From ec991ebcb90149281f8601f7a1dd7f621268fd9a Mon Sep 17 00:00:00 2001 From: Alex Crichton Date: Mon, 12 Feb 2018 09:27:11 -0800 Subject: [PATCH] Don't spin on empty fds in `read2` on Unix This commit fixes what I think is some pathological behavior in Cargo where if one stdio stream is closed before another then Cargo can accidentally spin in a tight loop and not block appropriately. Previously, for example, if stderr closed before stdout then Cargo would spin in a `poll` loop continuously getting notified that stderr is closed. The behavior is now changed so after a file descriptor is done we stop passing it to `poll` and instead only pass the one remaining readable file descriptor. --- src/cargo/util/read2.rs | 24 ++++++++++++++---------- 1 file changed, 14 insertions(+), 10 deletions(-) diff --git a/src/cargo/util/read2.rs b/src/cargo/util/read2.rs index 74d6d67f271..7b268108296 100644 --- a/src/cargo/util/read2.rs +++ b/src/cargo/util/read2.rs @@ -27,9 +27,12 @@ mod imp { fds[0].events = libc::POLLIN; fds[1].fd = err_pipe.as_raw_fd(); fds[1].events = libc::POLLIN; - loop { + let mut nfds = 2; + let mut errfd = 1; + + while nfds > 0 { // wait for either pipe to become readable using `select` - let r = unsafe { libc::poll(fds.as_mut_ptr(), 2, -1) }; + let r = unsafe { libc::poll(fds.as_mut_ptr(), nfds, -1) }; if r == -1 { let err = io::Error::last_os_error(); if err.kind() == io::ErrorKind::Interrupted { @@ -55,19 +58,20 @@ mod imp { } } }; - if !out_done && fds[0].revents != 0 && handle(out_pipe.read_to_end(&mut out))? { - out_done = true; - } - data(true, &mut out, out_done); - if !err_done && fds[1].revents != 0 && handle(err_pipe.read_to_end(&mut err))? { + if !err_done && fds[errfd].revents != 0 && handle(err_pipe.read_to_end(&mut err))? { err_done = true; + nfds -= 1; } data(false, &mut err, err_done); - - if out_done && err_done { - return Ok(()) + if !out_done && fds[0].revents != 0 && handle(out_pipe.read_to_end(&mut out))? { + out_done = true; + fds[0].fd = err_pipe.as_raw_fd(); + errfd = 0; + nfds -= 1; } + data(true, &mut out, out_done); } + Ok(()) } }