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Stopping eval code dinamically on event fired [duplicate]

What's the proper way to tell a looping thread to stop looping?
I have a fairly simple program that pings a specified host in a separate threading.Thread class. In this class it sleeps 60 seconds, the runs again until the application quits.
I'd like to implement a 'Stop' button in my wx.Frame to ask the looping thread to stop. It doesn't need to end the thread right away, it can just stop looping once it wakes up.
Here is my threading class (note: I haven't implemented looping yet, but it would likely fall under the run method in PingAssets)
class PingAssets(threading.Thread):
def __init__(self, threadNum, asset, window):
threading.Thread.__init__(self)
self.threadNum = threadNum
self.window = window
self.asset = asset
def run(self):
config = controller.getConfig()
fmt = config['timefmt']
start_time = datetime.now().strftime(fmt)
try:
if onlinecheck.check_status(self.asset):
status = "online"
else:
status = "offline"
except socket.gaierror:
status = "an invalid asset tag."
msg =("{}: {} is {}. \n".format(start_time, self.asset, status))
wx.CallAfter(self.window.Logger, msg)
And in my wxPyhton Frame I have this function called from a Start button:
def CheckAsset(self, asset):
self.count += 1
thread = PingAssets(self.count, asset, self)
self.threads.append(thread)
thread.start()

Threaded stoppable function
Instead of subclassing threading.Thread, one can modify the function to allow
stopping by a flag.
We need an object, accessible to running function, to which we set the flag to stop running.
We can use threading.currentThread() object.
import threading
import time
def doit(arg):
t = threading.currentThread()
while getattr(t, "do_run", True):
print ("working on %s" % arg)
time.sleep(1)
print("Stopping as you wish.")
def main():
t = threading.Thread(target=doit, args=("task",))
t.start()
time.sleep(5)
t.do_run = False
if __name__ == "__main__":
main()
The trick is, that the running thread can have attached additional properties. The solution builds
on assumptions:
the thread has a property "do_run" with default value True
driving parent process can assign to started thread the property "do_run" to False.
Running the code, we get following output:
$ python stopthread.py
working on task
working on task
working on task
working on task
working on task
Stopping as you wish.
Pill to kill - using Event
Other alternative is to use threading.Event as function argument. It is by
default False, but external process can "set it" (to True) and function can
learn about it using wait(timeout) function.
We can wait with zero timeout, but we can also use it as the sleeping timer (used below).
def doit(stop_event, arg):
while not stop_event.wait(1):
print ("working on %s" % arg)
print("Stopping as you wish.")
def main():
pill2kill = threading.Event()
t = threading.Thread(target=doit, args=(pill2kill, "task"))
t.start()
time.sleep(5)
pill2kill.set()
t.join()
Edit: I tried this in Python 3.6. stop_event.wait() blocks the event (and so the while loop) until release. It does not return a boolean value. Using stop_event.is_set() works instead.
Stopping multiple threads with one pill
Advantage of pill to kill is better seen, if we have to stop multiple threads
at once, as one pill will work for all.
The doit will not change at all, only the main handles the threads a bit differently.
def main():
pill2kill = threading.Event()
tasks = ["task ONE", "task TWO", "task THREE"]
def thread_gen(pill2kill, tasks):
for task in tasks:
t = threading.Thread(target=doit, args=(pill2kill, task))
yield t
threads = list(thread_gen(pill2kill, tasks))
for thread in threads:
thread.start()
time.sleep(5)
pill2kill.set()
for thread in threads:
thread.join()

This has been asked before on Stack. See the following links:
Is there any way to kill a Thread in Python?
Stopping a thread after a certain amount of time
Basically you just need to set up the thread with a stop function that sets a sentinel value that the thread will check. In your case, you'll have the something in your loop check the sentinel value to see if it's changed and if it has, the loop can break and the thread can die.

I read the other questions on Stack but I was still a little confused on communicating across classes. Here is how I approached it:
I use a list to hold all my threads in the __init__ method of my wxFrame class: self.threads = []
As recommended in How to stop a looping thread in Python? I use a signal in my thread class which is set to True when initializing the threading class.
class PingAssets(threading.Thread):
def __init__(self, threadNum, asset, window):
threading.Thread.__init__(self)
self.threadNum = threadNum
self.window = window
self.asset = asset
self.signal = True
def run(self):
while self.signal:
do_stuff()
sleep()
and I can stop these threads by iterating over my threads:
def OnStop(self, e):
for t in self.threads:
t.signal = False

