I've set up a simple appJar UI, which has an "execute" button that calls a function containing code that takes a minute to run. I have injected my gui() variable, app, into this function.
There are 4 major steps, after each of which I would like a Statusbar to update to reflect that a step has been completed. However, what tends to happen is that as the function code runs, the GUI becomes unresponsive and it isn't until the code completes execution that ALL of the changes to the status bar are displayed at once.
My question is how should I be handling the UI such that the Statusbar is updated in real time?
appJar is just a wrapper around python tkinter module from standard library.
While your code is running, the ui is not running, thus it becomes unresponsive. If you want the ui to remain responsible, you have to return control from your code to the ui library from time to time.
That can be done by calling gui.topLevel.update() in your code, or by using asynchronous programming and having the main async loop call it, or by using threads.
Which one of those is the best, depends on what your program is doing.
appJar also has built in support for threads: http://appjar.info/pythonThreads/
You can call the function that takes a long time in a thread: app.thread(myFunction, param1, param2)
And, if you want to get the thread to update the GUI, you'll need to use the update queue: app.queueFunction(app.setMeter, "myMeter", 50)
Related
MyButton1 =Button(master, text='Quit',bg="grey",width=20,
command=master.quit)
MyButton1.place(x=200, y=100)
MyButton2 =Button(master, text='Propagate', bg="grey",width=20,
command=mainmethod)
MyButton2.place(x=1000, y=100)
master.geometry("1500x1500")
master.mainloop( )
In the above code after pressing propagate button mainmethod is invoking..
I wrote my logic in main method where this method alone taking 2minutes to execute in the mean time GUI going unresponsive state for few min and later displaying all my required output on text box i inserted
whether any away to avoid the unresponsive issue apart from using multi threading
and i am looking such that after pressing propagate button button should disabled and window should not go unresponsive and display text.insert statements continuously which i added in main method ?????
To prevent hanging, you need to separate the calculations in the mainmethod from Tkinter's main loop by executing them in different threads. However, threading system in Python is not that well-developed as in other languages (AFAIK) because of GIL (Global Interpreter Lock), but there is an alternative - using processes just like threads. This is possible with multiprocessing library.
In order to just prevent hanging, you could create another function
from multiprocessing import Process
def mainmethodLaunch():
global mainmethodProcess
mainmethodProcess = Process(target=mainmethod)
mainmethodProcess.start()
And bind this function to MyButton2 instead of mainmethod itself.
Docs: https://docs.python.org/2/library/multiprocessing.html#the-process-class
You can see p.join in the example. join method will cause your main process to wait for the other one to complete, which you don't want.
So when you press the button, mainmethodLaunch function will be invoked, and it will create another process executing mainmethod. mainmethodLaunch function's own run duration should be insignificant. Due to usage of another process, Tkinter window will not hang. However, if you do just this, you will not be able to interact with mainmethod process in any kind while it will be working.
In order to let these processes communicate with each other, you could use pipes (https://docs.python.org/2/library/multiprocessing.html#exchanging-objects-between-processes)
I guess the example is quite clear.
In order to receive some data from the mainmethod process over time, you will have to poll the parent_conn once a little time, let's say, second. This can be achieved with Tkinter's after method
(tkinter: how to use after method)
IMPORTANT NOTE: when using multiprocessing, you MUST initialize the program in if __name__ == '__main__': block. I mean, there should be no doing-something code outside functions and this block, no doing-something code with zero indent.
This is because multiprocessing is going to fork the same Python executable file, and it will have to distinguish the main process from the forked one, and not do initializing stuff in the forked one.
Check twice if you have done that because if you make such a mistake, it can cost you hanging of not just Tkinter window, but the whole system :)
Because the process will be going to fork itself endlessly, consuming all RAM you have, regardless of how much you have.
I developed a simple Python application doing some stuff, then I decided to add a simple GUI using Tkinter.
The problem is that, while the main function is doing its stuff, the window freezes.
I know it's a common problem and I've already read that I should use multithreads (very complicated, because the function updates the GUI too) or divide my code in different function, each one working for a little time.
