1858f1c5fd5e528d0b16040ced74d4636046a42d8Mathieu Chartier/* 2858f1c5fd5e528d0b16040ced74d4636046a42d8Mathieu Chartier * Copyright (C) 2012 The Android Open Source Project 3858f1c5fd5e528d0b16040ced74d4636046a42d8Mathieu Chartier * 4858f1c5fd5e528d0b16040ced74d4636046a42d8Mathieu Chartier * Licensed under the Apache License, Version 2.0 (the "License"); 5858f1c5fd5e528d0b16040ced74d4636046a42d8Mathieu Chartier * you may not use this file except in compliance with the License. 6858f1c5fd5e528d0b16040ced74d4636046a42d8Mathieu Chartier * You may obtain a copy of the License at 7858f1c5fd5e528d0b16040ced74d4636046a42d8Mathieu Chartier * 8858f1c5fd5e528d0b16040ced74d4636046a42d8Mathieu Chartier * http://www.apache.org/licenses/LICENSE-2.0 9858f1c5fd5e528d0b16040ced74d4636046a42d8Mathieu Chartier * 10858f1c5fd5e528d0b16040ced74d4636046a42d8Mathieu Chartier * Unless required by applicable law or agreed to in writing, software 11858f1c5fd5e528d0b16040ced74d4636046a42d8Mathieu Chartier * distributed under the License is distributed on an "AS IS" BASIS, 12858f1c5fd5e528d0b16040ced74d4636046a42d8Mathieu Chartier * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 13858f1c5fd5e528d0b16040ced74d4636046a42d8Mathieu Chartier * See the License for the specific language governing permissions and 14858f1c5fd5e528d0b16040ced74d4636046a42d8Mathieu Chartier * limitations under the License. 15858f1c5fd5e528d0b16040ced74d4636046a42d8Mathieu Chartier */ 16858f1c5fd5e528d0b16040ced74d4636046a42d8Mathieu Chartier 172f62cfe690257d516233b399f68d322b1cf8e4f4Hans Boehm// CAUTION: THIS IS NOT A FULLY GENERAL BARRIER API. 182f62cfe690257d516233b399f68d322b1cf8e4f4Hans Boehm 192f62cfe690257d516233b399f68d322b1cf8e4f4Hans Boehm// It may either be used as a "latch" or single-use barrier, or it may be reused under 202f62cfe690257d516233b399f68d322b1cf8e4f4Hans Boehm// very limited conditions, e.g. if only Pass(), but not Wait() is called. Unlike a standard 212f62cfe690257d516233b399f68d322b1cf8e4f4Hans Boehm// latch API, it is possible to initialize the latch to a count of zero, repeatedly call 222f62cfe690257d516233b399f68d322b1cf8e4f4Hans Boehm// Pass() or Wait(), and only then set the count using the Increment() method. Threads at 232f62cfe690257d516233b399f68d322b1cf8e4f4Hans Boehm// a Wait() are only awoken if the count reaches zero AFTER the decrement is applied. 242f62cfe690257d516233b399f68d322b1cf8e4f4Hans Boehm// This works because, also unlike most latch APIs, there is no way to Wait() without 252f62cfe690257d516233b399f68d322b1cf8e4f4Hans Boehm// decrementing the count, and thus nobody can spuriosly wake up on the initial zero. 262f62cfe690257d516233b399f68d322b1cf8e4f4Hans Boehm 27fc0e3219edc9a5bf81b166e82fd5db2796eb6a0dBrian Carlstrom#ifndef ART_RUNTIME_BARRIER_H_ 28fc0e3219edc9a5bf81b166e82fd5db2796eb6a0dBrian Carlstrom#define ART_RUNTIME_BARRIER_H_ 29858f1c5fd5e528d0b16040ced74d4636046a42d8Mathieu Chartier 30700a402244a1a423da4f3ba8032459f4b65fa18fIan Rogers#include <memory> 3176b6167407c2b6f5d40ad895b2793a6b037f54b2Elliott Hughes#include "base/mutex.h" 32858f1c5fd5e528d0b16040ced74d4636046a42d8Mathieu Chartier 33858f1c5fd5e528d0b16040ced74d4636046a42d8Mathieu Chartiernamespace art { 34858f1c5fd5e528d0b16040ced74d4636046a42d8Mathieu Chartier 352f62cfe690257d516233b399f68d322b1cf8e4f4Hans Boehm// TODO: Maybe give this a better name. 36858f1c5fd5e528d0b16040ced74d4636046a42d8Mathieu Chartierclass Barrier { 37858f1c5fd5e528d0b16040ced74d4636046a42d8Mathieu Chartier public: 3893ba893c20532990a430741e0a97212900094e8cBrian Carlstrom explicit Barrier(int count); 39858f1c5fd5e528d0b16040ced74d4636046a42d8Mathieu Chartier virtual ~Barrier(); 40858f1c5fd5e528d0b16040ced74d4636046a42d8Mathieu Chartier 412f62cfe690257d516233b399f68d322b1cf8e4f4Hans Boehm // Pass through the barrier, decrement the count but do not block. 