I had a different approach. I've sub-classed a Thread class and in the constructor I've created an Event object. Then I've written custom join() method, which first sets this event and then calls a parent's version of itself.
Here is my class, I'm using for serial port communication in wxPython app:
import wx, threading, serial, Events, Queue
class PumpThread(threading.Thread):
def __init__ (self, port, queue, parent):
super(PumpThread, self).__init__()
self.port = port
self.queue = queue
self.parent = parent
self.serial = serial.Serial()
self.serial.port = self.port
self.serial.timeout = 0.5
self.serial.baudrate = 9600
self.serial.parity = 'N'
self.stopRequest = threading.Event()
def run (self):
try:
self.serial.open()
except Exception, ex:
print ("[ERROR]\tUnable to open port {}".format(self.port))
print ("[ERROR]\t{}\n\n{}".format(ex.message, ex.traceback))
self.stopRequest.set()
else:
print ("[INFO]\tListening port {}".format(self.port))
self.serial.write("FLOW?\r")
while not self.stopRequest.isSet():
msg = ''
if not self.queue.empty():
try:
command = self.queue.get()
self.serial.write(command)
except Queue.Empty:
continue
while self.serial.inWaiting():
char = self.serial.read(1)
if '\r' in char and len(msg) > 1:
char = ''
#~ print('[DATA]\t{}'.format(msg))
event = Events.PumpDataEvent(Events.SERIALRX, wx.ID_ANY, msg)
wx.PostEvent(self.parent, event)
msg = ''
break
msg += char
self.serial.close()
def join (self, timeout=None):
self.stopRequest.set()
super(PumpThread, self).join(timeout)
def SetPort (self, serial):
self.serial = serial
def Write (self, msg):
if self.serial.is_open:
self.queue.put(msg)
else:
print("[ERROR]\tPort {} is not open!".format(self.port))
def Stop(self):
if self.isAlive():
self.join()
The Queue is used for sending messages to the port and main loop takes responses back. I've used no serial.readline() method, because of different end-line char, and I have found the usage of io classes to be too much fuss.

Depends on what you run in that thread.
If that's your code, then you can implement a stop condition (see other answers).
However, if what you want is to run someone else's code, then you should fork and start a process. Like this:
import multiprocessing
proc = multiprocessing.Process(target=your_proc_function, args=())
proc.start()
now, whenever you want to stop that process, send it a SIGTERM like this:
proc.terminate()
proc.join()
And it's not slow: fractions of a second.
Enjoy :)

My solution is:
import threading, time
def a():
t = threading.currentThread()
while getattr(t, "do_run", True):
print('Do something')
time.sleep(1)
def getThreadByName(name):
threads = threading.enumerate() #Threads list
for thread in threads:
if thread.name == name:
return thread
threading.Thread(target=a, name='228').start() #Init thread
t = getThreadByName('228') #Get thread by name
time.sleep(5)
t.do_run = False #Signal to stop thread
t.join()

I find it useful to have a class, derived from threading.Thread, to encapsulate my thread functionality. You simply provide your own main loop in an overridden version of run() in this class. Calling start() arranges for the object’s run() method to be invoked in a separate thread.
Inside the main loop, periodically check whether a threading.Event has been set. Such an event is thread-safe.
Inside this class, you have your own join() method that sets the stop event object before calling the join() method of the base class. It can optionally take a time value to pass to the base class's join() method to ensure your thread is terminated in a short amount of time.
import threading
import time
class MyThread(threading.Thread):
def __init__(self, sleep_time=0.1):
self._stop_event = threading.Event()
self._sleep_time = sleep_time
"""call base class constructor"""
super().__init__()
def run(self):
"""main control loop"""
while not self._stop_event.isSet():
#do work
print("hi")
self._stop_event.wait(self._sleep_time)
def join(self, timeout=None):
"""set stop event and join within a given time period"""
self._stop_event.set()
super().join(timeout)
if __name__ == "__main__":
t = MyThread()
t.start()
time.sleep(5)
t.join(1) #wait 1s max
Having a small sleep inside the main loop before checking the threading.Event is less CPU intensive than looping continuously. You can have a default sleep time (e.g. 0.1s), but you can also pass the value in the constructor.

Sometimes you don't have control over the running target. In those cases you can use signal.pthread_kill to send a stop signal.
from signal import pthread_kill, SIGTSTP
from threading import Thread
from itertools import count
from time import sleep
def target():
for num in count():
print(num)
sleep(1)
thread = Thread(target=target)
thread.start()
sleep(5)
pthread_kill(thread.ident, SIGTSTP)
result
0
1
2
3
4
[14]+ Stopped

How to end with a thread from the main thread?

I'm looking for this question online but I can not find any way to do it directly I'm trying the following
class Test(Thread):
def __init__(self):
Thread.__init__(self)
def run(self):
for i in range(3):
time.sleep(1)
print(i)
def main():
test = Test()
test.start()
del test
time.sleep(5)
print('end')
main()
the only way to stop the thread is from the run method when the code ends but I can not find any way to end the thread.

