrupting `git clone ...` would not stop the actual download of the Git objects that was still running in a child process) was c4ba4e3357f. It simply enumerated all the processes' process IDs and parent process IDs and extracted the tree of (possibly transitive) child processes of the process to kill, then called TerminateProcess() on them. This solved the problem with interrupting `git clone`, but it did not address the problem that Git typically wants to "clean up" when being interrupted. In particular, Git installs atexit() and signal handlers to remove .lock files. The most common symptom was that a stale .git/index.lock file was still present after interrupting a Git process. Based on the idea presented in Dr Dobb's Journal in the article "A Safer Alternative to TerminateProcess()" by Andrew Tucker (July 1, 1999) http://www.drdobbs.com/a-safer-alternative-to-terminateprocess/184416547 we changed our handling to inject a remote thread calling ExitProcess() first, and fall back to TerminateProcess() the process tree instead: e9cb332976c This change was a little misguided in hindsight, as it only called TerminateProcess() on the process tree, but expected the atexit() handler of Git to take care of the child processes when killing the process via the remote ExitProcess() method. Therefore, we changed the strategy once again, to inject ExitProcess() threads into the child processes of the process to kill, too: 53e5c0313e1 (That commit also tries to handle Cygwin process among the child processes by sending Cygwin signals, but unfortunately that part of the commit was buggy.) This worked well for Git processes. However, Git Bash is used in all kinds of circumstances, including launching Maven, or node.js scripts that want to intercept SIGINT. Naturally, these callees have no idea that Git for Windows injects an ExitProcess() with exit code 130 (corresponding to 0x100 + SIGINT). Therefore, they never "got" the signal. So what is it that happens when ConHost generates a ConsoleCtrl event? This question was asked and answered in the excellent blog post at: http://stanislavs.org/stopping-command-line-applications-programatically-with-ctrl-c-events-from-net/#comment-2880 Essentially, the same happens as what we did with ExitProcess(): a remote thread gets injected, with the event type as parameter. Of course it is not ExitProcess() that is called, but CtrlRoutine(). This function lives in kernel32.dll, too, but it is not exported, i.e. GetProcAddress() won't find it. The trick proposed in the blog post (to send a test ConsoleCtrl event to the process itself, using a special handler that then inspects the stack trace to figure out the address of the caller) does not work for us, however: it would send a CTRL_BREAK_EVENT to *all* processes attached to the same Console, essentially killing MinTTY. But could we make this still work somehow? Yes, we could. We came up with yet another trick up our sleeves: instead of determining the address of kernel32!CtrlRoutine in our own process, we spawn a new one, with a new Console, to avoid killing MinTTY. To do that, we need a helper .exe, of course, which we put into /usr/libexec/. If this helper is not found, we fall back to the previous methods of injecting ExitProcess() or calling TerminateProcess(). This method (to spawn a helper .exe) has a further incidental benefit: by compiling 32-bit *and* 64-bit helpers and providing them as getprocaddr32.exe and getprocaddr64.exe, we can now also handle 32-bit processes in a 64-bit Git for Windows. Sadly not vice versa: calling CreateRemoteThread() on a 64-bit process from a 32-bit process seems to fail all the time (and require a lot of assembly hackery to fix that I am not really willing to include in Git for Windows' MSYS2 runtime). The current method was implemented in this commit: ca6188a7520 This is the hopeful final fix for git-for-windows/git#1491, git-for-windows/git#1470, git-for-windows/git#1248, git-for-windows/git#1239, git-for-windows/git#227, git-for-windows/git#1553, nodejs/node#16103, and plenty other tickets that petered out mostly due to a willingness of community members to leave all the hard work to a single, already overworked person. This fix also partially helps git-for-windows/git#1629 (only partially because the user wanted to quit the pager using Ctrl+C, which is not the intended consequence of a Ctrl+C: it should stop the Git process, but not the pager). Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
dscho
added a commit
to git-for-windows/msys2-runtime
that referenced
this issue
Feb 20, 2019
This thing again... Background: when you hit Ctrl+C on Linux or macOS, a signal (SIGINT) is sent to the foreground process and its child processes. This signal can be intercepted by installing a signal handler for this specific signal. On Windows, there is no precise equivalent for this system. Instead, the Ctrl+C is translated by the current ConHost (i.e. the container running the Console processes) to a ConsoleCtrl event that is sent to all processes attached to that Console. If any of these processes installed a handler via SetConsoleCtrlHandler(), they can intercept that event (and avoid exiting or doing some cleanup work). On Linux and macOS (and every Unix flavor, really), processes can also be killed via the `kill` executable, which really just sends a signal to the process, typically SIGTERM. Processes can intercept that signal, too. To force processes to terminate, without giving them any chance to prevent that, SIGKILL can be sent. There is no equivalent for SIGTERM on Windows. To emulate SIGKILL on Windows, TerminateProcess() can be used, but it only kills one process (unlike SIGKILL, which is sent also to the child processes). In Git for Windows, we struggled with emulating SIGINT, SIGTERM and SIGKILL handling essentially since the beginning of the efforts to port Git to Windows. At least the SIGINT part of the problem becomes a lot worse when using a terminal window other than cmd.exe's: as long as using cmd.exe (AKA "ConHost"), Ctrl+C is handled entirely outside of our code. But with the big jump from v1.x to v2.x, Git for Windows not only switched from MSys to MSYS2, but also started using MinTTY as the default terminal window, which uses the MSYS2 runtime-provided pseudo terminals (inherited from Cygwin thanks to the MSYS2 runtime being a "friendly fork" of Cygwin). When Ctrl+C is pressed in MinTTY, all of the signaling has to be done by our code. The original code to handle Ctrl+C comes straight from Cygwin. It simply ignores the entire conundrum for non-Cygwin processes and simply calls TerminateProcess() on them, leaving spawned child processes running. The first attempt at fixing "the Ctrl+C problem" (with the symptom that interrupting `git clone ...