Locator: Fix the fix of the deadlock

The all/current project searches use metacalls on the UI thread to work
around thread-unsafety of the Project::allFiles method, so we cannot jus
t block the UI thread to wait for the old search to cancel.
On the other hand, many of the ILocatorFilter::matchesFor implementation
s do not work when they are run in multiple threads simultaneously (most
implementations access unguarded member variables, help index filter tend
s to crash), so we _do_ have to wait for the search to cancel before sta
rting a new thread.
Broke with 05c267673f and 6fc39f0c41
00c5673ae80d03d115bf3739

Change-Id: I93c607c879e8ba6ef60f94719812edb3df43a154
Task-number: QTCREATORBUG-12875
Task-number: QTCREATORBUG-12592
Reviewed-by: Christian Kandeler <christian.kandeler@digia.com>

src/plugins/coreplugin/locator/locatorwidget.cpp

@@ -478,12 +478,18 @@ QList<ILocatorFilter *> LocatorWidget::filtersFor(const QString &text, QString &
 void LocatorWidget::updateCompletionList(const QString &text)
 {
     m_updateRequested = true;
+    if (m_entriesWatcher->future().isRunning()) {
+        // Cancel the old future. We may not just block the UI thread to wait for the search to
+        // actually cancel, so try again when the finshed signal of the watcher ends up in
+        // updateEntries() (which will call updateCompletionList again with the
+        // requestedCompletionText)
+        m_requestedCompletionText = text;
+        m_entriesWatcher->future().cancel();
+        return;
+    }
+
     QString searchText;
     const QList<ILocatorFilter *> filters = filtersFor(text, searchText);
-
-    // cancel the old future
-    m_entriesWatcher->future().cancel();
-
     QFuture<LocatorFilterEntry> future = QtConcurrent::run(runSearch, filters, searchText);
     m_entriesWatcher->setFuture(future);
 }
@@ -492,8 +498,9 @@ void LocatorWidget::updateEntries()
 {
     m_updateRequested = false;
     if (m_entriesWatcher->future().isCanceled()) {
-        // reset to usable state
-        m_acceptRequested = false;
+        const QString text = m_requestedCompletionText;
+        m_requestedCompletionText.clear();
+        updateCompletionList(text);
         return;
     }
 

src/plugins/coreplugin/locator/locatorwidget.h

@@ -94,6 +94,7 @@ private:
     QTimer *m_showPopupTimer;
     QFutureWatcher<LocatorFilterEntry> *m_entriesWatcher;
     QMap<Core::Id, QAction *> m_filterActionMap;
+    QString m_requestedCompletionText;
     bool m_updateRequested;
     bool m_acceptRequested;
     bool m_possibleToolTipRequest;