156 lines
4.1 KiB
Markdown
156 lines
4.1 KiB
Markdown
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# 增强信号量功能
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## 概述
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### 简介
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信号量是一个具有原子性的计数器，可以作一把锁，以实现互斥、同步等功能；在多线程环境下使用，可以实现临界区代码不被并发调用或者限制并发的数量。信号量根据种类又可以分为有名信号量和无名信号量。
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`#include <semaphore_ex.h>`
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Inherits from OHOS::NoCopyable
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## 涉及功能
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#### 接口说明
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### OHOS::NamedSemaphore
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| 返回值 | 名称 |
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| ------ | ------------------------------------------------------------ |
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| | **NamedSemaphore**(size_t size)<br/>构造函数(指定信号量初始值) |
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| | **NamedSemaphore**(const std::string&, size_t)<br/>构造函数(指定信号量名字和初始值) |
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| | **~NamedSemaphore**()<br/>析构函数 |
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| bool | **Create**()<br/>创建并初始化有名信号量 |
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| bool | **Unlink**()<br/>将有名信号量文件从系统中删除 |
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| bool | **Open**()<br/>打开一个已经创建的有名信号量文件 |
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| bool | **Close**()<br/>关闭有名信号量 |
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| bool | **Wait**()<br/>等待/获取信号量(信号量 -1) |
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| bool | **TryWait**()<br/>等待/获取信号量(信号量 -1)的接口；非阻塞版 |
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| bool | **TimedWait**(const struct timespec& ts)<br/>等待/获取信号量(信号量 -1)；指定阻塞时间版 |
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| bool | **Post**()<br/>释放信号量(信号量 +1) |
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| int | **GetValue**() const<br/>获取信号的值 |
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### OHOS::Semaphore
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| 返回值 | 名称 |
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| ------ | -------------------------------------------------------- |
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| | **Semaphore**(int value = 1) : count_(value)<br>构造函数 |
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| void | **Wait**()<br/>等待/获取信号量(信号量 -1) |
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| void | **Post**()<br/>释放信号量(信号量 +1) |
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## 使用示例
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1. 示例代码
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```c++
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#include <functional>
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#include <iostream>
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#include <chrono>
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#include "../include/semaphore_ex.h"
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using namespace OHOS;
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using namespace std;
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constexpr int COUNT_MAX = 3;
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constexpr int THREAD_NUM = 2 * COUNT_MAX;
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class WorkSpace
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{
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public:
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WorkSpace(const string &name, int maxSize) : sema(name, maxSize), count(0), max(0)
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{
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}
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bool CreateSema()
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{
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return sema.Create();
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}
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~WorkSpace()
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{
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sema.Close();
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sema.Unlink();
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}
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void Enter()
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{
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sema.Wait();
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count++;
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this_thread::sleep_for(chrono::microseconds(1));
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max = max > count ? max : count;
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count--;
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sema.Post();
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}
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bool Check()
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{
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if (COUNT_MAX >= max) {
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return true;
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}
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return false;
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}
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bool CloseAndUnlink()
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{
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return sema.Close() && sema.Unlink();
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}
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int GetCount()
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{
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return count;
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}
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int GetMax()
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{
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return max;
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}
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private:
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NamedSemaphore sema;
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int count;
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int max;
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};
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int main()
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{
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WorkSpace ws("mysem", COUNT_MAX);
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if (ws.CreateSema()) {
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cout << "NamedSemaphore created success!" << endl;
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} else {
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return 0;
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}
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thread threads[THREAD_NUM];
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for (int i = 0; i < THREAD_NUM; i++) {
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threads[i] = thread(&WorkSpace::Enter, ref(ws));
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}
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for (int i = 0; i < THREAD_NUM; i++) {
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threads[i].join();
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}
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if (ws.Check()) {
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cout << "Semaphore test success!" <<endl;
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}
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cout << "max: " << ws.GetMax() << " count: " << ws.GetCount() << endl;
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ws.CloseAndUnlink();
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}
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```
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2. 测试用例编译运行方法
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- 测试用例代码参见base/test/unittest/common/utils_semaphore_test.cpp
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- 使用开发者自测试框架，使用方法参见：[开发自测试执行框架-测试用例执行](https://gitee.com/openharmony/testfwk_developer_test#%E6%B5%8B%E8%AF%95%E7%94%A8%E4%BE%8B%E6%89%A7%E8%A1%8C)
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- 使用以下具体命令以运行`semaphore_ex.h`对应测试用例
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```bash
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run -t UT -tp utils -ts UtilsSemaphoreTest
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```
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## 常见问题
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