add AsyncQueue (needed for VIdeoImpl)

taken from gst-plugins-gl/tests/examples/qt/qglwtextureshare

AsyncQueue.h

@@ -0,0 +1,77 @@
+/*
+ * GStreamer
+ * Copyright (C) 2009 Andrey Nechypurenko <andreynech@gmail.com>
+ *
+ * This library is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Library General Public
+ * License as published by the Free Software Foundation; either
+ * version 2 of the License, or (at your option) any later version.
+ *
+ * This library 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
+ * Library General Public License for more details.
+ *
+ * You should have received a copy of the GNU Library General Public
+ * License along with this library; if not, write to the
+ * Free Software Foundation, Inc., 59 Temple Place - Suite 330,
+ * Boston, MA 02111-1307, USA.
+ */
+
+#ifndef __ASYNCQUEUE_H
+#define __ASYNCQUEUE_H
+
+#include <QMutex>
+#include <QWaitCondition>
+#include <QList>
+
+/**
+ * This is the thread safe implementation of the Queue.  It can be
+ * used in classical producers/consumers multithreaded scenario.  The
+ * template parameter is the class which can be put/get to/from the
+ * queue.
+ */
+template<class T>
+class AsyncQueue
+{
+public:
+    AsyncQueue() : waitingReaders(0) {}
+
+    int size()
+    {
+        QMutexLocker locker(&mutex);
+        return this->buffer.size();
+    }
+
+    void put(const T& item)
+    {
+        QMutexLocker locker(&mutex);
+        this->buffer.push_back(item);
+        if(this->waitingReaders)
+            this->bufferIsNotEmpty.wakeOne();
+    }
+
+    T get()
+    {
+        QMutexLocker locker(&mutex);
+        while(this->buffer.size() == 0)
+        {
+            ++(this->waitingReaders);
+            this->bufferIsNotEmpty.wait(&mutex);
+            --(this->waitingReaders);
+        }
+        T item = this->buffer.front();
+        this->buffer.pop_front();
+        return item;
+    }
+
+private:
+    typedef QList<T> Container;
+    QMutex mutex;
+    QWaitCondition bufferIsNotEmpty;
+    Container buffer;
+    short waitingReaders;
+};
+
+
+#endif // __ASYNCQUEUE_H