42858f1c5fd5e528d0b16040ced74d4636046a42d8Mathieu Chartier void Pass(Thread* self); 43858f1c5fd5e528d0b16040ced74d4636046a42d8Mathieu Chartier 44858f1c5fd5e528d0b16040ced74d4636046a42d8Mathieu Chartier // Wait on the barrier, decrement the count. 45858f1c5fd5e528d0b16040ced74d4636046a42d8Mathieu Chartier void Wait(Thread* self); 46858f1c5fd5e528d0b16040ced74d4636046a42d8Mathieu Chartier 472f62cfe690257d516233b399f68d322b1cf8e4f4Hans Boehm // The following three calls are only safe if we somehow know that no other thread both 482f62cfe690257d516233b399f68d322b1cf8e4f4Hans Boehm // - has been woken up, and 492f62cfe690257d516233b399f68d322b1cf8e4f4Hans Boehm // - has not left the Wait() or Increment() call. 502f62cfe690257d516233b399f68d322b1cf8e4f4Hans Boehm // If these calls are made in that situation, the offending thread is likely to go back 512f62cfe690257d516233b399f68d322b1cf8e4f4Hans Boehm // to sleep, resulting in a deadlock. 52858f1c5fd5e528d0b16040ced74d4636046a42d8Mathieu Chartier 53858f1c5fd5e528d0b16040ced74d4636046a42d8Mathieu Chartier // Increment the count by delta, wait on condition if count is non zero. 54858f1c5fd5e528d0b16040ced74d4636046a42d8Mathieu Chartier void Increment(Thread* self, int delta); 55858f1c5fd5e528d0b16040ced74d4636046a42d8Mathieu Chartier 560aded089f565008ba5908e395e5914ca4f91f2deDave Allison // Increment the count by delta, wait on condition if count is non zero, with a timeout 570aded089f565008ba5908e395e5914ca4f91f2deDave Allison void Increment(Thread* self, int delta, uint32_t timeout_ms) LOCKS_EXCLUDED(lock_); 580aded089f565008ba5908e395e5914ca4f91f2deDave Allison 592f62cfe690257d516233b399f68d322b1cf8e4f4Hans Boehm // Set the count to a new value. This should only be used if there is no possibility that 602f62cfe690257d516233b399f68d322b1cf8e4f4Hans Boehm // another thread is still in Wait(). See above. 612f62cfe690257d516233b399f68d322b1cf8e4f4Hans Boehm void Init(Thread* self, int count); 622f62cfe690257d516233b399f68d322b1cf8e4f4Hans Boehm 63858f1c5fd5e528d0b16040ced74d4636046a42d8Mathieu Chartier private: 64858f1c5fd5e528d0b16040ced74d4636046a42d8Mathieu Chartier void SetCountLocked(Thread* self, int count) EXCLUSIVE_LOCKS_REQUIRED(lock_); 65858f1c5fd5e528d0b16040ced74d4636046a42d8Mathieu Chartier 66858f1c5fd5e528d0b16040ced74d4636046a42d8Mathieu Chartier // Counter, when this reaches 0 all people blocked on the barrier are signalled. 67858f1c5fd5e528d0b16040ced74d4636046a42d8Mathieu Chartier int count_ GUARDED_BY(lock_); 68858f1c5fd5e528d0b16040ced74d4636046a42d8Mathieu Chartier 69858f1c5fd5e528d0b16040ced74d4636046a42d8Mathieu Chartier Mutex lock_ DEFAULT_MUTEX_ACQUIRED_AFTER; 70858f1c5fd5e528d0b16040ced74d4636046a42d8Mathieu Chartier ConditionVariable condition_ GUARDED_BY(lock_); 71858f1c5fd5e528d0b16040ced74d4636046a42d8Mathieu Chartier}; 72858f1c5fd5e528d0b16040ced74d4636046a42d8Mathieu Chartier 73858f1c5fd5e528d0b16040ced74d4636046a42d8Mathieu Chartier} // namespace art 74fc0e3219edc9a5bf81b166e82fd5db2796eb6a0dBrian Carlstrom#endif // ART_RUNTIME_BARRIER_H_ 75