C: How do you declare a recursive mutex with POSIX threads?

Question

I am a bit confused on how to declare a recursive mutex using pthread. What I try to do is have only one thread at a time be able to run a piece of code(including functions) but after scepticism I figured out that the use of mutexes would not work and that instead I should use recursive mutexes. Here is my code:

pthread_mutex_lock(&mutex);                   // LOCK

item = queue_peek(queue);                     // get last item in queue
item_buff=item;                               // save item to a buffer
queue_removelast(queue);                      // remove last item from queue

pthread_mutex_unlock(&mutex);                 // UNLOCK

So what I try to do is just read/remove from the queue serially.

The thing is that there isn't any example out there on how to declare recursive mutexes. Or there maybe a few but they don't compile for me.

Answer 1

The code from Michael Foukarakis is almost good but he initializes the mutex twice which leads to undefined behavior. It should just be:

pthread_mutex_t Mutex;
pthread_mutexattr_t Attr;

pthread_mutexattr_init(&Attr);
pthread_mutexattr_settype(&Attr, PTHREAD_MUTEX_RECURSIVE);
pthread_mutex_init(&Mutex, &Attr);

I actually use this code in production, and I know it works correctly on Linux, Solaris, HP-UX, AIX, Mac OSX and FreeBSD.

You also need to add proper linker flag to compile this:

AIX, Linux, FreeBSD:
CPLATFORM += -pthread

mingw32:
LDFLAGS += -lpthread