delibs/decpp/deSpinBarrier.cpp

/*-------------------------------------------------------------------------
 * 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 "deSpinBarrier.hpp"
#include "deThread.hpp"
#include "deRandom.hpp"
#include "deInt32.h"

#include <vector>

namespace de
{

SpinBarrier::SpinBarrier (deInt32 numThreads)
	: m_numCores	(deGetNumAvailableLogicalCores())
	, m_numThreads	(numThreads)
	, m_numEntered	(0)
	, m_numLeaving	(0)
	, m_numRemoved	(0)
{
	DE_ASSERT(numThreads > 0);
}

SpinBarrier::~SpinBarrier (void)
{
	DE_ASSERT(m_numEntered == 0 && m_numLeaving == 0);
}

void SpinBarrier::reset (deUint32 numThreads)
{
	// If last threads were removed, m_numEntered > 0 && m_numRemoved > 0
	DE_ASSERT(m_numLeaving == 0);
	DE_ASSERT(numThreads > 0);
	m_numThreads = numThreads;
	m_numEntered = 0;
	m_numLeaving = 0;
	m_numRemoved = 0;
}

inline SpinBarrier::WaitMode getWaitMode (SpinBarrier::WaitMode requested, deUint32 numCores, deInt32 numThreads)
{
	if (requested == SpinBarrier::WAIT_MODE_AUTO)
		return ((deUint32)numThreads <= numCores) ? SpinBarrier::WAIT_MODE_BUSY : SpinBarrier::WAIT_MODE_YIELD;
	else
		return requested;
}

inline void wait (SpinBarrier::WaitMode mode)
{
	DE_ASSERT(mode == SpinBarrier::WAIT_MODE_YIELD || mode == SpinBarrier::WAIT_MODE_BUSY);

	if (mode == SpinBarrier::WAIT_MODE_YIELD)
		deYield();
}

void SpinBarrier::sync (WaitMode requestedMode)
{
	const deInt32	cachedNumThreads	= m_numThreads;
	const WaitMode	waitMode			= getWaitMode(requestedMode, m_numCores, cachedNumThreads);

	deMemoryReadWriteFence();

	// m_numEntered must not be touched until all threads have had
	// a chance to observe it being 0.
	if (m_numLeaving > 0)
	{
		for (;;)
		{
			if (m_numLeaving == 0)
				break;

			wait(waitMode);
		}
	}

	// If m_numRemoved > 0, m_numThreads will decrease. If m_numThreads is decreased
	// just after atomicOp and before comparison, the branch could be taken by multiple
	// threads. Since m_numThreads only changes if all threads are inside the spinbarrier,
	// cached value at snapshotted at the beginning of the function will be equal for
	// all threads.
	if (deAtomicIncrement32(&m_numEntered) == cachedNumThreads)
	{
		// Release all waiting threads. Since this thread has not been removed, m_numLeaving will
		// be >= 1 until m_numLeaving is decremented at the end of this function.
		m_numThreads -= m_numRemoved;
		m_numLeaving  = m_numThreads;
		m_numRemoved  = 0;

		deMemoryReadWriteFence();
		m_numEntered  = 0;
	}
	else
	{
		for (;;)
		{
			if (m_numEntered == 0)
				break;

			wait(waitMode);
		}
	}

	deAtomicDecrement32(&m_numLeaving);
	deMemoryReadWriteFence();
}

void SpinBarrier::removeThread (WaitMode requestedMode)
{
	const deInt32	cachedNumThreads	= m_numThreads;
	const WaitMode	waitMode			= getWaitMode(requestedMode, m_numCores, cachedNumThreads);

	// Wait for other threads exiting previous barrier
	if (m_numLeaving > 0)
	{
		for (;;)
		{
			if (m_numLeaving == 0)
				break;

			wait(waitMode);
		}
	}

	// Ask for last thread entering barrier to adjust thread count
	deAtomicIncrement32(&m_numRemoved);

	// See sync() - use cached value
	if (deAtomicIncrement32(&m_numEntered) == cachedNumThreads)
	{
		// Release all waiting threads.
		m_numThreads -= m_numRemoved;
		m_numLeaving  = m_numThreads;
		m_numRemoved  = 0;

		deMemoryReadWriteFence();
		m_numEntered  = 0;
	}
}

namespace
{

void singleThreadTest (SpinBarrier::WaitMode mode)
{
	SpinBarrier barrier(1);

	barrier.sync(mode);
	barrier.sync(mode);
	barrier.sync(mode);
}

class TestThread : public de::Thread
{
public:
	TestThread (SpinBarrier& barrier, volatile deInt32* sharedVar, int numThreads, int threadNdx)
		: m_barrier		(barrier)
		, m_sharedVar	(sharedVar)
		, m_numThreads	(numThreads)
		, m_threadNdx	(threadNdx)
		, m_busyOk		((deUint32)m_numThreads <= deGetNumAvailableLogicalCores())
	{
	}

	void run (void)
	{
		const int	numIters	= 10000;
		de::Random	rnd			(deInt32Hash(m_numThreads) ^ deInt32Hash(m_threadNdx));

		for (int iterNdx = 0; iterNdx < numIters; iterNdx++)
		{
			// Phase 1: count up
			deAtomicIncrement32(m_sharedVar);

			// Verify
			m_barrier.sync(getWaitMode(rnd));

			DE_TEST_ASSERT(*m_sharedVar == m_numThreads);

			m_barrier.sync(getWaitMode(rnd));

			// Phase 2: count down
			deAtomicDecrement32(m_sharedVar);

			// Verify
			m_barrier.sync(getWaitMode(rnd));

