The thread started in the start_thread method does not stop. Why ?
import time
import threading
cont_running = True
def start_thread():
threading.Thread(target=run).start()
def stop_thread():
cont_running = False
def run():
while cont_running:
print 'Thread running : ' + str(cont_running)
time.sleep(0.2)
print 'Thread ended'
start_thread()
time.sleep(2)
stop_thread()
In stop_thread(), your assignment statement creates a local variable named cont_running. This local variable is unrelated to the global variable of the same name.
Try this:
def stop_thread():
global cont_running
cont_running = False
Related
import threading
from playsound import playsound
import time
soundList = []
bot_run = True
class myThread (threading.Thread):
def __init__(self):
global soundList
threading.Thread.__init__(self)
def run(self):
global soundList
global bot_run
while bot_run:
try:
time.sleep(1)
playsound(soundList.pop(0))
except:
pass
def main():
global soundList
global bot_run
input()
soundThread = myThread()
soundThread.start()
while not ((user_input := input('sound name: ')) == 'close'):
soundList.append(user_input)
bot_run = False
main()
I want to ensure someone who clicks the x on cmd doesn't end the program but the thread keeps going.
Does the thread die on its own when the main program ends? Does the bot_run variable cease to exist and therefore exit the while loop? How can I make sure I don't have this loop running forever when it's no longer being used if the user exited the program without following procedure?
from time import sleep
def foo():
sleep(3)
return True
while True:
print('Running')
if foo() == True:
print('Finished.')
break
I want to keep printing "Running" but when foo returns True I want to print "Finished" (once) and break out of the loop.
I have tried the above but it prints "Running" just once and waits for foo to finish executing and then continues.
import threading
from time import sleep
flag = True
def foo()->None:
global flag
sleep(1)
flag = False
if __name__ == "__main__":
t1 = threading.Thread(target=foo)
t1.start()
while flag:
print('Running')
print('Finished')
Because you worked with only one thread, when you call the function the main stops until the function returns.
Therefore, if you want the main code and the function to run together, you have to work with threads.
So, after trying somethings I found 2 solutions, of my own question, that uses threading.
1. Modifies the foo function
from time import sleep
from threading import Thread
x = True
def foo():
sleep(3)
global x
x = False
print('finished')
def printing():
while x:
print('Running')
foo_thread = Thread(target=foo)
foo_thread.start()
printing_thread = Thread(target=printing)
printing_thread.start()
2. Uses decorator to keep foo unchanged
from time import sleep
from threading import Thread
x = True
def sets_true(func):
def wrapper():
returned_value = func()
global x
x = False
print('finished')
return wrapper
#sets_true
def foo():
sleep(3)
return True
def printing():
while x:
print('Running')
foo_thread = Thread(target=foo)
foo_thread.start()
printing_thread = Thread(target=printing)
printing_thread.start()
I am new to python I have very little knowledge about threads in python. Here is my sample code.
import threading
from threading import Thread
import time
check = False
def func1():
print ("funn1 started")
while check:
print ("got permission")
def func2():
global check
print ("func2 started")
time.sleep(2)
check = True
time.sleep(2)
check = False
if __name__ == '__main__':
Thread(target = func1).start()
Thread(target = func2).start()
What I want is to see see "got permission" as the output. But with my current code it is not happening. I assume that the func1 thread is closed before func2 changes the check value to True.
How can I keep func1 alive?
I have researched on the internet but I could not found a solution.
Any help would be appreciated.
Thank you in advance!
The problem here is that func1 performs the check in the while loop, finds it is false, and terminates. So the first thread finishes without printing "got permission".
