How to implement distributed locks in Swoole

With the development of the Internet and mobile Internet, high concurrency and distributed systems have become inevitable problems in daily development. In this case, distributed locks become an indispensable tool that can help us avoid problems such as resource competition and data inconsistency. This article will introduce how to implement distributed locks in Swoole to help you better solve concurrency problems in distributed systems.

1. What is a distributed lock?

In a distributed system, there are situations where multiple processes access shared resources at the same time. In order to ensure that data is not destroyed or concurrency conflicts occur, these shared resources need to be locked. The distributed lock is a lock mechanism designed to achieve the correct use of shared resources in a distributed system.

The implementation of distributed locks is relatively complex, and generally the following aspects need to be considered:

1. Mutual exclusivity: only one process or thread can occupy the lock at the same time;
2. Reentrancy: The same process or thread can apply for a lock multiple times, but the same number of unlocking operations need to be performed when unlocking;
3. Prevent deadlock: the expiration time needs to be set when acquiring the lock. , to avoid infinite waiting due to exceptions or other reasons;
4. High availability: Issues such as node failures, network partitions, etc. need to be considered;
5. Performance: It is necessary to achieve high concurrency and low latency features.

2. Introduction to Swoole

Swoole is a high-performance asynchronous and parallel network communication engine for PHP language. It can implement various protocols such as TCP/UDP/HTTP/WebSocket. server side and client side. Swoole's features include:

1. High performance: using an asynchronous non-blocking IO model, which can greatly improve the server's concurrency capability;
2. Built-in coroutines: asynchronous programming can be easily implemented, no need Manually create threads or processes;
3. Built-in HTTP/WebSocket server: Web application development can be easily realized;
4. Supports the encapsulation of asynchronous MySQL, Redis, ElasticSearch and other common tools.

Therefore, Swoole has very good adaptability and can be used to build high-concurrency and high-performance distributed systems.

3. How to implement distributed locks in Swoole?

Below we will introduce how to implement distributed locks in Swoole.

1. Implementing distributed locks based on Redis

Redis is a memory-based key-value database and one of the most commonly used tools in distributed systems. It supports a variety of data structures, including strings, lists, sets, ordered sets, etc. Among them, the string type can be used to implement distributed locks.

The general process of using Redis to implement distributed locks is as follows:

(1) Obtain a Redis connection object through the Redis connection pool;
(2) Use the SETNX command to implement lock interaction. Exclusive, when the return value is 1, it means the occupation is successful;
(3) In order to prevent deadlock, set the expiration time for the lock;
(4) Use the DEL command to release the lock.

The following is the specific implementation code:

class RedisLock
{
    private $redis;

    public function __construct($config)
    {
        $this->redis = new Redis();
        $this->redis->connect($config['host'], $config['port'], $config['timeout']);
        if (!empty($config['auth'])) {
            $this->redis->auth($config['auth']);
        }
    }

    public function lock($key, $timeout = 10)
    {
        $startTime = time();
        do {
            $result = $this->redis->setnx($key, time() + $timeout);
            if ($result) {
                return true;
            }
            $lockTime = $this->redis->get($key);
            if ($lockTime && $lockTime < time()) {
                $oldTime = $this->redis->getset($key, time() + $timeout);
                if ($oldTime == $lockTime) {
                    return true;
                }
            }
            usleep(100); // 100毫秒等待
        } while (time() - $startTime < $timeout);
        return false;
    }

    public function unlock($key)
    {
        $this->redis->del($key);
    }
}

In the above code, the lock function uses a do-while loop to wait for the lock to be released. When the waiting time exceeds the given timeout, return false; the DEL command is used in the unlock function to release the lock. While this method is simple to implement and has low overhead, it also has a certain probability of deadlock.

2. Implementing distributed locks based on Zookeeper

Zookeeper is a distributed, open source coordination system that can be used to achieve data synchronization and configuration management in distributed systems. Wait for a series of functions. The temporary sequential node (EPHEMERAL_SEQUENTIAL) it provides can easily implement distributed locks.

The general process of using Zookeeper to implement distributed locks is as follows:

(1) Create a Zookeeper client and connect to the Zookeeper server;
(2) Use the createSequential function to create a temporary Sequential nodes;
(3) Get all the nodes in Zookeeper and sort them by node serial number;
(4) Compare your own node serial number with the serial number of the current smallest node. If they are equal, it means that the lock has been obtained, otherwise listen The most recent node with a sequence number smaller than its own;
(5) When a node with a sequence number smaller than its own is deleted, the current node receives an event notification and then repeats step 4.

The following is the specific implementation code:

class ZookeeperLock
{
    private $zk;
    private $basePath = '/lock';
    private $myNode;

    public function __construct($config)
    {
        $this->zk = new Zookeeper();
        $this->zk->connect($config['host'] . ':' . $config['port']);
        if (isset($config['auth'])) {
            $this->zk->addAuth('digest', $config['auth']);
        }
        if (!$this->zk->exists($this->basePath)) {
            $this->zk->create($this->basePath, null, array(array('perms' => Zookeeper::PERM_ALL, 'scheme' => 'world', 'id' => 'anyone')), null);
        }
    }

    public function lock()
    {
        $this->myNode = $this->zk->create($this->basePath . '/node_', null, array(array('perms' => Zookeeper::PERM_ALL, 'scheme' => 'world', 'id' => 'anyone')), Zookeeper::EPHEMERAL | Zookeeper::SEQUENCE);
        while (true) {
            $children = $this->zk->getChildren($this->basePath);
            sort($children);
            $pos = array_search(basename($this->myNode), $children);
            if ($pos === 0) {
                return true;
            } else {
                $this->zk->exists($this->basePath . '/' . $children[$pos - 1], function ($event_type, $s, $event_data) {
                    $this->unlock();
                });
                usleep(100); // 100毫秒等待
            }
        }
    }

    public function unlock()
    {
        if ($this->myNode) {
            $this->zk->delete($this->myNode);
            $this->myNode = null;
        }
    }
}

In the above code, the lock function uses a while loop to monitor the latest node with a smaller serial number than its own. When the node is deleted, it means that it has The lock is acquired; the unlock function uses the delete function to delete the current node.

3. Summary

This article introduces how to implement distributed locks in Swoole. We introduce two common implementation methods based on Redis and Zookeeper, and give Implement the code. As an important technical means to ensure data consistency in distributed systems, distributed locks can help us avoid problems such as concurrency conflicts and data inconsistencies. When implementing distributed locks, you need to consider issues such as mutual exclusivity, reentrancy, deadlock prevention, high availability, and performance, and choose different implementation methods based on actual application scenarios.

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