fix(process): read stdout and stderr together so large output can't deadlock - #1939
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mrrobot47 merged 2 commits intoSep 29, 2026
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…eadlock Process::run() read stdout to EOF before it read stderr. A child that wrote more than a pipe buffer (about 64 KB) to stderr blocked on that write while EE waited for stdout, so both hung forever. EE::runcommand() with 'return' read its pipes the same way. The new Utils\read_pipes() waits on both pipes with stream_select() and reads whichever has data until both reach EOF. On Windows, where stream_select() can't wait on process pipes, or if stream_select() fails, it falls back to the previous blocking reads.
stream_select() returns false on EINTR, and select() is never restarted after a caught signal. site-command installs pcntl handlers for SIGTERM, SIGHUP, SIGUSR1 and SIGINT, so a signal during a site command dropped read_pipes() back to the sequential blocking reads, where more than 64 KB of stderr could hang again. Retry on an interrupted system call, as Symfony Process does, and fall back only on other errors. Also say in the docblock that read_pipes() takes output pipes only.
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Copilot review overview
🟡 Changes recommended
The deadlock fix lacks an automated regression test covering outputs larger than the pipe buffer.
Review effort: Balanced
Findings: 1
What changed in this PR
Prevents process deadlocks by consuming stdout and stderr concurrently.
Changes:
- Adds non-blocking pipe reads using
stream_select(). - Handles interrupted selects and Windows fallback.
- Integrates concurrent reads into both process execution paths.
| File | Description |
|---|---|
php/utils.php |
Adds concurrent pipe-reading utility. |
php/EE/Process.php |
Uses concurrent reads in Process::run(). |
php/class-ee.php |
Uses concurrent reads in runcommand(). |
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EE\Process::run()read the child's stdout to EOF and only then read stderr. A child that writes more than a pipe buffer (about 64 KB on Linux) to stderr blocks on that write while EE is still waiting for stdout to close, soEE::exec()/EE::launch()hang forever.EE::runcommand()withreturnread its pipes the same way.This adds
Utils\read_pipes(), which makes both pipes non-blocking and reads whichever is ready withstream_select()until both reach EOF.run()returns the sameProcessRunfields as before.stream_select()(site-command installspcntlhandlers), the select is retried, as Symfony Process does.stream_select()can't wait on process pipes, or ifstream_select()fails for another reason, it falls back to the previous blocking reads.Testing
Process::create()->run()on PHP 7.4 and 8.0–8.5: 100 KB of stderr, 1 MB of stdout, 200 KB of both interleaved, output in bursts, binary bytes, a non-zero exit, no output, env and cwd, stdin passed through, and an stdin that is never closed. Before this change, every case with more than 64 KB of stderr hangs; after it, all cases pass.php -lon 7.4 and 8.5.