Issue 5179 - Implement asynchronous executor with a controllable lifetime

include/AdblockPlus/SynchronizedCollection.h

+/*
+ * This file is part of Adblock Plus <https://adblockplus.org/>,
+ * Copyright (C) 2006-present eyeo GmbH
+ *
+ * Adblock Plus is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License version 3 as
+ * published by the Free Software Foundation.
+ *
+ * Adblock Plus 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 General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with Adblock Plus. If not, see <http://www.gnu.org/licenses/>.
+ */
+#pragma once
+#include <mutex>
+#include <condition_variable>
+
+namespace AdblockPlus
+{
+  /**
+   * Wrapper around `Container` providing few generic methods which ensure
+   * that the underlying container is accessed only by one thread at the same
+   * time.
+   */
+  template<typename TContainer>
+  class SynchronizedCollection
+  {
+  protected:
+    typedef TContainer Container;
+  public:
+    /**
+     * The `value_type` represents the type of stored values.
+     */
+    typedef typename Container::value_type value_type;
+
+    /**
+     * Adds `value` normally to the end.
+     * @param value which is stored.
+     */
+    void push_back(const value_type& value)
+    {
+      {
+        std::lock_guard<std::mutex> lock(mutex);
+        collection.push_back(value);
+      }
+      conditionVar.notify_one();
+    }
+    void push_back(value_type&& value)
+    {
+      {
+        std::lock_guard<std::mutex> lock(mutex);
+        collection.push_back(std::move(value));
+      }
+      conditionVar.notify_one();
+    }
+
+    /**
+     * Extracts the first stored element and returns it.
+     * Pay attention that the call of this method blocks the execution until
+     * there is at least one element added to the collection.
+     */
+    value_type pop_front()
+    {
+      std::unique_lock<std::mutex> lock(mutex);
+      conditionVar.wait(lock, [this]()->bool
+      {
+        return !collection.empty();
+      });
+      value_type retValue = collection.front();
+      collection.pop_front();
+      return retValue;
+    }
+  protected:
+    Container collection;
+    std::mutex mutex;
+    std::condition_variable conditionVar;
+  };
+}