Why starting a non-responsive service from a QThread blocks the main GUI? - winapi

Question

PyQt 5
Python 3.5
I have a Windows service that cannot be started for a few seconds after it has been stopped. If you try it returns error 1053. When I try to start it during this "unresponsiveness period" with win32serviceutil. StartService() from a QThread (with a worker inside), StartService() runs for about 20 seconds and finally returns error 1053. The problem is that despite StartService() being run in a separate thread, it will also block the main GUI thread. Here's my sample code:
import sys
from PyQt5 import uic
from PyQt5.QtWidgets import QApplication, QMainWindow, QMessageBox
from PyQt5.QtCore import Qt, QObject, QThread, pyqtSignal, pyqtSlot
from win32serviceutil import StartService
class Worker(QObject):
finished = pyqtSignal()
done = pyqtSignal("PyQt_PyObject")
def __init__(self, func, *args):
super().__init__()
self.func = func
self.args = args
def run(self):
try:
result = self.func(*self.args)
except Exception as e:
result = e
self.done.emit(result) # Pass function return.
self.finished.emit()
Ui_MainWindow, QtBaseClass = uic.loadUiType("window.ui")
class TestApp(QMainWindow, Ui_MainWindow):
def __init__(self):
super().__init__()
self.setupUi(self)
# Hide What's This button and show only close button.
self.setWindowFlags(Qt.WindowTitleHint | Qt.WindowCloseButtonHint)
self.text_box.returnPressed.connect(self.run_thread)
self.worker = None
self.thread = None
self.go_button.clicked.connect(self.run_thread)
def run_thread(self):
if self.text_box.text().strip():
# Start service from generic worker inside a QThread.
self.worker = Worker(StartService, self.text_box.text().strip())
self.thread = QThread()
self.worker.moveToThread(self.thread)
self.thread.started.connect(self.worker.run)
self.worker.done.connect(self.done)
self.worker.finished.connect(self.thread.quit)
self.worker.finished.connect(self.worker.deleteLater)
self.thread.finished.connect(self.thread.deleteLater)
self.thread.start()
self.busy(True) # Activate progress busy mode.
def busy(self, status):
end = 0 if status else 100 # 0 is busy progress bar, 100 is inactive.
self.p_bar.setRange(0, end)
#pyqtSlot("PyQt_PyObject")
def done(self, result):
self.busy(False) # Deactivate progress bar.
if isinstance(result, Exception):
title = "Error"
msg = str(result)
icon = QMessageBox.Critical
else:
title = "Started"
msg = "Done"
icon = QMessageBox.Information
# Show message box with result.
dialog = QMessageBox(self)
dialog.setWindowTitle(title)
dialog.setText(msg)
dialog.setStandardButtons(QMessageBox.Ok)
dialog.setIcon(icon)
dialog.exec_()
def main():
program = QApplication(sys.argv)
svc_stopper = TestApp()
svc_stopper.show()
sys.exit(program.exec_())
if __name__ == "__main__":
main()
This is the window.ui file:
<?xml version="1.0" encoding="UTF-8"?>
<ui version="4.0">
<class>MainWindow</class>
<widget class="QMainWindow" name="MainWindow">
<property name="geometry">
<rect>
<x>0</x>
<y>0</y>
<width>230</width>
<height>120</height>
</rect>
</property>
<property name="windowTitle">
<string>Start Service</string>
</property>
<widget class="QWidget" name="centralwidget">
<widget class="QPushButton" name="go_button">
<property name="geometry">
<rect>
<x>76</x>
<y>13</y>
<width>81</width>
<height>31</height>
</rect>
</property>
<property name="text">
<string>Start Service</string>
</property>
<property name="autoDefault">
<bool>true</bool>
</property>
</widget>
<widget class="QProgressBar" name="p_bar">
<property name="geometry">
<rect>
<x>10</x>
<y>90</y>
<width>211</width>
<height>23</height>
</rect>
</property>
<property name="value">
<number>0</number>
</property>
<property name="textVisible">
<bool>false</bool>
</property>
</widget>
<widget class="QLineEdit" name="text_box">
<property name="geometry">
<rect>
<x>10</x>
<y>60</y>
<width>211</width>
<height>20</height>
</rect>
</property>
<property name="placeholderText">
<string>Service display name</string>
</property>
<property name="clearButtonEnabled">
<bool>false</bool>
</property>
</widget>
</widget>
</widget>
<tabstops>
<tabstop>go_button</tabstop>
</tabstops>
<resources/>
<connections/>
</ui>