In another class:
self.workerThread = WorkerThread()
def startThread():
self.workerThread.setGameName("pizza")
self.workerThread.start()
QThread class:
class WorkerThread(QThread):
def _init_(self, parent = None):
super(WorkerThread, self)._init_(parent)
self.gameName = ""
def setGameName(self, currGameName):
self.gameName = currGameName
def run(self):
#do something with self.gameName
In main:
startThread()
startThread()
When I run this, it uses the gameName from the first call and not the second. The function calls seem interleaved. Can someone explain how Qthread works? How do i set a gameName for each individual function call of startThread()?
If start() is called twice on a QThread then the second call will do nothing if the thread is still running. It looks like there's a good chance this is what's happening, and if not then it's only due to luck.
Related
I want to have a main program that works like a console from where I can call other processes (infinite loops) and kill them selectively whenever certain commands are entered.
For that I created this class:
class RunInThread(threading.Thread):
def __init__(self, function):
self.function = function
self.kill_pill = threading.Event()
threading.Thread.__init__(self)
def start(self): # This is controversial.
self.__init__(self.function)
threading.Thread.start(self)
def stop(self):
self.kill_pill.set()
def run(self):
while not self.kill_pill.is_set():
self.function()
The documentation for thread.Thread says that only the __init__() and run() methods should be overridden.
Is there any clear issue with my code? It works the way I intended but since it's going to be running for long periods of time I need to make sure I'm not creating any memory problems.
EDIT:
What about this solution?:
class StoppableThread(threading.Thread):
# threading.Thread class but can be stopped with the stop() method.
def __init__(self, function):
threading.Thread.__init__(self)
self.function = function
self.kill_pill = threading.Event()
def stop(self):
self.kill_pill.set()
def run(self):
while not self.kill_pill.is_set():
self.function()
class RunInThread():
def __init__(self, function, prnt=False):
self.function = function
self.running = False
self.prnt = prnt
def start(self):
if not self.running:
self.thread = StoppableThread(self.function)
self.thread.start()
self.running = True
else:
if self.prnt:
print('Thread already running.')
def stop(self):
self.thread.stop()
self.running = False
If you want to find out what things that could break, I'd suggest looking into the implementation of Thread class.
Among other things, Thread.__init__() initialises an Event() object to detect thread startup and shutdown, manages cleanup hooks/callbacks, some internal lock objects, and registers the thread to a list so you can introspect running threads. By calling Thread.__init__(), these variables gets reinitialised and screws up the internal mechanisms of many of these functionalities.
What could go wrong? I didn't test any of these, but from skimming through threading.py, these are likely some of the things that I expect could go wrong:
your python process now will be running a OS threads that doesn't show up in enumerate_thread()
multiple OS thread will now return the same Thread object when it calls current_thread(), which will likely also break threadlocal and anything that depends on threadlocal
Thread.join() depends on some internal locks, which likely would now become thread unsafe to call
Unhandled reception can go to the wrong exception hook handler
register_at_fork and shutdown handler likely will get confused
In other words, don't try to be sneaky. Create a new Thread object for each thread you want to start.
There's a good reason that the Thread class spent efforts trying to prevent you from accidentally calling start() twice. Don't try to subvert this.
I know this sounds a lot like this similarly-worded question, but there are differences, so bear with me.
I'm trying to create a reusable "Timer" class which calls a specified callback every N seconds, until you call stop. As inspiration, I used the link above, with a built-in event wrapped in a stop method. Here's how the basic class looks:
import time
import threading
from threading import Thread
from threading import Event
# Mostly inspired by https://stackoverflow.com/questions/12435211/python-threading-timer-repeat-function-every-n-seconds
class RepeatingTimer(Thread):
def __init__(self, interval_seconds, callback):
Thread.__init__(self)
self.stop_event = Event()
self.interval_seconds = interval_seconds
self.callback = callback
self.setDaemon(True)
def start(self):
while not self.stop_event.wait(self.interval_seconds):
self.callback()
time.sleep(0) # doesn't seem to do anything
def stop(self):
self.stop_event.set()
Looks good, even includes time.sleep(0) based on this question.
