| // Licensed to the Apache Software Foundation (ASF) under one |
| // or more contributor license agreements. See the NOTICE file |
| // distributed with this work for additional information |
| // regarding copyright ownership. The ASF licenses this file |
| // to you 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. |
| #ifndef KUDU_UTIL_COUNTDOWN_LATCH_H |
| #define KUDU_UTIL_COUNTDOWN_LATCH_H |
| |
| #include "kudu/gutil/macros.h" |
| #include "kudu/util/condition_variable.h" |
| #include "kudu/util/monotime.h" |
| #include "kudu/util/mutex.h" |
| #include "kudu/util/thread_restrictions.h" |
| |
| namespace kudu { |
| |
| // This is a C++ implementation of the Java CountDownLatch |
| // class. |
| // See http://docs.oracle.com/javase/6/docs/api/java/util/concurrent/CountDownLatch.html |
| class CountDownLatch { |
| public: |
| // Initialize the latch with the given initial count. |
| explicit CountDownLatch(int count) |
| : cond_(&lock_), |
| count_(count) { |
| } |
| |
| // Decrement the count of this latch by 'amount' |
| // If the new count is less than or equal to zero, then all waiting threads are woken up. |
| // If the count is already zero, this has no effect. |
| void CountDown(int amount) { |
| DCHECK_GE(amount, 0); |
| MutexLock lock(lock_); |
| if (count_ == 0) { |
| return; |
| } |
| |
| if (amount >= count_) { |
| count_ = 0; |
| } else { |
| count_ -= amount; |
| } |
| |
| if (count_ == 0) { |
| // Latch has triggered. |
| cond_.Broadcast(); |
| } |
| } |
| |
| // Decrement the count of this latch. |
| // If the new count is zero, then all waiting threads are woken up. |
| // If the count is already zero, this has no effect. |
| void CountDown() { |
| CountDown(1); |
| } |
| |
| // Wait until the count on the latch reaches zero. |
| // If the count is already zero, this returns immediately. |
| void Wait() const { |
| ThreadRestrictions::AssertWaitAllowed(); |
| MutexLock lock(lock_); |
| while (count_ > 0) { |
| cond_.Wait(); |
| } |
| } |
| |
| // Waits for the count on the latch to reach zero, or until 'until' time is reached. |
| // Returns true if the count became zero, false otherwise. |
| bool WaitUntil(const MonoTime& when) const { |
| ThreadRestrictions::AssertWaitAllowed(); |
| return WaitFor(when - MonoTime::Now()); |
| } |
| |
| // Waits for the count on the latch to reach zero, or until 'delta' time elapses. |
| // Returns true if the count became zero, false otherwise. |
| bool WaitFor(const MonoDelta& delta) const { |
| ThreadRestrictions::AssertWaitAllowed(); |
| MutexLock lock(lock_); |
| while (count_ > 0) { |
| if (!cond_.TimedWait(delta)) { |
| return false; |
| } |
| } |
| return true; |
| } |
| |
| // Reset the latch with the given count. This is equivalent to reconstructing |
| // the latch. If 'count' is 0, and there are currently waiters, those waiters |
| // will be triggered as if you counted down to 0. |
| void Reset(uint64_t count) { |
| MutexLock lock(lock_); |
| count_ = count; |
| if (count_ == 0) { |
| // Awake any waiters if we reset to 0. |
| cond_.Broadcast(); |
| } |
| } |
| |
| uint64_t count() const { |
| MutexLock lock(lock_); |
| return count_; |
| } |
| |
| private: |
| DISALLOW_COPY_AND_ASSIGN(CountDownLatch); |
| mutable Mutex lock_; |
| ConditionVariable cond_; |
| |
| uint64_t count_; |
| }; |
| |
| // Utility class which calls latch->CountDown() in its destructor. |
| class CountDownOnScopeExit { |
| public: |
| explicit CountDownOnScopeExit(CountDownLatch *latch) : latch_(latch) {} |
| ~CountDownOnScopeExit() { |
| latch_->CountDown(); |
| } |
| |
| private: |
| DISALLOW_COPY_AND_ASSIGN(CountDownOnScopeExit); |
| |
| CountDownLatch *latch_; |
| }; |
| |
| } // namespace kudu |
| #endif |