I don't think this mechanism is quite what you are looking for. I would opt to use a Condition like this,
import threading
from threading import Thread
import time
check = threading.Condition()
def func1():
print ("funn1 started")
check.acquire()
check.wait()
print ("got permission")
print ("funn1 finished")
def func2():
print ("func2 started")
check.acquire()
time.sleep(2)
check.notify()
check.release()
time.sleep(2)
print ("func2 finished")
if __name__ == '__main__':
Thread(target = func1).start()
Thread(target = func2).start()
Here the condition variable is using a mutex internally to communicate between the threads; So only one thread can acquire the condition variable at a time. The first function acquires the condition variable and then releases it but registers that it is going to wait until it receives a notification via the condition variable. The second thread can then acquire the condition variable and, when it has done what it needs to do, it notifies the waiting thread that it can continue.
from threading import Thread
import time
check = False
def func1():
print ("funn1 started")
while True:
if check:
print ("got permission")
break
def func2():
global check
print ("func2 started")
time.sleep(2)
check = True
time.sleep(2)
check = False
if __name__ == '__main__':
Thread(target = func1).start()
Thread(target = func2).start()
func1 must be like this
def func1():
print("func1 started")
while True:
if check:
print("got permission")
break
else:
time.sleep(0.1)
I have three files:
helper.py
from globalvariables import *
global exit_signal
global exited_signal
def helperstart():
global exited_signal
while True:
if exit_signal is True:
exited_signal = True
print ('Exiting from helper thread')
return
main.py
from globalvariables import *
import threading
import helper
global exit_signal
global exited_signal
def mainstart():
global exit_signal
helper_thread = threading.Thread(target = helper.helperstart)
input ('Press <enter> to start the thread')
helper_thread.start()
input ('Press <enter> to end the thread')
exit_signal = True
# check if helper has exited
if exited_signal is True:
print ('Helper exited successfully')
if __name__ == '__main__':
mainstart()
globalvariables.py
exit_signal = False
exited_signal = False
From main.py, the value of exit_signal should be edited to True. This should make the helper thread exit. But it is not exiting. I've tried printing the value of exit_signal from helperstart() function and it keeps showing as False. So, the main.py isn't editing the variable properly. Please help me figure out why.
I change a global variable in a signal handler and poll for it in the main program. But the value does not change in the main thread.
Is there a qualifier that I need to use to make it a volatile (like in Java) variable?
Here's the program:
test.py
import time
import signal
def debug():
closeSession = False
def sigint_handler(signal, frame):
global closeSession
print('Breaking the poll...')
closeSession=True
signal.signal(signal.SIGINT, sigint_handler)
# Start a program...
while not closeSession:
time.sleep(1)
print('Polling... closeSession = %r' % closeSession)
print('Exiting! Bye.')
# Sent 'quit' to stdin of the program
if __name__ == "__main__":
debug()
sigint_handler() gets called whenever I press Ctrl + C but the new value of closeSession is not used in the main thread.
I get the following output:
$ python test.py Polling... closeSession = False Polling...
closeSession = False
I press Ctrl + C
^CBreaking the poll... Polling... closeSession = False
Press Ctrl + C, again
^CBreaking the poll... Polling... closeSession = False
Press Ctrl + C, again
^CBreaking the poll... Polling... closeSession = False
Polling... closeSession = False
The problem is scope.
Inside the debug() function, you didn't declare closeSession as a global, which means that you have two variables called closeSession. One global and one scoped within the debug() function. And inside the sigint_handler() function, you've explicitly instructed to use global one, which is shadowed by the scoped one in the outer function.
You can solve this by declaring global before assignment in debug():
def debug():
global closeSession
closeSession = False
...
By the way, your code does not work on windows, it throws a IOError because the sleep function is interrupted. A workaround that worked for me is:
...
while not closeSession:
try:
time.sleep(1)
except IOError:
pass
print('Polling... closeSession = %r' % closeSession)
...
It's not pretty but it works.
You have to set global closeSession before accessing the variable, else you're creating a local variable with the same name and the loop will never end.
Try this:
import time
import signal
def debug():
global closeSession # <-- this was missing
closeSession = False
def sigint_handler(signal, frame):
global closeSession
print('Breaking the poll...')
closeSession=True
signal.signal(signal.SIGINT, sigint_handler)
# Start a program...
while not closeSession:
time.sleep(1)
print('Polling... closeSession = %r' % closeSession)
print('Exiting! Bye.')
# Sent 'quit' to stdin of the program
if __name__ == "__main__":
debug()