Description:
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Test Case
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1) Just start Apache with mod_php
2) generate some load (e.g. ab -t 120 http://.../hello.php)
3) run 'apachectl restart' for few times
4) 'apachectl stop'
5) Check Apache error_log

You will see warning and error messages:

[warn] child process 15317 still did not exit, sending a SIGTERM

[error] child process 15317 still did not exit, sending a SIGKILL

The reason of these errors is the fact that Apache/mod_php worker processws ignore SIGHIP and the main Apache process kills them using SIGTERM or SIGKILL.

I tried to analyze and debug zend_signal.c and found very wired behavior.

On first request zend_signal_activate() sets its own signal handler for SIGHUP and stores the original handler in SIGG(handlers)[SIGHUP-1].handler, but on second request the same zend_signal_activate() overwrites the original signal handler by handler from parent process.

zend_signal.c:284

memcpy(&SIGG(handlers), &global_orig_handlers, sizeof(global_orig_handlers));

As result the original signal handler for SIGHUP is never called.
Even worse after restart and two request SIGG(handlers)[SIGHUP-1].handler becomes SIG_IGN and SIGHUP is ignored at all.