` would not stop the actual download of the Git objects that was still running in a child process) was c4ba4e3357f. It simply enumerated all the processes' process IDs and parent process IDs and extracted the tree of (possibly transitive) child processes of the process to kill, then called TerminateProcess() on them. This solved the problem with interrupting `git clone`, but it did not address the problem that Git typically wants to "clean up" when being interrupted. In particular, Git installs atexit() and signal handlers to remove .lock files. The most common symptom was that a stale .git/index.lock file was still present after interrupting a Git process. Based on the idea presented in Dr Dobb's Journal in the article "A Safer Alternative to TerminateProcess()" by Andrew Tucker (July 1, 1999) http://www.drdobbs.com/a-safer-alternative-to-terminateprocess/184416547 we changed our handling to inject a remote thread calling ExitProcess() first, and fall back to TerminateProcess() the process tree instead: e9cb332976c This change was a little misguided in hindsight, as it only called TerminateProcess() on the process tree, but expected the atexit() handler of Git to take care of the child processes when killing the process via the remote ExitProcess() method. Therefore, we changed the strategy once again, to inject ExitProcess() threads into the child processes of the process to kill, too: 53e5c0313e1 (That commit also tries to handle Cygwin process among the child processes by sending Cygwin signals, but unfortunately that part of the commit was buggy.) This worked well for Git processes. However, Git Bash is used in all kinds of circumstances, including launching Maven, or node.js scripts that want to intercept SIGINT. Naturally, these callees have no idea that Git for Windows injects an ExitProcess() with exit code 130 (corresponding to 0x100 + SIGINT). Therefore, they never "got" the signal. So what is it that happens when ConHost generates a ConsoleCtrl event? This question was asked and answered in the excellent blog post at: http://stanislavs.org/stopping-command-line-applications-programatically-with-ctrl-c-events-from-net/#comment-2880 Essentially, the same happens as what we did with ExitProcess(): a remote thread gets injected, with the event type as parameter. Of course it is not ExitProcess() that is called, but CtrlRoutine(). This function lives in kernel32.dll, too, but it is not exported, i.e. GetProcAddress() won't find it. The trick proposed in the blog post (to send a test ConsoleCtrl event to the process itself, using a special handler that then inspects the stack trace to figure out the address of the caller) does not work for us, however: it would send a CTRL_BREAK_EVENT to *all* processes attached to the same Console, essentially killing MinTTY. But could we make this still work somehow? Yes, we could. We came up with yet another trick up our sleeves: instead of determining the address of kernel32!CtrlRoutine in our own process, we spawn a new one, with a new Console, to avoid killing MinTTY. To do that, we need a helper .exe, of course, which we put into /usr/libexec/. If this helper is not found, we fall back to the previous methods of injecting ExitProcess() or calling TerminateProcess(). This method (to spawn a helper .exe) has a further incidental benefit: by compiling 32-bit *and* 64-bit helpers and providing them as getprocaddr32.exe and getprocaddr64.exe, we can now also handle 32-bit processes in a 64-bit Git for Windows. Sadly not vice versa: calling CreateRemoteThread() on a 64-bit process from a 32-bit process seems to fail all the time (and require a lot of assembly hackery to fix that I am not really willing to include in Git for Windows' MSYS2 runtime). The current method was implemented in this commit: ca6188a7520 This is the hopeful final fix for git-for-windows/git#1491, git-for-windows/git#1470, git-for-windows/git#1248, git-for-windows/git#1239, git-for-windows/git#227, git-for-windows/git#1553, nodejs/node#16103, and plenty other tickets that petered out mostly due to a willingness of community members to leave all the hard work to a single, already overworked person. This fix also partially helps git-for-windows/git#1629 (only partially because the user wanted to quit the pager using Ctrl+C, which is not the intended consequence of a Ctrl+C: it should stop the Git process, but not the pager). Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
dscho
added a commit
to git-for-windows/msys2-runtime
that referenced
this issue
Feb 20, 2019
This thing again... Background: when you hit Ctrl+C on Linux or macOS, a signal (SIGINT) is sent to the foreground process and its child processes. This signal can be intercepted by installing a signal handler for this specific signal. On Windows, there is no precise equivalent for this system. Instead, the Ctrl+C is translated by the current ConHost (i.e. the container running the Console processes) to a ConsoleCtrl event that is sent to all processes attached to that Console. If any of these processes installed a handler via SetConsoleCtrlHandler(), they can intercept that event (and avoid exiting or doing some cleanup work). On Linux and macOS (and every Unix flavor, really), processes can also be killed via the `kill` executable, which really just sends a signal to the process, typically SIGTERM. Processes can intercept that signal, too. To force processes to terminate, without giving them any chance to prevent that, SIGKILL can be sent. There is no equivalent for SIGTERM on Windows. To emulate SIGKILL on Windows, TerminateProcess() can be used, but it only kills one process (unlike SIGKILL, which is sent also to the child processes). In Git for Windows, we struggled with emulating SIGINT, SIGTERM and SIGKILL handling essentially since the beginning of the efforts to port Git to Windows. At least the SIGINT part of the problem becomes a lot worse when using a terminal window other than cmd.exe's: as long as using cmd.exe (AKA "ConHost"), Ctrl+C is handled entirely outside of our code. But with the big jump from v1.x to v2.x, Git for Windows not only switched from MSys to MSYS2, but also started using MinTTY as the default terminal window, which uses the MSYS2 runtime-provided pseudo terminals (inherited from Cygwin thanks to the MSYS2 runtime being a "friendly fork" of Cygwin). When Ctrl+C is pressed in MinTTY, all of the signaling has to be done by our code. The original code to handle Ctrl+C comes straight from Cygwin. It simply ignores the entire conundrum for non-Cygwin processes and simply calls TerminateProcess() on them, leaving spawned child processes running. The first attempt at fixing "the Ctrl+C problem" (with the symptom that interrupting `git clone ...` would not stop the actual download of the Git objects that was still running in a child process) was c4ba4e3357f. It simply enumerated all the processes' process IDs and parent process IDs and extracted the tree of (possibly transitive) child processes of the process to kill, then called TerminateProcess() on them. This solved the problem with interrupting `git clone`, but it did not address the problem that Git typically wants to "clean up" when being interrupted. In particular, Git installs atexit() and signal handlers to remove .lock files. The most common symptom was that a stale .git/index.lock file was still present after interrupting a Git process. Based on the idea presented in Dr Dobb's Journal in the article "A Safer Alternative to TerminateProcess()" by Andrew Tucker (July 1, 1999) http://www.drdobbs.com/a-safer-alternative-to-terminateprocess/184416547 we changed our handling to inject a remote thread calling ExitProcess() first, and fall back to TerminateProcess() the process tree instead: e9cb332976c This change was a little misguided in hindsight, as it only called TerminateProcess() on the process tree, but expected the atexit() handler of Git to take care of the child processes when killing the process via the remote ExitProcess() method. Therefore, we changed the