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)

Answer 1

To create a recursive mutex, use:

#include 
int pthread_mutexatttr_settype(pthread_mutexattr_t *attr,
                               int type);

where type is PTHREAD_MUTEX_RECURSIVE.

Don't forget to check the return value!

Example:

/* or PTHREAD_RECURSIVE_MUTEX_INITIALIZER_NP */
pthread_mutex_t       mutex = PTHREAD_MUTEX_INITIALIZER;
pthread_mutexattr_t   mta;

or alternatively, initialize at runtime (don't do both, it's undefined behaviour):

pthread_mutexattr_init(&mta);
/* or PTHREAD_MUTEX_RECURSIVE_NP */
pthread_mutexattr_settype(&mta, PTHREAD_MUTEX_RECURSIVE);

pthread_mutex_init(&mutex, &mta);