Condition Variables

Condition variables are synchronization primitives that enable threads to wait until a particular condition occurs.

Condition variables are user-mode objects that cannot be shared across processes.

Condition variables enable threads to atomically release a lock and enter the sleeping state.

They can be used with critical sections or slim reader/writer (SRW) locks.

Condition variables support operations that "wake one" or "wake all" waiting threads.

After a thread is woken, it re-acquires the lock it released when the thread entered the sleeping state.

条件变量是能够在特殊条件满足前使线程处于等待状态的同步原语.

条件变量是不能被跨进程共享的用户模式下的同步对象.

条件变量能够使线程原子性释放一个锁同一时候进入sleep 状态. 条件变量和Critical Section Object一起使用.

条件变量支持wake one 或者wake all 等待的线程.

Windows Server 2003 and Windows XP:  Condition variables are not supported.

It is often convenient to use more than one condition variable with the same lock.

For example, an implementation of a reader/writer lock might use a single critical section but separate condition variables for readers and writers.

在同一个锁上面使用条件变量是很实用的.

比方:对于同一个临界区通过把读操作和写操作通过条件变量来分离能够实现读锁,写锁以及读写锁.

The following code implements a producer/consumer queue.

The queue is represented as a bounded circular buffer, and is protected by a critical section.

The code uses two condition variables: one used by producers (BufferNotFull) and one used by consumers (BufferNotEmpty).

The code calls the InitializeConditionVariable function to create the condition variables.

The consumer threads call the SleepConditionVariableCS function to wait for items to be added to the queue and

the WakeConditionVariable function to signal the producer that it is ready for more items.

The producer threads call SleepConditionVariableCS to wait for the consumer to remove items from the queue and

 WakeConditionVariable to signal the consumer that there are more items in the queue.

实现一个生产者/消费者队列.

队列是一个被Critical Section Object 保护的有界限圆形BUFFER.

通过调用InitializeConditionVariable()函数去创建一个条件变量.

消费者调用SleepConditionVariableCS()函数等待有物品被增加到队列中,通过WakeConditionVariable()函数通知生产者生产很多其它的物品.

生产者调用SleepConditionVariableCS()函数等待消费者把物品从队列中移除,通过WakeConditionVariable()函数来通知消费者去消费很多其它的物品.

