Python thread sigterm

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I have python code which runs continuously collecting sensor data. It is supposed to be launched at boot using start-stop-daemon. I'd like to be able to gracefully shut it down both when it is running as a daemon the start-stop-daemon will send a kill signal and when I launch it briefly for testing in a terminal myself me pressing ctrl-c. However, the signal handler doesn't seem to be called if I kill the process even without using the thread, the " done killed " never ends up in the file I've redirected to.

And when I press ctrl-cthe collecting just continues and keeps printing data in the terminal or to the file I am redirecting to.

So your signal handler never gets to run.

python thread sigterm

So once the main thread exits there's no signal handler function to call anymore. Learn more. Why is signal. Ask Question. Asked 6 years, 5 months ago. Active 6 years, 5 months ago. Viewed 6k times. What am I doing wrong in the following code? Rabarberski Rabarberski Active Oldest Votes. But how can the main thread then end? Also, I thought I read somewhere that when using Thread.

The significance of this flag is that the entire Python program exits when only daemon threads are left. The initial value is inherited from the creating thread. The flag can be set with the setDaemon method and retrieved with the isDaemon method. The main thread, in this case is not waiting for the other thread to finish. Even if it's daemon thread if you exit the main thread it will wait for the other threads to finish, but no code in the main thread will be executed.

Therefore you wont be able to call the sig handler. Hmm, this is sort of working, but not completely. But the main thread remains running, with the signal handler now printing correctly the called signal.

The behavior I see seems logical to me, as the main thread can not end if we have a while 1 loop, no? So the question remains Sign up or log in Sign up using Google.

Sign up using Facebook. Sign up using Email and Password. Post as a guest Name. Email Required, but never shown. The Overflow Blog.See also the queue module. Changed in version 3. While they are not listed below, the camelCase names used for some methods and functions in this module in the Python 2.

Return the number of Thread objects currently alive. The returned count is equal to the length of the list returned by enumerate. Handle uncaught exception raised by Thread.

Otherwise, the exception is printed out on sys. If this function raises an exception, sys. It should be cleared explicitly to break the reference cycle when the exception is no longer needed.

Storing thread using a custom hook can resurrect it if it is set to an object which is being finalized. Avoid storing thread after the custom hook completes to avoid resurrecting objects. This is a nonzero integer. Its value has no direct meaning; it is intended as a magic cookie to be used e.

Thread identifiers may be recycled when a thread exits and another thread is created. Return the native integral Thread ID of the current thread assigned by the kernel. This is a non-negative integer. Its value may be used to uniquely identify this particular thread system-wide until the thread terminates, after which the value may be recycled by the OS. Return a list of all Thread objects currently alive. It excludes terminated threads and threads that have not yet been started.

Return the main Thread object. In normal conditions, the main thread is the thread from which the Python interpreter was started. Set a trace function for all threads started from the threading module. The func will be passed to sys. Set a profile function for all threads started from the threading module. Return the thread stack size used when creating new threads.This module provides mechanisms to use signal handlers in Python.

Some general rules for working with signals and their handlers:.

python thread sigterm

A handler for a particular signal, once set, remains installed until it is explicitly reset Python emulates the BSD style interface regardless of the underlying implementationwith the exception of the handler for SIGCHLDwhich follows the underlying implementation. This means that signals arriving during long calculations implemented purely in C such as regular expression matches on large bodies of text may be delayed for an arbitrary amount of time.

All of these can be overridden. Some care must be taken if both signals and threads are used in the same program. The fundamental thing to remember in using signals and threads simultaneously is: always perform signal operations in the main thread of execution. Any thread can perform an alarmgetsignalpausesetitimer or getitimer ; only the main thread can set a new signal handler, and the main thread will be the only one to receive signals this is enforced by the Python signal module, even if the underlying thread implementation supports sending signals to individual threads.

Use locks instead. The variables defined in the signal module are:. This is one of two standard signal handling options; it will simply perform the default function for the signal. All the signal numbers are defined symbolically.

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For example, the hangup signal is defined as signal. Note that not all systems define the same set of signal names; only those names defined by the system are defined by this module. This signal can only be used with os. Decrements interval timer both when the process executes and when the system is executing on behalf of the process. The signal module defines one exception:. Raised to signal an error from the underlying setitimer or getitimer implementation.

Expect this error if an invalid interval timer or a negative time is passed to setitimer. This error is a subtype of IOError. The signal module defines the following functions:. Any previously scheduled alarm is canceled only one alarm can be scheduled at any time. The returned value is then the number of seconds before any previously set alarm was to have been delivered.By using our site, you acknowledge that you have read and understand our Cookie PolicyPrivacy Policyand our Terms of Service.

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I want to create a python program which runs as a systemd service. I want to be able to stop it gracefully. The example is following:. With threads. Just to be clear: my program requires multiple threads so I want to be able to stop service gracefully even if I use threads in my program. What am I doing wrong?

Thanks to Shawn who suggested this old postI have now solved the problem. The problem is in how signal handlers are implemented in python. The line t. There are 2 simple solutions:. Learn more. Asked 1 year, 8 months ago.

Active 1 year, 8 months ago. Viewed times. The example is following: Without threads. This old post is probably relevant. Active Oldest Votes.

There are 2 simple solutions: 1 Use python 3. Sign up or log in Sign up using Google. Sign up using Facebook. Sign up using Email and Password. Post as a guest Name. Email Required, but never shown. The Overflow Blog. Featured on Meta. Feedback on Q2 Community Roadmap. Technical site integration observational experiment live on Stack Overflow. Dark Mode Beta - help us root out low-contrast and un-converted bits.

