Execution policy (multithreading)

PdfForQtLib/sources/pdfexecutionpolicy.cpp

@@ -0,0 +1,92 @@
+//    Copyright (C) 2020 Jakub Melka
+//
+//    This file is part of PdfForQt.
+//
+//    PdfForQt is free software: you can redistribute it and/or modify
+//    it under the terms of the GNU Lesser General Public License as published by
+//    the Free Software Foundation, either version 3 of the License, or
+//    (at your option) any later version.
+//
+//    PdfForQt is distributed in the hope that it will be useful,
+//    but WITHOUT ANY WARRANTY; without even the implied warranty of
+//    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+//    GNU Lesser General Public License for more details.
+//
+//    You should have received a copy of the GNU Lesser General Public License
+//    along with PDFForQt.  If not, see <https://www.gnu.org/licenses/>.
+
+
+#include "pdfexecutionpolicy.h"
+
+#include <QThread>
+
+namespace pdf
+{
+
+struct PDFExecutionPolicyHolder
+{
+    PDFExecutionPolicy policy;
+} s_execution_policy;
+
+void PDFExecutionPolicy::setStrategy(Strategy strategy)
+{
+    s_execution_policy.policy.m_strategy.store(strategy, std::memory_order_relaxed);
+}
+
+bool PDFExecutionPolicy::isParallelizing(Scope scope)
+{
+    const Strategy strategy = s_execution_policy.policy.m_strategy.load(std::memory_order_relaxed);
+    switch (strategy)
+    {
+        case Strategy::SingleThreaded:
+            return false;
+
+        case Strategy::PageMultithreaded:
+        {
+            switch (scope)
+            {
+                case Scope::Page:
+                case Scope::Unknown:
+                    return true; // We are parallelizing pages...
+
+                case Scope::Content:
+                {
+                    // Jakub Melka: this is a bit complicated. We must count number of content streams
+                    // being processed and if it is large enough, then do not parallelize.
+                    const size_t threadLimit = s_execution_policy.policy.m_threadLimit.load(std::memory_order_relaxed);
+                    const size_t contentStreamsCount = s_execution_policy.policy.m_contentStreamsCount.load(std::memory_order_seq_cst);
+                    return contentStreamsCount < threadLimit;
+                }
+            }
+
+            break;
+        }
+
+        case Strategy::AlwaysMultithreaded:
+            return true;
+    }
+
+    // It should never go here...
+    Q_ASSERT(false);
+    return false;
+}
+
+void PDFExecutionPolicy::startProcessingContentStream()
+{
+    ++s_execution_policy.policy.m_contentStreamsCount;
+}
+
+void PDFExecutionPolicy::endProcessingContentStream()
+{
+    --s_execution_policy.policy.m_contentStreamsCount;
+}
+
+PDFExecutionPolicy::PDFExecutionPolicy() :
+    m_contentStreamsCount(0),
+    m_threadLimit(QThread::idealThreadCount()),
+    m_strategy(Strategy::PageMultithreaded)
+{
+
+}
+
+}   // namespace pdf