多线程同步与并发访问共享资源工具—Lock、Monitor、Mutex、Semaphore
“线程同步”的含义
当一个进程启动了多个线程时,如果需要控制这些线程的推进顺序(比如A线程必须等待B和C线程执行完毕之后才能继续执行),则称这些线程需要进行“线程同步(thread synchronization)”。
线程同步的道理虽然简单,但却是给多线程开发带来复杂性的根源之一。当线程同步不好时,有可能会出现一种特殊的情形——死锁(Dead Lock)。
“死锁”的含义
死锁表示系统进入了一个僵化状态,所有线程都没有执行完毕,但却谁也没法继续执行。究其根源,是因为“进程推进顺序不当”和“资源共享”。如例:
1)进程推进顺序不当造成死锁
- using System;
- using System.Collections.Generic;
- using System.Text;
- using System.Threading;
- namespace JoinLeadToDeadlock
- {
- class Program
- {
- static Thread mainThread;
- static void Main(string[] args)
- {
- Console.WriteLine("主线程开始运行");
- mainThread = Thread.CurrentThread;
- Thread ta = new Thread(new ThreadStart(ThreadAMethod));
- ta.Start(); //线程A开始执行
- Console.WriteLine("主线程等待线程A结束……");
- ta.Join(); //等待线程A结束
- Console.WriteLine("主线程退出");
- }
- static void ThreadAMethod()
- {
- for (int i = 0; i < 10; i++)
- {
- Console.WriteLine(Convert.ToString(i) + ": 线程A正在执行");
- Thread.Sleep(1000);
- }
- Console.WriteLine("线程A等待主线程退出……");
- mainThread.Join(); //等待主线程结束
- }
- }
- }
- using System;
- using System.Collections.Generic;
- using System.Text;
- using System.Threading;
- namespace JoinLeadToDeadlock
- {
- class Program
- {
- static Thread mainThread;
- static void Main(string[] args)
- {
- Console.WriteLine("主线程开始运行");
- mainThread = Thread.CurrentThread;
- Thread ta = new Thread(new ThreadStart(ThreadAMethod));
- ta.Start(); //线程A开始执行
- Console.WriteLine("主线程等待线程A结束……");
- ta.Join(); //等待线程A结束
- Console.WriteLine("主线程退出");
- }
- static void ThreadAMethod()
- {
- for (int i = 0; i < 10; i++)
- {
- Console.WriteLine(Convert.ToString(i) + ": 线程A正在执行");
- Thread.Sleep(1000);
- }
- Console.WriteLine("线程A等待主线程退出……");
- mainThread.Join(); //等待主线程结束
- }
- }
- }
using System; using System.Collections.Generic; using System.Text; using System.Threading; namespace JoinLeadToDeadlock { class Program { static Thread mainThread; static void Main(string[] args) { Console.WriteLine("主线程开始运行"); mainThread = Thread.CurrentThread; Thread ta = new Thread(new ThreadStart(ThreadAMethod)); ta.Start(); //线程A开始执行 Console.WriteLine("主线程等待线程A结束……"); ta.Join(); //等待线程A结束 Console.WriteLine("主线程退出"); } static void ThreadAMethod() { for (int i = 0; i < 10; i++) { Console.WriteLine(Convert.ToString(i) + ": 线程A正在执行"); Thread.Sleep(1000); } Console.WriteLine("线程A等待主线程退出……"); mainThread.Join(); //等待主线程结束 } } }
在该例中,主线程mainThread先开始执行,然后启动线程ta,线程ta执行结束前又要等待mainThread线程执行结束,这样就出现了“交叉等待”的局面,必然死锁!
2)共享资源造成死锁
所谓“共享资源”,指的是多个线程可以同时访问的数据结构、文件等信息实体。
- using System;
- using System.Collections.Generic;
- using System.Text;
- using System.Threading;
- namespace SharedResourceLeadToDeadlock
- {
- class Program
- {
- //共享资源
- static SharedResource R1 = new SharedResource();
- static SharedResource R2 = new SharedResource();
- static void Main(string[] args)
- {
- Thread th1 = new Thread(UseSharedResource1);
- Thread th2 = new Thread(UseSharedResource2);
- th1.Start();
- th2.Start();
- //等待两线程运行结束
- th1.Join();
- th2.Join();
- }
- static void UseSharedResource1()
- {
- System.Console.WriteLine("线程{0}申请使用资源R1", Thread.CurrentThread.ManagedThreadId);
- Monitor.Enter(R1); //对R1加锁
- System.Console.WriteLine("线程{0}独占使用资源R1", Thread.CurrentThread.ManagedThreadId);
- Thread.Sleep(1000);
- System.Console.WriteLine("线程{0}申请使用资源R2", Thread.CurrentThread.ManagedThreadId);
- Monitor.Enter(R2); //对R2加锁
- System.Console.WriteLine("线程{0}独占使用资源R2", Thread.CurrentThread.ManagedThreadId);
- Thread.Sleep(1000);
- System.Console.WriteLine("线程{0}资源R2使用完毕,放弃", Thread.CurrentThread.ManagedThreadId);
- Monitor.Exit(R2); //对R2解锁
- System.Console.WriteLine("线程{0}资源R1使用完毕,放弃", Thread.CurrentThread.ManagedThreadId);
- Monitor.Exit(R1); //对R1解锁
- }
