Detailed introduction of multi-process echo server in PHPSocket programming (picture and text)

This article brings you a detailed introduction (pictures and text) about the multi-process echo server in PHPSocket programming. It has certain reference value. Friends in need can refer to it. I hope it will be helpful to you. .

The last echo service program has a big shortcoming, that is, it can only connect to one client at the same time, which is obviously unreasonable.

So this time we use a multi-process approach to provide services to multiple clients at the same time.

The following is the final effect:

(The worker process we created can be viewed through the ps command)

(Open multiple terminals through xshell and connect multiple clients to the service program)

Begin coding Before, let’s introduce what a process is.

The process, that is, the running program that occupies memory, is an independent memory space. For example, when we open Notepad software on Windows, this operation is equivalent to opening a process.

Multi-process is to create multiple processes to complete one thing together.

We only need to implement the server-side program this time, and the client still uses the previous one. If you haven’t read the previous articles, you can check out the historical articles.

In PHP, we can use the pcntl_fork function to create a process.

The following is the prototype of the function:

int pcntl_fork ( void )

Official explanation:

When successful, the PID of the generated child process is returned in the execution thread of the parent process, and the PID of the child process is returned in the execution thread of the child process. Returns 0 within. On failure, -1 is returned in the parent process context, the child process is not created, and a PHP error is raised.

Why is it said to be the thread executed by the parent process? Because a process contains at least one thread, and this thread is the main thread of the process.

When the parent process calls pcntl_fork, it also copies an independent child process. This child process has the same context as the parent process. In other words, the two processes just share the same code.

Enter the encoding process:

By executing the pcntl_fork function, a child process is copied at the same time. At this time, if the context is The execution environment of the parent process, the return value is the process number of the child process. If it is the execution environment of a child process, 0 is returned. Therefore, in the following if program structure, both branches are executed.

The child process still has the same logic as before, used to receive messages from the client and send them to the client at the same time.

The penultimate line calls the pcntl_waitpid function. Before explaining this function, let us first understand what a zombie process is.

Under normal circumstances, the child process is created through the parent process. Since processes are independent memory structures, the parent process does not know the running status of the child process. After the child process completes its task, it cannot exit by itself. At this time, the parent process needs to obtain the status of the child process through the operating system to recycle the child process. Otherwise, our child process will become a garbage resource, that is, a zombie process.

The following is the function prototype of this function:

int pcntl_waitpid ( int $pid , int &$status [, int $options = 0 ] )

Official explanation:

Wait for or return the child process status of fork.

In fact, there is a problem with the above code. After calling pcntl_waitpid for the first time in foreach, the main process is actually blocked at this time, waiting for the first child process to exit, while other child processes If it exits abnormally at this time, it will not be recycled by the main process, and a zombie process will be generated. In actual development, the main process still has to do other things.

So the non-blocking method is recommended here. It is very simple. Just add the third parameter: WNOHANG. That is: pcntl_waitpid ($pid, $status, WNOHANG)

In this way, it can return immediately without the child process exiting, thus continuing to execute subsequent code.

Related recommendations:

Server-side PHP multi-process programming practice

Server-side PHP multi-process programming practice_PHP tutorial

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