Qt threading done right (thread pool for word counter)

nw/gui/doceditor.py

@@ -12,6 +12,7 @@
  Created:   2020-04-25 [0.4.5]  GuiDocEditHeader
  Rewritten: 2020-06-15 [0.9.0]  GuiDocEditSearch
  Created:   2020-06-27 [0.10.0] GuiDocEditFooter
+ Rewritten: 2020-10-07 [1.0b3]  BackgroundWordCounter
 
  This file is a part of novelWriter
  Copyright 2018–2020, Veronica Berglyd Olsen
@@ -36,7 +37,8 @@ import logging
 from time import time
 
 from PyQt5.QtCore import (
-    Qt, QSize, QThread, QTimer, pyqtSlot, QRegExp, QRegularExpression, QPointF
+    Qt, QSize, QTimer, pyqtSlot, pyqtSignal, QRegExp, QRegularExpression,
+    QPointF, QObject, QRunnable
 )
 from PyQt5.QtGui import (
     QTextCursor, QTextOption, QKeySequence, QFont, QColor, QPalette,
@@ -135,14 +137,15 @@ class GuiDocEditor(QTextEdit):
             activated=self._followTag
         )
 
-        # Set Up Word Count Thread and Timer
+        # Set Up Word Counter
         self.wcInterval = self.mainConf.wordCountTimer
         self.wcTimer = QTimer()
         self.wcTimer.setInterval(int(self.wcInterval*1000))
         self.wcTimer.timeout.connect(self._runCounter)
 
         self.wCounter = BackgroundWordCounter(self)
-        self.wCounter.finished.connect(self._updateCounts)
+        self.wCounter.setAutoDelete(False)
+        self.wCounter.signals.countsReady.connect(self._updateCounts)
 
         self.initEditor()
 
@@ -912,21 +915,18 @@ class GuiDocEditor(QTextEdit):
         """Decide whether to run the word counter, or stop the timer due
         to inactivity.
         """
-        sinceActive = time()-self.lastEdit
-        if sinceActive > 5*self.wcInterval:
-            logger.debug(
-                "Stopping word count timer: no activity last %.1f seconds" % sinceActive
-            )
-            self.wcTimer.stop()
-        elif self.wCounter.isRunning():
-            logger.verbose("Word counter thread is busy")
-        else:
-            logger.verbose("Starting word counter")
-            self.wCounter.start()
+        if self.wCounter.isRunning():
+            logger.verbose("Word counter is busy")
+            return
+
+        if time() - self.lastEdit < 5*self.wcInterval:
+            logger.verbose("Running word counter")
+            self.theParent.threadPool.start(self.wCounter)
+
         return
 
-    @pyqtSlot()
-    def _updateCounts(self):
+    @pyqtSlot(int, int, int)
+    def _updateCounts(self, cCount, wCount, pCount):
         """Slot for the word counter's finished signal
         """
         theItem = self.nwDocument.getCurrentItem()
@@ -935,19 +935,17 @@ class GuiDocEditor(QTextEdit):
 
         logger.verbose("Updating word count")
 
-        self.charCount = self.wCounter.charCount
-        self.wordCount = self.wCounter.wordCount
-        self.paraCount = self.wCounter.paraCount
-        theItem.setCharCount(self.charCount)
-        theItem.setWordCount(self.wordCount)
-        theItem.setParaCount(self.paraCount)
+        self.charCount = cCount
+        self.wordCount = wCount
+        self.paraCount = pCount
+        theItem.setCharCount(cCount)
+        theItem.setWordCount(wCount)
+        theItem.setParaCount(pCount)
 
-        self.theParent.treeView.propagateCount(self.theHandle, self.wordCount)
+        self.theParent.treeView.propagateCount(self.theHandle, wCount)
         self.theParent.treeView.projectWordCount()
-        self.theParent.treeMeta.updateCounts(
-            self.theHandle, self.charCount, self.wordCount, self.paraCount
-        )
-        self._checkDocSize(self.charCount)
+        self.theParent.treeMeta.updateCounts(self.theHandle, cCount, wCount, pCount)
+        self._checkDocSize(self.qDocument.characterCount())
         self.docFooter.updateCounts()
 
         return
@@ -1521,33 +1519,42 @@ class GuiDocEditor(QTextEdit):
 # END Class GuiDocEditor
 
 # =============================================================================================== #
-#  The Off GUI Thread Word Counter
-#  Runs the word counter in the background for the DocEditor
+#  The Off-GUI Thread Word Counter
+#  A runnable for the word counter to be run in the thread pool off the main GUI thread.
 # =============================================================================================== #
 
-class BackgroundWordCounter(QThread):
+class BackgroundWordCounter(QRunnable):
 
     def __init__(self, docEditor):
-        QThread.__init__(self, docEditor)
+        QRunnable.__init__(self)
         self.docEditor = docEditor
-        self.charCount = 0
-        self.wordCount = 0
-        self.paraCount = 0
+        self.signals = BackgroundWordCounterSignals()
+        self._isRunning = False
         return
 
+    def isRunning(self):
+        return self._isRunning
+
+    @pyqtSlot()
     def run(self):
         """Overloaded run function for the word counter, forwarding the
         call to the function that does the actual counting.
         """
+        self._isRunning = True
         theText = self.docEditor.getText()
         cC, wC, pC = countWords(theText)
-        self.charCount = cC
-        self.wordCount = wC
-        self.paraCount = pC
+        self.signals.countsReady.emit(cC, wC, pC)
+        self._isRunning = False
         return
 
 ## END Class BackgroundWordCounter
 
+class BackgroundWordCounterSignals(QObject):
+
+    countsReady = pyqtSignal(int, int, int)
+
+# END Class BackgroundWordCounterSignals
+
 # =============================================================================================== #
 #  The Embedded Document Search/Replace Feature
 #  Only used by DocEditor, and is at a fixed position in the QTextEdit's viewport