Anyway I don't want to change my code for such a stupid application.
My question is: is it possible there's no easy way to update my Tkinter window every second? I just want to apply the KISS rule!
I'll give you a pseudo code example below that I tried but didn't work:
class Gui:
[...]#costructor and other stuff
def refresh(self):
self.root.update()
self.root.after(1000,self.refresh)
def start(self):
self.refresh()
doingALotOfStuff()
#outside
GUI = Gui(Tk())
GUI.mainloop()
It simply will execute refresh only once, and I cannot understand why.
Thanks a lot for your help.
Tkinter is in a mainloop. Which basically means it's constantly refreshing the window, waiting for buttons to be clicked, words to be typed, running callbacks, etc. When you run some code on the same thread that mainloop is on, then nothing else is going to perform on the mainloop until that section of code is done. A very simple workaround is spawning a long running process onto a separate thread. This will still be able to communicate with Tkinter and update it's GUI (for the most part).
Here's a simple example that doesn't drastically modify your psuedo code:
import threading
class Gui:
[...]#costructor and other stuff
def refresh(self):
self.root.update()
self.root.after(1000,self.refresh)
def start(self):
self.refresh()
threading.Thread(target=doingALotOfStuff).start()
#outside
GUI = Gui(Tk())
GUI.mainloop()
This answer goes into some detail on mainloop and how it blocks your code.
Here's another approach that goes over starting the GUI on it's own thread and then running different code after.
'Not responding' problem can be avoided using Multithreading in python using the thread module.
If you've defined any function, say combine() due to which the Tkinter window is freezing, then make another function to start combine() in background as shown below:
import threading
def combine():
...
def start_combine_in_bg():
threading.Thread(target=combine).start()
Now instead of calling combine(), you have to call start_combine_in_bg()
I did this and now my window is not freezing so I shared it here. Remember you can run only one thread at a time.
Have a look for reference: stackoverflow - avoid freezing of tkinter window using one line multithreading code
Here's how I managed to work around this issue (maybe it's quite dirty I don't know):
Whenever I update my tkinter window through the doingALotOfStuff() function, I call myTk.update().
It avoids freezing for me.
I've been fighting for three hours now to get this process multithreaded, so that I can display a progress box. I finally got it working, insomuch as the process completes as expected, and all the functions call, including the ones to update the progress indicator on the window.
However, the window never actually displays. This is a PyGObject interface designed in Glade. I am not having fun.
def runCompile(obj):
compileWindow = builder.get_object("compilingWindow")
compileWindow.show_all()
pool = ThreadPool(processes=1)
async_result = pool.apply_async(compileStrings, ())
output = async_result.get()
#output = compileStrings() #THIS IS OLD
compileWindow.hide()
return output
As I mentioned, everything works well, except for the fact that the window doesn't appear. Even if I eliminate the compileWindow.hide() command, the window never shows until the process is done. In fact, the whole stupid program freezes until the process is done.
I'm at the end of my rope. Help?
(By the way, the "recommended" processes of using generators doesn't work, as I HAVE to have a return from the "long process".)
I'm not a pyGobject expert and i don't really understand your code. I think that you should post more. Why are you calling the builder in a function? you can call it at the init of the GUI?
Anyways.. It seems that you are having the common multithread problems..
are you using at the startup GObject.threads_init() and Gdk.threads_init() ?
Then, if you want to show a window from a thread you need to use Gdk.threads_enter() and Gdk.threads_leave().
here is an useful doc
I changed the overall flow of my project, so that may affect it. However, it is imperative that Gtk be given a chance to go through its own main loop, by way of...
if Gtk.events_pending():
Gtk.main_iteration()
In this instance, I only want to call it once, to ensure the program doesn't hang.
(The entire program source code can be found on SourceForge. The function in question is on line 372 as of this posting, in function compileModel().
