Listening signals

Listening signals: pcntl_signal()

One of the methods used by the operating system to communicate with the running processes is through signals. The operating system uses signals to communicate to the processes something like: “I want to stop your execution.” For example, if the user wants to stop the execution of the process, he can use the shell command kill or pressing CTRL+C to tell the operating system send a signal to the target process.

If in a PHP script you want to detect when the script receives a signal, you can use the pcntl_signal() function. The first argument is the signal you want to detect. The kill command, and CTRL+C both send a SIGINT signal. The second argument is the custom function to be executed, when the script receives the signal.

Note

In order to make pcntl_signal work in the right way, use declare(ticks=1);

declare(ticks=1);
echo "Installing signal handler...\n";
/**
 * listening SIGINT signal.
 * SIGINT is triggered by:
 * - kill command
 * - CTRL + C keys
 */
pcntl_signal(
    SIGINT,
    function ($signal) {
        echo "Hi, you sent SIGINT, -" . $signal . "-" . PHP_EOL;
    }
);
sleep(100);
echo "This is the end" . PHP_EOL;