Question Close Updates: Phase 1.The signal. A handler for a particular signal, once set, remains installed until it is explicitly reset Python emulates the BSD style interface regardless of the underlying implementationwith the exception of the handler for SIGCHLDwhich follows the underlying implementation.

A Python signal handler does not get executed inside the low-level C signal handler. Instead, the low-level signal handler sets a flag which tells the virtual machine to execute the corresponding Python signal handler at a later point for example at the next bytecode instruction. This has consequences:. Python signal handlers are always executed in the main Python thread, even if the signal was received in another thread.

You can use the synchronization primitives from the threading module instead. The variables defined in the signal module are:. This is one of two standard signal handling options; it will simply perform the default function for the signal. All the signal numbers are defined symbolically. For example, the hangup signal is defined as signal. Note that not all systems define the same set of signal names; only those names defined by the system are defined by this module.

This signal can only be used with os. Decrements interval timer both when the process executes and when the system is executing on behalf of the process. The signal module defines one exception:.

Python Catch SIGINT (CTRL-C)

Raised to signal an error from the underlying setitimer or getitimer implementation. Expect this error if an invalid interval timer or a negative time is passed to setitimer. This error is a subtype of OSError. New in version 3. The signal module defines the following functions:. Any previously scheduled alarm is canceled only one alarm can be scheduled at any time. The returned value is then the number of seconds before any previously set alarm was to have been delivered.

If time is zero, no alarm is scheduled, and any scheduled alarm is canceled. If the return value is zero, no alarm is currently scheduled. See the Unix man page alarm 2.

python thread sigterm

Availability: Unix. Return the current signal handler for the signal signalnum. The returned value may be a callable Python object, or one of the special values signal.

Python multithreaded daemon with SIGTERM support (a recipe)

Here, signal. Cause the process to sleep until a signal is received; the appropriate handler will then be called. Returns nothing. Not on Windows. See the Unix man page signal 2. See also sigwaitsigwaitinfosigtimedwait and sigpending. The target thread can be executing any code Python or not. However, if the target thread is executing the Python interpreter, the Python signal handlers will be executed by the main thread.There are some important details about handling signals in a Python program that uses threadsespecially if those threads perform tasks in an infinite loop.

After a thorough read of the documentation and some research on the web, I finally made it work and thought it would be a good idea to write a post that points out these important details using a sample code snippet. The first most important thing to remember is that all signal handler functions must be set in the main threadas this is the one that receives the signals.

The documentation of the signal module has a very informative note:. Some care must be taken if both signals and threads are used in the same program. The fundamental thing to remember in using signals and threads simultaneously is: always perform signal operations in the main thread of execution.

Any thread can perform an alarmgetsignalpausesetitimer or getitimer ; only the main thread can set a new signal handler, and the main thread will be the only one to receive signals this is enforced by the Python signal module, even if the underlying thread implementation supports sending signals to individual threads.

Use locks instead. This is actually a crucial stepotherwise all signals sent to your program will be ignored. Adding an infinite loop using time. Here is a basic Python program to demonstrate the functionality. The main thread starts two threads jobs that perform their task in an infinite loop. For more information about how it works, please refer to the next section containing some useful remarks.

Below, there are some remarks which aim to help you better understand how the code snippet above works:. Using signals to terminate or generally control a Python script, that does its work using threads running in a never-ending cycle, is very useful.

Learning to do it right gives you the opportunity to easily create a single service that performs various tasks simultaneously, for instance system monitoring, and control it by sending signals externally from the system.

Skip to main content. Maintenance time. How to set the Expires header correctly in Varnish. Set signal handlers in the main thread The first most important thing to remember is that all signal handler functions must be set in the main threadas this is the one that receives the signals.

Event object that indicates whether the thread should be terminated. Other thread setup code here Job code here Clean shutdown code here Set the shutdown flag on each thread to trigger a clean shutdown of each thread.

Related Articles Threads In Python ping.By using our site, you acknowledge that you have read and understand our Cookie PolicyPrivacy Policyand our Terms of Service. 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.

Let's suppose the current step performed is 2. And at this very moment we're sending TERM signal. I've found that I can handle the signal event using signal. So, my question is - is it possible to not interrupt the current execution but handle the TERM signal in a separated thread? Assuming you've got proper exception handling e.

The signal can be caught with signal. Based on the previous answers, I have created a context manager which protects from sigint and sigterm.

Found easiest way for me. Here an example with fork for clarity that this way is useful for flow control. Learn more. Ask Question. Asked 6 years, 7 months ago. Active 2 months ago. Viewed k times. Let's assume we have such a trivial daemon written in python: def mainloop : while True: 1. What happens is that the execution terminates immediately.

Active Oldest Votes. I was killed gracefully : ". Mayank Jaiswal Mayank Jaiswal 8, 6 6 gold badges 33 33 silver badges 38 38 bronze badges. Thanks for the idea!

I used a modified approach in reboot-guard. This is the best answer no threads requiredand should be the preferred first-try approach. Mausy Python allows you to not have parenthesis for defining classes. Although it's perfectly fine for python 3. Reason being: docs. Follow up, to keep you motivated, thank you. I use this all the time.

In worse case, that would simply mean doing another iteration before shuting down gracefully. The False value is set only once, and then it can only go from False to True so multiple access is not an issue. Example program signals-test. SherylHohman 9, 13 13 gold badges 53 53 silver badges 66 66 bronze badges. Will Manley Will Manley 1, 18 18 silver badges 16 16 bronze badges. If you put multiple statements into your worker loop you will see that your solution terminates a worker on a random position, which leaves the job in an unknown state.

Python Threading Tutorial: Run Code Concurrently Using the Threading Module

Works well for me, also in a Docker context. If you just set a flag and not raise exception then it will be the same as with thread.


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