Description:
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I did a lot of research regarding flock() and timeouts.

I found workarounds using pcntl_signal/alarm which only work on the CLI:
https://github.com/php-lock/lock/blob/8b254edfe1400a733e3cde571e981687e6f6d804/classes/util/PcntlTimeout.php#L68-L94

our current workaround is to use LOCK_NB in a loop + usleep() until it succeeds, which feels rather hacky and wastes a lot of IO especially on NFS based volumes.
This was the only way I found to get it working in a web sapi.

wouldn't it be possible to e.g. take a stream_set_timeout() into account for the blocking flock() case?

Test script:
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$fd = fopen("/path/to/my/file", 'c+');

stream_set_timeout($fd, 0, 1);
var_dump(flock($fd, LOCK_EX)); // should return false on timeout

$info = stream_get_meta_data($fd);
var_dump($info); // should report a timeout