[WIP] Reading I/O from processes is uninterruptible, leading to hangs #109
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In some Linux environments and on FreeBSD, I've observed frequent hangs due to Swift Concurrency task cancellation terminating a process via the teardown sequence, while reading the output hangs forever. I expect the present issues on GitHub Actions Linux CI are due to this as well, though strangely I haven't been able to reproduce it on my local aarch64 Linux VM. I'm not sure why this doesn't seem to occur on macOS and Windows, though a likely explanation is that Subprocess's Windows implementation doesn't use DispatchIO, and Dispatch is very buggy on non-Apple platforms. I/O reading needs to be cancellable so that the library doesn't hang. This is quite readily reproducible with testCancelProcessVeryEarlyOnStressTest on FreeBSD; sleep will get zombied from the cancellation but the library will sit waiting for output forever if it managed to get into DispatchIO.read before the cancellation took effect. To solve this, (ab)use an AsyncStream to force early cancellation when the parent task is cancelled. Closes #108
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In some Linux environments and on FreeBSD, I've observed frequent hangs due to Swift Concurrency task cancellation terminating a process via the teardown sequence, while reading the output hangs forever. I expect the present issues on GitHub Actions Linux CI are due to this as well, though strangely I haven't been able to reproduce it on my local aarch64 Linux VM.
I'm not sure why this doesn't seem to occur on macOS and Windows, though a likely explanation is that Subprocess's Windows implementation doesn't use DispatchIO, and Dispatch is very buggy on non-Apple platforms.
I/O reading needs to be cancellable so that the library doesn't hang. This is quite readily reproducible with testCancelProcessVeryEarlyOnStressTest on FreeBSD; sleep will get zombied from the cancellation but the library will sit waiting for output forever if it managed to get into DispatchIO.read before the cancellation took effect.
To solve this, (ab)use an AsyncStream to force early cancellation when the parent task is cancelled.
Closes #108