- static void UseSharedResource2()
- {
- System.Console.WriteLine("线程{0}申请使用资源R2", Thread.CurrentThread.ManagedThreadId);
- Monitor.Enter(R2); //对R2加锁
- System.Console.WriteLine("线程{0}独占使用资源R2", Thread.CurrentThread.ManagedThreadId);
- Thread.Sleep(500);
- System.Console.WriteLine("线程{0}申请使用资源R1", Thread.CurrentThread.ManagedThreadId);
- Monitor.Enter(R1); //对R1加锁
- System.Console.WriteLine("线程{0}独占使用资源R1", Thread.CurrentThread.ManagedThreadId);
- Thread.Sleep(500);
- System.Console.WriteLine("线程{0}资源R1使用完毕,放弃", Thread.CurrentThread.ManagedThreadId);
- Monitor.Exit(R1); //对R1解锁
- System.Console.WriteLine("线程{0}资源R2使用完毕,放弃", Thread.CurrentThread.ManagedThreadId);
- Monitor.Exit(R2); //对R2解锁
- }
- }
- class SharedResource
- {
- }
- }
- using System;
- using System.Collections.Generic;
- using System.Text;
- using System.Threading;
- namespace SharedResourceLeadToDeadlock
- {
- class Program
- {
- //共享资源
- static SharedResource R1 = new SharedResource();
- static SharedResource R2 = new SharedResource();
- static void Main(string[] args)
- {
- Thread th1 = new Thread(UseSharedResource1);
- Thread th2 = new Thread(UseSharedResource2);
- th1.Start();
- th2.Start();
- //等待两线程运行结束
- th1.Join();
- th2.Join();
- }
- static void UseSharedResource1()
- {
- System.Console.WriteLine("线程{0}申请使用资源R1", Thread.CurrentThread.ManagedThreadId);
- Monitor.Enter(R1); //对R1加锁
- System.Console.WriteLine("线程{0}独占使用资源R1", Thread.CurrentThread.ManagedThreadId);
- Thread.Sleep(1000);
- System.Console.WriteLine("线程{0}申请使用资源R2", Thread.CurrentThread.ManagedThreadId);
- Monitor.Enter(R2); //对R2加锁
- System.Console.WriteLine("线程{0}独占使用资源R2", Thread.CurrentThread.ManagedThreadId);
- Thread.Sleep(1000);
- System.Console.WriteLine("线程{0}资源R2使用完毕,放弃", Thread.CurrentThread.ManagedThreadId);
- Monitor.Exit(R2); //对R2解锁
- System.Console.WriteLine("线程{0}资源R1使用完毕,放弃", Thread.CurrentThread.ManagedThreadId);
- Monitor.Exit(R1); //对R1解锁
- }
- static void UseSharedResource2()
- {
- System.Console.WriteLine("线程{0}申请使用资源R2", Thread.CurrentThread.ManagedThreadId);
- Monitor.Enter(R2); //对R2加锁
- System.Console.WriteLine("线程{0}独占使用资源R2", Thread.CurrentThread.ManagedThreadId);
- Thread.Sleep(500);
- System.Console.WriteLine("线程{0}申请使用资源R1", Thread.CurrentThread.ManagedThreadId);
- Monitor.Enter(R1); //对R1加锁
- System.Console.WriteLine("线程{0}独占使用资源R1", Thread.CurrentThread.ManagedThreadId);
- Thread.Sleep(500);
- System.Console.WriteLine("线程{0}资源R1使用完毕,放弃", Thread.CurrentThread.ManagedThreadId);
- Monitor.Exit(R1); //对R1解锁
- System.Console.WriteLine("线程{0}资源R2使用完毕,放弃", Thread.CurrentThread.ManagedThreadId);
- Monitor.Exit(R2); //对R2解锁
- }
- }
- class SharedResource
- {
- }
- }
using System; using System.Collections.Generic; using System.Text; using System.Threading; namespace SharedResourceLeadToDeadlock { class Program { //共享资源 static SharedResource R1 = new SharedResource(); static SharedResource R2 = new SharedResource(); static void Main(string[] args) { Thread th1 = new Thread(UseSharedResource1); Thread th2 = new Thread(UseSharedResource2); th1.Start(); th2.Start(); //等待两线程运行结束 th1.Join(); th2.Join(); } static void UseSharedResource1() { System.Console.WriteLine("线程{0}申请使用资源R1", Thread.CurrentThread.ManagedThreadId); Monitor.Enter(R1); //对R1加锁 System.Console.WriteLine("线程{0}独占使用资源R1", Thread.CurrentThread.ManagedThreadId); Thread.Sleep(1000); System.Console.WriteLine("线程{0}申请使用资源R2", Thread.CurrentThread.ManagedThreadId); Monitor.Enter(R2); //对R2加锁 System.Console.WriteLine("线程{0}独占使用资源R2", Thread.CurrentThread.ManagedThreadId); Thread.Sleep(1000); System.Console.WriteLine("线程{0}资源R2使用完毕,放弃", Thread.CurrentThread.ManagedThreadId); Monitor.Exit(R2); //对R2解锁 