Does sys.exit() stop all threads in python?
No, `sys.exit()` does not stop all threads in Python. When `sys.exit()` is called, it throws a `SystemExit` exception, which can be caught by other parts of the code. If it is not caught, it causes the script to exit.
However, this only affects the thread that executed the `sys.exit()` function. Other threads that are running will continue to run. Python's threads are daemon threads by default, meaning they will keep running in the background until they complete their task or the main program exits.
If you have non-daemon threads (threads that you have explicitly set as non-daemon), they will continue running even after the main thread exits due to a `sys.exit()` call, and they can potentially prevent the Python program from exiting. To ensure that the entire program stops, including all threads, you may need to set your threads as daemon threads, explicitly kill them, or use a different strategy to signal them to stop.
To exit a program and ensure all threads are stopped, it's a good practice to:
1. Set threads as daemon threads if their work is not required to be fully completed when the main thread is done. You do this by setting the `daemon` attribute of a `Thread` object to `True`:
```python
import threading
def thread_function(name):
# do something
pass
thread = threading.Thread(target=thread_function, args=(1,), daemon=True)
thread.start()
```
2. Implement a signaling mechanism that lets threads know when to exit if threads are performing critical work that should be stopped cleanly. You can use a `threading.Event` or a similar construct to signal threads to finish:
```python
import threading
stop_event = threading.Event()
def thread_function(name, stop_event):
while not stop_event.is_set():
# perform your tasks
pass
thread = threading.Thread(target=thread_function, args=(1, stop_event))
thread.start()
# At some point in your program, call:
stop_event.set() # This will signal the thread to stop
thread.join() # This waits for the thread to finish
```
3. Explicitly join all non-daemon threads before exiting the main thread:
```python
# Starting threads
thread1 = threading.Thread(target=thread_function)
thread2 = threading.Thread(target=thread_function)
thread1.start()
thread2.start()
# Later on, before exiting
thread1.join()
thread2.join()
sys.exit()
```
It's important to be aware that forcibly killing threads can lead to various issues, such as deadlocks or corrupted data, if the threads are working with shared resources. Therefore, it's better to use a clean shutdown mechanism like the signaling method shown above.
