php-pcntlHow to use shared memory with the PCNTL_FORK function in PHP?

Shared memory is a memory segment that can be accessed by multiple processes. It can be used with the PCNTL_FORK function in PHP to allow multiple processes to access the same data.

Example code

<?php
$shm_key = ftok(__FILE__, 't');
$shm_id = shm_attach($shm_key, 1024, 0600);

if (pcntl_fork() == 0) {
    // Child process
    $data = shm_get_var($shm_id, 1);
    echo "Child read: $data\n";
    shm_detach($shm_id);
} else {
    // Parent process
    shm_put_var($shm_id, 1, "Hello world");
    pcntl_wait($status);
    shm_remove_var($shm_id, 1);
    shm_detach($shm_id);
}

Output example

Child read: Hello world

Code explanation

$shm_key = ftok(__FILE__, 't');: Generates a unique key for the shared memory segment.
$shm_id = shm_attach($shm_key, 1024, 0600);: Attaches the shared memory segment to the current process.
if (pcntl_fork() == 0) {: Creates a child process.
$data = shm_get_var($shm_id, 1);: Gets the value of the shared memory segment.
echo "Child read: $data\n";: Prints the value of the shared memory segment.
shm_put_var($shm_id, 1, "Hello world");: Sets the value of the shared memory segment.
pcntl_wait($status);: Waits for the child process to finish.
shm_remove_var($shm_id, 1);: Removes the shared memory segment.
shm_detach($shm_id);: Detaches the shared memory segment from the current process.

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