Tools: Introduce semaphore

fairmq/tools/Semaphore.cxx

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+/********************************************************************************
+ *    Copyright (C) 2019 GSI Helmholtzzentrum fuer Schwerionenforschung GmbH    *
+ *                                                                              *
+ *              This software is distributed under the terms of the             *
+ *              GNU Lesser General Public Licence (LGPL) version 3,             *
+ *                  copied verbatim in the file "LICENSE"                       *
+ ********************************************************************************/
+
+#include "Semaphore.h"
+
+namespace fair {
+namespace mq {
+namespace tools {
+
+Semaphore::Semaphore()
+    : Semaphore(0)
+{}
+
+Semaphore::Semaphore(std::size_t initial_count)
+    : fCount(initial_count)
+{}
+
+auto Semaphore::Wait() -> void
+{
+    std::unique_lock<std::mutex> lk(fMutex);
+    if (fCount > 0) {
+        --fCount;
+    } else {
+        fCv.wait(lk, [this] { return fCount > 0; });
+        --fCount;
+    }
+}
+
+auto Semaphore::Signal() -> void
+{
+    std::unique_lock<std::mutex> lk(fMutex);
+    ++fCount;
+    lk.unlock();
+    fCv.notify_one();
+}
+
+auto Semaphore::GetCount() -> std::size_t
+{
+    std::unique_lock<std::mutex> lk(fMutex);
+    return fCount;
+}
+
+} /* namespace tools */
+} /* namespace mq */
+} /* namespace fair */

fairmq/tools/Semaphore.h

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+/********************************************************************************
+ *    Copyright (C) 2019 GSI Helmholtzzentrum fuer Schwerionenforschung GmbH    *
+ *                                                                              *
+ *              This software is distributed under the terms of the             *
+ *              GNU Lesser General Public Licence (LGPL) version 3,             *
+ *                  copied verbatim in the file "LICENSE"                       *
+ ********************************************************************************/
+
+#ifndef FAIR_MQ_TOOLS_SEMAPHORE_H
+#define FAIR_MQ_TOOLS_SEMAPHORE_H
+
+#include <condition_variable>
+#include <cstdint>
+#include <functional>
+#include <mutex>
+
+namespace fair {
+namespace mq {
+namespace tools {
+
+/**
+ * @struct Semaphore Semaphore.h <fairmq/tools/Semaphore.h>
+ * @brief A simple blocking semaphore.
+ */
+struct Semaphore
+{
+  explicit Semaphore();
+  explicit Semaphore(std::size_t initial_count);
+
+  auto Wait() -> void;
+  auto Signal() -> void;
+  auto GetCount() -> std::size_t;
+
+private:
+  std::size_t fCount;
+  std::mutex fMutex;
+  std::condition_variable fCv;
+};
+
+} /* namespace tools */
+} /* namespace mq */
+} /* namespace fair */
+
+#endif /* FAIR_MQ_TOOLS_SEMAPHORE_H */