測试代码:UsingConditionVariables.cpp

#include <windows.h>
#include <stdlib.h>
#include <stdio.h> #define BUFFER_SIZE 10
#define PRODUCER_SLEEP_TIME_MS 500
#define CONSUMER_SLEEP_TIME_MS 2000 LONG Buffer[BUFFER_SIZE];
LONG LastItemProduced;
ULONG QueueSize;
ULONG QueueStartOffset; ULONG TotalItemsProduced;
ULONG TotalItemsConsumed; CONDITION_VARIABLE BufferNotEmpty;
CONDITION_VARIABLE BufferNotFull;
CRITICAL_SECTION BufferLock; BOOL StopRequested; DWORD WINAPI ProducerThreadProc (PVOID p)
{
ULONG ProducerId = (ULONG)(ULONG_PTR)p; while (true)
{
// Produce a new item. Sleep (rand() % PRODUCER_SLEEP_TIME_MS);
//原子锁
ULONG Item = InterlockedIncrement (&LastItemProduced);
//进入临界区,其它线程不能訪问下面被保护的资源
EnterCriticalSection (&BufferLock);
//仅仅有当有界缓冲区满了之后,才通知消费者来消费资源,否则就一直生产物品
while (QueueSize == BUFFER_SIZE && StopRequested == FALSE)
{
// Buffer is full - sleep so consumers can get items.
SleepConditionVariableCS (&BufferNotFull, &BufferLock, INFINITE);
} if (StopRequested == TRUE)
{
LeaveCriticalSection (&BufferLock);
break;
} // Insert the item at the end of the queue and increment size. Buffer[(QueueStartOffset + QueueSize) % BUFFER_SIZE] = Item;
QueueSize++;
TotalItemsProduced++; printf ("Producer %u: item %2d, queue size %2u\r\n", ProducerId, Item, QueueSize);
//离开临界区,其它线程可訪问该临界区
LeaveCriticalSection (&BufferLock); // If a consumer is waiting, wake it. WakeConditionVariable (&BufferNotEmpty);
} printf ("Producer %u exiting\r\n", ProducerId);
return 0;
}
//消费者线程
DWORD WINAPI ConsumerThreadProc (PVOID p)
{
//消费数量
ULONG ConsumerId = (ULONG)(ULONG_PTR)p; while (true)
{ //临界区,当一个线程在获取临界区权利时,其它线程都要等待.
EnterCriticalSection (&BufferLock);
//当前缓存区为零
while (QueueSize == 0 && StopRequested == FALSE)
{
// Buffer is empty - sleep so producers can create items.
//通知生产者进行生产物品.当生产者完毕生产后,则通知消费者来消费
SleepConditionVariableCS (&BufferNotEmpty, &BufferLock, INFINITE);
} if (StopRequested == TRUE && QueueSize == 0)
{
LeaveCriticalSection (&BufferLock);
break;
} // Consume the first available item. LONG Item = Buffer[QueueStartOffset]; QueueSize--;
QueueStartOffset++;
TotalItemsConsumed++; if (QueueStartOffset == BUFFER_SIZE)
{
QueueStartOffset = 0;
} printf ("Consumer %u: item %2d, queue size %2u\r\n",
ConsumerId, Item, QueueSize); LeaveCriticalSection (&BufferLock); // If a producer is waiting, wake it. WakeConditionVariable (&BufferNotFull); // Simulate processing of the item. Sleep (rand() % CONSUMER_SLEEP_TIME_MS);
} printf ("Consumer %u exiting\r\n", ConsumerId);
return 0;
} int main ( void )
{ InitializeConditionVariable (&BufferNotEmpty);
InitializeConditionVariable (&BufferNotFull); InitializeCriticalSection (&BufferLock); DWORD id;
HANDLE hProducer1 = CreateThread (NULL, 0, ProducerThreadProc, (PVOID)1, 0, &id);
HANDLE hConsumer1 = CreateThread (NULL, 0, ConsumerThreadProc, (PVOID)1, 0, &id);
HANDLE hConsumer2 = CreateThread (NULL, 0, ConsumerThreadProc, (PVOID)2, 0, &id); puts ("Press enter to stop...");
getchar(); EnterCriticalSection (&BufferLock);
StopRequested = TRUE;
LeaveCriticalSection (&BufferLock); WakeAllConditionVariable (&BufferNotFull);
WakeAllConditionVariable (&BufferNotEmpty); WaitForSingleObject (hProducer1, INFINITE);
WaitForSingleObject (hConsumer1, INFINITE);
WaitForSingleObject (hConsumer2, INFINITE); printf ("TotalItemsProduced: %u, TotalItemsConsumed: %u\r\n",
TotalItemsProduced, TotalItemsConsumed);
return 0;
}

Condition Variables的更多相关文章

  1. 使用Condition Variables 实现一个线程安全队列

    使用Condition Variables实现一个线程安全队列 测试机: i7-4800MQ .7GHz, logical core, physical core, 8G memory, 256GB ...

  2. 深入解析条件变量(condition variables)

    深入解析条件变量 什么是条件变量(condition variables) 引用APUE中的一句话: Condition variables are another synchronization m ...

  3. 并行编程条件变量(posix condition variables)

    在整理Java LockSupport.park()东方的,我看到了"Spurious wakeup",通过重新梳理. 首先,可以在<UNIX级别编程环境>在样本: # ...

  4. [development][C] 条件变量(condition variables)的应用场景是什么

    产生这个问题的起因是这样的: ‎[:] ‎<‎tong‎>‎ lilydjwg: 主线程要启动N个子线程, 一个局部变量作为把同样的参数传入每一个子线程. 子线程在开始的十行会处理完参数. ...

