Using Redis to implement distributed scheduled tasks in PHP

Redis is a high-performance in-memory database that has the advantages of fast read and write speeds, supports a certain level of persistence, and rich data types. Redis is often used in scenarios such as caching, message queues, and real-time rankings. During development, we sometimes need to implement distributed scheduled tasks, such as sending emails, cleaning temporary files, updating cache, etc. This article will introduce how to use Redis to implement distributed scheduled tasks.

1. Data types supported by Redis

The data types supported by Redis include: string, hash, list, set and ordered set. When implementing distributed scheduled tasks, we mainly focus on two data types: ordered sets and lists.

1. Ordered set

Ordered set is a data type provided by Redis. It is similar to a hash table and can store key-value pairs, but the value (also called a score) are repeatable, and each value is associated with a score, which is used for sorting. The elements in an ordered set are sorted from small to large by score.

When using ordered sets to implement distributed scheduled tasks, we can use the execution time of the task as a score, the task content as the value, and save each task into an ordered set.

2. List

List is a data type provided by Redis. It is similar to an array and can add or delete elements at the head or tail of the list. Redis provides a rich list of commands, such as: lpush, rpush, lpop, rpop, etc.

When using a list to implement distributed scheduled tasks, we can save the task content to the list and use the lpop command to obtain the task for execution.

2. Steps to implement distributed scheduled tasks

Implementing distributed scheduled tasks can be roughly divided into the following steps:

1. Add tasks to the ordered list collection and set the execution time of the task as a score.
2. Start a background process to scan the tasks in the ordered collection, determine whether the task needs to be executed, and add the tasks that need to be executed to the task list.
3. Start multiple Worker processes and pop tasks from the task list for execution.
4. After execution, delete the task from the ordered set.
5. Add tasks to an ordered collection

Use the following command to add tasks to an ordered collection:

ZADD tasks timestamp content

Among them, tasks is the name of the ordered collection, timestamp is the execution time of the task (Unix timestamp), and content is the content of the task.

For example, to add a task "Send Mail" to the ordered collection, after the execution time is 10 minutes, you can use the following command:

ZADD tasks $(date -d " 10 minutes " %s) "send email"

2. Scan the tasks in the ordered collection

Start a background process, use the following command to get all the required tasks from the ordered collection Tasks performed:

ZRANGEBYSCORE tasks -inf $(date %s) WITHSCORES

Where -inf represents the minimum value in the ordered set, $(date %s) represents the Unix of the current time timestamp.

The above command will return a list with scores, for example:

1) "clear temp files"
2) "1626387489"

Among them, "clear temp files" is the task content, and "1626387489" is the execution time of the task.

After obtaining all the tasks that need to be performed, add these tasks to the task list.

3. Execute tasks

Start multiple Worker processes and pop up tasks from the task list for execution. After execution, the task is removed from the ordered set.

Use the following command to pop a task from the list and execute it:

lpop tasks

where tasks is the name of the list.

4. Delete the task from the ordered set

After the task is executed, use the following command to delete the task from the ordered set:

ZREM tasks content

Among them, tasks is the name of the ordered collection, and content is the content of the task.

3. Code Implementation

Below we use PHP to implement the above steps.

1. Add a task to an ordered collection

Use the following code to add a task to an ordered collection:

$redis = new Redis();
$redis->connect('127.0.0.1', 6379);

// 添加任务到有序集合
$timestamp = strtotime("+10 minutes");
$redis->zAdd('tasks', $timestamp, 'send email');

2. Scan Tasks in an ordered collection

Use the following code to scan tasks in an ordered collection and add tasks that need to be executed to the task list:

while(true) {
    // 扫描有序集合中的任务
    $scoreTasks = $redis->zRangeByScore('tasks', '-inf', time(), array('withscores' => true));
    foreach($scoreTasks as $task => $score) {
        // 将需要执行的任务添加到任务列表中
        $redis->lpush('task_list', $task);
        // 将任务从有序集合中删除
        $redis->zRem('tasks', $task);
    }
    // 每隔5秒扫描一次
    sleep(5);
}

3. Execute Task

Use the following code to start multiple Worker processes and pop up tasks from the task list for execution:

$redis = new Redis();
$redis->connect('127.0.0.1', 6379);

for($i=0; $i<10; $i++) {
    // 启动10个Worker进程
    $pid = pcntl_fork();
    if($pid == -1) {
        echo 'fork error!' . PHP_EOL;
        exit;
    } else if($pid == 0) {
        // 子进程中获取任务列表中的任务并执行
        while(true) {
            // 从列表中弹出一条任务
            $task = $redis->rpop('task_list');
            if(empty($task)) {
                continue;
            }
            // 执行任务
            mail('user@example.com', 'Task', $task);
        }
    }
}

4. Summary

The above is implemented using Redis Steps and code implementation of distributed scheduled tasks. Using Redis can easily implement distributed task scheduling and improve the concurrent processing capabilities and execution efficiency of tasks. In actual applications, we need to optimize the code according to the actual situation, such as using locks to perform mutually exclusive access to the task list, using timers to obtain tasks regularly, etc.

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