mirror of https://gitee.com/bigwinds/arangodb
103 lines
3.7 KiB
C++
103 lines
3.7 KiB
C++
////////////////////////////////////////////////////////////////////////////////
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/// DISCLAIMER
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///
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/// Copyright 2014-2016 ArangoDB GmbH, Cologne, Germany
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/// Copyright 2004-2014 triAGENS GmbH, Cologne, Germany
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///
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/// Licensed under the Apache License, Version 2.0 (the "License");
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/// you may not use this file except in compliance with the License.
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/// You may obtain a copy of the License at
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///
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/// http://www.apache.org/licenses/LICENSE-2.0
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///
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/// Unless required by applicable law or agreed to in writing, software
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/// distributed under the License is distributed on an "AS IS" BASIS,
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/// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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/// See the License for the specific language governing permissions and
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/// limitations under the License.
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///
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/// Copyright holder is ArangoDB GmbH, Cologne, Germany
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///
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/// @author Dr. Frank Celler
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/// @author Achim Brandt
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////////////////////////////////////////////////////////////////////////////////
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#ifndef ARANGODB_BASICS_CONDITION_VARIABLE_H
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#define ARANGODB_BASICS_CONDITION_VARIABLE_H 1
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#include <chrono>
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#include "Basics/Common.h"
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#include "Basics/locks.h"
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namespace arangodb {
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namespace basics {
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/// @brief condition variable
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///
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/// A condition variable consists of a condition and a monitor.
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///
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/// There are only two operations that can be applied to a condition variable:
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/// wait and signal. When a thread executes a wait call in the monitor on a
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/// condition variable, it is immediately suspended and put into the waiting
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/// queue of that condition variable. Thus, this thread is suspended and is
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/// waiting for the event that is represented by the condition variable to
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/// occur. As the calling thread is the only thread that is running in the
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/// monitor, it "owns" the monitor lock. When it is put into the waiting queue
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/// of a condition variable, the system will automatically take the monitor lock
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/// back. As a result, the monitor becomes empty and another thread can enter.
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///
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/// Eventually, a thread will cause the event to occur. To indicate a particular
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/// event occurs, a thread calls the signal method on the corresponding
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/// condition variable. At this point, we have two cases to consider. First, if
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/// there are threads waiting on the signaled condition variable, the monitor
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/// will allow one of the waiting threads to resume its execution and give this
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/// thread the monitor lock back. Second, if there is no waiting thread on the
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/// signaled condition variable, this signal is lost as if it never occurs.
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///
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/// Therefore, wait and signal for a condition variable is very similar to the
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/// notification technique of a semaphore: One thread waits on an event and
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/// resumes its execution when another thread causes the event to
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/// occur. However, there are major differences as will be discussed on a later
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/// page.
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class ConditionVariable {
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ConditionVariable(ConditionVariable const&) = delete;
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ConditionVariable& operator=(ConditionVariable const&) = delete;
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public:
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/// @brief constructs a condition variable
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ConditionVariable();
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/// @brief deletes the condition variable
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~ConditionVariable();
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public:
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/// @brief locks the condition variable
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void lock();
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/// @brief releases the lock on the condition variable
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void unlock();
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/// @brief waits for an event
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void wait();
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/// @brief waits for an event with timeout in micro seconds
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/// returns true when the condition was signaled, false on timeout
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bool wait(uint64_t);
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bool wait(std::chrono::microseconds);
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/// @brief signals all waiting threads
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void broadcast();
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/// @brief signals a waiting thread
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void signal();
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private:
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/// @brief condition variable
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TRI_condition_t _condition;
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};
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} // namespace basics
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} // namespace arangodb
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#endif
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