gettid - get thread identification
gettid() returns the caller's thread ID (TID). In a single-threaded process, the thread ID is equal to the process ID (PID, as returned by getpid(2)). In a multithreaded process, all threads have the same PID, but each one has a unique TID. For further details, see the discussion of CLONE_THREAD in clone(2).
On success, returns the thread ID of the calling thread.
This call is always successful.
The thread ID returned by this call is not the same thing as a POSIX thread ID (i.e., the opaque value returned by pthread_self(3)).
In a new thread group created by a clone(2) call that does not specify the CLONE_THREAD flag (or, equivalently, a new process created by fork(2)), the new process is a thread group leader, and its thread group ID (the value returned by getpid(2)) is the same as its thread ID (the value returned by gettid()).
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