public function mustRun($callback = null)
{
if ($this->isSigchildEnabled() && !$this->enhanceSigchildCompatibility) {
throw new \RuntimeException('This PHP has been compiled with --enable-sigchild. You must use setEnhanceSigchildCompatibility() to use this method.');
}
if (0 !== $this->run($callback)) {
throw new ProcessFailedException($this);
}
return $this;
}