Why does a Linux process enter sleep state?

Why does the Linux process enter sleep state?

In a Linux system, a process may enter the sleep state. This is because factors such as the operating system's scheduling policy, resource allocation, and competition between processes may cause the process to enter the sleep state. The sleep state means that the process cannot be executed immediately and needs to wait for certain conditions to be met before it can continue to execute. Next, we will discuss in detail why the Linux process enters the sleep state, and will also attach specific code examples.

1. Waiting for the I/O operation to complete
   A common situation is when the process executes a system call that needs to wait for the I/O operation to complete, such as reading files, network data transmission, etc., the process Will be put to sleep until the I/O operation is completed. This can prevent the process from occupying CPU resources and improve the efficiency of the system. Here is a simple example code demonstration:

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

int main() {
    int fd = open("file.txt", O_RDWR);
    char buffer[100];
    read(fd, buffer, 100); // Read the file, the process will wait for the I/O operation to complete
    close(fd);
    
    return 0;
}

2. Waiting for signals
   The process may enter sleep state because it is waiting for a signal, such as the SIGCHLD signal waiting for the end of the child process. When the child process ends, the parent process will receive the signal and wake up the sleeping process. Here is a simple example code demonstration:

#include <stdio.h>
#include <signal.h>
#include <unistd.h>
#include <sys/wait.h>

void sigchld_handler(int signum) {
    printf("Received child process end signal
");
}

int main() {
    signal(SIGCHLD, sigchld_handler); // Register SIGCHLD signal processing function
    pid_t pid = fork();
    if (pid == 0) {
        printf("The child process is running
");
        sleep(2);
        printf("Subprocess ended
");
    } else {
        printf("The parent process is waiting for the child process to end
");
        wait(NULL); // Wait for the child process to end
    }
    
    return 0;
}

The above is a brief introduction and code examples on why the Linux process enters sleep state. It should be noted that it is a normal system scheduling process for processes to enter sleep state. At the appropriate time, the system will wake up these processes and continue execution, which is beneficial to system stability and resource utilization.

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