System.Console.WriteLine("线程{0}资源R1使用完毕,放弃", Thread.CurrentThread.ManagedThreadId); Monitor.Exit(R1); //对R1解锁 } static void UseSharedResource2() { System.Console.WriteLine("线程{0}申请使用资源R2", Thread.CurrentThread.ManagedThreadId); Monitor.Enter(R2); //对R2加锁 System.Console.WriteLine("线程{0}独占使用资源R2", Thread.CurrentThread.ManagedThreadId); Thread.Sleep(500); System.Console.WriteLine("线程{0}申请使用资源R1", Thread.CurrentThread.ManagedThreadId); Monitor.Enter(R1); //对R1加锁 System.Console.WriteLine("线程{0}独占使用资源R1", Thread.CurrentThread.ManagedThreadId); Thread.Sleep(500); System.Console.WriteLine("线程{0}资源R1使用完毕,放弃", Thread.CurrentThread.ManagedThreadId); Monitor.Exit(R1); //对R1解锁 System.Console.WriteLine("线程{0}资源R2使用完毕,放弃", Thread.CurrentThread.ManagedThreadId); Monitor.Exit(R2); //对R2解锁 } } class SharedResource { } }
在该例中,线程th1执行时先申请使用R1,然后再申请使用R2,而线程th2执行时先申请R2,然后再申请R1,这样对于线程th1和th2,就会造成各自拥有一个对方需要的资源部释放,而又同时申请一个对方已经占有的资源,必然会造成死锁。
多线程数据存取错误
当多个线程访问同一个数据时,如果不对读和写的顺序作出限定,例如一个线程正在读而另一个数据尝试写,则读数据的线程得到的数据就可能出错。这也是多线程带来的问题。如例:
- using System;
- using System.Collections.Generic;
- using System.Text;
- using System.Threading;
- namespace SharedResourceLeadToDataError
- {
- class Program
- {
- static void Main(string[] args)
- {
- Thread[] ths = new Thread[4];
- for (int i = 0; i < 4; i++)
- {
- ths[i]=new Thread(increaseCount);
- ths[i].Start();
- }
- System.Console.ReadKey();
- }
- static void increaseCount()
- {
- Random ran = new Random();
- Thread.Sleep(ran.Next(100, 5000));
- int beginNum = SharedResource.Count;
- System.Console.WriteLine("线程 {0} 读到的起始值为 {1} ", Thread.CurrentThread.ManagedThreadId, beginNum );
- for (int i = 0; i < 10000; i++)
- {
- beginNum ++;
- }
- SharedResource.Count = beginNum;
- System.Console.WriteLine("线程 {0} 结束,SharedResource.Count={1}", Thread.CurrentThread.ManagedThreadId,SharedResource.Count);
- }
- }
- class SharedResource
- {
- public static int Count = 0;
- }
- }
- using System;
- using System.Collections.Generic;
- using System.Text;
- using System.Threading;
- namespace SharedResourceLeadToDataError
- {
- class Program
- {
- static void Main(string[] args)
- {
- Thread[] ths = new Thread[4];
- for (int i = 0; i < 4; i++)
- {
- ths[i]=new Thread(increaseCount);
- ths[i].Start();
- }
- System.Console.ReadKey();
- }
- static void increaseCount()
- {
- Random ran = new Random();
- Thread.Sleep(ran.Next(100, 5000));
- int beginNum = SharedResource.Count;
- System.Console.WriteLine("线程 {0} 读到的起始值为 {1} ", Thread.CurrentThread.ManagedThreadId, beginNum );
- for (int i = 0; i < 10000; i++)
- {
- beginNum ++;
- }
- SharedResource.Count = beginNum;
- System.Console.WriteLine("线程 {0} 结束,SharedResource.Count={1}", Thread.CurrentThread.ManagedThreadId,SharedResource.Count);
- }
- }
- class SharedResource
- {
- public static int Count = 0;
- }
- }
using System; using System.Collections.Generic; using System.Text; using System.Threading; namespace SharedResourceLeadToDataError { class Program { static void Main(string[] args) { Thread[] ths = new Thread[4]; for (int i = 0; i < 4; i++) { ths[i]=new Thread(increaseCount); ths[i].Start(); } System.Console.ReadKey(); } static void increaseCount() { Random ran = new Random(); Thread.Sleep(ran.Next(100, 5000)); int beginNum = SharedResource.Count; System.Console.WriteLine("线程 {0} 读到的起始值为 {1} ", Thread.CurrentThread.ManagedThreadId, beginNum ); for (int i = 0; i < 10000; i++) { beginNum ++; } SharedResource.Count = beginNum; System.Console.WriteLine("线程 {0} 结束,SharedResource.Count={1}", Thread.CurrentThread.ManagedThreadId,SharedResource.Count); } } class SharedResource { public static int Count = 0; } }
四个线程同时读写共享变量ShareResource.Count,由于未对读写进行控制,所以必然会造成数据存取错误!
