I want to exec some code while Tk.mainloop() is running, so I think I need threading module.
I tried to put Tk.mainloop() inside the run method of a thread class and then I put the code I want to run while mainloop is running inside another thread.
from threading import Thread
import tkinter as tk
class MyThread(Thread):
def __init__(self):
Thread.__init__(self)
def run():
# window is tk.Tk()
window.mainloop()
class MyCode(Thread):
# my code
TkinterThread = MyThread()
TkinterThread.start()
OtherThread = MyCode()
OtherThread.start()
and tkinter report me an error
RuntimeError: Calling Tcl from different apartment
so I searched on internet and I understand that the mainloop can be runned only out from thread becouse work in only one of them.
So, is there a way to run others thread while mainloop is running?
You can run code in other threads. The problem isn't so much multiple threads per se, but that you've got tkinter code in more than one thread. All tkinter code needs to be in a single thread.
Usually it's best to make that your main thread (both creating the widgets and starting mainloop), and run your other code in a secondary thread or process. You can use a thread-safe queue to send information between the threads, such as when passing results back to the GUI.
Related
I am trying to display a loading gif on my PyQt5 QMainWindow while an intensive process is running. Rather than playing normally, the QMovie pauses. As far as I can tell, the event loop shouldn't be blocked as the intensive process is in its own QObject passed to its own QThread. Relevant code below:
QMainWindow:
class EclipseQa(QMainWindow):
def __init__(self):
QMainWindow.__init__(self)
self.initUI()
def initUI(self):
...
self.loadingMovie = QMovie("./loading.gif")
self.loadingMovie.setScaledSize(QSize(149, 43))
self.statusLbl = QLabel(self)
self.statusLbl.setMovie(self.loadingMovie)
self.grid.addWidget(self.statusLbl, 6, 2, 2, 2, alignment=Qt.AlignCenter)
self.statusLbl.hide()
...
def startLoadingGif(self):
self.statusLbl.show()
self.loadingMovie.start()
def stopLoadingGif(self):
self.loadingMovie.stop()
self.statusLbl.hide()
def maskDose(self):
self.startLoadingGif()
# Set up thread and associated worker object
self.thread = QThread()
self.worker = DcmReadWorker()
self.worker.moveToThread(self.thread)
self.worker.finished.connect(self.thread.quit)
self.worker.updateRd.connect(self.updateRd)
self.worker.updateRs.connect(self.updateRs)
self.worker.updateStructures.connect(self.updateStructures)
self.worker.clearRd.connect(self.clearRd)
self.worker.clearRs.connect(self.clearRs)
self.thread.started.connect(lambda: self.worker.dcmRead(caption, fname[0]))
self.thread.finished.connect(self.stopLoadingGif)
self.maskThread.start()
def showDoneDialog(self):
...
self.stopLoadingGif()
...
Worker class:
class DoseMaskWorker(QObject):
clearRd = pyqtSignal()
clearRs = pyqtSignal()
finished = pyqtSignal()
startLoadingGif = pyqtSignal()
stopLoadingGif = pyqtSignal()
updateMaskedRd = pyqtSignal(str)
def __init__(self, parent=None):
QObject.__init__(self, parent)
#pyqtSlot(name="maskDose")
def maskDose(self, rd, rdName, rdId, rs, maskingStructure_dict):
...
self.updateMaskedRd.emit(maskedRdName)
self.finished.emit()
For brevity, '...' indicates code that I figured is probably not relevant.
Your use of lambda to call the slot when the threads started signal is emitted is likely causing it to execute in the main thread. There are a couple of things you need to do to fix this.
Firstly, your use of pyqtSlot does not contain the types of the arguments to the maskDose method. You need to update it so that it does. Presumably you also need to do this for the dcmRead method which you call from the lambda but haven't included in your code. See the documentation for more details.
In order to remove the use of the lambda, you need to define a new signal and a new slot within the EclipseQa class. The new signal should be defined such that the required number of parameters for the dcmRead method are emitted, and the types correctly specified (documentation for this is also in the link above). This signal should be connected to the workers dcmRead slot (make sure to do it after the worker object has been moved to the thread or else you might run into this bug!). The slot should take no arguments, and be connected to the threads started signal. The code in the slot should simply emit your new signal with the appropriate arguments to be passed to dcmRead (e.g. like self.my_new_signal.emit(param1, param2)).
Note: You can check what thread any code is running in using the Python threading module (even when using QThreads) by printing threading.current_thread().name from the location you wish to check.
Note 2: If your thread is CPU bound rather than IO bound, you may still experience performance issues because of the Python GIL which only allows a single thread to execute at any one time (it will swap between the threads regularly though so code in both threads should run, just maybe not at the performance you expect). QThreads (which are implemented in C++ and are theoretically able to release the GIL) do not help with this because they are running your Python code and so the GIL is still held.
I'm trying to create a thread for a GUI that wraps a long-running function. My problem is thus phrased in terms of PyQt and QThreads, but I imagine the same concept could apply to standard python threads too, and would appreciate any suggestions generally.
Typically, to allow a thread to be exited while running, I understand that including a "wants_to_end" flag that is periodically checked within the thread is a good practice - e.g.:
Pseudocode (in my thread):
def run(self):
i = 0
while (not self.wants_to_end) and (i < 100):
function_step(i) # where this is some long-running function that includes many streps
i += 1
However, as my GUI is to wrap a pre-written long-running function, I cannot simply insert such a "wants_to_end" flag poll into the long running code.
Is there another way to forcibly terminate my worker thread from my main GUI (i.e. enabling me to include a button in the GUI to stop the processing)?
