Can a Running Python Thread Be Stopped Gracefully or Forcedly?

Can a Running Thread Be Abruptly Terminated?

While it's generally not a good approach, it's possible to abruptly terminate a running thread in Python. However, this approach is not universally applicable.

Considerations for Graceful Termination

Consider the following scenarios:

• Critical resource held by the thread needs proper closing.
• Multiple threads created by the target thread that also require termination.

For these cases, it's better to use an exit_request flag checked regularly by the target thread to trigger an exit when necessary.

Code Example for Graceful Termination:

import threading

class StoppableThread(threading.Thread):
    def __init__(self, *args, **kwargs):
        super().__init__(*args, **kwargs)
        self._stop_event = threading.Event()

    def stop(self):
        self._stop_event.set()

    def stopped(self):
        return self._stop_event.is_set()

Call stop() when the thread should exit, and then join() to ensure proper termination.

Forcing Thread Termination

In certain cases, forced thread termination may be necessary. Consider external library calls that introduce lengthy delays.

Raising Exceptions Using ThreadWithExc

The ThreadWithExc class allows exceptions to be raised within a thread from another thread:

def _async_raise(tid, exctype):
    # Raises an Exception (exctype) in thread with ID (tid)
    if not inspect.isclass(exctype):
        raise TypeError("Only types can be raised (not instances)")

class ThreadWithExc(threading.Thread):
    def raise_exc(self, exctype):
        # Raises exctype in the context of the current thread
        _async_raise(self._get_my_tid(), exctype)

Note that this method is not reliable if the thread is outside the Python interpreter. Ensure the thread catches the specific exception to perform necessary cleanup.

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