线程同步与并发访问控制手段
正如为了解决车辆交通问题,人们建立了红绿灯的交通控制手段一样,可以为线程设定一套控制机制,以实现线程间的同步,以及保证以正确的顺序来访问共享资源。为了保护应用程序的资源不被破坏,为多线程程序提供了三种加锁的机制,分别是:Monitor类、Lock关键字和Mutex类。
1、Monitor类
(1)使用方法
- Monitor对象的Enter方法可用于向共享资源申请一把“独占锁”。当一个线程拥有特定共享资源的独占锁时,尝试访问同一共享资源的其他线程只能等待。
- Monitor对象的Exit方法用于释放锁。
- 要注意:Enter与Exit方法必须严格配对,否则,有可能出现死锁情况。
- Monitor可以锁定单个对象,也可以锁定一个类型的静态字段或属性
1).Monitor.Enter(共享资源对象);
2).Monitor.Enter(typeof(共享资源类型));
2).Monitor.Enter(typeof(共享资源类型));
- using System;
- using System.Collections.Generic;
- using System.Text;
- using System.Threading;
- //展示用Monitor访问共享资源
- namespace UseMonitor1
- {
- class Program
- {
- static void Main(string[] args)
- {
- SharedResource obj = new SharedResource();
- Thread[] ths = new Thread[4];
- for (int i = 0; i < 4; i++)
- {
- ths[i] = new Thread(increaseCount);
- ths[i].Start(obj);
- }
- System.Console.ReadKey();
- }
- static void increaseCount(Object obj)
- {
- //访问实例字段
- VisitDynamicField(obj);
- //访问静态字段
- VisitStaticField();
- }
- //访问静态字段
- private static void VisitStaticField()
- {
- //访问静态字段
- Monitor.Enter(typeof(SharedResource));
- int beginNumber = SharedResource.StaticCount;
- System.Console.WriteLine("线程 {0} 读到的StaticCount起始值为 {1} ", Thread.CurrentThread.ManagedThreadId, beginNumber);
- for (int i = 0; i < 10000; i++)
- {
- beginNumber++;
- }
- SharedResource.StaticCount = beginNumber;
- System.Console.WriteLine("线程 {0} 结束, SharedResource.StaticCount={1}",
- Thread.CurrentThread.ManagedThreadId, SharedResource.StaticCount);
- Monitor.Exit(typeof(SharedResource));
- }
- //访问实例字段
- private static void VisitDynamicField(Object obj)
- {
- Monitor.Enter(obj);
- int beginNumber = (obj as SharedResource).DynamicCount;
- System.Console.WriteLine("线程 {0} 读到的DynamicCount起始值为 {1} ", Thread.CurrentThread.ManagedThreadId, beginNumber);
- for (int i = 0; i < 10000; i++)
- {
- beginNumber++;
- }
- (obj as SharedResource).DynamicCount = beginNumber;
- System.Console.WriteLine("线程 {0} 结束,Obj.DynamicCount={1}",
- Thread.CurrentThread.ManagedThreadId, (obj as SharedResource).DynamicCount);
- Monitor.Exit(obj);
- }
- }
- //共享资源类
- class SharedResource
- {
- public int DynamicCount = 0; //多线程共享的实例字段
- public static int StaticCount = 0; //多线程共享的静态字段
- }
- }
- using System;
- using System.Collections.Generic;
- using System.Text;
- using System.Threading;
- //展示用Monitor访问共享资源
- namespace UseMonitor1
- {
- class Program
- {
- static void Main(string[] args)
- {
- SharedResource obj = new SharedResource();
- Thread[] ths = new Thread[4];
- for (int i = 0; i < 4; i++)
- {
- ths[i] = new Thread(increaseCount);
- ths[i].Start(obj);
- }
- System.Console.ReadKey();
- }
- static void increaseCount(Object obj)
- {
- //访问实例字段
- VisitDynamicField(obj);
- //访问静态字段
- VisitStaticField();
- }
- //访问静态字段
- private static void VisitStaticField()
- {
- //访问静态字段
- Monitor.Enter(typeof(SharedResource));
- int beginNumber = SharedResource.StaticCount;
- System.Console.WriteLine("线程 {0} 读到的StaticCount起始值为 {1} ", Thread.CurrentThread.ManagedThreadId, beginNumber);
- for (int i = 0; i < 10000; i++)
- {
- beginNumber++;
- }
- SharedResource.StaticCount = beginNumber;
- System.Console.WriteLine("线程 {0} 结束, SharedResource.StaticCount={1}",
- Thread.CurrentThread.ManagedThreadId, SharedResource.StaticCount);
- Monitor.Exit(typeof(SharedResource));
- }
- //访问实例字段
- private static void VisitDynamicField(Object obj)
- {
- Monitor.Enter(obj);
- int beginNumber = (obj as SharedResource).DynamicCount;
- System.Console.WriteLine("线程 {0} 读到的DynamicCount起始值为 {1} ", Thread.CurrentThread.ManagedThreadId, beginNumber);
- for (int i = 0; i < 10000; i++)
- {
- beginNumber++;
- }
- (obj as SharedResource).DynamicCount = beginNumber;
- System.Console.WriteLine("线程 {0} 结束,Obj.DynamicCount={1}",
- Thread.CurrentThread.ManagedThreadId, (obj as SharedResource).DynamicCount);
- Monitor.Exit(obj);
- }
- }
- //共享资源类
- class SharedResource
- {
- public int DynamicCount = 0; //多线程共享的实例字段
- public static int StaticCount = 0; //多线程共享的静态字段
- }
- }
