Refactor the lifetime of future watcher inside QmakeProFile

Create future watcher only prior to starting an async task.
After the task is done, clean the watcher in order to release
the resources kept inside its QFuture's result.

Make setupFutureWatcher() a private member. Provide
a corresponding cleanupFutureWatcher().

Change-Id: I9d2b058250a3f749a2c9ad51323d2d38f66ee98d
Reviewed-by: Christian Kandeler <christian.kandeler@qt.io>

src/plugins/qmakeprojectmanager/qmakeparsernodes.cpp

@@ -1174,7 +1174,6 @@ QByteArray QmakeProFile::cxxDefines() const
 QmakeProFile::QmakeProFile(QmakeBuildSystem *buildSystem, const FilePath &filePath) :
     QmakePriFile(buildSystem, this, filePath)
 {
-    setupFutureWatcher();
 }
 
 QmakeProFile::QmakeProFile(const FilePath &filePath) : QmakePriFile(filePath) { }
@@ -1182,22 +1181,33 @@ QmakeProFile::QmakeProFile(const FilePath &filePath) : QmakePriFile(filePath) {
 QmakeProFile::~QmakeProFile()
 {
     qDeleteAll(m_extraCompilers);
-    if (m_parseFutureWatcher) {
-        m_parseFutureWatcher->cancel();
-        m_parseFutureWatcher->waitForFinished();
-        if (m_readerExact)
-            applyAsyncEvaluate(false);
-        delete m_parseFutureWatcher;
-    }
+    cleanupFutureWatcher();
     cleanupProFileReaders();
 }
 
+void QmakeProFile::cleanupFutureWatcher()
+{
+    if (!m_parseFutureWatcher)
+        return;
+
+    m_parseFutureWatcher->disconnect();
+    m_parseFutureWatcher->cancel();
+    m_parseFutureWatcher->waitForFinished();
+    m_parseFutureWatcher->deleteLater();
+    m_parseFutureWatcher = nullptr;
+    m_buildSystem->decrementPendingEvaluateFutures();
+}
+
 void QmakeProFile::setupFutureWatcher()
 {
+    QTC_ASSERT(!m_parseFutureWatcher, return);
+
     m_parseFutureWatcher = new QFutureWatcher<Internal::QmakeEvalResultPtr>;
     QObject::connect(m_parseFutureWatcher, &QFutureWatcherBase::finished, [this]() {
-        applyAsyncEvaluate(true);
+        applyEvaluate(m_parseFutureWatcher->result());
+        cleanupFutureWatcher();
     });
+    m_buildSystem->incrementPendingEvaluateFutures();
 }
 
 bool QmakeProFile::isParent(QmakeProFile *node)
@@ -1286,11 +1296,11 @@ void QmakeProFile::scheduleUpdate(QmakeProFile::AsyncUpdateDelay delay)
 
 void QmakeProFile::asyncUpdate()
 {
-    m_buildSystem->incrementPendingEvaluateFutures();
+    cleanupFutureWatcher();
+    setupFutureWatcher();
     setupReader();
     if (!includedInExactParse())
         m_readerExact->setExact(false);
-    m_parseFutureWatcher->waitForFinished();
     QmakeEvalInput input = evalInput();
     QFuture<QmakeEvalResultPtr> future = Utils::runAsync(ProjectExplorerPlugin::sharedThreadPool(),
                                                          QThread::LowestPriority,
@@ -1640,13 +1650,6 @@ void QmakeProFile::asyncEvaluate(QFutureInterface<QmakeEvalResultPtr> &fi, Qmake
     fi.reportResult(evaluate(input));
 }
 
-void QmakeProFile::applyAsyncEvaluate(bool apply)
-{
-    if (apply)
-        applyEvaluate(m_parseFutureWatcher->result());
-    m_buildSystem->decrementPendingEvaluateFutures();
-}
-
 bool sortByParserNodes(Node *a, Node *b)
 {
     return a->filePath() < b->filePath();
@@ -1720,7 +1723,6 @@ void QmakeProFile::applyEvaluate(const QmakeEvalResultPtr &result)
 
     for (QmakeProFile * const proFile : qAsConst(result->proFiles)) {
         proFile->finishInitialization(m_buildSystem, proFile);
-        proFile->setupFutureWatcher();
         proFile->asyncUpdate();
     }
     QmakePriFile::update(result->includedFiles.result);

src/plugins/qmakeprojectmanager/qmakeparsernodes.h

@@ -306,8 +306,6 @@ public:
     explicit QmakeProFile(const Utils::FilePath &filePath);
     ~QmakeProFile() override;
 
-    void setupFutureWatcher();
-
     bool isParent(QmakeProFile *node);
     QString displayName() const final;
 
@@ -351,11 +349,12 @@ public:
     bool isFileFromWildcard(const QString &filePath) const;
 
 private:
+    void cleanupFutureWatcher();
+    void setupFutureWatcher();
+
     void setParseInProgress(bool b);
     void setValidParseRecursive(bool b);
 
-    void applyAsyncEvaluate(bool apply);
-
     void setupReader();
     Internal::QmakeEvalInput evalInput() const;