I am building a Qt-based GUI using Pyside. Inside a specific class who has access to a QMainWindow (_theMainWindow) class which in turn has access to 2 other Qt Widgets (theScan & theScanProgress) I am trying to show() the last one by executing
def initiateScan(self):
self._theMainWindow.theScan.theScanProgress.show()
This works just fine, the theScanProgress widget appears.
However, when I add the line that makes the application sleep (and a print statement), as below
def initiateScan(self):
self._theMainWindow.theScan.theScanProgress.show()
print("test")
time.sleep(3)
the program seems to go to sleep BEFORE the widget appears, i.e. as if the time.sleep(3) gets executed before self._theMainWindow.theScan.theScanProgress.show()
Any ideas why this happens?
This is because of the main loop which processes gui events. If you are not using threads you can only execute one function at a time. I strongly suspect that show emits a signal which goes into the event queue, which is in turn blocked until the current function returns.
Put another way, Qt is event driven, and it can only do one event at a time. What ever you did call initiateScan added an event to the stack that was to execute the function (something like you pushed a button, which emitted a signal, which then triggered the function), and that function can do some computation, alter internal state of your objects, and add events to the stack. What show does underneath is emit a signal to all of it's children for them to show them selves. For that code to run, it has to wait for the current event (the function with your sleep) to return. During the sleep the entire gui will be unresponsive for the exact same reason.
[I probably butchered some of the terms of art]
show only schedules the appearance of the progress widget. But since you are blocking the main thread with your sleep, the main thread cannot perform the scheduled action until you release it.
You have to use threads or find another way to wait 3 seconds.
I have a Python script which uses Tkinter for the GUI. My little script should create a Toplevel widget every X seconds. When I run my code, the first Toplevel widget is created successfully, but when it tries to create a second one the program crashes.
What I am doing is using the after method to call the function startCounting every 5 seconds alongside root's mainloop. Every time this function is called, I append a Toplevel widget object into a list and start a new thread which hopefully will be running the new mainloop.
I would be very grateful if someone could figure this problem out. By the way, this is just a little script that I am currently using to solve my problem, which is preventing me from going on with my real school project.
The code:
import threading,thread
from Tkinter import *
def startCounting():
global root
global topLevelList
global classInstance
topLevelList.append (Toplevel())
topLevelList[len(topLevelList)-1].title("Child")
classInstance.append(mainLoopThread(topLevelList[len(topLevelList)-1]))
root.after(5000,startCounting)
class mainLoopThread(threading.Thread):
def __init__(self,toplevelW):
self.toplevelW = toplevelW
threading.Thread.__init__(self)
self.start()
def run(self):
self.toplevelW.mainloop()
global classInstance
classInstance = []
global topLevelList
topLevelList = []
global root
root = Tk()
root.title("Main")
startCounting()
root.mainloop()
Tkinter is designed to run from the main thread, only. See the docs:
Just run all UI code in the main
thread, and let the writers write to a
Queue object; e.g.
...and a substantial example follows, showing secondary threads writing requests to a queue, and the main loop being exclusively responsible for all direct interactions with Tk.
Many objects and subsystems don't like receiving requests from multiple various threads, and in the case of GUI toolkit it's not rare to need specfically to use the main thread only.
The right Python architecture for this issue is always to devote a thread (the main one, if one must) to serving the finicky object or subsystem; every other thread requiring interaction with said subsystem or object must them obtain it by queueing requests to the dedicated thread (and possibly waiting on a "return queue" for results, if results are required as a consequence of some request). This is also a very sound Python architecture for general-purpose threading (and I expound on it at length in "Python in a Nutshell", but that's another subject;-).
Tkinter has issues dealing with input from multiple threads, I use mtTkinter instead, you won't need to change any code and everything will work fine. Just import mtTkinter instead of Tkinter.
You can get it here:
http://tkinter.unpythonic.net/wiki/mtTkinter
Is there a reason you want (or think you need) one event loop per toplevel window? A single event loop is able to handle dozens (if not hundreds or thousands) of toplevel windows. And, as has been pointed out in another answer, you can't run this event loop in a separate thread.
So, to fix your code you need to only use a single event loop, and have that run in the main thread.