using System; using System.Collections.Generic; using System.Text; using System.Threading; //展示用Monitor访问共享资源 namespace UseMonitor1 { class Program { static void Main(string[] args) { SharedResource obj = new SharedResource(); Thread[] ths = new Thread[4]; for (int i = 0; i < 4; i++) { ths[i] = new Thread(increaseCount); ths[i].Start(obj); } System.Console.ReadKey(); } static void increaseCount(Object obj) { //访问实例字段 VisitDynamicField(obj); //访问静态字段 VisitStaticField(); } //访问静态字段 private static void VisitStaticField() { //访问静态字段 Monitor.Enter(typeof(SharedResource)); int beginNumber = SharedResource.StaticCount; System.Console.WriteLine("线程 {0} 读到的StaticCount起始值为 {1} ", Thread.CurrentThread.ManagedThreadId, beginNumber); for (int i = 0; i < 10000; i++) { beginNumber++; } SharedResource.StaticCount = beginNumber; System.Console.WriteLine("线程 {0} 结束, SharedResource.StaticCount={1}", Thread.CurrentThread.ManagedThreadId, SharedResource.StaticCount); Monitor.Exit(typeof(SharedResource)); } //访问实例字段 private static void VisitDynamicField(Object obj) { Monitor.Enter(obj); int beginNumber = (obj as SharedResource).DynamicCount; System.Console.WriteLine("线程 {0} 读到的DynamicCount起始值为 {1} ", Thread.CurrentThread.ManagedThreadId, beginNumber); for (int i = 0; i < 10000; i++) { beginNumber++; } (obj as SharedResource).DynamicCount = beginNumber; System.Console.WriteLine("线程 {0} 结束,Obj.DynamicCount={1}", Thread.CurrentThread.ManagedThreadId, (obj as SharedResource).DynamicCount); Monitor.Exit(obj); } } //共享资源类 class SharedResource { public int DynamicCount = 0; //多线程共享的实例字段 public static int StaticCount = 0; //多线程共享的静态字段 } }Monitor类的使用模板:
Monitor.Enter(共享资源对象); //申请对象锁
//得到了对象锁,可以对共享资源进行访问,
//其他线程只能等待
//访问共享资源
//对共享资源的访问完成,释放对象锁,
//让其他线程有机会访问共享资源
Monitor.Exit(obj);
(2)Monitor的特殊注意之处:
Monitor一般只用于访问引用类型的共享资源,如果将其施加于值类型变量,则值类型变量将会被装箱,而当调用Exit方法时,虽然是同一个值类型变量,但实际上此值类型变量又会被第二次装箱,这将导致Enter方法所访问的对象与Exit方法所访问的不是同一个,Monitor对象将会引发SynchronizationLockException。
因此,不要将Monitor用于值类型!
因此,不要将Monitor用于值类型!
(3) Monitor.Wait()和Monitor.Pulse()
Wait()释放对象上的锁,以便允许其他线程锁定和访问该对象。在其他线程访问对象时,调用线程将等待。
Pulse(),PulseAll()向一个或多个等待线程发送信号。该信号通知等待线程锁定对象的状态已更改,并且锁的所有者准备释放该锁。等待线程被放置在对象的就绪队列中以便它可以最后接收对象锁。一旦线程拥有了锁,它就可以检查对象的新状态以查看是否达到所需状态。PulseAll与Pulse方法类似,不过它是向所有在阻塞队列中的进程发送通知信号,如果只有一个线程被阻塞,那么请使用Pulse方法。
注意:Pulse、PulseAll和Wait方法必须从同步的代码块内调用。
Pulse(),PulseAll()向一个或多个等待线程发送信号。该信号通知等待线程锁定对象的状态已更改,并且锁的所有者准备释放该锁。等待线程被放置在对象的就绪队列中以便它可以最后接收对象锁。一旦线程拥有了锁,它就可以检查对象的新状态以查看是否达到所需状态。PulseAll与Pulse方法类似,不过它是向所有在阻塞队列中的进程发送通知信号,如果只有一个线程被阻塞,那么请使用Pulse方法。
注意:Pulse、PulseAll和Wait方法必须从同步的代码块内调用。
例1:
- using System;
- using System.Collections.Generic;
- using System.Text;
- using System.Threading;
- namespace UseMonitor2
- {
- class Program
- {
- static void Main(string[] args)
- {
- //创建共享资源
- SharedResource obj = new SharedResource();
- //创建线程对象并启动
- Thread tha = new Thread(ThreadMethodA);
- Thread thb = new Thread(ThreadMethodB);
- tha.Start(obj);
- thb.Start(obj);
- //程序暂停
- System.Console.ReadKey();
- }
- static void ThreadMethodA(Object obj)
- {
- Monitor.Enter(obj);
- (obj as SharedResource).DynamicCount += 100;
- System.Console.WriteLine("线程A完成工作,obj.DynamicCount={0}", (obj as SharedResource).DynamicCount);
- Monitor.Pulse(obj); //通知B线程进入准备队列
- Monitor.Exit(obj);
- }
- static void ThreadMethodB(Object obj)
- {
- Monitor.Enter(obj);
- //A线程还未工作,因为字段保持初始值0
- //如果注释掉此条件判断语句,则有可能会发生死锁
- if((obj as SharedResource).DynamicCount == 0)
- Monitor.Wait(obj);//将本线程阻塞,进入阻塞队列等待
- (obj as SharedResource).DynamicCount += 100;
- System.Console.WriteLine("线程B完成工作,obj.DynamicCount={0}", (obj as SharedResource).DynamicCount);
- Monitor.Exit(obj);
- }
- }
- //共享资源类
- class SharedResource
- {
- public int DynamicCount = 0; //多线程共享的实例字段
- }
- }
- using System;
- using System.Collections.Generic;
- using System.Text;
- using System.Threading;
- namespace UseMonitor2
- {
- class Program
- {
- static void Main(string[] args)
- {
- //创建共享资源
- SharedResource obj = new SharedResource();
- //创建线程对象并启动
- Thread tha = new Thread(ThreadMethodA);
- Thread thb = new Thread(ThreadMethodB);
- tha.Start(obj);
- thb.Start(obj);
- //程序暂停
- System.Console.ReadKey();
- }
- static void ThreadMethodA(Object obj)
- {
- Monitor.Enter(obj);
- (obj as SharedResource).DynamicCount += 100;
- System.Console.WriteLine("线程A完成工作,obj.DynamicCount={0}", (obj as SharedResource).DynamicCount);
