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Auto merge of #5030 - alexcrichton:better-poll, r=matklad
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.
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commit
cb30fba4a3
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@ -27,9 +27,12 @@ mod imp {
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fds[0].events = libc::POLLIN;
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fds[1].fd = err_pipe.as_raw_fd();
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fds[1].events = libc::POLLIN;
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loop {
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let mut nfds = 2;
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let mut errfd = 1;
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while nfds > 0 {
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// wait for either pipe to become readable using `select`
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let r = unsafe { libc::poll(fds.as_mut_ptr(), 2, -1) };
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let r = unsafe { libc::poll(fds.as_mut_ptr(), nfds, -1) };
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if r == -1 {
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let err = io::Error::last_os_error();
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if err.kind() == io::ErrorKind::Interrupted {
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@ -55,19 +58,20 @@ mod imp {
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}
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}
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};
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if !out_done && fds[0].revents != 0 && handle(out_pipe.read_to_end(&mut out))? {
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out_done = true;
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}
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data(true, &mut out, out_done);
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if !err_done && fds[1].revents != 0 && handle(err_pipe.read_to_end(&mut err))? {
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if !err_done && fds[errfd].revents != 0 && handle(err_pipe.read_to_end(&mut err))? {
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err_done = true;
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nfds -= 1;
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}
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data(false, &mut err, err_done);
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if out_done && err_done {
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return Ok(())
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if !out_done && fds[0].revents != 0 && handle(out_pipe.read_to_end(&mut out))? {
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out_done = true;
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fds[0].fd = err_pipe.as_raw_fd();
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errfd = 0;
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nfds -= 1;
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}
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data(true, &mut out, out_done);
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}
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Ok(())
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}
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}
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