framework/delibs/decpp/deSpinBarrier.hpp

#ifndef _DESPINBARRIER_HPP
#define _DESPINBARRIER_HPP
/*-------------------------------------------------------------------------
 * drawElements C++ Base Library
 * -----------------------------
 *
 * Copyright 2015 The Android Open Source Project
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 *
 *//*!
 * \file
 * \brief Cross-thread barrier.
 *//*--------------------------------------------------------------------*/

#include "deDefs.hpp"
#include "deAtomic.h"

namespace de
{

/*--------------------------------------------------------------------*//*!
 * \brief Cross-thread barrier
 *
 * SpinBarrier provides barrier implementation that uses spin loop for
 * waiting for other threads. Threads may choose to wait in tight loop
 * (WAIT_MODE_BUSY) or yield between iterations (WAIT_MODE_YIELD).
 *
 * It is not recommended to use WAIT_MODE_BUSY when there are more threads
 * than number of cores participating in the barrier as it will lead to
 * priority inversion and dramatic slowdown. For that reason WAIT_MODE_AUTO
 * is provided, which selects between busy and yielding waiting based on
 * number of threads.
 *//*--------------------------------------------------------------------*/
class SpinBarrier
{
public:
	enum WaitMode
	{
		WAIT_MODE_BUSY = 0,	//! Wait in tight spin loop.
		WAIT_MODE_YIELD,	//! Call deYield() between spin loop iterations.
		WAIT_MODE_AUTO,		//! Use WAIT_MODE_BUSY loop if #threads <= #cores, otherwise WAIT_MODE_YIELD.

		WAIT_MODE_LAST
	};

						SpinBarrier		(deInt32 numThreads);
						~SpinBarrier	(void);

	//! Reset barrier. Not thread-safe, e.g. no other thread can
	//! be calling sync() or removeThread() at the same time.
	void				reset			(deUint32 numThreads);

	//! Wait until all threads (determined by active thread count)
	//! have entered sync().
	void				sync			(WaitMode mode);

	//! Remove thread from barrier (decrements active thread count).
	//! Can be called concurrently with sync() or removeThread().
	void				removeThread	(WaitMode mode);

private:
						SpinBarrier		(const SpinBarrier&);
	SpinBarrier			operator=		(const SpinBarrier&);

	const deUint32		m_numCores;

	volatile deInt32	m_numThreads;
	volatile deInt32	m_numEntered;
	volatile deInt32	m_numLeaving;
	volatile deInt32	m_numRemoved;
};

void	SpinBarrier_selfTest	(void);

} // de

#endif // _DESPINBARRIER_HPP