two threads going to do func()

Question

2 threads going to use the same func().
The 2 threads should be mutually exclusive. How do I get it to work properly?
(output should be "abcdeabcde")

char arr[] = "ABCDE";
int len = 5;

void func(){
for(int i = 0; i <len;i++)
  printf("%c,arr[i]);   
}

Answer 1

Create a mutex? Assuming you're using pthread,

static pthread_mutex_t mutex = PTHREAD_MUTEX_INITIALIZER;

....

void func() {
    int errcode = pthread_mutex_lock(&mutex);
    // deal with errcode...
    // printf...
    errcode = pthread_mutex_unlock(&mutex);
    // deal with errcode...
}

See https://computing.llnl.gov/tutorials/pthreads/#Mutexes for a tutorial.

Answer 2

1. In the main thread, initialize mutex m.
2. In the main thread, create two threads that both start in some function x().
3. In x(), get mutex m.
4. In x(), Call func().
5. In x(), Release mutex m.

Answer 3

There is a good explanation on Wikipedia how to do this on both Linux and Windows