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stream_select() leaks a stream-error operation level on its FD_SETSIZE failure path #24506
Description
Description
Each stream_select() call that hits the PHP_SAFE_MAX_FD check (any fd >= FD_SETSIZE, 1024 on macOS and Linux) emits its "You MUST recompile PHP with a larger value of FD_SETSIZE" warning and returns false. It also leaves one operation level open.
After 1,000 such calls, every later stream operation in the process (fread, fwrite, ..etc) emits:
Warning: fread(): Stream error operation depth exceeded (1000), possible infinite recursion
The operation itself still succeeds. The warnings never stop until the process exits.
Example:
$keep = [];
while (true) { // open sockets until one has fd >= 1024
$p = stream_socket_pair(STREAM_PF_UNIX, STREAM_SOCK_STREAM, 0);
$keep[] = $p;
if (count($keep) * 2 > 1100) {
break;
}
}
[$hi] = end($keep);
[$a, $b] = stream_socket_pair(STREAM_PF_UNIX, STREAM_SOCK_STREAM, 0);
$calls = (int) ($argv[1] ?? 1001);
for ($i = 0; $i < $calls; $i++) {
$r = [$hi]; $w = $e = null;
@stream_select($r, $w, $e, 0);
}
fwrite($b, 'x');
$last = null;
set_error_handler(function ($no, $str) use (&$last) {
$last = $str;
return true;
});
$data = fread($a, 1);
restore_error_handler();
printf("after %d over-limit stream_select() calls: fread()=%s warning=%s\n", $calls, var_export($data, true), $last ?? 'none');ulimit -n 4096
php reproduce.php 2000 # 8.6.0RC3: warning=fread(): Stream error operation depth exceeded (1000)...
php reproduce.php 999 # no warningOn 8.5.4 the same script prints warning=none.
PHP Version
PHP 8.5.4 (cli) (built: Mar 31 2026 17:40:26) (NTS)
Copyright (c) The PHP Group
Zend Engine v4.5.4, Copyright (c) Zend Technologies
with Zend OPcache v8.5.4, Copyright (c), by Zend Technologies
Operating System
MacOS
Activity
ndossche commentedon Oct 22, 2026
Fixed via #24507