Clang: Process distinct documents concurrently

Speed ups the typical use cases that can profit from this:
 * Change a header file and switch then to source file
 * Open documents one after the other (Follow Symbol)
 * Change documents visible in splits (e.g. by refactoring action)
 * Restore a session with multiple splits

Fixes the test ClangIpcServer.GetCodeCompletionDependingOnArgumets.

Change-Id: Ia575bd59780df14146dfc091a4d48794e4a0543d
Reviewed-by: Tim Jenssen <tim.jenssen@qt.io>

src/tools/clangbackend/ipcsource/clangjobqueue.h

@@ -0,0 +1,77 @@
+/****************************************************************************
+**
+** Copyright (C) 2016 The Qt Company Ltd.
+** Contact: https://www.qt.io/licensing/
+**
+** This file is part of Qt Creator.
+**
+** Commercial License Usage
+** Licensees holding valid commercial Qt licenses may use this file in
+** accordance with the commercial license agreement provided with the
+** Software or, alternatively, in accordance with the terms contained in
+** a written agreement between you and The Qt Company. For licensing terms
+** and conditions see https://www.qt.io/terms-conditions. For further
+** information use the contact form at https://www.qt.io/contact-us.
+**
+** GNU General Public License Usage
+** Alternatively, this file may be used under the terms of the GNU
+** General Public License version 3 as published by the Free Software
+** Foundation with exceptions as appearing in the file LICENSE.GPL3-EXCEPT
+** included in the packaging of this file. Please review the following
+** information to ensure the GNU General Public License requirements will
+** be met: https://www.gnu.org/licenses/gpl-3.0.html.
+**
+****************************************************************************/
+
+#pragma once
+
+#include "clangjobrequest.h"
+
+#include <functional>
+
+namespace ClangBackEnd {
+
+class ClangCodeModelClientInterface;
+class ProjectParts;
+class TranslationUnits;
+class UnsavedFiles;
+
+class JobQueue
+{
+public:
+    JobQueue(TranslationUnits &translationUnits,
+             UnsavedFiles &unsavedFiles,
+             ProjectParts &projects,
+             ClangCodeModelClientInterface &client);
+
+    void add(const JobRequest &job);
+
+    JobRequests processQueue();
+
+    using IsJobRunningHandler = std::function<bool(const Utf8String &, const Utf8String &)>;
+    void setIsJobRunningHandler(const IsJobRunningHandler &isJobRunningHandler);
+
+public: // for tests
+    JobRequests queue() const;
+    int size() const;
+    void prioritizeRequests();
+
+private:
+    using DocumentId = QPair<Utf8String, Utf8String>;
+    bool isJobRunningForDocument(const DocumentId &documentId);
+    JobRequests takeJobRequestsToRunNow();
+    void removeOutDatedRequests();
+    bool isJobRequestOutDated(const JobRequest &jobRequest) const;
+
+private:
+    TranslationUnits &m_translationUnits;
+    UnsavedFiles &m_unsavedFiles;
+    ProjectParts &m_projectParts;
+    ClangCodeModelClientInterface &m_client;
+
+    IsJobRunningHandler m_isJobRunningHandler;
+
+    JobRequests m_queue;
+};
+
+} // namespace ClangBackEnd