In general, killing threads abruptly is considered a bad programming practice. Killing a thread abruptly might leave a critical resource that must be closed properly, open. But you might want to kill a thread once some specific time period has passed or some interrupt has been generated.
There are the various methods by which you can kill a thread in python. For Example. This is because as soon as an exception is raised, program control jumps out of the try block and run function is terminated.
After that join function can be called to kill the thread. For Example. But one may refrain from using global variable due to certain reasons.
For those situations, function objects can be passed to provide a similar functionality as shown below. Using traces to kill threads : This methods works by installing traces in each thread. Each trace terminates itself on the detection of some stimulus or flag, thus instantly killing the associated thread.
In this code, start is slightly modified to set the system trace function using settrace. The local trace function is defined such that, whenever the kill flag killed of the respective thread is set, a SystemExit exception is raised upon the excution of the next line of code, which end the execution of the target function func.
Now the thread can be killed with join. Using the multiprocessing module to kill threads : The multiprocessing module of Python allows you to spawn processes in the similar way you spawn threads using the threading module. The interface of the multithreading module is similar to that of the threading module. For Example, in a given code we created three threads processes which count from 1 to 9. The functionality of the above code can also be implemented by using the multiprocessing module in a similar manner, with very few changes.
See the code given below. Though the interface of the two modules is similar, the two modules have very different implementations. All the threads share global variables, whereas processes are completely separate from each other. Hence, killing processes is much safer as compared to killing threads. The Process class is provided a method, terminateto kill a process.
Now, getting back to the initial problem. Suppose in the above code, we want to kill all the processes after 0. This functionality is achieved using the multiprocessing module in the following code. Though the two modules have different implementations. This functionality provided by the multiprocessing module in the above code is similar to killing threads. Hence, the multiprocessing module can be used as a simple alternative whenever we are required to implement the killing of threads in Python.
Killing Python thread by setting it as daemon : Daemon threads are those threads which are killed when the main program exits. Notice that, thread t1 stays alive and prevents the main program to exit via sys. In Python, any alive non-daemon thread blocks the main program to exit. Whereas, daemon threads themselves are killed as soon as the main program exits. In other words, as soon as the main program exits, all the daemon threads are killed.
To declare a thread as daemon, we set the keyword argument, daemon as True. For Example in the given code it demonstrates the property of daemon threads.
Notice that, as soon as the main program exits, the thread t1 is killed.GitHub is home to over 40 million developers working together to host and review code, manage projects, and build software together. Have a question about this project?
Sign up for a free GitHub account to open an issue and contact its maintainers and the community. Already on GitHub? Sign in to your account. Maybe it's a bug, maybe it's by design. Documentation doesn't mention anything about whether or not the "exit" event should fire, but it's a bit silly I have to write:. Just because the built-in handler won't do it for me.
When node doesn't immediately exit. I start to think there's either something wrong with my computer, something wrong with node. It seems to me that the fact that the exit event is not guaranteed to actually fire in situations like this should be mentioned in the docs.
Is it there and I'm just overlooking it? If not, I'm happy to put together a minimal PR for it. Probably only needs to be a sentence or two. It would be great to be able to point to something official like that when people have problems like this. Trott nice PR, I just left you a comment on the diff.
Note that Windows does not support sending Signals.Where is my Hello, World!?
The language here feels contradictory to me and it would be good to clarify that description as well. Yeah, I'm not sure what that second line you quote is supposed to mean. The issue he stated here calls for more fix than just the docs. I dont think we should allow the whole other assortment of termination signals, like SIGHUP for instance to bypass the exit event.Today I learned something about Python's at least CPython's multiprocessing and signal handling, and I would like to share it here.
Basically my situation was such when developing pydoc that powers this blog :. Given this context, I learned the following two critical concepts at least true in the current version of CPython through trial and error:. Both concepts can be used to one's benefit or detriment. Below is how I solved my problem, using the two concepts. The proof of concept script is as follows the production code is here :. Beware that with this solution, if there are external programs or OS level operations happening in the main process, then the operation at the time of SIGINT will still be interrupted 1 for example, in the script above, the time.
I'm not sure how to explain this — maybe the handler isn't capturing the signal fast enough? CPython's multiprocessing is written in Cso the behavior might depend on the OS. I'm talking about OS X here. I haven't inspected and won't inspect the C source code. That's awfully naive and layman-sounding, I know, but I am almost a layman when it comes to system-level programming. That's assuming your build isn't interdependent in which any single failure corrupts everything.
The dark mode beta is finally here. Change your preferences any time. Stack Overflow for Teams is a private, secure spot for you and your coworkers to find and share information. I'm working on a python script that starts several processes and database connections. More documentation on signal can be found here. You can treat it like an exception KeyboardInterruptlike any other.
