Signals

Ian Littman / @iansltx

AustinPHP January 2017 / http://ian.im/sig1701

kill -9 some-bad-app

pcntl

this is for CLIs and daemons

pcntl_signal(signal, callback)

• signal == integer signal number (use built-in constants!)
  • SIGINT (ctrl-c)
  • SIGHUP (restart)
  • SIGTERM (normal kill behavior)
  • SIGCONT, SIGUSR1, etc.
  • Nope, you can't override SIGKILL (kill -9)
• Callback works with any callable
  • 1st arg: signal #
  • 2nd arg (PHP 7.1+): SIGINFO_T struct, as an array

NOTE

Signal handlers are one level deep

Listening for signals

• Ticks
  • >= 4.3.0
  • Slow
• pcntl_signal_dispatch()
  • >= 5.3.0
  • Faster, but manual
• pcntl_async_signals(true)
  • >= 7.1.0
  • Great if you've got it!

Waiting on signals

• OS-dependent (no OS X support)
• Can wait with or without a timeout
  • pcntl_sigtimedwait() with timeout
  • pcntl_sigwaitinfo() without
• Don't need to use ticks/dispatch/etc.
• DO need to make sure callbacks are set
• DON'T expect those callbacks to be called
• Can wait on a set of signals (e.g. SIGCONT + SIGHUP)

Alarms are special

• SIGALRM
• pcntl_alarm(int)
  • Fires a SIGARLM at this process in int seconds
  • Replaces any set, pending alarm
• If the script is sleep()ing, ends that statement early
  • Consecutive sleep() will happen normally
  • Other signals behave the same way

Putting it all together

zombie.php (Repo)

Thanks!

Questions?