Multithreading in PHP

In PHP programming, if we need to perform multiple tasks or handle multiple requests at the same time, multi-threading is a very important programming technology. Multi-threading can enable multiple threads to run at the same time, improving program efficiency and user experience.

1. Introduction to PHP multi-threading

PHP multi-threading refers to a program that executes two or more threads at the same time. Each thread is an independent sub-process and can be executed independently. Task. In PHP, multithreading can be handled through the pcntl extension.

The pcntl extension is a process control extension supported by PHP. It supports the creation, management and control of processes, including forking out child processes, waiting for the child process to end, and signal processing.

2. PHP multi-thread implementation principle

In PHP multi-thread implementation, we can use the pcntl_fork() function to create a child process. It will completely copy the memory space of the parent process and start executing the child process code from the location where the function was called. After this, both parent and child processes execute simultaneously.

Here, let’s look at a piece of code that will use the pcntl_fork() function to perform simple multi-threaded operations:

$pid = pcntl_fork();
if ($pid == -1) {
    // 错误处理
    // ...
} elseif ($pid) {
    // 父进程执行的代码
    // ...
} else {
    // 子进程执行的代码
    // ...
}

?>

In the above code, we create a child process by calling the pcntl_fork() function. If the child process is successfully created, the pid of the child process will be returned in the parent process, and 0 will be returned in the child process. If the creation of the child process fails, -1 is returned.

3. PHP multi-threading practice

1. User task distribution

In PHP, we usually classify the tasks uploaded by users and then enable multiple Subprocesses handle different task categories respectively. For example, use the following method:

$pid = array();
foreach ($taskList as $taskId => $taskData) {

$pid[$taskId] = pcntl_fork();
if ($pid[$taskId] == -1) {
    // 子进程创建失败
    exit(1);
} elseif ($pid[$taskId]) {
    // 父进程
    continue;
} else {
    // 子进程
    processTask($taskId, $taskData);
    exit(0);
}

}

at In this example, we use PHP's foreach loop to create a child process for each different task. Each child process executes its own task for processing, and ends after the processing is completed. This way, our main process won't be blocked with a time-consuming task.

2. Collection classification tasks

For another example, we need to collect product information under website categories. Here we will create a sub-process for each category to collect.

$pid = array();
foreach ($categoryList as $categoryId => $categoryUrl) {

$pid[$categoryId] = pcntl_fork();
if ($pid[$categoryId] == -1) {
    // 子进程创建失败
    exit(1);
} elseif ($pid[$categoryId]) {
    // 父进程
    continue;
} else {
    // 子进程
    collectProductData($categoryId, $categoryUrl);
    exit(0);
}

}

In this example, we Use PHP's foreach loop to create a child process for each different category. Each sub-process executes its own task for collection, and ends after the collection is completed. In this way, we can collect product information under different categories concurrently with multiple threads.

4. Issues that need attention

In PHP multi-threading implementation, you need to pay attention to the following issues:

1. The parent process must wait for the child process to end Only then can you exit. Otherwise, the child process will become a "zombie process", resulting in a waste of resources.
2. After the child process is started, all variables in the parent process will be copied by the child process. Therefore, variable values ​​in the parent process cannot be modified in the child process.
3. PHP multi-threading can only be used in command line mode. In a Web Server environment, since each process can only handle one client request, the implementation of multi-threading is also limited.

4. Summary

PHP multi-threading is a very important technology to improve the processing efficiency of PHP programs. This article briefly introduces the implementation principle of PHP multi-threading, explains how to use the pcntl_fork() function to create a child process, and some common multi-threading practices. When using PHP multi-threading, you need to pay attention to avoid some common problems.

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