Fix a possible crash in ClangEditorDocumentProcessor

Use QFutureSynchronizer in order to ensure that all
threads have finished on shutdown.

Fixes: QTCREATORBUG-25673
Change-Id: I3a6a808ada389bc51a1f0149dfc112768929a20d
Reviewed-by: Christian Kandeler <christian.kandeler@qt.io>

src/plugins/clangcodemodel/clangeditordocumentprocessor.cpp

@@ -91,15 +91,14 @@ ClangEditorDocumentProcessor::ClangEditorDocumentProcessor(
             this, &ClangEditorDocumentProcessor::cppDocumentUpdated);
     connect(&m_builtinProcessor, &CppTools::BuiltinEditorDocumentProcessor::semanticInfoUpdated,
             this, &ClangEditorDocumentProcessor::semanticInfoUpdated);
+
+    m_parserSynchronizer.setCancelOnWait(true);
 }
 
 ClangEditorDocumentProcessor::~ClangEditorDocumentProcessor()
 {
     m_updateBackendDocumentTimer.stop();
 
-    m_parserWatcher.cancel();
-    m_parserWatcher.waitForFinished();
-
     if (m_projectPart)
         closeBackendDocument();
 }
@@ -120,6 +119,7 @@ void ClangEditorDocumentProcessor::runImpl(
             this, &ClangEditorDocumentProcessor::onParserFinished);
     const QFuture<void> future = ::Utils::runAsync(&runParser, parser(), updateParams);
     m_parserWatcher.setFuture(future);
+    m_parserSynchronizer.addFuture(future);
 
     // Run builtin processor
     m_builtinProcessor.runImpl(updateParams);

src/plugins/clangcodemodel/clangeditordocumentprocessor.h

@@ -33,6 +33,7 @@
 
 #include <utils/id.h>
 
+#include <QFutureSynchronizer>
 #include <QFutureWatcher>
 #include <QTimer>
 
@@ -145,6 +146,7 @@ private:
     QVector<ClangBackEnd::TokenInfoContainer> m_tokenInfos;
     CppTools::SemanticHighlighter m_semanticHighlighter;
     CppTools::BuiltinEditorDocumentProcessor m_builtinProcessor;
+    QFutureSynchronizer<void> m_parserSynchronizer;
 };
 
 } // namespace Internal