C 中使用 pthread_mutex 的进程间互斥锁

Question

I am trying to understand how inter-process communication works with pthread_mutex I've read a bunch of info on the topic but I still cannot wrap my head around it.

I understand that there seems to be an easier way using semaphores but I am not trying to use that but to learn how mmap and inter-process communication works in C.

Let's say I have the following code in "Process 1"

...
if (!initialized) {
    pthread_mutexattr_init(&attr);
    pthread_mutexattr_setpshared(&attr, PTHREAD_PROCESS_SHARED);
    pthread_mutexattr_settype(&attr, PTHREAD_MUTEX_NORMAL);
    pthread_mutex_init(&mtx->mtx, &attr);
    // save to shared memory
} else {
    // get the mutex from shared memory
}
...

Then I start the a copy of the same process and want to check if the mutex is already initialized and in shared memory. How to:

1. Initialize the mutex only in the first process and not try to initialize it in the next ones
2. Allocate the memory with mmap.

Answer 1

Ended up using Shawn's solution and just used a lock on a file it is a whole lot easier to setup and works similarly on Windows so I can easily write cross-platform wrapper code if needed.