It doesn't do what I thought; the call to start never seems to return or yield, ever. Consider this use-case:
def print_status(message):
print(message)
def print_r1():
print_status("R1")
def print_r2():
print_status("R2")
r1 = RepeatingTimer(1, print_r1)
r2 = RepeatingTimer(0.5, print_r2)
r1.start()
r2.start()
The call to r1.start never terminates. It continues on forever. The output on the console, after four seconds, is:
R1
R1
R1
R1
This prompted me to introduce the time.sleep(0) call, although that doesn't seem to do anything.
I also tried with and without self.setDaemon(True), but that also seems to have no effect.
I also tried converting this into two classes: one with just the event wrappers (a StoppableTimer class), and another that simply creates and recreates the StoppableTimer in the callback, but that doesn't work either. Here's what it looks like:
class StoppableTimer(Thread):
def __init__(self, interval_seconds, callback):
Thread.__init__(self)
self.stop_event = Event()
self.interval_seconds = interval_seconds
self.callback = callback
self.setDaemon(True)
def start(self):
time.sleep(self.interval_seconds)
self.callback()
def stop(self):
self.stop_event.set()
class RepeatingTimer:
def __init__(self, interval_seconds, callback):
self.interval_seconds = interval_seconds
self.callback = callback
self.timer = StoppableTimer(interval_seconds, self.refresh_timer)
def start(self):
self.timer.start()
def stop(self):
self.timer.stop()
def refresh_timer(self):
self.stop()
self.callback()
self.timer = StoppableTimer(self.interval_seconds, self.refresh_timer)
self.timer.start()
I'm completely at a loss on how to make this work. I'm also mostly a beginner to Python, so please add sufficient explanation to your answer so I can grasp what the fundamental issue is.
I also read a bit about the Global Interpreter Lock on SO, but I don't understand how that could be an issue.
For reference, I'm running Python 3.6.3 on Ubuntu 17.10
Short answer :
Don't override start(). Override run() instead.
Long answer because you're asking for details :
With the class definition in your first snippet, you've created a class which inherits from Thread, however you've overriden the start() method supposed to start your thread by a new method which is looping until the stop_event is set, that is to say, the method supposed to actually start your thread doesn't do this anymore.
So, when you try to start your thread, you actually run the loop calling your callback function in your current and only thread. And since it's an infinite loop, your second "thread" is not started, and you have no way to "stop" it.
You mustn't override start (well not in this way). Instead, override the run method. This is the method that will be run by your thread when you start it.
Also, you should do super().__init__() instead of Thread.__init__(self). The first one is the proper way to call an inherited method in Python.
class RepeatingTimer(Thread):
def __init__(self, interval_seconds, callback):
super().__init__()
self.stop_event = Event()
self.interval_seconds = interval_seconds
self.callback = callback
def run(self):
while not self.stop_event.wait(self.interval_seconds):
self.callback()
def stop(self):
self.stop_event.set()
And with the functions you've defined you can do :
r1 = RepeatingTimer(1, print_r1)
r2 = RepeatingTimer(0.5, print_r2)
r1.start()
r2.start()
time.sleep(4)
r1.stop()
r2.stop()
Here is the relevant documentation for Thread.
I have a thread class, in it, I want to create a thread function to do its job corrurently with the thread instance. Is it possible, if yes, how ?
run function of thread class is doing a job at every, excatly, x seconds. I want to create a thread function to do a job parallel with the run function.
class Concurrent(threading.Thread):
def __init__(self,consType, consTemp):
# something
def run(self):
# make foo as a thread
def foo (self):
# something
If not, think about below case, is it possible, how ?
class Concurrent(threading.Thread):
def __init__(self,consType, consTemp):
# something
def run(self):
# make foo as a thread
def foo ():
# something
If it is unclear, please tell . I will try to reedit
Just launch another thread. You already know how to create them and start them, so simply write another sublcass of Thread and start() it along the ones you already have.
