script_runner: Kill sub-processes on exit

bazel_tools/script_runner.bzl

@@ -75,6 +75,10 @@ def script_runner(ctx, name, script, data = [], collect_data = True, interpreter
 
 #include <unistd.h>
 
+#ifdef _WIN32
+#include <Windows.h>
+#endif
+
 #include "tools/cpp/runfiles/runfiles.h"
 using bazel::tools::cpp::runfiles::Runfiles;
 
@@ -100,6 +104,19 @@ int main(int argc, char** argv) {{
     argv_new[argc + 1] = nullptr;
 
 #ifdef _WIN32
+    // Create a JobObject to ensure that spawned subprocesses are killed.
+    // See https://docs.microsoft.com/en-us/windows/win32/api/winbase/nf-winbase-createjobobjecta.
+    std::unique_ptr<std::remove_pointer<HANDLE>::type, std::function<void(HANDLE)>> job_object(
+        CreateJobObject(NULL, NULL),
+        [](HANDLE h) {{ CloseHandle(h); }}
+    );
+    // Ensure that sub-processes are assigned to the same JobObject.
+    AssignProcessToJobObject(job_object.get(), GetCurrentProcess());
+    // Ensure that sub-processes are killed on exit.
+    JOBOBJECT_EXTENDED_LIMIT_INFORMATION info = {{0}};
+    info.BasicLimitInformation.LimitFlags = JOB_OBJECT_LIMIT_KILL_ON_JOB_CLOSE;
+    SetInformationJobObject(job_object.get(), JobObjectExtendedLimitInformation, &info, sizeof(info));
+
     // On Windows execv does not behave as expected,
     // see https://github.com/austriancoder/ccache-win32/issues/3#issuecomment-120084234.
     int status = spawnv(_P_WAIT, argv_new[0], argv_new.get());