What is the fork function in Linux

"fork()" in Linux is a system call function used to create a new process. It will create a copy of the current process, called a child process. The child process is almost identical to the parent process, including Code, data and open file descriptors, etc., have the prototype "pid_t fork(void);".

In Linux, fork() is a system call function used to create a new process. This function creates a copy of the current process, called a child process. The child process is almost identical to the parent process, including code, data, open file descriptors, etc.

The prototype of the fork() function is as follows:

#include <sys/types.h>
#include <unistd.h>

pid_t fork(void);

Among them, pid_t is an integer type used to represent the process ID (PID). The fork() function has no parameters.

There will be two return values ​​after the fork() function is called:

• In the parent process, fork() returns the PID of the child process (the ID of the child process).
• In the child process, fork() returns 0.

Therefore, you can determine whether the current code is executed in the parent process or the child process by judging the return value of fork().

The following is a simple sample code that demonstrates the basic usage of the fork() function:

#include <stdio.h>
#include <unistd.h>

int main() {
    pid_t pid = fork();

    if (pid < 0) {
        fprintf(stderr, "Fork failed.
");
        return 1;
    }
    else if (pid == 0) {
        printf("This is the child process. PID: %d
", getpid());
    }
    else {
        printf("This is the parent process. Child PID: %d
", pid);
    }

    return 0;
}

In the above code, we call the fork() function and determine the current value based on the return value In the parent process or the child process. In the parent process, we print the PID of the child process; in the child process, we print our own PID.

It should be noted that the fork() function will completely copy the memory of the parent process to the child process, including the heap, stack and global variables. Therefore, after fork(), the parent process and the child process will execute their own codes separately without interfering with each other.

The above is the detailed content of What is the fork function in Linux. For more information, please follow other related articles on the PHP Chinese website!