Do pthread mutexes work across threads if in shared memory?

Question

I found this: Fast interprocess synchronization method

I used to believe that a pthread mutex can only be shared between two threads in the same address space

Answer 1

If your C/pthread library is conforming, you should be able to tell if it supports mutexes shared across multiple process by checking if the _POSIX_THREAD_PROCESS_SHARED feature test macro is defined to a value other than -1 or by querying the system configuration at run-time using sysconf(_SC_THREAD_PROCESS_SHARED) if that feature test macro is undefined.

EDIT: As Steve pointed out, you'll need to explicitly configure the mutex for sharing across processes assuming the platform supports that feature as I described above.