Is there an invalid pthread_t id?

Question

I would like to call pthread_join for a given thread id, but only if that thread has been started. The safe solution might be to add a variable to track which thread where s

Answer 1

Your assumption is incorrect to start with. pthread_t objects are opaque. You cannot compare pthread_t types directly in C. You should use pthread_equal instead.

Another consideration is that if pthread_create fails, the contents of your pthread_t will be undefined. It may not be set to your invalid value any more.

My preference is to keep the return values of the pthread_create calls (along with the thread IDs) and use that to determine whether each thread was started correctly.