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diff --git a/src/engine/QueuedEventSource.hpp b/src/engine/QueuedEventSource.hpp
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+/* This file is part of Ingen.
+ * Copyright (C) 2007 Dave Robillard <http://drobilla.net>
+ * 
+ * Ingen is free software; you can redistribute it and/or modify it under the
+ * terms of the GNU General Public License as published by the Free Software
+ * Foundation; either version 2 of the License, or (at your option) any later
+ * version.
+ * 
+ * Ingen 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 details.
+ * 
+ * You should have received a copy of the GNU General Public License along
+ * with this program; if not, write to the Free Software Foundation, Inc.,
+ * 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA
+ */
+
+#ifndef QUEUEDEVENTSOURCE_H
+#define QUEUEDEVENTSOURCE_H
+
+#include <cstdlib>
+#include <pthread.h>
+#include "types.hpp"
+#include <raul/Semaphore.hpp>
+#include <raul/AtomicInt.hpp>
+#include <raul/SRSWQueue.hpp>
+#include <raul/Slave.hpp>
+#include "Event.hpp"
+#include "EventSource.hpp"
+
+using Raul::AtomicInt;
+
+namespace Ingen {
+
+class QueuedEvent;
+class PostProcessor;
+
+
+/** Queue of events that need processing before reaching the audio thread.
+ *
+ * Implemented as a deque (ringbuffer) in a circular array.  Pushing and
+ * popping are threadsafe, as long as a single thread pushes and a single
+ * thread pops (ie this data structure is threadsafe, but the push and pop
+ * methods themselves are not).  Creating an instance of this class spawns
+ * a pre-processing thread to prepare queued events.
+ *
+ * This class is it's own slave. :)
+ */
+class QueuedEventSource : public EventSource, protected Raul::Slave
+{
+public:
+	QueuedEventSource(size_t queued_size, size_t stamped_size);
+	~QueuedEventSource();
+
+	void activate()   { Slave::start(); }
+	void deactivate() { Slave::stop(); }
+
+	void process(PostProcessor& dest, ProcessContext& context);
+
+	void unblock();
+
+protected:
+	void          push_queued(QueuedEvent* const ev);
+	inline void   push_stamped(Event* const ev) { _stamped_queue.push(ev); } 
+	Event*        pop_earliest_queued_before(const SampleCount time);
+	inline Event* pop_earliest_stamped_before(const SampleCount time);
+
+	inline bool unprepared_events() { return (_prepared_back.get() != _back.get()); }
+	
+	virtual void _whipped(); ///< Prepare 1 event
+
+private:
+	// Note that it's crucially important which functions access which of these
+	// variables, to maintain threadsafeness.
+	
+	//(FIXME: make this a separate class?)
+	// 2-part queue for events that require pre-processing: 
+	AtomicInt       _front;         ///< Front of queue
+	AtomicInt       _back;          ///< Back of entire queue (1 past index of back element)
+	AtomicInt       _prepared_back; ///< Back of prepared section (1 past index of back prepared element)
+	const size_t    _size;
+	QueuedEvent**   _events;
+	Raul::Semaphore _blocking_semaphore;
+
+	Raul::Semaphore _full_semaphore;
+
+	/** Queue for timestamped events (no pre-processing). */
+	Raul::SRSWQueue<Event*> _stamped_queue;
+};
+
+
+/** Pops the realtime (timestamped, not preprocessed) event off the realtime queue.
+ *
+ * Engine will use the sample timestamps of returned events directly and execute the
+ * event with sample accuracy.  Timestamps in the past will be bumped forward to
+ * the beginning of the cycle (offset 0), when eg. skipped cycles occur.
+ */
+inline Event*
+QueuedEventSource::pop_earliest_stamped_before(const SampleCount time)
+{
+	Event* ret = NULL;
+
+	if (!_stamped_queue.empty()) {
+		if (_stamped_queue.front()->time() < time) {
+			ret = _stamped_queue.front();
+			_stamped_queue.pop();
+		}
+	}
+
+	return ret;
+}
+
+
+/** Signal that the blocking event is finished.
+ *
+ * When this is called preparing will resume.  This MUST be called by
+ * blocking events in their post_process() method.
+ */
+inline void
+QueuedEventSource::unblock()
+{
+	_blocking_semaphore.post();
+}
+
+
+} // namespace Ingen
+
+#endif // QUEUEDEVENTSOURCE_H