Easy to read 60 lines of code, minimal threading example, shows blank widget! 😊

[enjoysmath]

@fcarney

Knowing that, what do I do? The widget is blank for one. That's unrelated to the threading. But you've seen my next question.

So for that, why can't I have two running threads? I'm not doing anything high-frequency. It's all > 1ms loop sleeps.

I did it once for a "record mode" of my app, and that works fine. Then I do it with another button toggling the "playback" mode, and only one thread will run at a time:

I have 3 thread types A, B, C, all subclassed from D.

A,B work together 1 minute,
click another button and A, C don't run together, all in the same fashion and nature as the first pair!

Thanks.

[fcarney]

You may consider this library if you want true parallelism in Python:
https://docs.python.org/2/library/multiprocessing.html
Available for both 2.7 and 3.x

[enjoysmath]

Okay, here is the updated code, thanks @SGaist .

from PyQt5.QtCore import QObject, QThread, pyqtSignal
from PyQt5.QtWidgets import (QMainWindow, QWidget, QVBoxLayout, 
                             QPushButton, QPlainTextEdit, QApplication, QGridLayout)
import sys


class Thread1(QThread):
    statusMessage = pyqtSignal(str)
    
    def __init__(self):
        super().__init__()
        
    def run(self):
        while self._running:
            self.statusMessage.emit('Doing the work of thread 1.')
            self.sleep(1)
            
    def startRunning(self):
        self._running = True
        self.start()    
            
class Thread2(QThread):
    statusMessage = pyqtSignal(str)
    
    def __init__(self):
        super().__init__()
        
    def run(self):
        while self._running:
            self.statusMessage.emit('Doing the work of thread 2.')
            self.sleep(2)
            
    def startRunning(self):
        self._running = True
        self.start()
        

class Widget(QWidget):
    def __init__(self):
        super().__init__()
        self.textEdit = QPlainTextEdit(parent=self)
        self.button = QPushButton('click me')
        lyt = QVBoxLayout()
        self.setLayout(lyt)
        lyt.addWidget(self.button)
        lyt.addWidget(self.textEdit)
        self.button.clicked.connect(self.runTwoThreads)
        
    def runTwoThreads(self):
        self.thread1 = Thread1()
        self.thread1.statusMessage.connect(self.showStatusMessage)
        self.thread2 = Thread2()
        self.thread2.statusMessage.connect(self.showStatusMessage)
        self.thread1.startRunning()
        self.thread2.startRunning()
        
    def showStatusMessage(self, msg):
        self.textEdit.appendPlainText(msg)
        
        
if __name__ == '__main__':
    app = QApplication([])
    
    window = Widget()
    window.show()
    
    sys.exit(app.exec_())

And it demonstrates the bug I'm seeing at a higher level with my app. For me, when I click the button, only thread two is running, and thread 1 never emits a message, or if you put a breakpoint in thread1's run() method, it will not be hit.

Thanks all for your help.

[SGaist]

What version of PyQt5 and Qt are you using ?
On what OS ?

I have both thread outputs here.

[enjoysmath]

@SGaist

Python 3.6.5 (v3.6.5:f59c0932b4, Mar 28 2018, 16:07:46) [MSC v.1900 32 bit (Intel)] on win32
Type "help", "copyright", "credits" or "license" for more information.
>>>

Name: PyQt5
Version: 5.12.1
Summary: Python bindings for the Qt cross platform UI and application toolkit
Home-page: https://www.riverbankcomputing.com/software/pyqt/
Author: Riverbank Computing Limited
Author-email: info@riverbankcomputing.com
License: GPL v3
Location: c:\python36-32\lib\site-packages
Requires: PyQt5-sip
Required-by: QScintilla, PyQtChart

[enjoysmath]

I know I'm running 32-bit python because it's installed to C:\Python36-32 and that's my convention. I think I updated everything a few days ago in order to look at a pyinstaller issue.

[enjoysmath]

@SGaist

What are your versions, maybe I should try those out?

[SGaist]

Just tested with the latest version available on macOS through pip and it worked as expected.

[enjoysmath]

This post is deleted!

[enjoysmath]

@SGaist

I'm trying out Python 3.7 now, but maybe PyQt5 won't even install, so... I'll try some things out. Any ideas? Should I just combine the work of the two threads into one thread, since I do have exactly the same loop sleep set of 1 ms (the practical min).

I'm testing 3.7.3 both 32 and 64-bit.

[enjoysmath]

I tried 3.7.3 64-bit and the latest PyQt5 did install. However, the minimal app is having the exact same issue on my system.

So I will just combine the different threads all into one, and switch between the cases.

[SGaist]

Might be a silly test, but did you try using the QThread method to start your thread ? As I wrote earlier, I don't know how startRunning is implemented.

[enjoysmath]

@SGaist said in Easy to read 60 lines of code, minimal threading example, shows blank widget! 😊:

Might be a silly test, but did you try using the QThread method to start your thread ? As I wrote earlier, I don't know how startRunning is implemented.

Nope, that had no effect.