Using Swoole Table for Shared Memory and High‑Performance Data Sharing in PHP

Because the PHP language does not support multithreading, Swoole operates in a multi‑process mode, which results in memory isolation between processes; modifying global or super‑global variables in one worker process does not affect others.

The recommended solutions are to use external storage services such as databases (e.g., MySQL , MongoDB ), cache servers (e.g., Redis , Memcache ), or disk files with proper locking. However, these approaches involve significant I/O latency, so using an in‑memory solution like Redis or the memory filesystem /dev/shm is preferred for higher performance.

For true shared memory within Swoole, the Swoole\Table structure provides a high‑performance concurrent data container based on shared memory and locks, solving multi‑process data sharing and synchronization issues. Its memory capacity is not limited by PHP's memory_limit .

Advantages of Swoole\Table :

Strong performance – up to 200 万 (2 million) read/write operations per second per thread.

No need for user‑level locking; the table has built‑in row spin locks, making all operations safe for multi‑thread/multi‑process.

Supports multi‑process data sharing.

Uses row‑level locks instead of a global lock, only contending when two processes access the same row simultaneously.

Capacity calculation : the total memory used by a table equals (HashTable struct length + 64‑byte key length + $size) * (1 + $conflict_proportion) * column_size . If the key or hash conflict rate exceeds 20 %, you may encounter “Unable to allocate memory” errors and need to increase $size and restart the service.

Handling strings longer than the defined column size : values exceeding the column's maximum length are automatically truncated by the underlying implementation.

Example code demonstrates creating a Swoole\Table , defining columns, initializing a Swoole\Server , handling the receive event, storing and retrieving data in the table, and sending responses back to the client.

<?php
$table = new Swoole\Table(1024);
$table->column('fd', Swoole\Table::TYPE_INT);
$table->column('reactor_id', Swoole\Table::TYPE_INT);
$table->column('data', Swoole\Table::TYPE_STRING, 64);
$table->create();

$serv = new Swoole\Server('127.0.0.1', 9501);
$serv->set(['dispatch_mode' => 1]);
$serv->table = $table;

$serv->on('receive', function ($serv, $fd, $reactor_id, $data) {
    $cmd = explode(' ', trim($data));
    if ($cmd[0] == 'get') {
        if (count($cmd) < 2) return;
        $fdKey = intval($cmd[1]);
        $info = $serv->table->get($fdKey);
        $serv->send($fd, var_export($info, true) . "\n");
    } elseif ($cmd[0] == 'set') {
        $ret = $serv->table->set($fd, [
            'reactor_id' => $reactor_id,
            'fd' => $fd,
            'data' => $cmd[1]
        ]);
        if ($ret === false) {
            $serv->send($fd, "ERROR\n");
        } else {
            $serv->send($fd, "OK\n");
        }
    } else {
        $serv->send($fd, "command error.\n");
    }
});

$serv->start();
?>