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fix: keep Go's preemption signal off the PHP threads - #2833
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nicolas-grekas wants to merge 1 commit into
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The Go runtime preempts goroutines with SIGURG, sent to the thread that runs them. A PHP thread runs Go code during each callback, and the signal may only land once the thread is back in PHP and entering a system call, which then fails with EINTR: stream_select() returns false with a warning, a poll context throws. Blocking the signal when the thread starts does not hold, Go unblocks it at the first call into Go. Blocked after that call, it stays blocked, since the thread keeps its M.
henderkes
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Nov 12, 2026
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I'm starting to understand why everyone hates Cgo. I wish there was a long-term solution to all these Go runtime things without kicking the project into manual go library build mode.
dunglas
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Nov 12, 2026
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The Go runtime preempts goroutines with
SIGURG, sent to the thread that runs them. A PHP thread runs Go code during each callback, and the signal may only land once the thread is back in PHP and entering a system call, which then fails withEINTR:stream_select()returnsfalsewith a warning,Io\Poll\Context::wait()throws aFailedPollWaitException.I get one interrupted wait in 240k when a script follows tasks through a poll context (#2636), and none with
GODEBUG=asyncpreemptoff=1.Blocking the signal when the thread starts doesn't hold: Go unblocks it at the first call into Go. Blocked after that call, it stays blocked, since the thread keeps its M. The Go code of a PHP thread is then preempted at its safe points only, which its callbacks reach quickly.