How do you make a cross-process locking in Linux (C/C++)?

Question

I need to make sure one process executes only in one instance at a time. On Windows you could use named mutex. But I have no idea what to use on Linux.

I think I've seen an approach were app creates an exclusive file, but I can't find it anymore. Do you use regular file functions, busy-loop?

See if help: http://stackoverflow.com/questions/5339200/how-to-create-a-single-instance-application-in-c — enzotib, Sep 15 '11 at 09:26
There is a first call to fopen which will try to overwrite a possibly locked file, is this ok? — Coder, Sep 15 '11 at 09:50

score 9 · Answer 1 · edited Oct 21 '19 at 22:57

If you only want one instance of your app running you can use a lock file. Open it with O_CREAT|O_EXCL flags and it will fail if the file already exists.

If you want to synchronize access to a file use flock. It is also possible to lock parts of files with fcntl. Flock is only for advisory locking meaning a program can ignore the locks and access it anyway. Mandatory locking is possible with fcntl but it requires a special mount option and special file permissions.

semget and semop can be used for interprocess synchronization too.

score 1 · Answer 2 · edited Mar 18 '18 at 15:33

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Interprocess mutexes are an optional part of POSIX (see _POSIX_THREAD_PROCESS_SHARED on the unistd.h page) and as they are implemented on Linux you can use them too - see examples.

edited Mar 18 '18 at 15:33

Community

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answered May 20 '16 at 09:42

Milan Kerslager

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The point here is to have mutexes across processes. Is this part of POSIX? – Alfe Nov 17 '17 at 15:09
yeah, it's one of several Posix IPC mechanisms. That stands for interprocess communications, so the whole idea is to communicate between processes. this looks pretty good: http://www.chandrashekar.info/articles/linux-system-programming/introduction-to-linux-ipc-mechanims.html – erik258 Oct 05 '19 at 01:45

How do you make a cross-process locking in Linux (C/C++)?

2 Answers2