I'm very new to python development, I need to call a function every x seconds.
So I'm trying to use a timer for that, something like:
def start_working_interval():
def timer_tick():
do_some_work() // need to be called on the main thread
timer = threading.Timer(10.0, timer_tick)
timer.start()
timer = threading.Timer(10.0, timer_tick)
timer.start()
the do_some_work() method need to be called on the main thread, and I think using the timer causing it to execute on different thread.
so my question is, how can I call this method on the main thread?
I'm now sure what you trying to achive but i played with your code and did this:
import threading
import datetime
def do_some_work():
print datetime.datetime.now()
def start_working_interval():
def timer_tick():
do_some_work()
timer = threading.Timer(10.0, timer_tick)
timer.start()
timer_tick()
start_working_interval()
So basically what i did was to set the Time inside the timer_tick() so it will call it-self after 10 sec and so on, but i removed the second timer.
I needed to do this too, here's what I did:
import time
MAXBLOCKINGSECONDS=5 #maximum time that a new task will have to wait before it's presence in the queue gets noticed.
class repeater:
repeatergroup=[] #our only static data member it holds the current list of the repeaters that need to be serviced
def __init__(self,callback,interval):
self.callback=callback
self.interval=abs(interval) #because negative makes no sense, probably assert would be better.
self.reset()
self.processing=False
def reset(self):
self.nextevent=time.time()+self.interval
def whennext(self):
return self.nextevent-time.time() #time until next event
def service(self):
if time.time()>=self.nextevent:
if self.processing=True: #or however you want to be re-entrant safe or thread safe
return 0
self.processing==True
self.callback(self) #just stuff all your args into the class and pull them back out?
#use this calculation if you don't want slew
self.nextevent+=self.interval
#reuse this calculation if you do want slew/don't want backlog
#self.reset()
#or put it just before the callback
self.processing=False
return 1
return 0
#this the transition code between class and classgroup
#I had these three as a property getter and setter but it was behaving badly/oddly
def isenabled(self):
return (self in self.repeatergroup)
def start(self):
if not (self in self.repeatergroup):
self.repeatergroup.append(self)
#another logical place to call reset if you don't want backlog:
#self.reset()
def stop(self):
if (self in self.repeatergroup):
self.repeatergroup.remove(self)
#group calls in c++ I'd make these static
def serviceall(self): #the VB hacker in me wants to name this doevents(), the c hacker in me wants to name this probe
ret=0
for r in self.repeatergroup:
ret+=r.service()
return ret
def minwhennext(self,max): #this should probably be hidden
ret=max
for r in self.repeatergroup:
ret=min(ret,r.whennext())
return ret
def sleep(self,seconds):
if not isinstance(threading.current_thread(), threading._MainThread): #if we're not on the main thread, don't process handlers, just sleep.
time.sleep(seconds)
return
endtime=time.time()+seconds #record when caller wants control back
while time.time()<=endtime: #spin until then
while self.serviceall()>0: #service each member of the group until none need service
if (time.time()>=endtime):
return #break out of service loop if caller needs control back already
#done with servicing for a while, yield control to os until we have
#another repeater to service or it's time to return control to the caller
minsleeptime=min(endtime-time.time(),MAXBLOCKINGPERIOD) #smaller of caller's requested blocking time, and our sanity number (1 min might be find for some systems, 5 seconds is good for some systems, 0.25 to 0.03 might be better if there could be video refresh code waiting, 0.15-0.3 seems a common range for software denouncing of hardware buttons.
minsleeptime=self.minwhennext(minsleeptime)
time.sleep(max(0,minsleeptime))
###################################################################
# and now some demo code:
def handler1(repeater):
print("latency is currently {0:0.7}".format(time.time()-repeater.nextevent))
repeater.count+=repeater.interval
print("Seconds: {0}".format(repeater.count))
def handler2(repeater): #or self if you prefer
print("Timed message is: {0}".format(repeater.message))
if repeater.other.isenabled():
repeater.other.stop()
else:
repeater.other.start()
repeater.interval+=1
def demo_main():
counter=repeater(handler1,1)
counter.count=0 #I'm still new enough to python
counter.start()
greeter=repeater(handler2,2)
greeter.message="Hello world." #that this feels like cheating
greeter.other=counter #but it simplifies everything.
greeter.start()
print ("Currently {0} repeaters in service group.".format(len(repeater.repeatergroup)))
print("About to yield control for a while")
greeter.sleep(10)
print("Got control back, going to do some processing")
time.sleep(5)
print("About to yield control for a while")
counter.sleep(20) #you can use any repeater to access sleep() but
#it will only service those currently enabled.
#notice how it gets behind but tries to catch up, we could add repeater.reset()
#at the beginning of a handler to make it ignore missed events, or at the
#end to let the timing slide, depending on what kind of processing we're doing
#and what sort of sensitivity there is to time.