strategy once again, to inject ExitProcess() threads into the child processes of the process to kill, too: 53e5c0313e1 (That commit also tries to handle Cygwin process among the child processes by sending Cygwin signals, but unfortunately that part of the commit was buggy.) This worked well for Git processes. However, Git Bash is used in all kinds of circumstances, including launching Maven, or node.js scripts that want to intercept SIGINT. Naturally, these callees have no idea that Git for Windows injects an ExitProcess() with exit code 130 (corresponding to 0x100 + SIGINT). Therefore, they never "got" the signal. So what is it that happens when ConHost generates a ConsoleCtrl event? This question was asked and answered in the excellent blog post at: http://stanislavs.org/stopping-command-line-applications-programatically-with-ctrl-c-events-from-net/#comment-2880 Essentially, the same happens as what we did with ExitProcess(): a remote thread gets injected, with the event type as parameter. Of course it is not ExitProcess() that is called, but CtrlRoutine(). This function lives in kernel32.dll, too, but it is not exported, i.e. GetProcAddress() won't find it. The trick proposed in the blog post (to send a test ConsoleCtrl event to the process itself, using a special handler that then inspects the stack trace to figure out the address of the caller) does not work for us, however: it would send a CTRL_BREAK_EVENT to *all* processes attached to the same Console, essentially killing MinTTY. But could we make this still work somehow? Yes, we could. We came up with yet another trick up our sleeves: instead of determining the address of kernel32!CtrlRoutine in our own process, we spawn a new one, with a new Console, to avoid killing MinTTY. To do that, we need a helper .exe, of course, which we put into /usr/libexec/. If this helper is not found, we fall back to the previous methods of injecting ExitProcess() or calling TerminateProcess(). This method (to spawn a helper .exe) has a further incidental benefit: by compiling 32-bit *and* 64-bit helpers and providing them as getprocaddr32.exe and getprocaddr64.exe, we can now also handle 32-bit processes in a 64-bit Git for Windows. Sadly not vice versa: calling CreateRemoteThread() on a 64-bit process from a 32-bit process seems to fail all the time (and require a lot of assembly hackery to fix that I am not really willing to include in Git for Windows' MSYS2 runtime). The current method was implemented in this commit: ca6188a7520 This is the hopeful final fix for git-for-windows/git#1491, git-for-windows/git#1470, git-for-windows/git#1248, git-for-windows/git#1239, git-for-windows/git#227, git-for-windows/git#1553, nodejs/node#16103, and plenty other tickets that petered out mostly due to a willingness of community members to leave all the hard work to a single, already overworked person. This fix also partially helps git-for-windows/git#1629 (only partially because the user wanted to quit the pager using Ctrl+C, which is not the intended consequence of a Ctrl+C: it should stop the Git process, but not the pager). Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
git-for-windows-ci
pushed a commit
to git-for-windows/msys2-runtime
that referenced
this issue
Mar 5, 2019
This thing again... Background: when you hit Ctrl+C on Linux or macOS, a signal (SIGINT) is sent to the foreground process and its child processes. This signal can be intercepted by installing a signal handler for this specific signal. On Windows, there is no precise equivalent for this system. Instead, the Ctrl+C is translated by the current ConHost (i.e. the container running the Console processes) to a ConsoleCtrl event that is sent to all processes attached to that Console. If any of these processes installed a handler via SetConsoleCtrlHandler(), they can intercept that event (and avoid exiting or doing some cleanup work). On Linux and macOS (and every Unix flavor, really), processes can also be killed via the `kill` executable, which really just sends a signal to the process, typically SIGTERM. Processes can intercept that signal, too. To force processes to terminate, without giving them any chance to prevent that, SIGKILL can be sent. There is no equivalent for SIGTERM on Windows. To emulate SIGKILL on Windows, TerminateProcess() can be used, but it only kills one process (unlike SIGKILL, which is sent also to the child processes). In Git for Windows, we struggled with emulating SIGINT, SIGTERM and SIGKILL handling essentially since the beginning of the efforts to port Git to Windows. At least the SIGINT part of the problem becomes a lot worse when using a terminal window other than cmd.exe's: as long as using cmd.exe (AKA "ConHost"), Ctrl+C is handled entirely outside of our code. But with the big jump from v1.x to v2.x, Git for Windows not only switched from MSys to MSYS2, but also started using MinTTY as the default terminal window, which uses the MSYS2 runtime-provided pseudo terminals (inherited from Cygwin thanks to the MSYS2 runtime being a "friendly fork" of Cygwin). When Ctrl+C is pressed in MinTTY, all of the signaling has to be done by our code. The original code to handle Ctrl+C comes straight from Cygwin. It simply ignores the entire conundrum for non-Cygwin processes and simply calls TerminateProcess() on them, leaving spawned child processes running. The first attempt at fixing "the Ctrl+C problem" (with the symptom that interrupting `git clone ...` would not stop the actual download of the Git objects that was still running in a child process) was c4ba4e3357f. It simply enumerated all the processes' process IDs and parent process IDs and extracted the tree of (possibly transitive) child processes of the process to kill, then called TerminateProcess() on them. This solved the problem with interrupting `git clone`, but it did not address the problem that Git typically wants to "clean up" when being interrupted. In particular, Git installs atexit() and signal handlers to remove .lock files. The most common symptom was that a stale .git/index.lock file was still present after interrupting a Git process. Based on the idea presented in Dr Dobb's Journal in the article "A Safer Alternative to TerminateProcess()" by Andrew Tucker (July 1, 1999) http://www.drdobbs.com/a-safer-alternative-to-terminateprocess/184416547 we changed our handling to inject a remote thread calling ExitProcess() first, and fall back to TerminateProcess() the process tree instead: e9cb332976c This change was a little misguided in hindsight, as it only called TerminateProcess() on the process tree, but expected the atexit() handler of Git to take care of the child processes when killing the process via the remote ExitProcess() method. Therefore, we changed the strategy once again, to inject ExitProcess() threads into the child processes of the process to kill, too: 53e5c0313e1 (That commit also tries to handle Cygwin process among the child processes by sending Cygwin signals, but unfortunately that part of the commit was buggy.) This worked well for Git processes. However, Git Bash is used in all kinds of circumstances, including launching Maven, or node.js scripts that want to intercept SIGINT. Naturally, these callees have no idea that Git for Windows injects an ExitProcess() with exit code 130 (corresponding to 0x100 + SIGINT). Therefore, they never "got" the signal. So what is it that happens