ensure that only one instance of program is running

**tbscope** · 5th January 2011, 19:21

One cross platform technique but flawed in some contexes.

Create a file with the PID of the program.

1. check if this file exists.
If it does, check the PID, is it running or not? If it is running, close the new application.
If for some reason the file didn't get erased, the PID will most likely not be running (a flaw) and the file can be updated with the new PID.

2. When the program starts, write the PID to a file.

3. When the program exits, remove that file.

Or set an environment variable.

**alireza.mirian** · 5th January 2011, 19:36

Originally Posted by tbscope

One cross platform technique but flawed in some contexes.

Create a file with the PID of the program.

1. check if this file exists.
If it does, check the PID, is it running or not? If it is running, close the new application.
If for some reason the file didn't get erased, the PID will most likely not be running (a flaw) and the file can be updated with the new PID.

2. When the program starts, write the PID to a file.

3. When the program exits, remove that file.

Or set an environment variable.

thanks alot. this is like my "flag" solution and checking PID that U suggest will solve the problem of my solution. this solve the problem but my question is that, is this the formal and usual way to solve this? I ask it because it seems a little unsecure. if anyone removes the file, he/she can have more than one instance of program and if its critical to not have more than one instance, it may make mistake.