Usually a program can be executed multiple times, and there are multiple identical processes. Sometimes we only allow a single process to access some global resources. In order to prevent multiple processes, we need to implement the method that a process can only have one instance on a machine.
After searching, you can use the flock method to build a lock file, and let the program check whether there is an instance in execution before executing it, that is, lock the file.
single_program.c
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/file.h>
#include <sys/stat.h>
#include <sys/types.h>
#include <errno.h>
#include <unistd.h>
int main()
{
int lock_file = open("/tmp/single_proc.lock", O_CREAT|O_RDWR, 0666);
int rc = flock(lock_file, LOCK_EX|LOCK_NB);
if (rc)
{
if (EWOULDBLOCK == errno)
{
printf("该实例已经运行!\nExit...");
}
}
else
{
char buffer[64];
sprintf(buffer, "pid:%d\n", getpid());
write(lock_file, buffer, strlen(buffer));
printf("已启动新实例，输入任何字符退出...\n");
scanf("%s",buffer);
printf("Exit\n",buffer);
close(lock_file); // 不要忘记释放文件指针
}
exit(0);
}
Running result
[root@centos6 data]# gcc single_program.c -o single_program
[root@centos6 data]# ./single_program
has started a new instance, enter any character to exit...
The above program will block and wait, then open a new terminal, and execute the program
[root@centos6 data]# ./single_program
The instance is already running, exit!
[root@centos6 data]#
You can see that the program exits as soon as it starts. Viewing the lock file
[root@centos6 data]# cat /tmp/single_proc.lock
pid:7162
indicates that a global lock file has been added, and a new process cannot be started. View the started process
[root@centos6 data]# ps -ef|grep -v grep|grep single_program
root 7162 6521 0 22:13 pts/0 00:00:00 ./single_program
really has only one process, in this way we It can be used in some special scenarios where only a single process is allowed to be started on one machine.