Question

I have a function (my_func) which can be called by a program that has multiple thread. And I don’t want this function to be executed twice or more in the same time. Because I’m writing in memory, and I don’t want them to write in the same time.

void my_func()
{
    // I want a line that blocks the execution if one is still pending
    /* the code here */
}

Answer 1

use mutex lock at the beginning of your function and mutex unlock before going out from your function

pthread_mutex_t my_func_mutex = PTHREAD_MUTEX_INITIALIZER;

 void my_func()
    {
        pthread_mutex_lock(&my_func_mutex); // at the beginning of your function
        .....
        pthread_mutex_unlock(&my_func_mutex); // do not forget to unlock your mutex before going out from your function
    }

You can do it in other way if you want:

pthread_mutex_t my_func_mutex = PTHREAD_MUTEX_INITIALIZER;
#define MY_FUNC_MACRO() \
    do { \
        pthread_mutex_lock(&my_func_mutex); \
        my_func(); \
        pthread_mutex_unlock(&my_func_mutex); \
    } while(0)

 void my_func()
    {
        .....
    }

and in your code you call MY_FUNC_MACRO() instead of my_func()