2019-05-30 Create a single instance application in Linux C++

We would like to create a single instance application.

Solutions

The general approach is to write your own pid to a file in /var/run/ (/var/run/myprog.pid), When starting the program, check to see if the file exists.
This method can also be used as a communication entry when two identical programs are executed at the same time.

My program

#include <stdlib.h>     /* exit, EXIT_FAILURE */

// for execution instance
#include <sys/file.h>
#include <errno.h>
...
int main (){
    // ---------------------
    // Check first instance, 
    // This can prevent multiple instance execution
    int pid_file = open("./timer-test.pid", O_CREAT | O_RDWR, 0666);
    int rc = flock(pid_file, LOCK_EX | LOCK_NB);
    if(rc) {
        if(EWOULDBLOCK == errno)
        {
            // another instance is running
            printf ("Another Instance running\n");
            exit(0);
        }
    }
    else {
       // this is the first instance
    }
    // ---------------------
...

Program normal exit:
Program break by Ctrl-C

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2019-05-30 Create a single instance application in Linux C++

Solutions

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