- Monitor.Pulse(obj); //通知B线程进入准备队列
- Monitor.Exit(obj);
- }
- static void ThreadMethodB(Object obj)
- {
- Monitor.Enter(obj);
- //A线程还未工作,因为字段保持初始值0
- //如果注释掉此条件判断语句,则有可能会发生死锁
- if((obj as SharedResource).DynamicCount == 0)
- Monitor.Wait(obj);//将本线程阻塞,进入阻塞队列等待
- (obj as SharedResource).DynamicCount += 100;
- System.Console.WriteLine("线程B完成工作,obj.DynamicCount={0}", (obj as SharedResource).DynamicCount);
- Monitor.Exit(obj);
- }
- }
- //共享资源类
- class SharedResource
- {
- public int DynamicCount = 0; //多线程共享的实例字段
- }
- }
using System; using System.Collections.Generic; using System.Text; using System.Threading; namespace UseMonitor2 { class Program { static void Main(string[] args) { //创建共享资源 SharedResource obj = new SharedResource(); //创建线程对象并启动 Thread tha = new Thread(ThreadMethodA); Thread thb = new Thread(ThreadMethodB); tha.Start(obj); thb.Start(obj); //程序暂停 System.Console.ReadKey(); } static void ThreadMethodA(Object obj) { Monitor.Enter(obj); (obj as SharedResource).DynamicCount += 100; System.Console.WriteLine("线程A完成工作,obj.DynamicCount={0}", (obj as SharedResource).DynamicCount); Monitor.Pulse(obj); //通知B线程进入准备队列 Monitor.Exit(obj); } static void ThreadMethodB(Object obj) { Monitor.Enter(obj); //A线程还未工作,因为字段保持初始值0 //如果注释掉此条件判断语句,则有可能会发生死锁 if((obj as SharedResource).DynamicCount == 0) Monitor.Wait(obj);//将本线程阻塞,进入阻塞队列等待 (obj as SharedResource).DynamicCount += 100; System.Console.WriteLine("线程B完成工作,obj.DynamicCount={0}", (obj as SharedResource).DynamicCount); Monitor.Exit(obj); } } //共享资源类 class SharedResource { public int DynamicCount = 0; //多线程共享的实例字段 } }
- using System.Threading;
- public class Program
- {
- static object ball = new object();
- public static void Main()
- {
- Thread threadPing = new Thread( ThreadPingProc );
- Thread threadPong = new Thread( ThreadPongProc );
- threadPing.Start(); threadPong.Start();
- }
- static void ThreadPongProc()
- {
- System.Console.WriteLine("ThreadPong: Hello!");
- lock ( ball )
- for (int i = 0; i < 5; i++)
- {
- System.Console.WriteLine("ThreadPong: Pong ");
- Monitor.Pulse( ball );
- Monitor.Wait( ball );
- }
- System.Console.WriteLine("ThreadPong: Bye!");
- }
- static void ThreadPingProc()
- {
- System.Console.WriteLine("ThreadPing: Hello!");
- lock ( ball )
- for(int i=0; i< 5; i++)
- {
- System.Console.WriteLine("ThreadPing: Ping ");
- Monitor.Pulse( ball );
- Monitor.Wait( ball );
- }
- System.Console.WriteLine("ThreadPing: Bye!");
- }
- }
- using System.Threading;
- public class Program
- {
- static object ball = new object();
- public static void Main()
- {
- Thread threadPing = new Thread( ThreadPingProc );
- Thread threadPong = new Thread( ThreadPongProc );
- threadPing.Start(); threadPong.Start();
- }
- static void ThreadPongProc()
- {
- System.Console.WriteLine("ThreadPong: Hello!");
- lock ( ball )
- for (int i = 0; i < 5; i++)
- {
- System.Console.WriteLine("ThreadPong: Pong ");
- Monitor.Pulse( ball );
- Monitor.Wait( ball );
- }
- System.Console.WriteLine("ThreadPong: Bye!");
- }
- static void ThreadPingProc()
- {
- System.Console.WriteLine("ThreadPing: Hello!");
- lock ( ball )
- for(int i=0; i< 5; i++)
- {
- System.Console.WriteLine("ThreadPing: Ping ");
- Monitor.Pulse( ball );
- Monitor.Wait( ball );
- }
- System.Console.WriteLine("ThreadPing: Bye!");
- }
- }
using System.Threading; public class Program { static object ball = new object(); public static void Main() { Thread threadPing = new Thread( ThreadPingProc ); Thread threadPong = new Thread( ThreadPongProc ); threadPing.Start(); threadPong.Start(); } static void ThreadPongProc() { System.Console.WriteLine("ThreadPong: Hello!"); lock ( ball ) for (int i = 0; i < 5; i++) { System.Console.WriteLine("ThreadPong: Pong "); Monitor.Pulse( ball ); Monitor.Wait( ball ); } System.Console.WriteLine("ThreadPong: Bye!"); } static void ThreadPingProc() { System.Console.WriteLine("ThreadPing: Hello!"); lock ( ball ) for(int i=0; i< 5; i++) { System.Console.WriteLine("ThreadPing: Ping "); Monitor.Pulse( ball ); Monitor.Wait( ball ); } System.Console.WriteLine("ThreadPing: Bye!"); } }
可能的执行结果:
- ThreadPing: Hello!
- ThreadPing: Ping
- ThreadPong: Hello!
