C 避免产生多个进程副本

代码展示

#include <stdio.h>
#include <unistd.h>
#include <stdlib.h>
#include <fcntl.h>
#include <string.h>
#include <errno.h>
#define TEST_PID_FILE "/var/run/pid_output.pid"

int lock_file(int fd){
   struct flock fl;
   fl.l_type = F_WRLCK;
   fl.l_whence = SEEK_SET;
   fl.l_len = 0;
   return (fcntl(fd, F_SETLK, &fl));
}

int pid_output(char *file){
   int fd = -1;
   char buf[12] = {0};
   
   if(file == NULL){
   	printf("pid file pointer is null\n");
   	return -1;
   }
   
   fd=open(file, O_RDWR | O_CREAT, 0666);
   if(fd < 0){
   	printf("can't open %s: %s\n",file, strerror(errno));
   	exit(1);
   }else{
   	if(lock_file(fd) < 0){
   		close(fd);
   		printf("can't lock %s:%s\n",TEST_PID_FILE, strerror(errno));
   		exit(1);
   	}else{
   		ftruncate(fd, 0);
   		sprintf(buf, "%ld\n", (long)getpid());
   		write(fd, buf, strlen(buf));
   	}
   }
   return 0;
   
}

void main(){
   pid_output(TEST_PID_FILE);
   while(1){
   	sleep(3);
   }
}

执行结果