Function of fork function in Linux

The role of the fork function in Linux and code examples

Overview:
In the Linux system, the fork function is a very important system call, and its main function is to create a new process.

Function:

1. Create process: After calling the fork function, the operating system will create a new process, called a child process. The execution code of the child process is exactly the same as the parent process. The child process starts execution from the return point of the fork function.
2. Copy the context of the parent process: The child process will copy many attributes of the parent process, including code segments, data segments, stacks, and file descriptors.
3. Separate parent and child processes: The parent and child processes run without interfering with each other. They run independently and have their own process IDs.

Code example:
The following is a simple code example that illustrates how to use the fork function to create a child process:

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

int main() {
    pid_t pid = fork(); // 调用fork函数创建子进程
    
    // 根据fork函数的返回值判断是在子进程还是父进程中执行
    if (pid < 0) {
        printf("创建子进程失败
");
    } else if (pid == 0) {
        // 子进程中执行的代码
        printf("这是子进程，进程ID为%d，父进程ID为%d
", getpid(), getppid());
    } else {
        // 父进程中执行的代码
        printf("这是父进程，进程ID为%d，创建的子进程ID为%d
", getpid(), pid);
    }

    return 0;
}

Parsing:

1. pid_t pid = fork();: Call the fork function to create a child process and save the return value in the variable pid.
2. if (pid : Determine whether the fork function successfully created the child process based on the return value. If the pid is less than 0, the creation fails.
3. else if (pid == 0): If pid is 0, it means that the current process is a child process.
4. else: If pid is greater than 0, it means that the current process is the parent process.
5. The code in the child process will output "This is the child process, the process ID is xx, the parent process ID is xx", the code in the parent process will output "This is the parent process, the process ID is xx, create The child process ID is xx".

Summary:
Through the fork function, we can easily create a child process in the Linux system and run it separately from the parent process. Other tasks can be performed in the child process, and the running of the child process will not affect the parent process.

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