when ConHost generates a ConsoleCtrl event? This question was asked and answered in the excellent blog post at: http://stanislavs.org/stopping-command-line-applications-programatically-with-ctrl-c-events-from-net/#comment-2880 Essentially, the same happens as what we did with ExitProcess(): a remote thread gets injected, with the event type as parameter. Of course it is not ExitProcess() that is called, but CtrlRoutine(). This function lives in kernel32.dll, too, but it is not exported, i.e. GetProcAddress() won't find it. The trick proposed in the blog post (to send a test ConsoleCtrl event to the process itself, using a special handler that then inspects the stack trace to figure out the address of the caller) does not work for us, however: it would send a CTRL_BREAK_EVENT to *all* processes attached to the same Console, essentially killing MinTTY. But could we make this still work somehow? Yes, we could. We came up with yet another trick up our sleeves: instead of determining the address of kernel32!CtrlRoutine in our own process, we spawn a new one, with a new Console, to avoid killing MinTTY. To do that, we need a helper .exe, of course, which we put into /usr/libexec/. If this helper is not found, we fall back to the previous methods of injecting ExitProcess() or calling TerminateProcess(). This method (to spawn a helper .exe) has a further incidental benefit: by compiling 32-bit *and* 64-bit helpers and providing them as getprocaddr32.exe and getprocaddr64.exe, we can now also handle 32-bit processes in a 64-bit Git for Windows. Sadly not vice versa: calling CreateRemoteThread() on a 64-bit process from a 32-bit process seems to fail all the time (and require a lot of assembly hackery to fix that I am not really willing to include in Git for Windows' MSYS2 runtime). The current method was implemented in this commit: ca6188a7520 This is the hopeful final fix for git-for-windows/git#1491, git-for-windows/git#1470, git-for-windows/git#1248, git-for-windows/git#1239, git-for-windows/git#227, git-for-windows/git#1553, nodejs/node#16103, and plenty other tickets that petered out mostly due to a willingness of community members to leave all the hard work to a single, already overworked person. This fix also partially helps git-for-windows/git#1629 (only partially because the user wanted to quit the pager using Ctrl+C, which is not the intended consequence of a Ctrl+C: it should stop the Git process, but not the pager). Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
git-for-windows-ci
pushed a commit
to git-for-windows/msys2-runtime
that referenced
this issue
Mar 9, 2019
This thing again... Background: when you hit Ctrl+C on Linux or macOS, a signal (SIGINT) is sent to the foreground process and its child processes. This signal can be intercepted by installing a signal handler for this specific signal. On Windows, there is no precise equivalent for this system. Instead, the Ctrl+C is translated by the current ConHost (i.e. the container running the Console processes) to a ConsoleCtrl event that is sent to all processes attached to that Console. If any of these processes installed a handler via SetConsoleCtrlHandler(), they can intercept that event (and avoid exiting or doing some cleanup work). On Linux and macOS (and every Unix flavor, really), processes can also be killed via the `kill` executable, which really just sends a signal to the process, typically SIGTERM. Processes can intercept that signal, too. To force processes to terminate, without giving them any chance to prevent that, SIGKILL can be sent. There is no equivalent for SIGTERM on Windows. To emulate SIGKILL on Windows, TerminateProcess() can be used, but it only kills one process (unlike SIGKILL, which is sent also to the child processes). In Git for Windows, we struggled with emulating SIGINT, SIGTERM and SIGKILL handling essentially since the beginning of the efforts to port Git to Windows. At least the SIGINT part of the problem becomes a lot worse when using a terminal window other than cmd.exe's: as long as using cmd.exe (AKA "ConHost"), Ctrl+C is handled entirely outside of our code. But with the big jump from v1.x to v2.x, Git for Windows not only switched from MSys to MSYS2, but also started using MinTTY as the default terminal window, which uses the MSYS2 runtime-provided pseudo terminals (inherited from Cygwin thanks to the MSYS2 runtime being a "friendly fork" of Cygwin). When Ctrl+C is pressed in MinTTY, all of the signaling has to be done by our code. The original code to handle Ctrl+C comes straight from Cygwin. It simply ignores the entire conundrum for non-Cygwin processes and simply calls TerminateProcess() on them, leaving spawned child processes running. The first attempt at fixing "the Ctrl+C problem" (with the symptom that interrupting `git clone ...` would not stop the actual download of the Git objects that was still running in a child process) was c4ba4e3357f. It simply enumerated all the processes' process IDs and parent process IDs and extracted the tree of (possibly transitive) child processes of the process to kill, then called TerminateProcess() on them. This solved the problem with interrupting `git clone`, but it did not address the problem that Git typically wants to "clean up" when being interrupted. In particular, Git installs atexit() and signal handlers to remove .lock files. The most common symptom was that a stale .git/index.lock file was still present after interrupting a Git process. Based on the idea presented in Dr Dobb's Journal in the article "A Safer Alternative to TerminateProcess()" by Andrew Tucker (July 1, 1999) http://www.drdobbs.com/a-safer-alternative-to-terminateprocess/184416547 we changed our handling to inject a remote thread calling ExitProcess() first, and fall back to TerminateProcess() the process tree instead: e9cb332976c This change was a little misguided in hindsight, as it only called TerminateProcess() on the process tree, but expected the atexit() handler of Git to take care of the child processes when killing the process via the remote ExitProcess() method. Therefore, we changed the strategy once again, to inject ExitProcess() threads into the child processes of the process to kill, too: 53e5c0313e1 (That commit also tries to handle Cygwin process among the child processes by sending Cygwin signals, but unfortunately that part of the commit was buggy.) This worked well for Git processes. However, Git Bash is used in all kinds of circumstances, including launching Maven, or node.js scripts that want to intercept SIGINT. Naturally, these callees have no idea that Git for Windows injects an ExitProcess() with exit code 130 (corresponding to 0x100 + SIGINT). Therefore, they never "got" the signal. So what is it that happens when ConHost generates a ConsoleCtrl event? This question was asked and answered in the excellent blog post at: http://stanislavs.org/stopping-command-line-applications-programatically-with-ctrl-c-events-from-net/#comment-2880 Essentially, the same happens as what we did with ExitProcess(): a remote thread gets injected, with the event type as parameter. Of course it is not ExitProcess() that is called, but CtrlRoutine(). This function lives in kernel32.dll, too, but it is not exported, i.e. GetProcAddress() won't find it. The trick proposed in the blog post (to send a test ConsoleCtrl event to the process itself, using a special handler