Question

Given the following:

pthread_t thread;
pthread_create(&thread, NULL, function, NULL);

• What exactly does pthread_create do to thread?

• What happens to thread after it has joined the main thread and terminated?

• What happens if, after thread has joined, you do this:

  pthread_create(&thread, NULL, another_function, NULL);
  

Answer 1

What exactly does pthread_create do to thread?

thread is an object, it can hold a value to identify a thread. If pthread_create succeeds, it fills in a value that identifies the newly-created thread. If it fails, then the value of thread after the call is undefined. (reference: http://pubs.opengroup.org/onlinepubs/009695399/functions/pthread_create.html)

What happens to thread after it has joined the main thread and terminated?

Nothing happens to the object, but the value it holds no longer refers to any thread (so for example you can no longer pass it to functions that take a pthread_t, and if you accidentally do then you might get ESRCH errors back).

What happens if, after thread has joined, you do this:

Same as before: if pthread_create succeeds, a value is assigned that identifies the newly-created thread.