2021-09-08单例守护进程实现_单实例守护进程的实现方法-优快云博客

该博客详细介绍了如何使用C语言实现一个单例守护进程。通过定义LOCKFILE和LOCKMODE常量，以及lock_reg和lockfile函数，确保了进程的唯一运行。主要流程包括打开指定的PID文件，尝试获取写锁，如果失败则判断已有进程在运行，否则记录当前进程ID并继续执行。这是一个关键的系统管理任务，确保了服务的稳定性和资源的有效利用。

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单例守护进程实现

#include <unistd.h>
#include <stdlib.h>
#include <fcntl.h>
#include <syslog.h>
#include <string.h>
#include <errno.h>
#include <stdio.h>
#include <sys/stat.h>
//#include "apue.h"

//#define LOCKFILE "var/run/daemon.pid"
#define LOCKFILE "daemon.pid"
#define LOCKMODE (S_IRUSR|S_IWUSR|S_IRGRP|S_IROTH)

int
lock_reg(int fd, int cmd, int type, off_t offset, int whence, off_t len)
{
    struct flock	lock;

    lock.l_type = type;		/* F_RDLCK, F_WRLCK, F_UNLCK */
    lock.l_start = offset;	/* byte offset, relative to l_whence */
    lock.l_whence = whence;	/* SEEK_SET, SEEK_CUR, SEEK_END */
    lock.l_len = len;		/* #bytes (0 means to EOF) */

    return(fcntl(fd, cmd, &lock));
}

//extern int lockfile(int);
//lock_reg(int fd, int cmd, int type, off_t offset, int whence, off_t len)
int lockfile(int fd){
    return lock_reg(fd,F_SETLK,F_WRLCK,0,SEEK_SET,0);
}

int already_running(void){
    int fd;
    char buf[16];

    fd=open(LOCKFILE,O_RDWR|O_CREAT,LOCKMODE);
    if(fd<0){
        syslog(LOG_ERR,"can't open %s:%s",LOCKFILE,strerror(errno));
        exit(1);
    }

    if(lockfile(fd)<0){
        if(errno==EACCES||errno==EAGAIN){
            close(fd);
            exit(1);
        }
        syslog(LOG_ERR,"can't lock %s:%s",LOCKFILE,strerror(errno));
        exit(1);
    }
    ftruncate(fd,0);
    sprintf(buf,"%ld",(long)getpid());
    write(fd,buf,strlen(buf)+1);
    return 0;
}

int main(int argc, char *argv[])
{
    if(already_running()==0)
        printf("can running");
    else
        printf("already running");

    sleep(1000);
    return 0;
}