PHP IPC demo using pcntl_fork

ipc_fork.php

<?php

const SHM_KEY = 0x1337;

function printfln($str, ...$args) {
    printf($str . "\n", ...$args);
}

function sprintfln($str, $args) {
    return sprintf($str . "\n", ...$args);
}

function signal_handler($errno) {
    global $child_pid;

    switch ($errno) {
        case SIGTERM:
            printfln("SIGTERM");
            break;
        case SIGINT:
            printfln("SIGINT");
            break;
        default:
            printfln("signal %d received\n", $errno);
    }

    // parent process received the signal
    if ($child_pid > 0) {
        printf("Killing child process (PID %d)\n", $child_pid);
        // not sure if the child process will ever receive this
        // because the terminal output still shows SIGINT
        // regardless of whether posix_kill is called or not
        posix_kill($child_pid, SIGTERM);
        pcntl_wait($status); // Wait for the child to exit
        printf("Child process exited\n");
    }

    die();
}

pcntl_signal(SIGTERM, 'signal_handler');
pcntl_signal(SIGINT, 'signal_handler');

$mem = shm_attach(SHM_KEY, 1024);

if ($mem === false) {
    die("failed to create shared memory area");
}

$child_pid = pcntl_fork();

if ($child_pid < 0) {
    $errcode = pcntl_get_last_error();
    $errmsg = pcntl_strerror($errcode);
    die(sprintfln("failed to fork (%d): %s", $errcode, $errmsg));
} else if ($child_pid) { // in parent
    printfln("parent process started");
    printfln("child pid: %d", $child_pid);

    $i = 0;
    while (true) {
        sleep(3); // simulate some work
        shm_put_var($mem, 1, "some data " . $i);
        $i++;

        pcntl_signal_dispatch();
    }

    // unreachable
    printfln("parent process finished");
} else { // in child process
    printfln("child process started");

    while (true) {
        printfln("waiting for data");
        while (shm_has_var($mem, 1) === false) {}

        printfln("received data");
        $val = shm_get_var($mem, 1);
        var_dump($val);
        $ret = shm_remove_var($mem, 1);

        if ($ret === true) {
            printfln("key removed");
        } else {
            printfln("failed to remove key");
        }

        pcntl_signal_dispatch();
    }

    printfln("child process finished");
}