#now just replace all your main thread's calls to time.sleep() with calls to mycounter.sleep()
#now just add a repeater.sleep(.01) or a while repeater.serviceall(): pass to any loop that will take too long.
demo_main()
There's a couple of odd things left to consider:
Would it be better to sort handlers that you'd prefer to run on main thread from handlers that you don't care? I later went on to add a threadingstyle property, which depending on it's value would run on main thread only, on either main thread or a shared/group thread, or stand alone on it's own thread. That way longer or more time-sensitive tasks, could run without causing the other threads to be as slowed down, or closer to their scheduled time.
I wonder whether, depending on the implementation details of threading: is my 'if not main thread: time.sleep(seconds); return' effectively make it sufficiently more likely to be the main thread's turn, and I shouldn't worry about the difference.
(It seems like adding our MAXBLOCKINGPERIOD as the 3rd arg to the sched library could fix it's notorious issue of not servicing new events after older longer in the future events have already hit the front of the queue.)
Related
I'm trying to implement a decorator that allows to limit the rate with which a function is executed.
I would like the decorator to start a timer when the function is called. If the function is called before the timer runs out, I'd like to cancel the previous call and restart the timer. When the timer ends, the function should run.
I've serched around and found this decorator. However, this decorator stops the execution of the program while the timer is running, which is something I need to avoid.
How can I achieve this?
this is rather complicated, but a simple idea is to start a timer thread and cancel it if the function is called again and start another timer thread.
now we need somewhere to store this timer ... so a dictionary should suffice, and to allow the user to choose the delay, we will just do a double wrap of functions.
from threading import Timer
from functools import wraps
import time
functions_store = {}
def main_decorator(interval):
def sub_decorator(fun):
function_id = id(fun) # since no two objects have the same id
#wraps(fun)
def new_fun(*args,**kwargs):
if function_id in functions_store:
functions_store[function_id].cancel() # cancel old timer
new_timer = Timer(interval,fun,args=args,kwargs=kwargs) # make new timer
functions_store[function_id] = new_timer # store timer to stop it later
new_timer.start()
return new_fun
return sub_decorator
#main_decorator(1) # must be called again before 1 second passes.
def func_to_run():
print("hi")
func_to_run()
time.sleep(0.5)
func_to_run()
the word "hi" will be printed after 1.5 seconds instead of 1 second because we called the function again before it fired the first time.
I have a script, let's say "sensors.py" in which I have a Class "Meas", that reads measurements from several sensors. These comes from serial ports, program makes some calculations on them and changes the class "self.variable_a value" and another self variables also. The readings are in continuous mode, i.e. the program automatically waits for a message to come from the sensor to the serial port and read whole line (it's done via pyserial library). Some transmit readings at frequency of 10Hz, others 20Hz or 100Hz. This is a really big and messy class, therefore I put it in a separate file.
In my "main.py" script I import this "sensors" file and instantiate the "Meas" Class. Now I have a problem. How can I run immediately some "on_changed_var_a" function in "main" script, only when the "variable_a" in "Meas" object has changed - without consuming CPU power with while loop (constatly checking whether by any chance the variable has not changed) or waiting with time.sleep()? I need to get the sensors readings changes and then run another functions in "main" script in the most efficient way, as fast as possible. Thanks in advance!
EDIT: added example files
"sensors.py" file:
import random
import time
import threading
running = True
class Meas1:
def __init__(self, xyz):
self.xyz = xyz
self.var_a = None
thr1 = threading.Thread(target=self.readings, daemon=True)
thr1.start()
def readings(self):
while running:
# simulating 5Hz sensor readings:
self.var_a = self.xyz * random.randint(1, 1000)
print(self.var_a)
time.sleep(0.2)
"main.py" file:
import time
import sensors
import threading
class MainClass:
def __init__(self):
print("started")
self.sensor1 = sensors.Meas1(xyz=7)
thr_ksr = threading.Thread(target=self.thr_keep_script_running, daemon=True)
thr_ksr.start()
# in this part I would like to run the on_changed_var_a function, immediately when var_a changes
thr_ksr.join()
def on_changed_var_a(self):
print("var_a changed: ", self.sensor1.var_a)
def thr_keep_script_running(self, t=10):
time.sleep(t)
sensors.running = False
print("stopped, sleeping 1 sec")
time.sleep(1)
mc = MainClass()
Not sure why this is tagged mutithreading. You need this function to be run on different thread?
To the problem. The easiest way would be to make Meas call function you will pass to it.
You could make variable_a a property and then in it's setter call the function you want. Function could be passed and assigned to self.call_on_a_change attr for example.
Edit:
I don't think there is a way to make function execute on different thread (well, you could start a new one for that purpose, which sounds like a great solution to me).
Another problem with threads is that you give control to the system. It decides when and for how long which thread runs. So "as fast as possible" is constrained by that.
