Basic usage

    Example #1 Shared Memory Operations Overview

    <?php

    // Create 100 byte shared memory block with system id of 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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    User Contributed Notes 1 note

    up
    3
    Anonymous
    6 years ago
    Simple class for SHMOP implementation.

    # Warning #

    You can write/read only one direction. If you try read and write at the same time you get corrupt data. (Its works like STD in/out)
    If you need bi-directional communication create 2 instance of shmop class.
    Don't try attach more than one readers or writers for some shmid, you get corrupt data. This class use kludged spinlocks for improve speed, and not real atomic operations. You can add semaphore with flock, but it very slow. (~x3)

    Benchmark:

    Reads per sec: 6316 Data size per sec: 6.17 gb

    <?php
    ########################
    # shmopwriter.php
    ########################

    $blockSize = 1024 * 1024 * 100;
    $data = random_bytes($blockSize);

    try
    {
    $shm = new SHMOP('shmopwriter.php', 'c', 644, $blockSize);

    while(    1)
    {
    if(!    $shm->canWrite())
    continue;

    $shm->write($data);
    }

    $shm->close();

    } catch (    Exception $e) {
    echo     'Error: ', $e->getMessage(), PHP_EOL;
    exit;
    }

    ########################

    ########################
    # shmopreader.php
    ########################

    $blockSize = 1024 * 1024 * 100;
    $shm = new SHMOP('shmopwriter.php', 'c', 644, $blockSize);
    $readsMT = 0;
    $readsPS = 0;

    while(!    $shm->eof())
    {
    $times = microtime(true);

    if((    $data = $shm->read()) === false)
    continue;

    $readsPS++;
    $readsMT += round(((microtime(true) - $times ) * 1000), 3);

    if(    $readsMT > 1000)
    {
    echo     'Reads per sec: ', $readsPS, ' Data size per sec: ', convert($blockSize * $readsPS), PHP_EOL;
    $readsPS = 0;
    $readsMT = 0;
    }
    }

    function     convert($size)
    {
    $unit=array('b','kb','mb','gb','tb','pb');
    return @    round($size/pow(1024,($i=floor(log($size,1024)))),2).' '.$unit[$i];
    }
    ########################

    ########################
    # shmop.class.php
    ########################

    class SHMOP
    {
    private     $shmId;
    private     $shmHeaderSize;
    private     $shmHeaderOffset;
    private     $shmBlockSize;
    private     $shmMaxBlockSize;

    function     __construct(string $pathname, string $flags, int $mode, int $size)
    {
    $this->shmHeaderSize = strlen($size);
    $this->shmHeaderOffset = $this->shmHeaderSize + 1;
    $this->shmMaxBlockSize = $size;
    $this->shmBlockSize = $size + $this->shmHeaderOffset + 1;

    $this->shmId = shmop_open(ftok($pathname, 's'), $flags, $mode, $this->shmBlockSize);

    if(!    $this->shmId)
    throw new     Exception('shmop_open error');
    }

    function     __destruct()
    {
    if(!    $this->shmId)
    return;

    $this->close();
    }

    public function     read()
    {
    // Check SpinLock
    if(shmop_read($this->shmId, 0, 1) === "\0")
    return     false;

    // Get Header
    $dataSize = (int)shmop_read($this->shmId, 1, $this->shmHeaderSize);

    $data = shmop_read($this->shmId, $this->shmHeaderOffset, $dataSize);
    // release spinlock
    shmop_write($this->shmId, "\0", 0);
    return     $data;
    }

    public function     write(string $data)
    {
    // Check SpinLock
    if(shmop_read($this->shmId, 0, 1) !== "\0")
    return     false;

    $dataSize = strlen($data);

    if(    $dataSize < 1)
    throw new     Exception('dataSize < 1');

    if(    $dataSize > $this->shmMaxBlockSize)
    throw new     Exception('dataSize > shmMaxBlockSize: '. $this->shmMaxBlockSize);

    // pack very slow use kludge
    $dataSize .= "\0";

    // Write Header
    shmop_write($this->shmId, $dataSize, 1);
    // Write Data
    shmop_write($this->shmId, $data, $this->shmHeaderOffset);
    // Write spinlock
    shmop_write($this->shmId, "\1", 0);
    return     true;
    }

    public function     eof()
    {
    return (    shmop_read($this->shmId, 0, 1) === "\2") ? true : false;
    }

    public function     sendeof()
    {
    // Check SpinLock
    if(shmop_read($this->shmId, 0, 1) !== "\0")
    return     false;

    shmop_write($this->shmId, "\2", 0);
    return     true;
    }

    public function     canWrite()
    {
    // Check SpinLock
    return (shmop_read($this->shmId, 0, 1) === "\0") ? true : false;
    }

    public function     close()
    {
    return @    shmop_close($this->shmId);
    }

    private function     delete()
    {
    $del = @shmop_delete($this->shmId);

    if(    $del === false)
    return     false;

    return @    shmop_close($this->shmId);
    }
    }

    ?>
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