- ThreadPong: Pong
- ThreadPing: Ping
- ThreadPong: Pong
- ThreadPing: Ping
- ThreadPong: Pong
- ThreadPing: Ping
- ThreadPong: Pong
- ThreadPing: Ping
- ThreadPong: Pong
- ThreadPing: Bye!
- ThreadPing: Hello!
- ThreadPing: Ping
- ThreadPong: Hello!
- ThreadPong: Pong
- ThreadPing: Ping
- ThreadPong: Pong
- ThreadPing: Ping
- ThreadPong: Pong
- ThreadPing: Ping
- ThreadPong: Pong
- ThreadPing: Ping
- ThreadPong: Pong
- ThreadPing: Bye!
ThreadPing: Hello! ThreadPing: Ping ThreadPong: Hello! ThreadPong: Pong ThreadPing: Ping ThreadPong: Pong ThreadPing: Ping ThreadPong: Pong ThreadPing: Ping ThreadPong: Pong ThreadPing: Ping ThreadPong: Pong ThreadPing: Bye!
当threadPing进程进入ThreadPingProc锁定ball并调用Monitor.Pulse( ball )后,它通知threadPong从阻塞队列进入准备队列,当threadPing调用Monitor.Wait( ball )阻塞自己后,它放弃了了对ball的锁定,所以threadPong得以执行。
因此,可以借助Monitor.Pulse()来控制进程的推进顺序。
- //A线程执行的代码
- lock(obj)
- {
- //访问共享资源obj
- Monitor.Pulse(obj); //通知B 线程可以访问共享资源obj了
- }
- ---------------------------------------------------------------
- //B线程执行的代码
- lock(obj)
- {
- Monitor.Wait(obj); //等待A 线程完成
- //访问共享资源obj
- }
- //A线程执行的代码
- lock(obj)
- {
- //访问共享资源obj
- Monitor.Pulse(obj); //通知B 线程可以访问共享资源obj了
- }
- ---------------------------------------------------------------
- //B线程执行的代码
- lock(obj)
- {
- Monitor.Wait(obj); //等待A 线程完成
- //访问共享资源obj
- }
//A线程执行的代码 lock(obj) { //访问共享资源obj Monitor.Pulse(obj); //通知B 线程可以访问共享资源obj了 } --------------------------------------------------------------- //B线程执行的代码 lock(obj) { Monitor.Wait(obj); //等待A 线程完成 //访问共享资源obj }
2、Lock关键字
C#使用Lock关键字来简化Monitor的用法。lock就是对Monitor的Enter和Exit的一个封装,而且使用起来更简洁,因此Monitor类的Enter()和Exit()方法的组合使用可以用lock关键字替代。
lock (obj)
{
//访问共享资源代码段
}
等价于:
Monitor.Enter(obj);
//访问共享资源代码段
Monitor.Exit(obj);
//访问共享资源代码段
Monitor.Exit(obj);
- using System;
- using System.Collections.Generic;
- using System.Text;
- using System.Threading;
- //展示用Monitor访问共享资源
- namespace UseMonitor1
- {
- class Program
- {
- static void Main(string[] args)
- {
- SharedResource obj = new SharedResource();
- Thread[] ths = new Thread[4];
- for (int i = 0; i < 4; i++)
- {
- ths[i] = new Thread(increaseCount);
- ths[i].Start(obj);
- }
- System.Console.ReadKey();
- }
- static void increaseCount(Object obj)
- {
- //访问实例字段
- VisitDynamicField(obj);
- //访问静态字段
- VisitStaticField();
- }
- //访问静态字段
- private static void VisitStaticField()
- {
- //访问静态字段
- lock (typeof(SharedResource))
- {
- int beginNumber = SharedResource.StaticCount;
- System.Console.WriteLine("线程 {0} 读到的StaticCount起始值为 {1} ", Thread.CurrentThread.ManagedThreadId, beginNumber);
- for (int i = 0; i < 10000; i++)
- {
- beginNumber++;
- }
- SharedResource.StaticCount = beginNumber;
- System.Console.WriteLine("线程 {0} 结束, SharedResource.StaticCount={1}",
- Thread.CurrentThread.ManagedThreadId, SharedResource.StaticCount);
- }
- }
- //访问实例字段
- private static void VisitDynamicField(Object obj)
- {
- lock (obj)
- {
- int beginNumber = (obj as SharedResource).DynamicCount;
- System.Console.WriteLine("线程 {0} 读到的DynamicCount起始值为 {1} ", Thread.CurrentThread.ManagedThreadId, beginNumber);
- for (int i = 0; i < 10000; i++)
- {
- beginNumber++;
- }
- (obj as SharedResource).DynamicCount = beginNumber;
- System.Console.WriteLine("线程 {0} 结束,Obj.DynamicCount={1}",
- Thread.CurrentThread.ManagedThreadId, (obj as SharedResource).DynamicCount);
- }
- }
- }
- //共享资源类
- class SharedResource
- {
- public int DynamicCount = 0; //多线程共享的实例字段
- public static int StaticCount = 0; //多线程共享的静态字段
- }
- }
- using System;
- using System.Collections.Generic;
- using System.Text;
- using System.Threading;
- //展示用Monitor访问共享资源
- namespace UseMonitor1
- {
- class Program
- {
- static void Main(string[] args)
- {
- SharedResource obj = new SharedResource();
- Thread[] ths = new Thread[4];
- for (int i = 0; i < 4; i++)
- {
- ths[i] = new Thread(increaseCount);
- ths[i].Start(obj);
- }
- System.Console.ReadKey();
- }