that then inspects the stack trace to figure out the address of the caller) does not work for us, however: it would send a CTRL_BREAK_EVENT to *all* processes attached to the same Console, essentially killing MinTTY. But could we make this still work somehow? Yes, we could. We came up with yet another trick up our sleeves: instead of determining the address of kernel32!CtrlRoutine in our own process, we spawn a new one, with a new Console, to avoid killing MinTTY. To do that, we need a helper .exe, of course, which we put into /usr/libexec/. If this helper is not found, we fall back to the previous methods of injecting ExitProcess() or calling TerminateProcess(). This method (to spawn a helper .exe) has a further incidental benefit: by compiling 32-bit *and* 64-bit helpers and providing them as getprocaddr32.exe and getprocaddr64.exe, we can now also handle 32-bit processes in a 64-bit Git for Windows. Sadly not vice versa: calling CreateRemoteThread() on a 64-bit process from a 32-bit process seems to fail all the time (and require a lot of assembly hackery to fix that I am not really willing to include in Git for Windows' MSYS2 runtime). The current method was implemented in this commit: ca6188a7520 This is the hopeful final fix for git-for-windows/git#1491, git-for-windows/git#1470, git-for-windows/git#1248, git-for-windows/git#1239, git-for-windows/git#227, git-for-windows/git#1553, nodejs/node#16103, and plenty other tickets that petered out mostly due to a willingness of community members to leave all the hard work to a single, already overworked person. This fix also partially helps git-for-windows/git#1629 (only partially because the user wanted to quit the pager using Ctrl+C, which is not the intended consequence of a Ctrl+C: it should stop the Git process, but not the pager). Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
git-for-windows-ci
pushed a commit
to git-for-windows/msys2-runtime
that referenced
this issue
Mar 16, 2019
This thing again... Background: when you hit Ctrl+C on Linux or macOS, a signal (SIGINT) is sent to the foreground process and its child processes. This signal can be intercepted by installing a signal handler for this specific signal. On Windows, there is no precise equivalent for this system. Instead, the Ctrl+C is translated by the current ConHost (i.e. the container running the Console processes) to a ConsoleCtrl event that is sent to all processes attached to that Console. If any of these processes installed a handler via SetConsoleCtrlHandler(), they can intercept that event (and avoid exiting or doing some cleanup work). On Linux and macOS (and every Unix flavor, really), processes can also be killed via the `kill` executable, which really just sends a signal to the process, typically SIGTERM. Processes can intercept that signal, too. To force processes to terminate, without giving them any chance to prevent that, SIGKILL can be sent. There is no equivalent for SIGTERM on Windows. To emulate SIGKILL on Windows, TerminateProcess() can be used, but it only kills one process (unlike SIGKILL, which is sent also to the child processes). In Git for Windows, we struggled with emulating SIGINT, SIGTERM and SIGKILL handling essentially since the beginning of the efforts to port Git to Windows. At least the SIGINT part of the problem becomes a lot worse when using a terminal window other than cmd.exe's: as long as using cmd.exe (AKA "ConHost"), Ctrl+C is handled entirely outside of our code. But with the big jump from v1.x to v2.x, Git for Windows not only switched from MSys to MSYS2, but also started using MinTTY as the default terminal window, which uses the MSYS2 runtime-provided pseudo terminals (inherited from Cygwin thanks to the MSYS2 runtime being a "friendly fork" of Cygwin). When Ctrl+C is pressed in MinTTY, all of the signaling has to be done by our code. The original code to handle Ctrl+C comes straight from Cygwin. It simply ignores the entire conundrum for non-Cygwin processes and simply calls TerminateProcess() on them, leaving spawned child processes running. The first attempt at fixing "the Ctrl+C problem" (with the symptom that interrupting `git clone ...` would not stop the actual download of the Git objects that was still running in a child process) was c4ba4e3357f. It simply enumerated all the processes' process IDs and parent process IDs and extracted the tree of (possibly transitive) child processes of the process to kill, then called TerminateProcess() on them. This solved the problem with interrupting `git clone`, but it did not address the problem that Git typically wants to "clean up" when being interrupted. In particular, Git installs atexit() and signal handlers to remove .lock files. The most common symptom was that a stale .git/index.lock file was still present after interrupting a Git process. Based on the idea presented in Dr Dobb's Journal in the article "A Safer Alternative to TerminateProcess()" by Andrew Tucker (July 1, 1999) http://www.drdobbs.com/a-safer-alternative-to-terminateprocess/184416547 we changed our handling to inject a remote thread calling ExitProcess() first, and fall back to TerminateProcess() the process tree instead: e9cb332976c This change was a little misguided in hindsight, as it only called TerminateProcess() on the process tree, but expected the atexit() handler of Git to take care of the child processes when killing the process via the remote ExitProcess() method. Therefore, we changed the strategy once again, to inject ExitProcess() threads into the child processes of the process to kill, too: 53e5c0313e1 (That commit also tries to handle Cygwin process among the child processes by sending Cygwin signals, but unfortunately that part of the commit was buggy.) This worked well for Git processes. However, Git Bash is used in all kinds of circumstances, including launching Maven, or node.js scripts that want to intercept SIGINT. Naturally, these callees have no idea that Git for Windows injects an ExitProcess() with exit code 130 (corresponding to 0x100 + SIGINT). Therefore, they never "got" the signal. So what is it that happens when ConHost generates a ConsoleCtrl event? This question was asked and answered in the excellent blog post at: http://stanislavs.org/stopping-command-line-applications-programatically-with-ctrl-c-events-from-net/#comment-2880 Essentially, the same happens as what we did with ExitProcess(): a remote thread gets injected, with the event type as parameter. Of course it is not ExitProcess() that is called, but CtrlRoutine(). This function lives in kernel32.dll, too, but it is not exported, i.e. GetProcAddress() won't find it. The trick proposed in the blog post (to send a test ConsoleCtrl event to the process itself, using a special handler that then inspects the stack trace to figure out the address of the caller) does not work for us, however: it would send a CTRL_BREAK_EVENT to *all* processes attached to the same Console, essentially killing MinTTY. But could we make this still work somehow? Yes, we could. We came up with yet another trick up our sleeves: instead of determining the address of kernel32!CtrlRoutine in our own process, we spawn a new one, with a new Console, to avoid killing MinTTY. To do that, we need a helper .exe, of course, which we put into /usr/libexec/. If this helper is not found, we fall back to the previous methods of injecting ExitProcess() or calling