PHP CLI process hangs forever on exit

Question

I have a PHP script that I run on the command line, and when the script is supposed to exit, it just hangs forever instead. It happens on both Windows and Linux so it is not OS related.

I have tried debugging the code with XDebug, stepping into the final exit statement (have tried die as well with no luck). After running through a few destructors on some objects, there is nothing more to step through and the process just waits forever. It does not do anything, not consuming any resources. The only way to get the process to exit is to kill it, e.g Ctrl+C

It does not happen in all my scripts, but I have a case that I can reproduce. I am not sure if it is in my code, library code (mostly Symfony, Doctrince etc.) or in PHP itself.

I have run the script using strace, and the end of the output is attached below. I do not know how to debug this output, but it seems like PHP is polling for something in the last statement.

How can I debug this further? Any help would be appreciated.

strace output:

fstat(12, {st_mode=S_IFREG|0777, st_size=1314, ...}) = 0
fstat(12, {st_mode=S_IFREG|0777, st_size=1314, ...}) = 0
fstat(12, {st_mode=S_IFREG|0777, st_size=1314, ...}) = 0
fstat(12, {st_mode=S_IFREG|0777, st_size=1314, ...}) = 0
mmap(NULL, 1314, PROT_READ, MAP_SHARED, 12, 0) = 0x7fb8b969c000
munmap(0x7fb8b969c000, 1314)            = 0
close(12)                               = 0
umask(022)                              = 022
close(3)                                = 0
close(4)                                = 0
write(11, "\1\0\0\0\1", 5)              = 5
shutdown(11, SHUT_RDWR)                 = 0
close(11)                               = 0
write(6, "\1\0\0\0\0\0\0\0", 8)         = 8
close(2)                                = 0
close(1)                                = 0
munmap(0x7fb8b969a000, 4096)            = 0
close(0)                                = 0
munmap(0x7fb8b969b000, 4096)            = 0
munmap(0x7fb8b3191000, 790528)          = 0
munmap(0x7fb8b32d3000, 266240)          = 0
munmap(0x7fb8b3314000, 266240)          = 0
munmap(0x7fb8b3355000, 266240)          = 0
munmap(0x7fb8b3396000, 266240)          = 0
munmap(0x7fb8b33d7000, 266240)          = 0
munmap(0x7fb8b3418000, 266240)          = 0
munmap(0x7fb8b3459000, 266240)          = 0
munmap(0x7fb8b349a000, 266240)          = 0
munmap(0x7fb8b34db000, 266240)          = 0
munmap(0x7fb8b351c000, 266240)          = 0
munmap(0x7fb8b94ba000, 266240)          = 0
write(10, "\1\0\0\0\0\0\0\0", 8)        = 8
poll([{fd=5, events=POLLIN}], 1, 4294967295Process 1358 detached
 <detached ...>

Answer 1

I found that the issue was related to the ZMQ extension. My script was trying to send a message to a non-existing host, and even when disconnecting the socket at the end of my script, the socket was waiting forever trying to send the data.

For anyone having the same problem, it can be resolved by setting the \ZMQ::SOCKOPT_LINGER option on the socket to a low value, e.g.

<?php

$context = new \ZMQContext(1);
$socket = new \ZMQSocket($context, \ZMQ::SOCKET_PUSH);
$dsn = 'tcp://127.0.0.1:1337';
$socket->connect($dsn);
$socket->send('hi');
echo 'Message sent' . PHP_EOL;

// Without this line, the script will wait forever after the exit statement
$socket->setSockOpt(\ZMQ::SOCKOPT_LINGER, 1000);
$socket->disconnect($dsn);
echo 'Socket disconnected' . PHP_EOL;
exit();