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"0644100);
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_id0$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

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Anonymous
1 month 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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