TerminateProcess(). This method (to spawn a helper .exe) has a further incidental benefit: by compiling 32-bit *and* 64-bit helpers and providing them as getprocaddr32.exe and getprocaddr64.exe, we can now also handle 32-bit processes in a 64-bit Git for Windows. Sadly not vice versa: calling CreateRemoteThread() on a 64-bit process from a 32-bit process seems to fail all the time (and require a lot of assembly hackery to fix that I am not really willing to include in Git for Windows' MSYS2 runtime). The current method was implemented in this commit: ca6188a7520 This is the hopeful final fix for git-for-windows/git#1491, git-for-windows/git#1470, git-for-windows/git#1248, git-for-windows/git#1239, git-for-windows/git#227, git-for-windows/git#1553, nodejs/node#16103, and plenty other tickets that petered out mostly due to a willingness of community members to leave all the hard work to a single, already overworked person. This fix also partially helps git-for-windows/git#1629 (only partially because the user wanted to quit the pager using Ctrl+C, which is not the intended consequence of a Ctrl+C: it should stop the Git process, but not the pager). Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
git-for-windows-ci
pushed a commit
to git-for-windows/msys2-runtime
that referenced
this issue
Mar 31, 2019
This thing again... Background: when you hit Ctrl+C on Linux or macOS, a signal (SIGINT) is sent to the foreground process and its child processes. This signal can be intercepted by installing a signal handler for this specific signal. On Windows, there is no precise equivalent for this system. Instead, the Ctrl+C is translated by the current ConHost (i.e. the container running the Console processes) to a ConsoleCtrl event that is sent to all processes attached to that Console. If any of these processes installed a handler via SetConsoleCtrlHandler(), they can intercept that event (and avoid exiting or doing some cleanup work). On Linux and macOS (and every Unix flavor, really), processes can also be killed via the `kill` executable, which really just sends a signal to the process, typically SIGTERM. Processes can intercept that signal, too. To force processes to terminate, without giving them any chance to prevent that, SIGKILL can be sent. There is no equivalent for SIGTERM on Windows. To emulate SIGKILL on Windows, TerminateProcess() can be used, but it only kills one process (unlike SIGKILL, which is sent also to the child processes). In Git for Windows, we struggled with emulating SIGINT, SIGTERM and SIGKILL handling essentially since the beginning of the efforts to port Git to Windows. At least the SIGINT part of the problem becomes a lot worse when using a terminal window other than cmd.exe's: as long as using cmd.exe (AKA "ConHost"), Ctrl+C is handled entirely outside of our code. But with the big jump from v1.x to v2.x, Git for Windows not only switched from MSys to MSYS2, but also started using MinTTY as the default terminal window, which uses the MSYS2 runtime-provided pseudo terminals (inherited from Cygwin thanks to the MSYS2 runtime being a "friendly fork" of Cygwin). When Ctrl+C is pressed in MinTTY, all of the signaling has to be done by our code. The original code to handle Ctrl+C comes straight from Cygwin. It simply ignores the entire conundrum for non-Cygwin processes and simply calls TerminateProcess() on them, leaving spawned child processes running. The first attempt at fixing "the Ctrl+C problem" (with the symptom that interrupting `git clone ...` would not stop the actual download of the Git objects that was still running in a child process) was c4ba4e3357f. It simply enumerated all the processes' process IDs and parent process IDs and extracted the tree of (possibly transitive) child processes of the process to kill, then called TerminateProcess() on them. This solved the problem with interrupting `git clone`, but it did not address the problem that Git typically wants to "clean up" when being interrupted. In particular, Git installs atexit() and signal handlers to remove .lock files. The most common symptom was that a stale .git/index.lock file was still present after interrupting a Git process. Based on the idea presented in Dr Dobb's Journal in the article "A Safer Alternative to TerminateProcess()" by Andrew Tucker (July 1, 1999) http://www.drdobbs.com/a-safer-alternative-to-terminateprocess/184416547 we changed our handling to inject a remote thread calling ExitProcess() first, and fall back to TerminateProcess() the process tree instead: e9cb332976c This change was a little misguided in hindsight, as it only called TerminateProcess() on the process tree, but expected the atexit() handler of Git to take care of the child processes when killing the process via the remote ExitProcess() method. Therefore, we changed the strategy once again, to inject ExitProcess() threads into the child processes of the process to kill, too: 53e5c0313e1 (That commit also tries to handle Cygwin process among the child processes by sending Cygwin signals, but unfortunately that part of the commit was buggy.) This worked well for Git processes. However, Git Bash is used in all kinds of circumstances, including launching Maven, or node.js scripts that want to intercept SIGINT. Naturally, these callees have no idea that Git for Windows injects an ExitProcess() with exit code 130 (corresponding to 0x100 + SIGINT). Therefore, they never "got" the signal. So what is it that happens when ConHost generates a ConsoleCtrl event? This question was asked and answered in the excellent blog post at: http://stanislavs.org/stopping-command-line-applications-programatically-with-ctrl-c-events-from-net/#comment-2880 Essentially, the same happens as what we did with ExitProcess(): a remote thread gets injected, with the event type as parameter. Of course it is not ExitProcess() that is called, but CtrlRoutine(). This function lives in kernel32.dll, too, but it is not exported, i.e. GetProcAddress() won't find it. The trick proposed in the blog post (to send a test ConsoleCtrl event to the process itself, using a special handler that then inspects the stack trace to figure out the address of the caller) does not work for us, however: it would send a CTRL_BREAK_EVENT to *all* processes attached to the same Console, essentially killing MinTTY. But could we make this still work somehow? Yes, we could. We came up with yet another trick up our sleeves: instead of determining the address of kernel32!CtrlRoutine in our own process, we spawn a new one, with a new Console, to avoid killing MinTTY. To do that, we need a helper .exe, of course, which we put into /usr/libexec/. If this helper is not found, we fall back to the previous methods of injecting ExitProcess() or calling TerminateProcess(). This method (to spawn a helper .exe) has a further incidental benefit: by compiling 32-bit *and* 64-bit helpers and providing them as getprocaddr32.exe and getprocaddr64.exe, we can now also handle 32-bit processes in a 64-bit Git for Windows. Sadly not vice versa: calling CreateRemoteThread() on a 64-bit process from a 32-bit process seems to fail all the time (and require a lot of assembly hackery to fix that I am not really willing to include in Git for Windows' MSYS2 runtime). The current method was implemented in this commit: ca6188a7520 This is the hopeful final fix for git-for-windows/git#1491, git-for-windows/git#1470, git-for-windows/git#1248, git-for-windows/git#1239, git-for-windows/git#227, git-for-windows/git#1553, nodejs/node#16103, and plenty other tickets that petered out mostly due to a willingness of community members to leave all the hard work to a single, already overworked person. This fix also partially helps git-for-windows/git#1629 (only partially because the user wanted to quit the pager using Ctrl+C, which is not the intended consequence of a Ctrl+C: it should stop the Git process, but not the pager). Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