			DE_TEST_ASSERT(*m_sharedVar == 0);

			m_barrier.sync(getWaitMode(rnd));
		}
	}

private:
	SpinBarrier&			m_barrier;
	volatile deInt32* const	m_sharedVar;
	const int				m_numThreads;
	const int				m_threadNdx;
	const bool				m_busyOk;

	SpinBarrier::WaitMode getWaitMode (de::Random& rnd)
	{
		static const SpinBarrier::WaitMode	s_allModes[]	=
		{
			SpinBarrier::WAIT_MODE_YIELD,
			SpinBarrier::WAIT_MODE_AUTO,
			SpinBarrier::WAIT_MODE_BUSY,
		};
		const int							numModes		= DE_LENGTH_OF_ARRAY(s_allModes) - (m_busyOk ? 0 : 1);

		return rnd.choose<SpinBarrier::WaitMode>(DE_ARRAY_BEGIN(s_allModes), DE_ARRAY_BEGIN(s_allModes) + numModes);
	}
};

void multiThreadTest (int numThreads)
{
	SpinBarrier					barrier		(numThreads);
	volatile deInt32			sharedVar	= 0;
	std::vector<TestThread*>	threads		(numThreads, static_cast<TestThread*>(DE_NULL));

	for (int ndx = 0; ndx < numThreads; ndx++)
	{
		threads[ndx] = new TestThread(barrier, &sharedVar, numThreads, ndx);
		DE_TEST_ASSERT(threads[ndx]);
		threads[ndx]->start();
	}

	for (int ndx = 0; ndx < numThreads; ndx++)
	{
		threads[ndx]->join();
		delete threads[ndx];
	}

	DE_TEST_ASSERT(sharedVar == 0);
}

void singleThreadRemoveTest (SpinBarrier::WaitMode mode)
{
	SpinBarrier barrier(3);

	barrier.removeThread(mode);
	barrier.removeThread(mode);
	barrier.sync(mode);
	barrier.removeThread(mode);

	barrier.reset(1);
	barrier.sync(mode);

	barrier.reset(2);
	barrier.removeThread(mode);
	barrier.sync(mode);
}

class TestExitThread : public de::Thread
{
public:
	TestExitThread (SpinBarrier& barrier, int numThreads, int threadNdx, SpinBarrier::WaitMode waitMode)
		: m_barrier		(barrier)
		, m_numThreads	(numThreads)
		, m_threadNdx	(threadNdx)
		, m_waitMode	(waitMode)
	{
	}

	void run (void)
	{
		const int	numIters	= 10000;
		de::Random	rnd			(deInt32Hash(m_numThreads) ^ deInt32Hash(m_threadNdx) ^ deInt32Hash((deInt32)m_waitMode));
		const int	invExitProb	= 1000;

		for (int iterNdx = 0; iterNdx < numIters; iterNdx++)
		{
			if (rnd.getInt(0, invExitProb) == 0)
			{
				m_barrier.removeThread(m_waitMode);
				break;
			}
			else
				m_barrier.sync(m_waitMode);
		}
	}

private:
	SpinBarrier&				m_barrier;
	const int					m_numThreads;
	const int					m_threadNdx;
	const SpinBarrier::WaitMode	m_waitMode;
};

void multiThreadRemoveTest (int numThreads, SpinBarrier::WaitMode waitMode)
{
	SpinBarrier						barrier		(numThreads);
	std::vector<TestExitThread*>	threads		(numThreads, static_cast<TestExitThread*>(DE_NULL));

	for (int ndx = 0; ndx < numThreads; ndx++)
	{
		threads[ndx] = new TestExitThread(barrier, numThreads, ndx, waitMode);
		DE_TEST_ASSERT(threads[ndx]);
		threads[ndx]->start();
	}

	for (int ndx = 0; ndx < numThreads; ndx++)
	{
		threads[ndx]->join();
		delete threads[ndx];
	}
}

} // anonymous

void SpinBarrier_selfTest (void)
{
	singleThreadTest(SpinBarrier::WAIT_MODE_YIELD);
	singleThreadTest(SpinBarrier::WAIT_MODE_BUSY);
	singleThreadTest(SpinBarrier::WAIT_MODE_AUTO);
	multiThreadTest(1);
	multiThreadTest(2);
	multiThreadTest(4);
	multiThreadTest(8);
	multiThreadTest(16);

	singleThreadRemoveTest(SpinBarrier::WAIT_MODE_YIELD);
	singleThreadRemoveTest(SpinBarrier::WAIT_MODE_BUSY);
	singleThreadRemoveTest(SpinBarrier::WAIT_MODE_AUTO);
	multiThreadRemoveTest(1, SpinBarrier::WAIT_MODE_BUSY);
	multiThreadRemoveTest(2, SpinBarrier::WAIT_MODE_AUTO);
	multiThreadRemoveTest(4, SpinBarrier::WAIT_MODE_AUTO);
	multiThreadRemoveTest(8, SpinBarrier::WAIT_MODE_AUTO);
	multiThreadRemoveTest(16, SpinBarrier::WAIT_MODE_AUTO);
	multiThreadRemoveTest(1, SpinBarrier::WAIT_MODE_YIELD);
	multiThreadRemoveTest(2, SpinBarrier::WAIT_MODE_YIELD);
	multiThreadRemoveTest(4, SpinBarrier::WAIT_MODE_YIELD);
	multiThreadRemoveTest(8, SpinBarrier::WAIT_MODE_YIELD);
	multiThreadRemoveTest(16, SpinBarrier::WAIT_MODE_YIELD);
}

} // de