Shared Memory Operations (SHMOP)

shmop is a PHP extension that gives direct, low-level access to Unix shared memory segments. It exposes a small set of functions, shmop_open(), shmop_read(), shmop_write(), shmop_size(), and shmop_delete(), to allocate a block of shared memory, read from it, write to it, and release it.

Because the memory segment is identified by a system id and lives outside the memory of any single PHP process, it can be opened and shared by multiple, otherwise unrelated processes: several PHP-FPM workers, or a mix of PHP and non-PHP processes, can all attach to the same segment and see each other’s writes immediately, without going through a database, a file, or a network round-trip.

shmop provides no built-in locking or synchronization, so concurrent writers must coordinate themselves, typically using the sysvsem semaphore functions, to avoid corrupting the segment with interleaved writes.

<?php

    // adapted from the PHP manual: https://www.php.net/manual/en/shmop.examples-basic.php
    $shm_id = shmop_open(0xff3, 'c', 0644, 100);

    $data = 'shared payload';
    shmop_write($shm_id, $data, 0);

    $read = shmop_read($shm_id, 0, strlen($data));
    echo $read . PHP_EOL;

    shmop_delete($shm_id);

?>

Documentation

See also shmop basic examples.

Related : Shared Memory, Shared, Semaphore, Concurrency