Pthread Mutex lock help

I have multiple threads accessing shared data. I want to put a lock on that code so that the clients access it one at a time. How should i do this?

Code:

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pthread_mutex_t lock;
int shared_data;

pthread_mutex_init(&lock,NULL);
....
pthread_mutex_lock(&lock);
// use shared_data
pthread_mutex_unlock(&lock);

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There're many resources out there.
Multithreaded Programming (POSIX pthreads Tutorial)