You can't. All you can do is ask it nicely (by implementing some sort of inter thread communication like a threading.Queue object, then making your thread check it for instructions) and hope for the best.

You can use this simple approach to stop/kill/end a child thread from the parent thread using some variable that is being checked in child thread periodically:
from threading import Thread
from time import time, sleep
class Test:
some_var = True
def __init__(self):
self.t = Thread(target=self.worker)
#self.t.setDaemon(True)
self.t.start()
def worker(self):
while self.some_var is True:
print("%s > I'm running" % str(time()))
test = Test()
sleep(2)
test.some_var = False
print("End!")
Let me know if I didn't understand your question, but I think I've answered your question "How to end with a thread from the main thread?".

Repeat function at an interval?

I'm making a wxPython app that I need to update a value from the internet every 15 seconds. Is there any way I can have a function to set the value, and make it run in the background at this interval, without interrupting the program?
EDIT: Here's what I'm trying:
import thread
class UpdateThread(Thread):
def __init__(self):
self.stopped = False
UpdateThread.__init__(self)
def run(self):
while not self.stopped:
downloadValue()
time.sleep(15)
def downloadValue():
print x
UpdateThread.__init__()

What you want is to add a thread that runs your task at a specified pace.
You may have a look at this great answer here : https://stackoverflow.com/a/12435256/667433 to help you achieve this.
EDIT : Here is the code that should work for you :
import time
from threading import Thread # This is the right package name
class UpdateThread(Thread):
def __init__(self):
self.stopped = False
Thread.__init__(self) # Call the super construcor (Thread's one)
def run(self):
while not self.stopped:
self.downloadValue()
time.sleep(15)
def downloadValue(self):
print "Hello"
myThread = UpdateThread()
myThread.start()
for i in range(10):
print "MainThread"
time.sleep(2)
Hope it helps

I have made something similar to this:
-you need a thread to run in the background .
-And a define a 'custom' event , so that the tread can notify the UI when needed
Create the custom WX event
(MyEVENT_CHECKSERVER, EVT_MYEVENT_CHECKSERVER) =
wx.lib.newevent.NewEvent()
on UI "init" you can bind the event , and start the thread
# bind the custom event
self.Bind(EVT_MYEVENT_CHECKSERVER, self.foo)
# and start the worker thread
checkServerThread = threading.Thread(target=worker_checkServerStatus
,args=(self,) )
checkServerThread.daemon = True
checkServerThread.start()
the worker thread can be something like this ,ps. caller is the UI instance
def worker_checkServerStatus(caller):
while True:
# check the internet code here
evt = MyEVENT_CHECKSERVER(status='Some internet Status' ) #make a new event
wx.PostEvent(caller, evt) # send the event to the UI
time.sleep(15) #ZZZzz for a bit
Edit: miss read the question...

Another way to do that is with a timer:
import threading
stopNow = 0
def downloadValue():
print("Running downloadValue")
if not stopNow: threading.Timer(15,downloadValue).start()
downloadValue()
This is a classic pattern for repeating a function: the function itself adds a timed call to itself. To start the cycle, call the function (it returns immediately). To break the cycle set stopNow to 1.

How can I invoke a thread multiple times in Python?

I'm sorry if it is a stupid question. I am trying to use a number of classes of multi-threading to finish different jobs, which involves invoking these multi-threadings at different times for many times. But I am not sure which method to use. The code looks like this:
class workers1(Thread):
def __init__(self):
Thread.__init__(self)
def run(self):
do some stuff
class workers2(Thread):
def __init__(self):
Thread.__init__(self)
def run(self):
do some stuff
class workers3(Thread):
def __init__(self):
Thread.__init__(self)
def run(self):
do some stuff
WorkerList1=[workers1(i) for i in range(X)]
WorkerList2=[workers2(i) for i in range(XX)]
WorkerList2=[workers3(i) for i in range(XXX)]
while True:
for thread in WorkerList1:
thread.run (start? join? or?)
for thread in WorkerList2:
thread.run (start? join? or?)
for thread in WorkerList3:
thread.run (start? join? or?)
do sth .
I am trying to have all the threads in all the WorkerList to start functioning at the same time, or at least start around the same time. After sometime once they were all terminated, I would like to invoke all the threads again.
If there were no loop, I can just use .start; but since I can only start a thread once, start apparently does not fit here. If I use run, it seems that all the threads start sequentially, not only the threads in the same list, but also threads from different lists.
Can anyone please help?

there are a lot of misconceptions here:
you can only start a specific instance of a thread once. but in your case, the for loop is looping over different instances of a thread, each instance being assigned to the variable thread in the loop, so there is no problem at all in calling the start() method over each thread. (you can think of it as if the variable thread is an alias of the Thread() object instantiated in your list)
run() is not the same as join(): calling run() performs as if you were programming sequentially. the run() method does not start a new thread, it simply execute the statements in in the method, as for any other function call.
join() does not start executing anything: it only waits for a thread to finish. in order for join() to work properly for a thread, you have to call start() on this thread first.
additionally, you should note that you cannot restart a thread once it has finished execution: you have to recreate the thread object for it to be started again. one workaround to get this working is to call Thread.__init__() at the end of the run() method. however, i would not recommend doing this since this will disallow the use of the join() method to detect the end of execution of the thread.

