PHP RFC: Additional Context in pcntl_signal Handler

• Version: 0.1
• Date: 2016-06-14
• Author: David Walker dave@mudsite.com, Bishop Bettini bishop@php.net
• Status: Draft
• First Published at: http://wiki.php.net/rfc/additional-context-in-pcntl-signal-handler

Modern UNIX kernels include additional context when delivering a signal, however the callable handler for pcntl_signal does not receive this information. Developers coordinating multiple processes through signals must arrange to gather and send this same information using alternative channels, which is time-consuming, error-prone, and unnecessary.

Currently the signal handler receives only one formal argument, the number of the signal sent. This proposal would add a second formal argument, an array of signal info as provided by the kernel, as seen here:

<?php
pcntl_signal(SIGUSR1, function ($signo, $siginfo) {
    print_r($siginfo);
});
posix_kill(0, SIGUSR1);

The $siginfo array may contain one or more of the following keys, depending upon the system support for signal information and the nature of the sent signal:

• si_signo, the signal number being sent (duplicates the first argument).
• si_code, the signal code, which depends upon the signal sent and provides context-specific reason why the signal was sent.
• si_value, the value for the code, if appropriate.

These are generally useful to a wide range of process interactions.

There are no backward compatibility breaks.

Next PHP 7.x.

TODO

The pcntl extension will be updated.

TODO

• Should we send null if the underlying system doesn't support siginfo_t, or should we send array ()?
• Should we normalize the array keys (for example, si_signo is removed because it's a duplicate, and si_code becomes just code)?
• Are there any effects to opcache or web SAPI?

Vote shall be Yes or No to deliver kernel-provided additional context to the pcntl_signal handler.

Requires a 50%+1 majority.

• Work in Progress

• Initial ping to php.internals