How to use PHP's process control function?

PHP is a very popular programming language that can be executed on the server side. When running PHP scripts on the server side, we often need to control the running of the process in order to coordinate the execution of different tasks and ensure the reliability of the program. PHP provides a set of simple and easy-to-use process control functions that can help us achieve these goals. In this article, we will introduce the basic principles, usage and precautions of PHP process control.

1. Basic concepts of PHP process control

PHP process control mainly includes functions such as process creation, termination, waiting, and signal capture. Among them, process creation is the most basic function. It can create a new sub-process in the context of the current process so that subsequent tasks can be executed in the sub-process to achieve concurrent processing. The process termination function allows us to actively end the running of the child process after the program execution is completed. The process waiting function allows the parent process to wait for the completion of the child process and obtain the return value of the child process for subsequent processing based on the execution results of the child process. The signal capture function allows us to control the behavior of the program by sending signals, such as interrupting the executing child process or forcibly terminating the execution of the program.

2. How to use PHP process control

1. Process creation

PHP provides the pcntl_fork function to realize the process creation function. This function will create a new child process and return an integer value used to distinguish between the parent process and the child process. In the child process, the return value of this function is 0; in the parent process, this function returns the process ID of the new process. The following is a code example of process creation:

$pid = pcntl_fork();
if ($pid == -1) {
  // 进程创建失败
  exit(1);
} else if ($pid) {
  // 父进程
  echo "父进程，子进程ID：$pid
";
} else {
  // 子进程
  echo "子进程，ID：" . getmypid() . "
";
}

In this example, we create a new child process through the pcntl_fork function, and output different information in the parent process and child process. It is worth noting that when the pcntl_fork function is called, the parent process and the child process will copy a copy of the program's execution environment, including variables, file descriptors, running status and other information. Since the child process inherits this information from the parent process, we need to be extra careful to avoid unexpected errors.

2. Process termination

PHP provides the pcntl_exit function to terminate the process. This function allows us to actively end the running of the child process after the program is executed. You can pass in an integer value as the return value to pass the execution result of the child process to the parent process. The following is a code example of process termination:

$pid = pcntl_fork();
if ($pid == -1) {
  // 进程创建失败
  exit(1);
} else if ($pid) {
  // 父进程
  pcntl_wait($status); // 等待子进程执行完毕
  echo "子进程执行完成，返回值：".$status."
";
} else {
  // 子进程
  echo "子进程执行中...
";
  pcntl_exit(123); // 终止子进程，并返回123
}

In this example, we end the running of the child process through the pcntl_exit function and pass the return value 123. The parent process calls the pcntl_wait function to wait for the end of the child process, and uses the $status variable to receive the return value of the child process. It should be noted that the pcntl_exit function can only be used to terminate the current process and cannot terminate other processes.

3. Process waiting

PHP provides the pcntl_wait function to wait for the end of the child process and obtain the return value of the child process. This function can be called in the parent process to obtain the execution result of the child process after the execution of the child process is completed. The following is a code example of process waiting:

$pid = pcntl_fork();
if ($pid == -1) {
  // 进程创建失败
  exit(1);
} else if ($pid) {
  // 父进程
  pcntl_wait($status); // 等待子进程执行完毕
  echo "子进程执行完成，返回值：".$status."
";
} else {
  // 子进程
  echo "子进程执行中...
";
  sleep(3); // 模拟子进程执行
  pcntl_exit(123); // 终止子进程，并返回123
}

In this example, we wait for the end of the child process through the pcntl_wait function, and use the $status variable to receive the return value of the child process. It should be noted that if there are multiple child processes in the parent process that need to wait, you can use the pcntl_waitpid function to specifically wait for a specified child process.

4. Signal Capture

PHP provides the pcntl_signal function to implement the signal capture function. This function allows us to specify a signal and bind the signal processing function to process the signal. The following is a code example of signal capture:

function signal_handler($signal)
{
  echo "接收到信号：".$signal."
";
}

pcntl_signal(SIGINT, "signal_handler"); // 捕捉Ctrl+C信号

while (true) {
  // 循环执行
  sleep(1);
}

In this example, we capture the Ctrl C signal through the pcntl_signal function and bind a processing function signal_handler. When the user presses the Ctrl C key, the program will receive this signal and execute the code in the signal_handler function. It should be noted that in the signal processing function, we cannot directly call the pcntl_exit function, because this may cause the process to be interrupted during execution, resulting in unpredictable errors. If you want to end the process, you should use the posix_kill function to send an end signal to the process and end it by the process itself.

3. Notes

When using the PHP process control function, you need to pay attention to the following points:

1. Process creation and termination will occupy system resources. If not If necessary, excessive creation and termination operations should be avoided as much as possible.
2. The child process needs to inherit the file descriptors and variables of the parent process, so the status of these resources needs to be handled carefully during program execution.
3. When waiting for a child process in the parent process, you should wait for all possible child processes to avoid zombie processes.
4. In the signal processing function of the process, you should avoid calling the pcntl_exit function directly. Instead, you should use the posix_kill function to send an end signal to the process and end it by the process itself.

To sum up, PHP process control is a very powerful function. Through process control, we can easily implement concurrent processing, inter-process communication, exception handling and other functions, helping us build more reliable programs. However, when using process control, you need to be careful to avoid unpredictable errors.

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