Change def foo() for a Thread subclass with run() instead of foo().
First of all, I suggest the you will reconsider using threads. In most cases in Python you should use multiprocessing instead.. That is because Python's GIL.
Unless you are using Jython or IronPython..
If I understood you correctly, just open another thread inside the thread you already opened:
import threading
class FooThread(threading.Thread):
def __init__(self, consType, consTemp):
super(FooThread, self).__init__()
self.consType = consType
self.consTemp = consTemp
def run(self):
print 'FooThread - I just started'
# here will be the implementation of the foo function
class Concurrent(threading.Thread):
def __init__(self, consType, consTemp):
super(Concurrent, self).__init__()
self.consType = consType
self.consTemp = consTemp
def run(self):
print 'Concurrent - I just started'
threadFoo = FooThread('consType', 'consTemp')
threadFoo.start()
# do something every X seconds
if __name__ == '__main__':
thread = Concurrent('consType', 'consTemp')
thread.start()
The output of the program will be:
Concurrent - I just startedFooThread - I just started
I tried using self.terminate() in the QThread class, and also self.thread.terminate() in the GUI class. I also tried putting self.wait() in both cases. However, there are two scenarios that happen:
1) The thread does not terminate at all, and the GUI freezes waiting for the thread to finish. Once the thread finished, the GUI unfreezes and everything is back to normal.
2) The thread indeed does terminate, but at the same time it freezes the entire application.
I also tried using self.thread.exit(). No joy.
To further clarify, I am trying to implement a user-abort button in GUI which would terminate the executing of the thread at any point in time.
Thanks in advance.
EDIT:
Here is the run() method:
def run(self):
if self.create:
print "calling create f"
self.emit(SIGNAL("disableCreate(bool)"))
self.create(self.password, self.email)
self.stop()
self.emit(SIGNAL("finished(bool)"), self.completed)
def stop(self):
#Tried the following, one by one (and all together too, I was desperate):
self.terminate()
self.quit()
self.exit()
self.stopped = True
self.terminated = True
#Neither works
And here is the GUI class' method for aborting the thread:
def on_abort_clicked(self):
self.thread = threadmodule.Thread()
#Tried the following, also one by one and altogether:
self.thread.exit()
self.thread.wait()
self.thread.quit()
self.thread.terminate()
#Again, none work
From the Qt documentation for QThread::terminate:
Warning: This function is dangerous and its use is discouraged. The
thread can be terminated at any point in its code path. Threads can be
terminated while modifying data. There is no chance for the thread to
clean up after itself, unlock any held mutexes, etc. In short, use
this function only if absolutely necessary.
It's probably a much better idea to re-think your threading strategy such that you can e.g. use QThread::quit() to signal the thread to quit cleanly, rather than trying to get the thread to terminate this way. Actually calling thread.exit() from within the thread should do that depending on how you have implemented run(). If you'd like to share the code for your thread run method that might hint as to why it doesn't work.
This is what I did:
class MainWindow(QtWidgets.QMainWindow, Ui_MainWindow):
stop_flag = 1
...
#=========500 ms class ===================
class Timer500msThread(QThread):
signal_500ms = pyqtSignal(str)
....
def timer500msProcess(self):
if MainWindow.stop_flag == 0 :
self.timer_500ms.stop()
#==========
#=========Main Window ===================
app = QtWidgets.QApplication(sys.argv)
window = MainWindow()
window.show()
app.exec()
MainWindow.stop_flag=0 #this sets the flag to 0 and when the next 500ms triggers the
#the thread ends
print("Program Ending")
I had a similar problem and solved it with use of pyqtSignals and pyqtSlots.
