Allow waitpid(-1) to be woken if a waitpid(pid) call is pending (3.1 backport) #8246
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If two threads are running, with one calling waitpid(-1), and another calling waitpid($some_pid), and then $some_other_pid exits, we would expect the waitpid(-1) call to retrieve that exit status; however, it cannot actually do so until $some_pid _also_ exits. This patch fixes the issue by unconditionally checking for pending process group waits on SIGCHLD, and then allowing pending pid-only waits to "steal" the notification. [Fixes #19387]
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Apologies @hsbt - I had messed up my merging and a previous version of this PR failed the test I added. I've fixed that now. The current CI failures all seem to be build infrastructure issues... |
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@unak Do you know if there is a timeline for another Ruby 3.1 or 3.2 release? We hit this bug in production (puma/puma#3313), and it caused some significant performance issues. |
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If two threads are running, with one calling waitpid(-1), and another calling waitpid($some_pid), and then $some_other_pid exits, we would expect the waitpid(-1) call to retrieve that exit status; however, it cannot actually do so until $some_pid also exits.
This patch fixes the issue by unconditionally checking for pending process group waits on SIGCHLD, and then allowing pending pid-only waits to "steal" the notification.
https://bugs.ruby-lang.org/issues/19837
[Fixes #19387]