1 #ifndef _DESPINBARRIER_HPP 2 #define _DESPINBARRIER_HPP 3 /*------------------------------------------------------------------------- 4 * drawElements C++ Base Library 5 * ----------------------------- 6 * 7 * Copyright 2015 The Android Open Source Project 8 * 9 * Licensed under the Apache License, Version 2.0 (the "License"); 10 * you may not use this file except in compliance with the License. 11 * You may obtain a copy of the License at 12 * 13 * http://www.apache.org/licenses/LICENSE-2.0 14 * 15 * Unless required by applicable law or agreed to in writing, software 16 * distributed under the License is distributed on an "AS IS" BASIS, 17 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 18 * See the License for the specific language governing permissions and 19 * limitations under the License. 20 * 21 *//*! 22 * \file 23 * \brief Cross-thread barrier. 24 *//*--------------------------------------------------------------------*/ 25 26 #include "deDefs.hpp" 27 #include "deAtomic.h" 28 29 namespace de 30 { 31 32 /*--------------------------------------------------------------------*//*! 33 * \brief Cross-thread barrier 34 * 35 * SpinBarrier provides barrier implementation that uses spin loop for 36 * waiting for other threads. Threads may choose to wait in tight loop 37 * (WAIT_MODE_BUSY) or yield between iterations (WAIT_MODE_YIELD). 38 * 39 * It is not recommended to use WAIT_MODE_BUSY when there are more threads 40 * than number of cores participating in the barrier as it will lead to 41 * priority inversion and dramatic slowdown. For that reason WAIT_MODE_AUTO 42 * is provided, which selects between busy and yielding waiting based on 43 * number of threads. 44 *//*--------------------------------------------------------------------*/ 45 class SpinBarrier 46 { 47 public: 48 enum WaitMode 49 { 50 WAIT_MODE_BUSY = 0, //! Wait in tight spin loop. 51 WAIT_MODE_YIELD, //! Call deYield() between spin loop iterations. 52 WAIT_MODE_AUTO, //! Use WAIT_MODE_BUSY loop if #threads <= #cores, otherwise WAIT_MODE_YIELD. 53 54 WAIT_MODE_LAST 55 }; 56 57 SpinBarrier(int32_t numThreads); 58 ~SpinBarrier(void); 59 60 //! Reset barrier. Not thread-safe, e.g. no other thread can 61 //! be calling sync() or removeThread() at the same time. 62 void reset(uint32_t numThreads); 63 64 //! Wait until all threads (determined by active thread count) 65 //! have entered sync(). 66 void sync(WaitMode mode); 67 68 //! Remove thread from barrier (decrements active thread count). 69 //! Can be called concurrently with sync() or removeThread(). 70 void removeThread(WaitMode mode); 71 72 private: 73 SpinBarrier(const SpinBarrier &); 74 SpinBarrier operator=(const SpinBarrier &); 75 76 const uint32_t m_numCores; 77 78 volatile int32_t m_numThreads; 79 volatile int32_t m_numEntered; 80 volatile int32_t m_numLeaving; 81 volatile int32_t m_numRemoved; 82 }; 83 84 void SpinBarrier_selfTest(void); 85 86 } // namespace de 87 88 #endif // _DESPINBARRIER_HPP 89