You could create a pyqtSignal in your MainWindow-class and use the aboutToQuit-function to your QApplication instance.
Then you connect this aboutToQuit-function with another which emit a signal to the slot in your separate thread.
Then you can define a stop() function in this Thread which runs if the signal is emitted.
In this case the thread would not terminate during its work.
MainWindow:
class mainSignals(QObject):
isClosed = pyqtSignal()
class mainwindow(QMainWindow, Ui_MainWindow):
def __init__(self):
super(mainwindow, self).__init__()
self.mainSignal = mainSignals()
...
...
if __name__ = "__main__":
# This function runs if the application is closed.
# (app.aboutToQuit.connect(windowClose))
def windowClose():
window.mainSignal.isClosed.emit() # Emit the signal to the slot in (sepThread)
app = QApplication(sys.argv)
app.aboutToQuit.connect(windowClose)
window = mainwindow()
window.show()
sys.exit(app.exec())
sepThread:
class sepThread(QRunnable):
def __init__(self, parent):
super(sepThread,self).__init__()
self._parent = parent
self.mainOpen = True
self._parent.mainSignal.isClosed.connect(self.stopThread)
# If the signal was emitted by the Mainapplication
# the stopThread function runs and set the mainOpen-attribute to False
def stopThread(self):
self.mainOpen = False
def run(self):
while self.mainOpen == True:
# Do something in a loop while mainOpen-attribute is True
...
...
I have a Manager (main thread), that creates other Threads to handle various operations.
I would like my Manager to be notified when a Thread it created ends (when run() method execution is finished).
I know I could do it by checking the status of all my threads with the Thread.isActive() method, but polling sucks, so I wanted to have notifications.
I was thinking of giving a callback method to the Threads, and call this function at the end of the run() method:
class Manager():
...
MyThread(self.on_thread_finished).start() # How do I pass the callback
def on_thread_finished(self, data):
pass
...
class MyThread(Thread):
...
def run(self):
....
self.callback(data) # How do I call the callback?
...
Thanks!
The thread can't call the manager unless it has a reference to the manager. The easiest way for that to happen is for the manager to give it to the thread at instantiation.
class Manager(object):
def new_thread(self):
return MyThread(parent=self)
def on_thread_finished(self, thread, data):
print thread, data
class MyThread(Thread):
def __init__(self, parent=None):
self.parent = parent
super(MyThread, self).__init__()
def run(self):
# ...
self.parent and self.parent.on_thread_finished(self, 42)
mgr = Manager()
thread = mgr.new_thread()
thread.start()
If you want to be able to assign an arbitrary function or method as a callback, rather than storing a reference to the manager object, this becomes a bit problematic because of method wrappers and such. It's hard to design the callback so it gets a reference to both the manager and the thread, which is what you will want. I worked on that for a while and did not come up with anything I'd consider useful or elegant.
Anything wrong with doing it this way?
from threading import Thread
class Manager():
def Test(self):
MyThread(self.on_thread_finished).start()
def on_thread_finished(self, data):
print "on_thread_finished:", data
class MyThread(Thread):
def __init__(self, callback):
Thread.__init__(self)
self.callback = callback
def run(self):
data = "hello"
self.callback(data)
m = Manager()
m.Test() # prints "on_thread_finished: hello"
If you want the main thread to wait for children threads to finish execution, you are probably better off using some kind of synchronization mechanism. If simply being notified when one or more threads has finished executing, a Condition is enough:
import threading
class MyThread(threading.Thread):
def __init__(self, condition):
threading.Thread.__init__(self)
self.condition = condition
def run(self):
print "%s done" % threading.current_thread()
with self.condition:
self.condition.notify()
condition = threading.Condition()
condition.acquire()
thread = MyThread(condition)
thread.start()
condition.wait()
However, using a Queue is probably better, as it makes handling multiple worker threads a bit easier.