thread.start_new_thread vs threading.Thread.start

Question

What is the difference between thread.start_new_thread and threading.Thread.start in python?
I have noticed that when start_new_thread is called, the new thread terminates as soon as the calling thread terminates. threading.Thread.start is the opposite: the calling thread waits for other threads to terminate.

Answer 1

The thread module is the low-level threading API of Python. Its direct usage isn't recommended, unless you really need to. The threading module is a high-level API, built on top of thread . The Thread.start method is actually implemented using thread.start_new_thread .

The daemon attribute of Thread must be set before calling start , specifying whether the thread should be a daemon. The entire Python program exits when no alive non-daemon threads are left. By default, daemon is False , so the thread is not a daemon, and hence the process will wait for all its non-daemon thread to exit, which is the behavior you're observing.

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PS start_new_thread really is very low-level. It's just a thin wrapper around the Python core thread launcher, which itself calls the OS thread spawning function.

Answer 2

See the threading.Thread.daemon flag - basically whenever no non-daemon threads are running, the interpreter terminates.