git-for-windows-ci
pushed a commit
to git-for-windows/msys2-runtime
that referenced
this issue
Apr 6, 2019
This thing again... Background: when you hit Ctrl+C on Linux or macOS, a signal (SIGINT) is sent to the foreground process and its child processes. This signal can be intercepted by installing a signal handler for this specific signal. On Windows, there is no precise equivalent for this system. Instead, the Ctrl+C is translated by the current ConHost (i.e. the container running the Console processes) to a ConsoleCtrl event that is sent to all processes attached to that Console. If any of these processes installed a handler via SetConsoleCtrlHandler(), they can intercept that event (and avoid exiting or doing some cleanup work). On Linux and macOS (and every Unix flavor, really), processes can also be killed via the `kill` executable, which really just sends a signal to the process, typically SIGTERM. Processes can intercept that signal, too. To force processes to terminate, without giving them any chance to prevent that, SIGKILL can be sent. There is no equivalent for SIGTERM on Windows. To emulate SIGKILL on Windows, TerminateProcess() can be used, but it only kills one process (unlike SIGKILL, which is sent also to the child processes). In Git for Windows, we struggled with emulating SIGINT, SIGTERM and SIGKILL handling essentially since the beginning of the efforts to port Git to Windows. At least the SIGINT part of the problem becomes a lot worse when using a terminal window other than cmd.exe's: as long as using cmd.exe (AKA "ConHost"), Ctrl+C is handled entirely outside of our code. But with the big jump from v1.x to v2.x, Git for Windows not only switched from MSys to MSYS2, but also started using MinTTY as the default terminal window, which uses the MSYS2 runtime-provided pseudo terminals (inherited from Cygwin thanks to the MSYS2 runtime being a "friendly fork" of Cygwin). When Ctrl+C is pressed in MinTTY, all of the signaling has to be done by our code. The original code to handle Ctrl+C comes straight from Cygwin. It simply ignores the entire conundrum for non-Cygwin processes and simply calls TerminateProcess() on them, leaving spawned child processes running. The first attempt at fixing "the Ctrl+C problem" (with the symptom that interrupting `git clone ...` would not stop the actual download of the Git objects that was still running in a child process) was c4ba4e3357f. It simply enumerated all the processes' process IDs and parent process IDs and extracted the tree of (possibly transitive) child processes of the process to kill, then called TerminateProcess() on them. This solved the problem with interrupting `git clone`, but it did not address the problem that Git typically wants to "clean up" when being interrupted. In particular, Git installs atexit() and signal handlers to remove .lock files. The most common symptom was that a stale .git/index.lock file was still present after interrupting a Git process. Based on the idea presented in Dr Dobb's Journal in the article "A Safer Alternative to TerminateProcess()" by Andrew Tucker (July 1, 1999) http://www.drdobbs.com/a-safer-alternative-to-terminateprocess/184416547 we changed our handling to inject a remote thread calling ExitProcess() first, and fall back to TerminateProcess() the process tree instead: e9cb332976c This change was a little misguided in hindsight, as it only called TerminateProcess() on the process tree, but expected the atexit() handler of Git to take care of the child processes when killing the process via the remote ExitProcess() method. Therefore, we changed the strategy once again, to inject ExitProcess() threads into the child processes of the process to kill, too: 53e5c0313e1 (That commit also tries to handle Cygwin process among the child processes by sending Cygwin signals, but unfortunately that part of the commit was buggy.) This worked well for Git processes. However, Git Bash is used in all kinds of circumstances, including launching Maven, or node.js scripts that want to intercept SIGINT. Naturally, these callees have no idea that Git for Windows injects an ExitProcess() with exit code 130 (corresponding to 0x100 + SIGINT). Therefore, they never "got" the signal. So what is it that happens when ConHost generates a ConsoleCtrl event? This question was asked and answered in the excellent blog post at: http://stanislavs.org/stopping-command-line-applications-programatically-with-ctrl-c-events-from-net/#comment-2880 Essentially, the same happens as what we did with ExitProcess(): a remote thread gets injected, with the event type as parameter. Of course it is not ExitProcess() that is called, but CtrlRoutine(). This function lives in kernel32.dll, too, but it is not exported, i.e. GetProcAddress() won't find it. The trick proposed in the blog post (to send a test ConsoleCtrl event to the process itself, using a special handler that then inspects the stack trace to figure out the address of the caller) does not work for us, however: it would send a CTRL_BREAK_EVENT to *all* processes attached to the same Console, essentially killing MinTTY. But could we make this still work somehow? Yes, we could. We came up with yet another trick up our sleeves: instead of determining the address of kernel32!CtrlRoutine in our own process, we spawn a new one, with a new Console, to avoid killing MinTTY. To do that, we need a helper .exe, of course, which we put into /usr/libexec/. If this helper is not found, we fall back to the previous methods of injecting ExitProcess() or calling TerminateProcess(). This method (to spawn a helper .exe) has a further incidental benefit: by compiling 32-bit *and* 64-bit helpers and providing them as getprocaddr32.exe and getprocaddr64.exe, we can now also handle 32-bit processes in a 64-bit Git for Windows. Sadly not vice versa: calling CreateRemoteThread() on a 64-bit process from a 32-bit process seems to fail all the time (and require a lot of assembly hackery to fix that I am not really willing to include in Git for Windows' MSYS2 runtime). The current method was implemented in this commit: ca6188a7520 This is the hopeful final fix for git-for-windows/git#1491, git-for-windows/git#1470, git-for-windows/git#1248, git-for-windows/git#1239, git-for-windows/git#227, git-for-windows/git#1553, nodejs/node#16103, and plenty other tickets that petered out mostly due to a willingness of community members to leave all the hard work to a single, already overworked person. This fix also partially helps git-for-windows/git#1629 (only partially because the user wanted to quit the pager using Ctrl+C, which is not the intended consequence of a Ctrl+C: it should stop the Git process, but not the pager). Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
naveen521kk
pushed a commit
to naveen521kk/msys2-runtime
that referenced
