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Bug #73783 SIG_IGN doesn't work when Zend Signals is enabled
Submitted: 2016-12-19 10:25 UTC Modified: 2016-12-29 20:17 UTC
From: zorg at razza dot org Assigned:
Status: Closed Package: PCNTL related
PHP Version: 7.1.0 OS: Ubuntu 16.04.1 LTS
Private report: No CVE-ID:
 [2016-12-19 10:25 UTC] zorg at razza dot org
The use of pcntl_signal(SIGCHLD, SIG_IGN) breaks sleep(). In 7.0 the below script would sleep for 60 seconds then exit, in 7.1 the script does not sleep at all.

Test script:
pcntl_signal(SIGCHLD, SIG_IGN);

Expected result:
Sleep for 60 seconds, print 'Done' and exit.

Actual result:
Instantly prints 'Done' and exist.


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 [2016-12-19 10:30 UTC] zorg at razza dot org
Sorry, the test script is incorrect. It should be:

pcntl_signal(SIGCHLD, SIG_IGN);
$pid = @pcntl_fork();
if ($pid == -1)
  exit(pcntl_get_last_error() . ': ' . pcntl_strerror(pcntl_get_last_error()));
elseif ($pid == 0)


This also creates a <defunct> process when pcntl_signal(SIGCHLD, SIG_IGN) should have removed it.
 [2016-12-19 14:00 UTC]
-Package: *General Issues +Package: PCNTL related
 [2016-12-19 20:54 UTC] dave at mudsite dot com
This bug exists because ZEND_SIGNALS was defaulted to "yes" with PHP 7.1.  The problem with this is that sleep() will sleep for the number of seconds, OR, is interrupted by a signal that is not ignored.

With your test script with pcntl_signal(SIGCHLD, SIG_IGN), you're instructing PHP to ignore the end of a child.  However, ZEND_SIGNALS, zend_sigaction() sets the set handler into the SIGG(handlers), but, will set the actual signal handler to zend_signal_handler_defer, which is not SIG_IGN.  As such, during the sleeping, when a SIGCHLD is raised, sleep bails because it is not "ignored" at the system level, and ends up calling zend_signal_handler_defer which will not process the signal.

I believe a safe fix would be to in zend_sigaction, only set the defer handler IF the incoming sigact's handler is not SIG_IGN.  Will make a PR and see if it's acceptable or not.
 [2016-12-20 08:15 UTC] zorg at razza dot org
Would this also fix the issue where pcntl_signal(SIGCHLD, SIG_IGN) no longer stops <defunct> threads from remaining until the main process has ended? In 7.0 threads would exit cleanly, but since upgrading to 7.1 they all sit as <defunct> now.
 [2016-12-20 15:41 UTC] dave at mudsite dot com
I would assume as much, I wasn't directly able to replicate the <defunct> process. I tried on both my Debian setup & MacOS 10.12, which both lack the <defunct> but do both sleep correctly with the fix in place.
The output I get with PHP 7.1, and my fix are as follows:

dwalker@linux:~/src/php PHP-7.1 › time sapi/cli/php e.php && ps aux | grep defunc
Child Dying
After Sleep
real    0m0.022s
user    0m0.004s
sys     0m0.016s
dwalker  24037  0.0  0.0  12784   940 pts/3    S+   08:38   0:00 grep --color=auto defunc

dwalker@linux:~/src/php fix-73783 › time sapi/cli/php e.php && ps aux | grep defunc
Child Dying
After Sleep

real    0m10.015s
user    0m0.012s
sys     0m0.004s
dwalker  16683  0.0  0.0  12784   900 pts/3    S+   08:37   0:00 grep --color=auto defunc
 [2016-12-29 20:17 UTC]
-Summary: pcntl_signal() issue +Summary: SIG_IGN doesn't work when Zend Signals is enabled
 [2016-12-29 20:19 UTC]
Automatic comment on behalf of
Log: Fixed bug #73783
 [2016-12-29 20:19 UTC]
-Status: Open +Status: Closed
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