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# XCI. Shared Memory Functions

Shmop is an easy to use set of functions that allows php to read, write, create and delete UNIX shared memory segments. The functions will not work on windows, as it does not support shared memory. To use shmop you will need to compile php with the --enable-shmop parameter in your configure line.

> Note: In PHP 4.0.3, there functions were prefixed by `shm` rather than `shmop`.

Example 1. Shared Memory Operations Overview
    <?php

    // Create 100 byte shared memory block with system id if 0xff3
    $shm_id = shmop_open(0xff3, "c", 0644, 100);
    if(!$shm_id) {
    	echo "Couldn't create shared memory segment\n";
    }

    // Get shared memory block's size
    $shm_size = shmop_size($shm_id);
    echo "SHM Block Size: ".$shm_size. " has been created.\n";

    // Lets write a test string into shared memory
    $shm_bytes_written = shmop_write($shm_id, "my shared memory block", 0);
    if($shm_bytes_written != strlen("my shared memory block")) {
    	echo "Couldn't write the entire length of data\n";
    }

    // Now lets read the string back
    $my_string = shmop_read($shm_id, 0, $shm_size);
    if(!$my_string) {
    	echo "Couldn't read from shared memory block\n";
    }
    echo "The data inside shared memory was: ".$my_string."\n";

    //Now lets delete the block and close the shared memory segment
    if(!shmop_delete($shm_id)) {
    	echo "Couldn't mark shared memory block for deletion.";
    }
    shmop_close($shm_id);

    ?>

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