My simple example case is:
class Worker(QObject):
finished = pyqtSignal()
def __init__(self, parent=None, **kwargs):
super().__init__(parent)
self.kwargs = kwargs
#pyqtSlot()
def run(self):
result = SomeLongComplicatedProcess(**self.kwargs)
self.finished.emit(result)
with usage within my MainWindow GUI:
self.thread = QThread()
self.worker = Worker(arg_a=1, arg_b=2)
self.worker.finished.connect(self.doSomethingInGUI)
self.worker.moveToThread(self.thread)
self.thread.started.connect(self.worker.run)
self.thread.start()
If the long-running function blocks, the only way to forcibly stop the thread is via its terminate() method (it may also be necessary to call wait() as well). However, there is no guarantee that this will always work, and the docs also state the following:
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.
A much cleaner solution is to use a separate process, rather than a separate thread. In python, this could mean using the multiprocessing module. But if you aren't familiar with that, it might be simpler to run the function as a script via QProcess (which provides signals that should allow easier integration with your GUI). You can then simply kill() the worker process whenever necessary. However, if that solution is somehow unsatisfactory, there are many other IPC approaches that might better suit your requirements.
Python 3.4, I'm trying to make a server using the websockets module (I was previously using regular sockets but wanted to make a javascript client) when I ran into an issue (because it expects async, at least if the examples are to be trusted, which I didn't use before). Threading simply does not work. If I run the following code, bar will never be printed, whereas if I comment out the line with yield from, it works as expected. So yield is probably doing something I don't quite understand, but why is it never even executed? Should I install python 3.5?
import threading
class SampleThread(threading.Thread):
def __init__(self):
super(SampleThread, self).__init__()
print("foo")
def run(self):
print("bar")
yield from var2
thread = SampleThread()
thread.start()
This is not the correct way to handle multithreading. run is neither a generator nor a coroutine. It should be noted that the asyncio event loop is only defined for the main thread. Any call to asyncio.get_event_loop() in a new thread (without first setting it with asyncio.set_event_loop() will throw an exception.
Before looking at running the event loop in a new thread, you should first analyze to see if you really need the event loop running in its own thread. It has a built-in thread pool executor at: loop.run_in_executor(). This will take a pool from concurrent.futures (either a ThreadPoolExecutor or a ProcessPoolExecutor) and provides a non-blocking way of running processes and threads directly from the loop object. As such, these can be await-ed (with Python3.5 syntax)
That being said, if you want to run your event loop from another thread, you can do it thustly:
import asyncio
class LoopThread(threading.Thread):
def __init__(self):
self.loop = asyncio.new_event_loop()
def run():
ayncio.set_event_loop(self.loop)
self.loop.run_forever()
def stop():
self.loop.call_soon_threadsafe(self.loop.stop)
From here, you still need to device a thread-safe way of creating tasks, etc. Some of the code in this thread is usable, although I did not have a lot of success with it: python asyncio, how to create and cancel tasks from another thread
I'm using the following template to recreate threads that I need to run into infinity.
I want to know if this template is scalable in terms of memory. Are threaded destroyed properly?
import threading
import time
class aLazyThread(threading.Thread):
def __init__(self):
threading.Thread.__init__(self)
def run(self):
time.sleep(10)
print "I don not want to work :("
class aWorkerThread(threading.Thread):
def __init__(self):
threading.Thread.__init__(self)
def run(self):
time.sleep(1)
print "I want to work!!!!!!!"
threadA = aLazyThread()
threadA.start()
threadB = aWorkerThread()
threadB.start()
while True:
if not (threadA.isAlive()):
threadA = aLazyThread()
threadA.start()
if not (threadB.isAlive()):
threadB = aWorkerThread()
threadB.start()
The thing that bother me is the following picture taking in eclipse which show debug info, and It seems that thread are stacking it.
I see nothing wrong with the image. There's the main thread and the 2 threads that you created (according to the code, 3 threads are supposed to be running at any time)
Like any other Python objects, threads are garbage collected when they're not used; e.g. in your main while cycle, when you instantiate the class (let's say aLazyThread), the old threadA value is destroyed (maybe not exactly at that point, but shortly after)
The main while cycle, could also use a sleep (e.g. time.sleep(1)), otherwise it will consume the processor, uselessly checking if the other threads are running.
I am trying to create a GUI with wxPython. After I create the GUI I want the code to continue to execute, so I have tried to throw the app.MainLoop() onto a new thread. This gives me issues. Also when I try to change the background color for example, it freezes up the GUI.
import wx
import threading
from threading import Thread
from multiprocessing import Process
class Display(wx.Frame):
def __init__(self, *args, **kwargs):
print 'here'
self.app = wx.App(False)
super(Display, self).__init__(*args, **kwargs)
self.SetTitle("Yo mama")
self.Show(True)
thread = Thread(target = self.app.MainLoop)
thread.start()
self.Close()
def DisplayGUI(self):
self.SetTitle("MyTitle")
self.Show(True)
def Changetitle(self):
self.SetTitle("Title2")
display = Display(None)
# do stuff
display.ChangeTitle()
# do stuff
So basically I want to be able to run a GUI, and control it later on within my program (not through the GUI itself with events). I plan on having pictures display at random times.
The GUI's MainLoop needs to run in the main thread. So do this, and if you want events at random times, you can use a timer, for example, wx.Timer.
Using this approach, all the changes you mention (displaying pictures, changing the titles, colors, etc) should be straightforward. Plus, you'll get a lot more control this way, where you can start and stop timers, change the interval, have multiple timers, setup timers that trigger each other, and many other options.
To learn more about wx.Timer, a good place to start is always the demo. There's also a tutorial here, and a video here.
(I've heard that there are ways to run the MainLoop in a separate thread, but nothing you mention requires that, and it will be much, much easier to just use a timer.)