  5. 4.锁--并行编程之条件变量(posix condition variables)

    在整理Java LockSupport.park()的东东.看到了个"Spurious wakeup".又一次梳理下. 首先来个<UNIX环境高级编程>里的样例: [c ...

  6. c++11多线程记录6:条件变量(condition variables)

    https://www.youtube.com/watch?v=13dFggo4t_I视频地址 实例1 考虑这样一个场景:存在一个全局队列deque,线程A向deque中推入数据(写),线程B从deq ...

  7. 第8章 用户模式下的线程同步(4)_条件变量(Condition Variable)

    8.6 条件变量(Condition Variables)——可利用临界区或SRWLock锁来实现 8.6.1 条件变量的使用 (1)条件变量机制就是为了简化 “生产者-消费者”问题而设计的一种线程同 ...

  8. java线程并发控制:ReentrantLock Condition使用详解

    本文摘自:http://outofmemory.cn/java/java.util.concurrent/lock-reentrantlock-condition java的java.util.con ...

  9. android分析之Condition

    Condition的含义是条件变量,其实现依赖于系统,一般都要配合Mutex使用,使用步骤为:给mutex上锁(Lock),调用wait等待"条件"发生,如果没有发生则re-wai ...

随机推荐

  1. FIR滤波原理及verilog设计

    FIR(Finite Impulse Response)Filter:有限冲激响应滤波器,又称为非递归线性滤波器. FIR滤波器的冲击响应是一个值为滤波器抽头系数的采样序列,其脉冲响应由有限个采样值构 ...

  2. [leetcode]Edit Distance @ Python

    原题地址:https://oj.leetcode.com/problems/edit-distance/ 题意: Given two words word1 and word2, find the m ...

  3. Mediator 中介者 MD

    中介者模式 简介 用一个中介者对象封装一系列的对象交互,中介者使各对象不需要显示地相互作用,从而使耦合松散,而且可以独立地改变它们之间的交互. 中介者模式也称为调解者模式或者调停者模式. 当程序存在大 ...

  4. java log4j日志配置

    1.首先看pom.xml文件,需要以下配置 <dependency> <groupId>log4j</groupId> <artifactId>log4 ...

  5. 大数据开发实战:Spark Streaming流计算开发

    1.背景介绍 Storm以及离线数据平台的MapReduce和Hive构成了Hadoop生态对实时和离线数据处理的一套完整处理解决方案.除了此套解决方案之外,还有一种非常流行的而且完整的离线和 实时数 ...

  6. 条件随机场(CRF)原理和实现

    版权声明:作者:金良山庄,欲联系请评论博客或私信,个人主页:http://www.jinliangxu.com/,CSDN博客: http://blog.csdn.net/u012176591   目 ...

  7. HMM与分词、词性标注、命名实体识别

    http://www.hankcs.com/nlp/hmm-and-segmentation-tagging-named-entity-recognition.html HMM(隐马尔可夫模型)是用来 ...

  8. 条件随机场CRF HMM,MEMM的区别

    http://blog.sina.com.cn/s/blog_605f5b4f010109z3.html 首先,CRF,HMM(隐马模型),MEMM(最大熵隐马模型)都常用来做序列标注的建模,像词性标 ...

  9. [转]shell脚本每行的执行顺序是怎样

    原文:https://blog.csdn.net/weixin_42609121/article/details/83028000 ---------------------------------- ...

  10. 自己定义View时,用到Paint Canvas的一些温故,简单的帧动画(动画一 ,&quot;掏粪男孩Gif&quot;顺便再提提onWindowFocusChanged)

    转载请注明出处:王亟亟的大牛之路 之前在绘画的过程中提到了静态的旋转啊,缩放啊,平移等一些效果.那么自己定义的View当然也有动态的效果也就是我们的Animation.经常使用的有三种 View An ...