Clang: Suspend least recently used translation units

...to free some memory.

The translation units of the 7 most recently used documents ("hot
documents", tracked by document visibility) are kept in memory.
Translation units of other documents are suspended and will be resumed
once they become visible again.

The resumption of a translation unit needs the same time as reparse
(since it is a reparse effectively).

The number of hot documents can be modified by the run time environment
variable QTC_CLANG_HOT_DOCUMENTS=N. Visible documents are always hot.

Task-number: QTCREATORBUG-11640
Change-Id: I68ecd2b1373e303372300203e42d90f65a4b39b3
Reviewed-by: Ivan Donchevskii <ivan.donchevskii@qt.io>
Reviewed-by: Marco Bubke <marco.bubke@qt.io>

src/tools/clangbackend/ipcsource/clangdocumentsuspenderresumer.cpp

@@ -0,0 +1,141 @@
+/****************************************************************************
+**
+** Copyright (C) 2017 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.
+**
+****************************************************************************/
+
+#include "clangdocumentsuspenderresumer.h"
+
+#include "clangbackendipc_global.h"
+#include "clangdocumentprocessors.h"
+#include "clangdocuments.h"
+
+#include <utils/algorithm.h>
+
+#include <algorithm>
+
+namespace ClangBackEnd {
+
+constexpr int DefaultHotDocumentsSize = 7;
+
+void categorizeHotColdDocuments(int hotDocumentsSize,
+                                const std::vector<Document> &inDocuments,
+                                std::vector<Document> &hotDocuments,
+                                std::vector<Document> &coldDocuments)
+{
+    // Sort documents, most recently used/visible at top
+    std::vector<Document> documents = inDocuments;
+    std::stable_sort(documents.begin(), documents.end(), [](const Document &a, const Document &b) {
+        return a.visibleTimePoint() > b.visibleTimePoint();
+    });
+
+    // Ensure that visible documents are always hot, otherwise not all visible
+    // documents will be resumed.
+    const auto isVisible = [](const Document &document) { return document.isVisibleInEditor(); };
+    const int visibleDocumentsSize = Utils::count(documents, isVisible);
+    hotDocumentsSize = std::max(hotDocumentsSize, visibleDocumentsSize);
+
+    if (documents.size() <= uint(hotDocumentsSize)) {
+        hotDocuments = documents;
+        coldDocuments.clear();
+    } else {
+        const auto firstColdIterator = documents.begin() + hotDocumentsSize;
+        hotDocuments = std::vector<Document>(documents.begin(), firstColdIterator);
+        coldDocuments = std::vector<Document>(firstColdIterator,  documents.end());
+    }
+}
+
+#ifdef IS_SUSPEND_SUPPORTED
+static int hotDocumentsSize()
+{
+    static int hotDocuments = -1;
+    if (hotDocuments == -1) {
+        bool ok = false;
+        const int fromEnvironment = qEnvironmentVariableIntValue("QTC_CLANG_HOT_DOCUMENTS", &ok);
+        hotDocuments = ok && fromEnvironment >= 1 ? fromEnvironment : DefaultHotDocumentsSize;
+    }
+
+    return hotDocuments;
+}
+
+static SuspendResumeJobs createJobs(const Document &document, JobRequest::Type type)
+{
+    SuspendResumeJobs jobs;
+
+    jobs.append({document, type, PreferredTranslationUnit::RecentlyParsed});
+    if (document.isResponsivenessIncreased())
+        jobs.append({document, type, PreferredTranslationUnit::PreviouslyParsed});
+
+    return jobs;
+}
+
+static bool isFineDocument(const Document &document)
+{
+    return !document.isNull() && document.isIntact();
+}
+
+static bool isSuspendable(const Document &document)
+{
+    return isFineDocument(document)
+        && !document.isSuspended()
+        && !document.isVisibleInEditor();
+}
+
+static bool isResumable(const Document &document)
+{
+    return isFineDocument(document)
+        && document.isSuspended()
+        && document.isVisibleInEditor();
+}
+
+#endif // IS_SUSPEND_SUPPORTED
+
+SuspendResumeJobs createSuspendResumeJobs(const std::vector<Document> &documents,
+                                          int customHotDocumentSize)
+{
+    Q_UNUSED(documents);
+    Q_UNUSED(customHotDocumentSize);
+
+    SuspendResumeJobs jobs;
+
+#ifdef IS_SUSPEND_SUPPORTED
+    std::vector<Document> hotDocuments;
+    std::vector<Document> coldDocuments;
+
+    const int size = (customHotDocumentSize == -1) ? hotDocumentsSize() : customHotDocumentSize;
+    categorizeHotColdDocuments(size, documents, hotDocuments, coldDocuments);
+
+    // Cold documents should be suspended...
+    const std::vector<Document> toSuspend = Utils::filtered(coldDocuments, &isSuspendable);
+    for (const Document &document : toSuspend)
+        jobs += createJobs(document, JobRequest::Type::SuspendDocument);
+
+    // ...and hot documents that were suspended should be resumed
+    const std::vector<Document> toResume = Utils::filtered(hotDocuments, &isResumable);
+    for (const Document &document : toResume)
+        jobs += createJobs(document, JobRequest::Type::ResumeDocument);
+#endif // IS_SUSPEND_SUPPORTED
+
+    return jobs;
+}
+
+} // namespace ClangBackEnd