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Auto merge of #5030 - alexcrichton:better-poll, r=matklad

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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.
This commit is contained in:
bors 2018-02-12 17:53:00 +00:00
commit cb30fba4a3
1 changed files with 14 additions and 10 deletions
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24
src/cargo/util/read2.rs
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@ -27,9 +27,12 @@ mod imp {
fds[0].events = libc::POLLIN; fds[0].events = libc::POLLIN;
fds[1].fd = err_pipe.as_raw_fd(); fds[1].fd = err_pipe.as_raw_fd();
fds[1].events = libc::POLLIN; 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` // 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 { if r == -1 {
let err = io::Error::last_os_error(); let err = io::Error::last_os_error();
if err.kind() == io::ErrorKind::Interrupted { 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))? { if !err_done && fds[errfd].revents != 0 && handle(err_pipe.read_to_end(&mut err))? {
out_done = true;
}
data(true, &mut out, out_done);
if !err_done && fds[1].revents != 0 && handle(err_pipe.read_to_end(&mut err))? {
err_done = true; err_done = true;
nfds -= 1;
} }
data(false, &mut err, err_done); data(false, &mut err, err_done);
if !out_done && fds[0].revents != 0 && handle(out_pipe.read_to_end(&mut out))? {
if out_done && err_done { out_done = true;
return Ok(()) fds[0].fd = err_pipe.as_raw_fd();
errfd = 0;
nfds -= 1;
} }
data(true, &mut out, out_done);
} }
Ok(())
} }
} }