Make a new file and run it from your shell with the following contents to see what I mean:. You can implement any clean-up code in the exception handler. From Python's documentation :. In contrast to Matt J his answer, I use a simple object. This gives me the possibily to parse this handler to all the threads that needs to be stopped securlery.
Interrupt the Python multiprocessing.Pool in graceful way
You can use the functions in Python's built-in signal module to set up signal handlers in python. Specifically the signal. On the other hand, this only works for an actual terminal. Also, there are "Exceptions" and "BaseExceptions" in Python, which differ in the sense that interpreter needs to exit cleanly itself, so some exceptions have a higher priority than others Exceptions is derived from BaseException.
Terminate multi process/thread in Python correctly and gracefully
The dark mode beta is finally here. Change your preferences any time. Stack Overflow for Teams is a private, secure spot for you and your coworkers to find and share information. I currently have code that basically runs an infinite while loop to collect data from users. For reference:. Basically, my problem is that I do not know when I want this to end, but after this while loop runs I want to use the information collected, not lose it by crashing my program.
Is there a simple, elegant way to simply exit out of the while loop whenever I want? Something like pressing a certain key on my keyboard would be awesome. You could use exceptions. But you only should use exceptions for stuff that isn't supposed to happen. So not for this. You import sys and signals. Then you make a function that executes on exit. When the program get the SIGINT either by ctrl-c or by a kill command in the terminal you program will shutdown gracefully. I think the easiest solution would be to catch the KeyboardInterrupt when the interrupt key is pressedand use that to determine when to stop the loop.
The disadvantage of looking for this exception is that it may prevent the user from terminating the program while the loop is still running. From here, while the program is in the forever loop spamming away requests for data from my broker's API, using the CTRL - C keyboard interrupt function toggles the exception to the try loop, which nullifies the while loop, allowing the script to finalize the data saving protocol without bringing the entire script to an abrupt halt.
Learn more. Ending an infinite while loop Ask Question. Asked 6 years, 6 months ago. Active 1 year, 2 months ago. Viewed 71k times.
Python | Different ways to kill a Thread
I've tried the following:. The previously accepted solution has race conditions and it does not work with map and async functions. Pool is to:. As YakovShklarov noted, there is a window of time between ignoring the signal and unignoring it in the parent process, during which the signal can be lost.
The solution is based on this link and this link and it solved the problem, I had to moved to Pool though:. Learn more. Asked 7 years, 9 months ago. Active 2 months ago. Viewed 62k times.
Active Oldest Votes. Wait on the results with timeout because the default blocking waits to ignore all signals. Putting it together:! Pool 2 signal. Muhammad Usman 2, 2 2 gold badges 10 10 silver badges 30 30 bronze badges. Maxim Egorushkin Maxim Egorushkin k 11 11 gold badges silver badges bronze badges. This didn't work for me with Python 3.
Boop I am not sure, one would need to investigate that. This solution is not portable as it works only on Unix.
Moreover, it would not work if the user sets the maxtasksperchild Pool parameter. Note that the blocking calls issue has been resolved in Python 3.
That's a bit too late: there is a race condition window between fork return in the child process and signal call. The signal must be blocked before forking. This only works because of the time. This is a wrong answer. Correct answer: stackoverflow. Sure it works. But it's wrong. So: a race condition. Here's what can happen: The subprocess is created, but before signal.
The subprocess aborts with an uncaught KeyboardInterrupt.At two-second interval Task. But we want our program to handle the interrupt signal gracefully, i. Notice, that we handle the receiving from channel c in another goroutine. Otherwise, the select construct would block the execution, and we would never get to creating and starting our Task.
The channel is used to tell all interested parties, that there is an intention to stop the execution of a Task. What matters is the fact of receiving a value from this channel. All long-running processes, that want to shut down gracefully, will, in addition to performing their actual job, listen for a value from this channel, and terminate, if there is one.
In our example, the long-running process is Run function. If we receive a value from closed channel, then we simply exit from Run with return. To express the intention to terminate the task we need to send some value to the channel. But we can do better. Since a receive from a closed channel returns the zero value immediately we can just close the channel. We call this function upon receiving a signal to interrupt. In order to close the channel, we first need to create it with make.
This works. Despite that we got an interrupt signal, the currently running handle finished printing. But there is a tricky part. This works, because task. Run is called from the main goroutine, and handling of an interrupt signal happens in another.
When the signal is caught, and the task. Stop is called, this another goroutine dies, while the main goroutine continues to execute the select in Runreceives a value from t.