How to stop and start a thread at will - python

So I'm doing some testing with threads and I realised I could not stop and then start a thread. I could stop it, but starting it again was the issue.I want a script that adds 1 to a var when it is on then its stops when off by pressing shift to turn on and off.I have the detecting shift working (it is on another part of my code), but I just need to find out how to stop and start threadsHere is my test code:
from threading import Thread as th
import time as t
var = 0
def testDef():
global var
var += 1:
t.sleep(1)
test = th(target = testDef)
test.start()
while True:
menu = input("On, Off, Show Var")
if menu == "On":
test.start()
elif menu == "Off":
test._stop():
elif menu == "S":
print(var)
I know there are a few errors, but I mainly need the on and off threading to work.
Thanks, Jeff.

As far as I know, you can't actually stop and restart a thread as you can't use test.start() when the method has been terminated. However, you may be wondering to something similar by using threading.Condition to pause and later resume the execution.
You can read more about it in the documentation.
There is also an error in var += 1:, change it to var += 1

Here's a simple example on how to use threading.Event to enable two threads to communicate. This works by setting the internal flag of the Event to either True or False. While this internal flag is False you can ask thread a to wait (effectively block, which is not very efficient by the way). Then we use the two timers (b, c) to simulate a shift press every 5 seconds. In order to release a we set the event (internal flag = True). 5 seconds later, we clear the value of the internal flag and this will make thread a to block again.
import threading
def do(event):
flag = True
while flag:
if not event.isSet():
print "blocking"
event.wait()
else:
print "resuming"
def pressShift(event, enable):
print "Shift pressed"
if enable:
event.set()
else:
event.clear()
def main():
event = threading.Event()
a = threading.Thread(target=do, args=(event,))
b = threading.Timer(5, pressShift, args=(event, True)).start()
c = threading.Timer(10, pressShift, args=(event, False)).start()
a.start()
a.join()
if __name__ == "__main__":
main()

You cannot restart a thread that has already been started. What you can do, however, is to create another thread.
from threading import Thread as th
import time as t
var = 0
def testDef():
global var
var += 1
t.sleep(1)
test = th(target = testDef)
test.start()
while True:
menu = input("On, Off, Show Var")
if menu == "On":
test = th(target = testDef)
test.start()
elif menu == "Off":
test._stop()
elif menu == "S":
print(var)

Use an event object like this post, and check that event in your target functoin. Also, you need a new thread each time you re-start. The code shown below adds some debugging that should be useful. (Another approach is to build a custom stop function.)
import logging
import threading
import time as t
var = 0
logging.basicConfig(level=logging.DEBUG,
format='[%(levelname)s] (%(threadName)-10s) %(message)s',
)
def testDef(stop_event):
global var
print 'Thread Running', var
# inThread.stop()
while not stop_event.isSet():
var += 1
logging.debug('Var is %i' % var)
t.sleep(1)
# Use an event to track user input
testStopEvent = threading.Event()
testStopEvent.clear()
test = threading.Thread(name = 'test', target=testDef, args=((testStopEvent,)))
test.setDaemon(True)
while True:
menu = input("On = 1, Off = 2, Show Var = 3")
if menu == 1:
test.start()
elif menu == 2:
testStopEvent.set()
test.join() # Wait for the thread to finish
test = threading.Thread(target=testDef, args=((testStopEvent,))) # "re-start" thread
testStopEvent.clear() # Reset the stop event
elif menu == 3:
print(var)

Related

Stopping a thread after a certain amount of time while keeping the main thread responsive

I'm looking to terminate a thread after a certain amount of time. The thread is called from an infinite while loop that waits for users input. Thread starts after user inputs number 4 from command line, after which thread writes some text to the console in another infinite loop. After x amount of time the started thread should terminate. How can I make the thread stop after the set time while keeping the main thread with user input responsive (active)?
Here is some sample code:
def loop():
while True:
print("ON")
print("OFF")
if __name__ == "__main__":
t = threading.Thread(target=loop)
try:
while True:
print(">>", end='')
command = int(input())
if command == 1:
...
elif command == 2:
...
elif command == 3:
...
elif command == 4:
print("Insert time:")
time = float(input())
t.start()
elif command == 5:
...
It is possible to pass an argument to the loop and that can be used to stop the thread, something like this:
def loop(running):
while running[0]:
print("HELLO")
if __name__ == "__main__":
running = [True]
t = threading.Thread(target=loop, args=(running,))
t.start()
while True:
command = input()
running[0] = False
running is shared by both the main thread and the other thread, so changing the value in one changes it in the other.

