php: Basic flock() example

basic_flock_example.php

<?php
/*

basic flock() example

1. open 2 terminals
2. in first terminal, execute `./basic_flock_example.php --first`
3. then *quickly* in second terminal, execute `./basic_flock_example --second`
4. once both have finished, view the output file: `cat file`

*/
$longopts = array('first', 'second');
$opts = getopt('', $longopts);
if (isset($opts['second'])) {

    run_trying_to_access_file_with_lock();

} else {

    create_and_write_to_a_file_with_lock();
}

function create_and_write_to_a_file_with_lock() {

    $seconds = 10;

    echo "Locking a file and writing for {$seconds} seconds before unlocking...\n";

    $handle = fopen("file", "a");
    if ($handle === false) {
        die("Unable to open `file` for appending. Check your permissions!\n");
    }

    echo "Opened `file`...\n";

    // attempt to lock the file
    if (flock($handle, LOCK_EX)) {

        echo "Obtained the lock...\n";

        for ($i = 1; $i < $seconds + 1; $i++) {

            fwrite($handle, "--first\n");
            sleep(1);

            echo "{$i}...\n";
        }

        echo "Unlocking `file`...\n";
        flock($handle, LOCK_UN);

    } else {

        echo "Unable to acquire lock on `file`!\n";
    }

    fclose($handle);
    echo "Closed `file`...\n";

    echo "Done!\n";
}

function run_trying_to_access_file_with_lock() {

    echo "Attempting to write to a file which is locked by another process...\n";

    $handle = fopen("file", "a");
    if ($handle === false) {
        die("Unable to open `file` for appending. Check your permissions!\n");
    }

    echo "Opened `file`...\n";

    // flock() blocks waiting to lock
    // you can adjust this behavior by adding
    // LOCK_NB to the second paramter ($operation):
    //      LOCK_EX | LOCK_NB
    if (flock($handle, LOCK_EX)) {

        echo "Obtained the lock...\n";

        fwrite($handle, "--second\n");

        echo "Unlocking `file`...\n";
        flock($handle, LOCK_UN);

    } else {

        echo "Unable to acquire lock on `file`!\n";
    }

    fclose($handle);
    echo "Closed `file`...\n";

    echo "Done!\n";
}