92 lines
2.8 KiB
C++
92 lines
2.8 KiB
C++
/*
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* Copyright (c) 2021-2023 Huawei Device Co., Ltd.
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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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/**
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* @file semaphore_ex.h
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*
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* @brief Provides interfaces of semaphores in c_utils,
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* including nameless and named semaphores.
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*
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* A semaphore is an atomic counter, which can act as a lock
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* to achieve mutual exclusion, synchronization, and other functions.
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* Used in a multithreaded environment, it prevents concurrent
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* calling of a critical piece of code or restricts the maximum number
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* of threads entering the code section.
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*/
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#ifndef SEMAPHORE_EX_H
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#define SEMAPHORE_EX_H
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#include "nocopyable.h"
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#include <iostream>
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#include <thread>
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#include <mutex>
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#include <condition_variable>
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#include <string>
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#include <ctime> // timespec since c11
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namespace OHOS {
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/**
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* @brief Provides interfaces for operating semaphores.
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*
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* A semaphore is a counter used to implement functions, such as
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* mutual exclusion between processes/threads, synchronization, and more.
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* The difference between nameless semaphores and named semaphores lies
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* in the form of creation and destruction.
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* Semaphores exist only in memory. The process/thread
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* using the semaphore must access the memory where the semaphore is located.
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* Therefore, the nameless semaphore can only be in the thread of
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* the same process, or threads in different processes that have mapped
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* the same memory to their address space, that is, the nameless semaphores
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* can only be accessed through shared memory.
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*/
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class Semaphore : public NoCopyable {
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public:
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/**
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* @brief A constructor used to create a semaphore object.
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*
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* @param Value Indicates the initial value of the semaphore object.
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*/
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explicit Semaphore(int value = 1) : count_(value) {}
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/**
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* @brief Acquires the semaphore.
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*
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* If the current semaphore count >= 0, the current thread continues.
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* If the current semaphore count < 0, the current thread will be blocked.
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*/
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void Wait();
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/**
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* @brief Releases the semaphore.
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*
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* If the current semaphore count > 0, there is no blocked thread.
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* If the current semaphore count <= 0, there are still
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* blocked threads. Then this method will wake one of them up.
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*/
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void Post();
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private:
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int count_; // Initial value of the semaphore object.
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std::mutex mutex_;
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std::condition_variable cv_;
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};
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} // OHOS
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#endif
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