If you would call thread.start() in the loops, you would actually start every thread only once, because all the entries in your list are distinct thread objects (it does not matter they belong to the same class). You should never call the run() method of a thread directly -- it is meant to be called by the start() method. Calling it directly would not call it in a separate thread.

The code below creates a class that is just a thread but the start and calls the initialization of the Thread class again so that the thread doesn't know it has been called.
from threading import Thread
class MTThread(Thread):
def __init__(self, name = "", target = None):
self.mt_name = name
self.mt_target = target
Thread.__init__(self, name = name, target = target)
def start(self):
super().start()
Thread.__init__(self, name = self.mt_name, target = self.mt_target)
def run(self):
super().run()
Thread.__init__(self, name = self.mt_name, target = self.mt_target)
def code():
#Some code
thread = MTThread(name = "SomeThread", target = code)
thread.start()
thread.start()

I had this same dilemma and came up with this solution which has worked perfectly for me. It also allows a thread-killing decorator to be used efficiently.
The key feature is the use of a thread refresher which is instantiated and .started in main. This thread-refreshing thread will run a function that instantiates and starts all other (real, task-performing) threads. Decorating the thread-refreshing function with a thread-killer allows you to kill all threads when a certain condition is met, such as main terminating.
#ThreadKiller(arg) #qu'est-ce que c'est
def RefreshThreads():
threadTask1 = threading.Thread(name = "Task1", target = Task1, args = (anyArguments))
threadTask2 = threading.Thread(name = "Task2", target = Task2, args = (anyArguments))
threadTask1.start()
threadTask2.start()
#Main
while True:
#do stuff
threadRefreshThreads = threading.Thread(name = "RefreshThreads", target = RefreshThreads, args = ())
threadRefreshThreads.start()

from threading import Thread
from time import sleep
def runA():
while a==1:
print('A\n')
sleep(0.5)
if __name__ == "__main__":
a=1
t1 = Thread(target = runA)
t1.setDaemon(True)
t1.start()
sleep(2)
a=0
print(" now def runA stops")
sleep(3)
print("and now def runA continue")
a=1
t1 = Thread(target = runA)
t1.start()
sleep(2)

Non-blocking class in python (detached Thread)

I'm trying to create a kind of non-blocking class in python, but I'm not sure how.
I'd like a class to be a thread itself, detached from the main thread so other threads can interact with it.
In a little example:
#!/usr/bin/python2.4
import threading
import time
class Sample(threading.Thread):
def __init__(self):
super(Sample, self).__init__()
self.status = 1
self.stop = False
def run(self):
while not(self.stop):
pass
def getStatus(self):
return self.status
def setStatus(self, status):
self.status = status
def test(self):
while self.status != 0:
time.sleep(2)
#main
sample = Sample()
sample.start()
sample.test()
sample.setStatus(0)
sample.stop()
What I'd like is having the "sample" instance running as a separate thread (detached from the main one) so, in the example, when the main thread reaches sample.test(), sample (and only "sample") would go to sleep for 2 seconds. In the meanwhile, the main thread would continue its execution and set sample's status to 0. When after the 2 seconds "sample" wakes up it would see the status=0 and exit the while loop.
The problem is that if I do this, the line sample.setStatus(0) is never reached (creating an infinite loop). I have named the threads, and it turns out that by doing this, test() is run by the main thread.
I guess I don't get the threading in python that well...
Thank you in advance

The object's run() method is what executes in a separate thread. When you call sample.test(), that executes in the main thread, so you get your infinite loop.

Perhaps something like this?
import threading
import time
class Sample(threading.Thread):
def __init__(self):
super(Sample, self).__init__()
self.stop = False
def run(self):
while not(self.stop):
print('hi')
time.sleep(.1)
def test(self):
print('testing...')
time.sleep(2)
#main
sample = Sample()
sample.start() # Initiates second thread which calls sample.run()
sample.test() # Main thread calls sample.test
sample.stop=True # Main thread sets sample.stop
sample.join() # Main thread waits for second thread to finish