Concurrency using POSIX

Question

I came across a passage:

The definition of concurrent execution in POSIX requires that "functions that suspend the execution of the calling thread shall not cause the execution of the other threads to be indefinitely suspended".

Can someone please explain this to me (especially what is calling thread - I understand what calling function is).

Answer 1

The calling thread is the thread of execution where a blocking function is called. If you have two threads, then one can call a blocking function like sleep to sleep for an hour and the other thread may not be stopped for the duration of one hour too because of the call that happened in the first one.