FrankenPHP: mutex not unlocked in `zend_bailout` case

[realFlowControl]

parallel replaces the sapi_module.ub_write function with a simple function that locks a mutex, calls whatever was in that function pointer before and upon return unlocks the mutex again. This hanging/freezing happens in the following situation:

• a thread does echo/printf/...
• parallel locks a mutex and calls frankenphp_ub_write()
• go_ub_write() returns an error for a closed connection (this is an assumption)
• FrankenPHP calls into php_handle_aborted_connection() https://github.com/dunglas/frankenphp/blob/ebdb2656b6d8af3e0e8aa96359b02dba013ab88c/frankenphp.c#L509
• ignore_user_abort is set to false (default) which will lead to a call to zend_bailout() in https://github.com/php/php-src/blob/70861c82df7ff944090a771cc40698d2cd7bd164/main/main.c#L2591
• the call will never return and the mutex wont be unlocked

The mutex around echo/printf is necessary to make them atomic from a PHP user land perspective. I'll have a look if I can detect a zend_bailout() somehow and release the mutex parallel holds.

Relates to:

• https://github.com/dunglas/frankenphp/issues/858#issuecomment-2175825212
• https://github.com/krakjoe/parallel/issues/308

[dunglas]

Thanks, I'll try to hack Static PHP CLI to see if this fixes this issue this afternoon.

[realFlowControl]

PR #314 will unlock the mutex in RSHUTDOWN and seems to solve the problem

[dunglas]

ok, let me know when there is a branch ready with all needed patches and I'll give it a try.

[realFlowControl]

You can try the florian/deadlock-in-echo branch from #314