I want to run and kill a thread on a button press

I have a program that is supposed to send a few data points over a serial connection to an arduino which will control some motors to move. I can send the control signals individually as well as by txt file which will run repeatedly until the file is complete. While running a txt file, I want to be able to exit the loop like a pause or stop button. I think the best way to do that is via a thread that I can close. I have never done any threading before and my rudimentary attempts have not worked. Here is the function that sends the file data.
def send_file():
# Global vars
global moto1pos
global motor2pos
# Set Ready value
global isready
# Get File location
program_file_name = file_list.get('active')
file_path = "/home/evan/Documents/bar_text_files/"
program_file = Path(file_path + program_file_name)
file = open(program_file)
pos1 = []
pos2 = []
speed1 = []
speed2 = []
accel1 = []
accel2 = []
for each in file:
vals = each.split()
pos1.append(int(vals[0]))
pos2.append(int(vals[1]))
speed1.append(int(vals[2]))
speed2.append(int(vals[3]))
accel1.append(int(vals[4]))
accel2.append(int(vals[5]))
# Send file values
try:
while isready == 1:
for i in range(len(pos1)):
print("Step: " + str(i+1))
data = struct.pack("!llhhhh", pos1[i], pos2[i], speed1[i], speed2[i], accel1[i], accel2[i])
ser.write(data)
try:
pos1time = abs(pos1[i]/speed1[i])
except:
pos1time = 0
try:
pos2time = abs(pos2[i]/speed2[i])
except:
pos2time = 0
time_array = (pos1time, pos2time)
time.sleep(max(time_array))
motor1pos = ser.readline()
motor2pos = ser.readline()
if i < (len(pos1)-1):
isready = ord(ser.read(1))
else:
isready = 0
except:
print("Error: data not sent. Check serial port is open")
Here is the threading command which I want the sendfile command to work from.
def thread():
try:
global isready
isready = 1
t = threading.Thread(name='sending_data', target=command)
t.start()
except:
print("Threading Error: you don't know what you are doing")
And here is the stop function I want the thread to be killed by:
def stop():
try:
global isready
isready = 0
t.kill()
except:
print("Error: thread wasn't killed")
I know you aren't supposed to kill a thread but the data isn't very important. Whats more important is to stop the motors before something breaks.
The button in tkinter is:
run_file_butt = tk.Button(master = file_frame, text = "Run File", command = thread)
When I click the button, the program runs but the stop function does nothing to stop the motion.
Question: run and kill a thread on a button press
There is no such a thing called .kill(....
Start making your def send_file(... a Thread object which is waiting your commands.
Note: As it stands, your inner while isready == 1: will not stop by using m.set_state('stop').
It's mandatory to start the Thread object inside:
if __name__ == '__main__':
m = MotorControl()
import threading, time
class MotorControl(threading.Thread):
def __init__(self):
super().__init__()
self.state = {'is_alive'}
self.start()
def set_state(self, state):
if state == 'stop':
state = 'idle'
self.state.add(state)
def terminate(self):
self.state = {}
# main function in a Thread object
def run(self):
# Here goes your initalisation
# ...
while 'is_alive' in self.state:
if 'start' in self.state:
isready = 1
while isready == 1:
# Here goes your activity
# Simulate activity
print('running')
time.sleep(2)
isready = 0
self.state = self.state - {'start'}
self.state.add('idle')
elif 'idle' in self.state:
print('idle')
time.sleep(1)
if __name__ == '__main__':
m = MotorControl()
time.sleep(2)
m.set_state('start')
time.sleep(3)
m.set_state('stop')
time.sleep(3)
m.set_state('start')
time.sleep(4)
m.terminate()
print('EXIT __main__')
Your tk.Button should look like:
tk.Button(text = "Run File", command = lambda:m.set_state('start'))
tk.Button(text = "Stop File", command = lambda:m.set_state('stop'))
tk.Button(text = "Terminate", command = m.terminate)
The answer I have gone with is simple due to my simple understanding of threading and unique circumstances with which I am using the threading. Instead of terminating the thread in a way I was hoping, I added another conditional statement to the sending line of the send_file function.
while isready == 1:
for i in range(len(pos1)):
if motorstop == False:
print("Step: " + str(i+1))
#data = struct.pack('!llllhhhhhhhh', pos1[i], pos2[i], pos3[i], pos4[i], speed1[i], speed2[i], speed3[i], speed[4], accel1[i], accel2[i], accel3[i], accel4[i])
data = struct.pack("!llhhhh", pos1[i], pos2[i], speed1[i], speed2[i], accel1[i], accel2[i])
ser.write(data)
else:
isready = 0
break
and I have updated my stop() func to the following:
def stop():
try:
global motorstop
global t
motorstop = True
t.join()
except:
print("Error: thread wasn't killed")
I'm not exactly sure how it works but it is much simpler than what was mentioned by #stovefl.
With this code, since the function is mostly just sleeping, it can run but it won't send any new information and then will .join() after the next iteration.