Nonetheless, you could create a threading.Lock and try to acquire it from main thread. Then in the reading thread upon change you could release the Lock and allow main thread to execute all call_on_a_change. Something like this:
import time
import threading
lock = threading.Lock()
# change to locked
lock.acquire()
a_change_callbacks = []
def on_changed_var_a(new_a):
print(new_a)
def readings():
a_change_callbacks.append(lambda: on_changed_var_a('first `a` change'))
lock.release()
time.sleep(5)
a_change_callbacks.append(lambda: on_changed_var_a('second `a` change'))
lock.release()
time.sleep(5)
a_change_callbacks.append(lambda: on_changed_var_a('third `a` change'))
lock.release()
thr = threading.Thread(target=readings, daemon=True)
thr.start()
while True:
lock.acquire()
for callback in list(a_change_callbacks):
callback()
a_change_callbacks.remove(callback)
if not thr.is_alive():
break
It's not your class model, but I hope it's enough to show the idea :D
How can I run 2 functions in parallel and wait for the return of one of them.
Basically what I have is a keypad, which I call a function where you enter a pin and a function where i read an NFC Tag. So which one returns first I will use the return value on the rest of the code.
I've looked into threading and what I get from it, is that it hangs until all the threads are finished.
Any insight?
You could let the threads call a method when they are done that only handles one call. Hopefully the following shows what I mean:
# consider this as pseudo code, I am commuting right know
def task1(callback):
# do something
callback(*args)
class SomeCallback:
available = True
def __call__(*args):
if not SomeCallback.available: return # a second call will do nothing
# work with nfc tag response or keyphrase
SomeCallback.available = False
# maybe even end all other threads here
thread = Thread(target=task1, (callback,))
thread.start()
# start a second thread or do the other thing on the mainthread
I have been searching for different schedule in Python such as Sched (Im a Windows user) etc. However I can't really get a grip on it and I don't know if it is possible. My plan is to make like the picture below:
We can see at Time:00.21 is etc the time I want the program to do the function 2 BUT the function 1 should be add into a list I have made as many as possible in the list as it works in 2 minutes before the timer hits. Basically...
The function 1 is doing its function 2 minutes before the timer. When it hits 00:21 then stop the function 1 and do the function 2 where it takes the List and uses it in its own function and when its done then its done.
However I don't know how to do this or to start. I was thinking to do a own timer but it feels like that is not the solution. What do you guys suggest?
I think I would approach a problem like this by creating a class that subclasses threading.Thread. From there, you override the run method with the function that you want to perform, which in this case will put stuff in a list. Then, in main, you start that thread followed by a call to sleep. The class would look like this:
class ListBuilder(threading.Thread):
def__init__(self):
super().__init__()
self._finished = False
self.lst = []
def get_data():
# This is the data retrieval function
# It could be imported in, defined outside the class, or made static.
def run(self):
while not self._finished:
self.lst.append(self.get_data())
def stop(self):
self._finished = True
Your main would then look something like
import time
if __name__ == '__main__':
lb = ListBuilder()
lb.start()
time.sleep(120) # sleep for 120 seconds, 2 minutes
lb.stop()
time.sleep(.1) # A time buffer to make sure the final while loop finishes
# Depending on how long each while loop iteration takes,
# it may not be necessary or it may need to be longer
do_stuf(lb.lst) # performs actions on the resulting list
Now, all you have to do is use the Windows Task Scheduler to run it at 00:19 and you should be set.
Is there a non-blocking way to wait or come back to this function within twisted?
I have a loop ticker that is just set to tick on a set interval and that is all working GREAT. However, when stopping it I want to make sure that it isn't currently in a Tick doing any work. If it is I just want twisted to come back to it and kill it in a moment.
def stop(self):
import time
while self.in_tick:
time.sleep(.001) # Blocking
self.active = False
self.reset()
self.timer.stop()
Sometimes this above function gets called while another thread is running a Tick operation and I want to finish the Tick and then come back and stop this.
I DO NOT want to block the loop in anyway during this operation. How could I do so?
It looks a bit strange to do a time.sleep() instead of just waiting for an event to signal and fire a deferred to do what you want. With threads you might wake up this thread, check 'self.in_tick == False' and before you reach 'self.active = False', the other thread starts the new tick, so this might have a race condition and may not work as you expect anyway. So hopefully you have some other thread synchronization somewhere to make it work.
You can try to split your code into two functions and have one that schedules itself if not done.
def stop(self):
# avoid reentracy
if not self._stop_call_running:
self._stop()
def _stop(self):
if self.in_tick:
# reschedule itself
self._stop_call_running = reactor.callLater(0.001, self._stop)
return
self.active = False
self.reset()
self.timer.stop()
self._stop_call_running = None
You might also look at twisted.internet.task.LoopingCall.