PHPCon Poland 2024

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

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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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