Python pause loop on user input

Hey I am trying to have a loop be pausable from user input like having a input box in the terminal that if you type pause it will pause the loop and then if you type start it will start again.
while True:
#Do something
pause = input('Pause or play:')
if pause == 'Pause':
#Paused
Something like this but having the #Do something continually happening without waiting for the input to be sent.
Ok I get it now, here is a solution with Threads:
from threading import Thread
import time
paused = "play"
def loop():
global paused
while not (paused == "pause"):
print("do some")
time.sleep(3)
def interrupt():
global paused
paused = input('pause or play:')
if __name__ == "__main__":
thread2 = Thread(target = interrupt, args = [])
thread = Thread(target = loop, args = [])
thread.start()
thread2.start()
You can't directly, as input blocks everything until it returns.
The _thread module, though, can help you with that:
import _thread
def input_thread(checker):
while True:
text = input()
if text == 'Pause':
checker.append(True)
break
else:
print('Unknown input: "{}"'.format(text))
def do_stuff():
checker = []
_thread.start_new_thread(input_thread, (checker,))
counter = 0
while not checker:
counter += 1
return counter
print(do_stuff())

How to ask Question by if statement via timeout

is there any way for ask question by if statement and after afew sec if user didnot give any answer , if state use a default answer?
inp = input("change music(1) or close the app(2)")
if inp = '1':
print("Music changed)
elif inp = '2':
print("good by")
in this case if user dont give any answer after 30 sec by default if statement choose number 3
from threading import Timer
out_of_time = False
def time_ran_out():
print ('You didn\'t answer in time') # Default answer
out_of_time = True
seconds = 5 # waiting time in seconds
t = Timer(seconds,time_ran_out)
t.start()
inp = input("change music(1) or close the app(2):\n")
if inp != None and not out_of_time:
if inp == '1':
print("Music changed")
elif inp == '2':
print("good by")
else:
print ("Wrong input")
t.cancel()
Timer Objects
This class represents an action that should be run only after a certain amount of time has passed — a timer. Timer is a
subclass of Thread and as such also functions as an example of
creating custom threads.
Timers are started, as with threads, by calling their start() method.
The timer can be stopped (before its action has begun) by calling the
cancel() method. The interval the timer will wait before executing its
action may not be exactly the same as the interval specified by the
user.
For example:
def hello():
print("hello, world")
t = Timer(30.0, hello)
t.start() # after 30 seconds, "hello, world" will be printed
class threading.Timer(interval, function, args=None, kwargs=None)
Create a timer that will run function with arguments args and keyword
arguments kwargs, after interval seconds have passed. If args is None
(the default) then an empty list will be used. If kwargs is None (the
default) then an empty dict will be used.
cancel()
Stop the timer, and cancel the execution of the timer’s action. This will only work if the timer is still in its waiting
stage.
Here's an alternative way to do it (python 3), using multiprocessing. Note, to get the stdin to work in the child process, you have to re open it first. I'm also converting the input from string to int to use with the multiprocessing value, so you might want to error check there as well.
import multiprocessing as mp
import time
import sys
import os
TIMEOUT = 10
DEFAULT = 3
def get_input(resp: mp.Value, fn):
sys.stdin = os.fdopen(fn)
v = input('change music(1) or close the app (2)')
try:
resp.value = int(v)
except ValueError:
pass # bad input, maybe print error message, try again in loop.
# could also use another mp.Value to signal main to restart the timer
if __name__ == '__main__':
now = time.time()
end = now + TIMEOUT
inp = 0
resp = mp.Value('i', 0)
fn = sys.stdin.fileno()
p = mp.Process(name='Get Input', target=get_input, args=(resp, fn))
p.start()
while True:
t = end - time.time()
print('Checking for timeout: Time = {:.2f}, Resp = {}'.format(t, resp.value))
if t <= 0:
print('Timeout occurred')
p.terminate()
inp = DEFAULT
break
elif resp.value > 0:
print('Response received:', resp.value)
inp = resp.value
break
else:
time.sleep(1)
print()
if inp == 1:
print('Music Changed')
elif inp == 2:
print('Good Bye')
else:
print('Other value:', inp)

