进程

创建子进程

#include <cstdio>
#include <unistd.h>
#include <sys/types.h>
#include <fcntl.h>
#include <wait.h>

void create_task()
{
    int ret;

    ret = fork();

    if (ret < 0)
    {
        perror("Cant't create child task.\n");

    } else if (ret > 0)
    {
        int chpid = ret;

        int ppid = getpid();

        printf("Parent pid = %d \n", ppid);

    } else if (ret == 0)
    {

        printf("Child pid = %d \n", getpid());

    }

}

循环创建N个子进程

#include <cstdio>
#include <unistd.h>
#include <sys/types.h>
#include <fcntl.h>
#include <wait.h>

void create_task()
{
    int ret;

    ret = fork();

    if (ret < 0)
    {
        perror("Cant't create child task.\n");

    } else if (ret > 0)
    {
        int chpid = ret;

        int ppid = getpid();

        printf("Parent pid = %d \n", ppid);

    } else if (ret == 0)
    {

        printf("Child pid = %d \n", getpid());

    }

}

回收子进程

#include <cstdio>
#include <unistd.h>
#include <sys/types.h>
#include <fcntl.h>
#include <wait.h>

void recycle_child_task()
{

    const int N = 5;

    int childPidSet[N];

    int i = 0;

    for (; i < N; i++)
    {
        int ret = fork();

        if (ret == 0)
            break;

        childPidSet[i] = ret;
    }


    if (i == N)
        for (const int &pid : childPidSet)
            printf("Child pid=%d\n", pid);


    if (i == N)
        for (const int &pid: childPidSet)
        {
            int stat;

            waitpid(pid, &stat, 0);

            printf("Recycle child pid %d\n", pid);

        }


}

守护进程

#include <cstdio>
#include <unistd.h>
#include <sys/types.h>
#include <fcntl.h>
#include <wait.h>

void create_daemon_task()
{
    pid_t pid, sid;

    pid = fork();

    if (pid > 0)
        exit(0);

    setsid();

    if (chdir("/tmp"))
    {
        perror("Change dir error");

        exit(1);
    }

    umask(0002);

    close(STDIN_FILENO);

    open("/dev/null", O_RDWR);

    dup2(0, STDOUT_FILENO);

    dup2(0, STDERR_FILENO);

    int count = 0;

    while (1)
    {
        count++;

        write(STDOUT_FILENO, &count, sizeof(count));

        sleep(1);

    }

}