I'm trying to understand why this Worker
thread, which deliberately uses a fairly intense amount of processing (sorting of these dictionaries in particular) causes the GUI thread to become unresponsive. Here is an MRE:
from PyQt5 import QtCore, QtWidgets
import sys, time, datetime, random
def time_print(msg):
ms_now = datetime.datetime.now().isoformat(sep=' ', timespec='milliseconds')
thread = QtCore.QThread.currentThread()
print(f'{thread}, {ms_now}: {msg}')
def dict_reorder(dictionary):
return {k: v for k, v in sorted(dictionary.items())}
class Sequence(object):
n_sequence = 0
simple_sequence_map = {}
sequence_to_sequence_map = {}
prev_seq = None
def __init__(self):
Sequence.n_sequence += 1
if Sequence.n_sequence % 1000 == 0:
print(f'created sequence {Sequence.n_sequence}')
rand_int = random.randrange(100000)
self.text = str(rand_int)
Sequence.simple_sequence_map[self] = rand_int
if Worker.stop_ordered:
time_print(f'init() A: stop ordered... stopping now')
return
dict_reorder(Sequence.simple_sequence_map)
if Sequence.prev_seq:
Sequence.sequence_to_sequence_map[self] = Sequence.prev_seq
if Worker.stop_ordered:
time_print(f'init() B: stop ordered... stopping now')
return
dict_reorder(Sequence.sequence_to_sequence_map)
Sequence.prev_seq = self
def __lt__(self, other):
return self.text < other.text
class WorkerSignals(QtCore.QObject):
progress = QtCore.pyqtSignal(int)
stop_me = QtCore.pyqtSignal()
class Worker(QtCore.QRunnable):
def __init__(self, *args, **kwargs):
super().__init__()
self.signals = WorkerSignals()
def stop_me_slot(self):
time_print('stop me slot')
Worker.stop_ordered = True
@QtCore.pyqtSlot()
def run(self):
total_n = 30000
Worker.stop_ordered = False
for n in range(total_n):
progress_pc = int(100 * float(n+1)/total_n)
self.signals.progress.emit(progress_pc)
Sequence()
if Worker.stop_ordered:
time_print(f'run(): stop ordered... stopping now, n {n}')
return
class MainWindow(QtWidgets.QMainWindow):
def __init__(self):
super().__init__()
layout = QtWidgets.QVBoxLayout()
self.progress = QtWidgets.QProgressBar()
layout.addWidget(self.progress)
start_button = QtWidgets.QPushButton('Start')
start_button.pressed.connect(self.execute)
layout.addWidget(start_button)
self.stop_button = QtWidgets.QPushButton('Stop')
layout.addWidget(self.stop_button)
w = QtWidgets.QWidget()
w.setLayout(layout)
self.setCentralWidget(w)
self.show()
self.threadpool = QtCore.QThreadPool()
self.resize(800, 600)
def execute(self):
self.worker = Worker()
self.worker.signals.progress.connect(self.update_progress)
self.stop_button.pressed.connect(self.worker.stop_me_slot)
self.threadpool.start(self.worker)
def update_progress(self, progress):
self.progress.setValue(progress)
app = QtWidgets.QApplication(sys.argv)
window = MainWindow()
app.exec_()
On my machine, up until about 12%, the GUI is significantly unresponsive: the buttons do not acquire their "hover-over" colour (light blue) and seem not to be able to be clicked (although clicking "Stop" does cause stop after many seconds). Intermittently the dreaded spinner appears (blue circle in a W10 OS).
After 12% or so it becomes possible to use the buttons normally.
What am I doing wrong?
A very simple solution is to "sleep" the thread by using a basic time.sleep
: even with a very small interval, it will give enough time for the main thread to process its event queue avoiding UI locking:
def run(self):
total_n = 30000
Worker.stop_ordered = False
for n in range(total_n):
progress_pc = int(100 * float(n+1)/total_n)
self.signals.progress.emit(progress_pc)
Sequence()
if Worker.stop_ordered:
time_print(f'run(): stop ordered... stopping now, n {n}')
return
time.sleep(.0001)
Note: that pyqtSlot
decorator is useless, because it only works for QObject subclasses (which QRunnable isn't); you can remove it.