termio/exec: fix 100% CPU usage after wait-after-command process exits #4171
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I haven't looked into it more closely, but I'm still seeing 100% CPU usage even with your changes in. Reproduction:
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Oh, my rebase... removed your change. Looking at it now. |
If the read thread has already exited, it will have closed the read end of the quit pipe. Unless SIGPIPE is masked with signal(SIGPIPE, SIG_IGN), or the macOS-specific fcntl(F_SETNOSIGPIPE), writing to the write end of a broken pipe kills the writer with SIGPIPE instead of returning -EPIPE as an error. This causes a crash if the read thread exits before threadExit. This was already a possible race condition if read() returns error.NotOpenForReading or error.InputOutput, but it's now much easier to trigger due to the recent "termio/exec: fix 100% CPU usage after wait-after-command process exits" fix. Fix this by closing the quit pipe instead of writing to it.
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Alright this looks clean to me. Thank you |
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read(2) returning 0 means that the other end of the pipe/pty has been
closed (EOF), so there cannot be any more output to read on the pipe, and
the io reader thread can just exit.
If exec.wait_after_command=false, the read thread's quit pipe is
immediately written to after the child process dies, so all is well.
However, if wait_after_command=true (which is the case when using Ghostty
to run a .command/.sh file on macOS), the read thread keeps spinning,
causing persistent 100% CPU usage per exited process.
Fix it by exiting the reader thread on EOF.