Python realtime timer

Could anybody advise me on converting the Java Timer class to Python? Currently I am converting a Java program to a Python script. However, Python does not have the Timer/TimerTask library (if it does have this, please enlighten me. Thanks!). I need to be able to reset the Timer. Java has Timer.cancel, but Python doesn't have this. Is there any replacement for it?
timer.cancel();
timer = new Timer("Printer");
MyTask t = new MyTask();
timer.schedule(t, 0, 1000);
Java script timer
class Timerclass extends TimerTask {
//times member represent calling times.
private int times = 0;
public void run() {
times++;
if (times <= 5) {
System.out.println(""+times);
} else {
this.cancel();
//Stop Timer.
System.out.println("Timer Finish");
}
}
}
Currently my code
import time
import threading
class Variable:
count = 0
people = 0
times = 0
def enter():
if int(Variable.count == 1):
print("Entered")
t = threading.Timer(5.0, countdown)
t.start()
else:
print("Entered +1")
t.clear() // Stuck Help
t = threading.Timer(5.0, countdown)
t.start()
def out():
if int(Variable.count > 0):
print("Exited")
elif int(Variable.count < 0):
print("Error")
def countdown():
print("TIMEUP")
while True:
sensor1 = input("Sensor 1: ")
sensor2 = input("Sensor 2: ")
Variable.count+=1
if int(sensor1) == int(sensor2):
Variable.count -= 1
print(Variable.count)
print("error")
elif int(sensor1) == 1:
Variable.people += 1
print(Variable.people)
enter()
elif int(sensor2) == 1:
Variable.people -= 1
print(Variable.people)
out()
else:
print("Error")
i have one problems that i'm stuck in i need to stop the current counting and start a new one whenever the method call
Basically what i want or im looking out for is when i recall this method it will reset or cancel any existing and recount again
Update latest
import time
import threading
class Variable:
count = 0
people = 0
times = 0
def countdown():
print("TIMEUP")
t = threading.Timer(5.0, countdown)
def enter():
if int(Variable.count == 1):
print("Entered")
t.start()
else:
print("Entered +1")
t.cancel()
t.join() # here you block the main thread until the timer is completely stopped
t.start()
def out():
if int(Variable.count > 0):
print("Exited")
elif int(Variable.count < 0):
print("Error")
while True:
sensor1 = input("Sensor 1: ")
sensor2 = input("Sensor 2: ")
Variable.count+=1
if int(sensor1) == int(sensor2):
Variable.count -= 1
print(Variable.count)
print("error")
elif int(sensor1) == 1:
Variable.people += 1
print(Variable.people)
enter()
elif int(sensor2) == 1:
Variable.people -= 1
print(Variable.people)
out()
else:
print("Error")
Anybody can spot my ,istake im getting this error but i t.clear() the process
in start raise RuntimeError("threads can only be started once")
RuntimeError: threads can only be started once
I would suggest using the time module for something like this:
from time import time, sleep
from datetime import datetime, timedelta
nowtime = time()
#Put your script here
x = 1
for k in range(1000):
x+=1
sleep(0.01)
sec = timedelta(seconds=int(time()-nowtime))
d = datetime(1,1,1)+sec
print("DAYS:HOURS:MIN:SEC")
print("%d:%d:%d:%d" % (d.day-1, d.hour, d.minute, d.second))
This assigns the time in seconds at the beginning to a variable, and after the main script has finished, it subtracts the previous time from the current time and formats it in days, hours, minutes, and seconds.
Here is it running:
bash-3.2$ python timing.py
DAYS:HOURS:MIN:SEC
0:0:0:10
bash-3.2$
You could also use the Threading module, which has a built-in cancel method:
>>> import threading
>>> def hello():
... print "This will print after a desired period of time"
...
>>> timer = threading.Timer(3.0, hello)
>>> timer.start() #After 3.0 seconds, "This will print after a desired period of time" will be printed
>>> This will print after a desired period of time
>>> timer.start()
>>> timer = threading.Timer(3.0, hello)
>>> timer.start()
>>> timer.cancel()
>>>
Python actually has a class for this, which includes a cancel method: threading.Timer. It seems to be close enough to the Java Timer class for your needs (The Java Timer also runs in background thread). Here's the example usage from the docs:
def hello():
print "hello, world"
t = Timer(30.0, hello)
t.start() # after 30 seconds, "hello, world" will be printed
Edit:
The problem with your updated code is that you're trying to use the same Timer object more than once. That may be possible in the Java implementation, but in Python you can't reuse a Thread object (Timer is a Thread subclass). You'll need to create a new Timer object after you join() it. Like this:
t = threading.Timer(5.0, countdown)
def enter():
global t # You need this to tell Python that you're going to change the global t variable. If you don't do this, using 't = ..' will just create a local t variable.
if int(Variable.count == 1):
print("Entered")
t.start()
else:
print("Entered +1")
t.cancel()
t.join() # here you block the main thread until the timer is completely stopped
t = threading.Timer(5.0, countdown)
t.start()

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