this issue
Mar 15, 2021
This thing again... Background: when you hit Ctrl+C on Linux or macOS, a signal (SIGINT) is sent to the foreground process and its child processes. This signal can be intercepted by installing a signal handler for this specific signal. On Windows, there is no precise equivalent for this system. Instead, the Ctrl+C is translated by the current ConHost (i.e. the container running the Console processes) to a ConsoleCtrl event that is sent to all processes attached to that Console. If any of these processes installed a handler via SetConsoleCtrlHandler(), they can intercept that event (and avoid exiting or doing some cleanup work). On Linux and macOS (and every Unix flavor, really), processes can also be killed via the `kill` executable, which really just sends a signal to the process, typically SIGTERM. Processes can intercept that signal, too. To force processes to terminate, without giving them any chance to prevent that, SIGKILL can be sent. There is no equivalent for SIGTERM on Windows. To emulate SIGKILL on Windows, TerminateProcess() can be used, but it only kills one process (unlike SIGKILL, which is sent also to the child processes). In Git for Windows, we struggled with emulating SIGINT, SIGTERM and SIGKILL handling essentially since the beginning of the efforts to port Git to Windows. At least the SIGINT part of the problem becomes a lot worse when using a terminal window other than cmd.exe's: as long as using cmd.exe (AKA "ConHost"), Ctrl+C is handled entirely outside of our code. But with the big jump from v1.x to v2.x, Git for Windows not only switched from MSys to MSYS2, but also started using MinTTY as the default terminal window, which uses the MSYS2 runtime-provided pseudo terminals (inherited from Cygwin thanks to the MSYS2 runtime being a "friendly fork" of Cygwin). When Ctrl+C is pressed in MinTTY, all of the signaling has to be done by our code. The original code to handle Ctrl+C comes straight from Cygwin. It simply ignores the entire conundrum for non-Cygwin processes and simply calls TerminateProcess() on them, leaving spawned child processes running. The first attempt at fixing "the Ctrl+C problem" (with the symptom that interrupting `git clone ...` would not stop the actual download of the Git objects that was still running in a child process) was git-for-windows/msys2-runtime@c4ba4e3357f. It simply enumerated all the processes' process IDs and parent process IDs and extracted the tree of (possibly transitive) child processes of the process to kill, then called TerminateProcess() on them. This solved the problem with interrupting `git clone`, but it did not address the problem that Git typically wants to "clean up" when being interrupted. In particular, Git installs atexit() and signal handlers to remove .lock files. The most common symptom was that a stale .git/index.lock file was still present after interrupting a Git process. Based on the idea presented in Dr Dobb's Journal in the article "A Safer Alternative to TerminateProcess()" by Andrew Tucker (July 1, 1999) http://www.drdobbs.com/a-safer-alternative-to-terminateprocess/184416547 we changed our handling to inject a remote thread calling ExitProcess() first, and fall back to TerminateProcess() the process tree instead: git-for-windows/msys2-runtime@e9cb332976c This change was a little misguided in hindsight, as it only called TerminateProcess() on the process tree, but expected the atexit() handler of Git to take care of the child processes when killing the process via the remote ExitProcess() method. Therefore, we changed the strategy once again, to inject ExitProcess() threads into the child processes of the process to kill, too: git-for-windows/msys2-runtime@53e5c0313e1 (That commit also tries to handle Cygwin process among the child processes by sending Cygwin signals, but unfortunately that part of the commit was buggy.) This worked well for Git processes. However, Git Bash is used in all kinds of circumstances, including launching Maven, or node.js scripts that want to intercept SIGINT. Naturally, these callees have no idea that Git for Windows injects an ExitProcess() with exit code 130 (corresponding to 0x100 + SIGINT). Therefore, they never "got" the signal. So what is it that happens when ConHost generates a ConsoleCtrl event? This question was asked and answered in the excellent blog post at: http://stanislavs.org/stopping-command-line-applications-programatically-with-ctrl-c-events-from-net/#comment-2880 Essentially, the same happens as what we did with ExitProcess(): a remote thread gets injected, with the event type as parameter. Of course it is not ExitProcess() that is called, but CtrlRoutine(). This function lives in kernel32.dll, too, but it is not exported, i.e. GetProcAddress() won't find it. The trick proposed in the blog post (to send a test ConsoleCtrl event to the process itself, using a special handler that then inspects the stack trace to figure out the address of the caller) does not work for us, however: it would send a CTRL_BREAK_EVENT to *all* processes attached to the same Console, essentially killing MinTTY. But could we make this still work somehow? Yes, we could. We came up with yet another trick up our sleeves: instead of determining the address of kernel32!CtrlRoutine in our own process, we spawn a new one, with a new Console, to avoid killing MinTTY. To do that, we need a helper .exe, of course, which we put into /usr/libexec/. If this helper is not found, we fall back to the previous methods of injecting ExitProcess() or calling TerminateProcess(). This method (to spawn a helper .exe) has a further incidental benefit: by compiling 32-bit *and* 64-bit helpers and providing them as getprocaddr32.exe and getprocaddr64.exe, we can now also handle 32-bit processes in a 64-bit Git for Windows. Sadly not vice versa: calling CreateRemoteThread() on a 64-bit process from a 32-bit process seems to fail all the time (and require a lot of assembly hackery to fix that I am not really willing to include in Git for Windows' MSYS2 runtime). The current method was implemented in this commit: git-for-windows/msys2-runtime@ca6188a7520 This is the hopeful final fix for git-for-windows/git#1491, git-for-windows/git#1470, git-for-windows/git#1248, git-for-windows/git#1239, git-for-windows/git#227, git-for-windows/git#1553, nodejs/node#16103, and plenty other tickets that petered out mostly due to a willingness of community members to leave all the hard work to a single, already overworked person. This fix also partially helps git-for-windows/git#1629 (only partially because the user wanted to quit the pager using Ctrl+C, which is not the intended consequence of a Ctrl+C: it should stop the Git process, but not the pager). Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
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I was not able to find an open or closed issue matching what I'm seeing
Which version of Git for Windows are you using? Is it 32-bit or 64-bit?
Windows 7, 64-bit
defaults?
to the issue, you're seeing?
No
Bash
Minimal, Complete, and Verifiable example
this will help us understand the issue.
git log
git should work normally, i.e it should execute any git commands that are entered.
git stucks no keyboard input shows response in bash terminal
URL to that repository to help us with testing?
Private repository
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