- static void increaseCount(Object obj)
- {
- //访问实例字段
- VisitDynamicField(obj);
- //访问静态字段
- VisitStaticField();
- }
- //访问静态字段
- private static void VisitStaticField()
- {
- //访问静态字段
- lock (typeof(SharedResource))
- {
- int beginNumber = SharedResource.StaticCount;
- System.Console.WriteLine("线程 {0} 读到的StaticCount起始值为 {1} ", Thread.CurrentThread.ManagedThreadId, beginNumber);
- for (int i = 0; i < 10000; i++)
- {
- beginNumber++;
- }
- SharedResource.StaticCount = beginNumber;
- System.Console.WriteLine("线程 {0} 结束, SharedResource.StaticCount={1}",
- Thread.CurrentThread.ManagedThreadId, SharedResource.StaticCount);
- }
- }
- //访问实例字段
- private static void VisitDynamicField(Object obj)
- {
- lock (obj)
- {
- int beginNumber = (obj as SharedResource).DynamicCount;
- System.Console.WriteLine("线程 {0} 读到的DynamicCount起始值为 {1} ", Thread.CurrentThread.ManagedThreadId, beginNumber);
- for (int i = 0; i < 10000; i++)
- {
- beginNumber++;
- }
- (obj as SharedResource).DynamicCount = beginNumber;
- System.Console.WriteLine("线程 {0} 结束,Obj.DynamicCount={1}",
- Thread.CurrentThread.ManagedThreadId, (obj as SharedResource).DynamicCount);
- }
- }
- }
- //共享资源类
- class SharedResource
- {
- public int DynamicCount = 0; //多线程共享的实例字段
- public static int StaticCount = 0; //多线程共享的静态字段
- }
- }
using System; using System.Collections.Generic; using System.Text; using System.Threading; //展示用Monitor访问共享资源 namespace UseMonitor1 { class Program { static void Main(string[] args) { SharedResource obj = new SharedResource(); Thread[] ths = new Thread[4]; for (int i = 0; i < 4; i++) { ths[i] = new Thread(increaseCount); ths[i].Start(obj); } System.Console.ReadKey(); } static void increaseCount(Object obj) { //访问实例字段 VisitDynamicField(obj); //访问静态字段 VisitStaticField(); } //访问静态字段 private static void VisitStaticField() { //访问静态字段 lock (typeof(SharedResource)) { int beginNumber = SharedResource.StaticCount; System.Console.WriteLine("线程 {0} 读到的StaticCount起始值为 {1} ", Thread.CurrentThread.ManagedThreadId, beginNumber); for (int i = 0; i < 10000; i++) { beginNumber++; } SharedResource.StaticCount = beginNumber; System.Console.WriteLine("线程 {0} 结束, SharedResource.StaticCount={1}", Thread.CurrentThread.ManagedThreadId, SharedResource.StaticCount); } } //访问实例字段 private static void VisitDynamicField(Object obj) { lock (obj) { int beginNumber = (obj as SharedResource).DynamicCount; System.Console.WriteLine("线程 {0} 读到的DynamicCount起始值为 {1} ", Thread.CurrentThread.ManagedThreadId, beginNumber); for (int i = 0; i < 10000; i++) { beginNumber++; } (obj as SharedResource).DynamicCount = beginNumber; System.Console.WriteLine("线程 {0} 结束,Obj.DynamicCount={1}", Thread.CurrentThread.ManagedThreadId, (obj as SharedResource).DynamicCount); } } } //共享资源类 class SharedResource { public int DynamicCount = 0; //多线程共享的实例字段 public static int StaticCount = 0; //多线程共享的静态字段 } }
3、自旋锁SpinLock
当一个线程需要访问共享资源时,它可以调用SpinLock.Enter或SpinLock.TryEnter方法申请独占锁,如果暂时不能获得锁(这时可能运行于另一个CPU核上的线程正在访问共享资源),当前线程就会“空转”若干个时钟周期,然后再次尝试。在这个过程中,线程的状态仍是Running,从而避免了操作系统进行一次线程上下文切换所带来的开销。
- public class MyType
- {
- //创建自旋锁对象
- private SpinLock _spinLock = new SpinLock();
- //将被多线程执行的代码,
- //由于使用了自旋锁,可以保证被“锁定”代码一次只会被一个线程执行
- public void DoWork()
- {
- bool lockTaken = false;
- try
- {
- _spinLock.Enter(ref lockTaken); //申请获取“锁”
- // 获得了锁,在此书写工作代码,这些工作代码不会同时被两个线程执行
- }
- finally
- {
- //工作完毕,或者发生异常时,检查一下当前线程是否占有了锁
- //如果占有了锁,释放它,以避免出现死锁的情况。
- if (lockTaken) _spinLock.Exit();
- }
- }
- }
- public class MyType
- {
- //创建自旋锁对象
- private SpinLock _spinLock = new SpinLock();
- //将被多线程执行的代码,
- //由于使用了自旋锁,可以保证被“锁定”代码一次只会被一个线程执行
- public void DoWork()
- {
- bool lockTaken = false;
- try
- {
- _spinLock.Enter(ref lockTaken); //申请获取“锁”
- // 获得了锁,在此书写工作代码,这些工作代码不会同时被两个线程执行
- }
- finally
- {
- //工作完毕,或者发生异常时,检查一下当前线程是否占有了锁
- //如果占有了锁,释放它,以避免出现死锁的情况。
- if (lockTaken) _spinLock.Exit();
- }
- }
- }
public class MyType { //创建自旋锁对象 private SpinLock _spinLock = new SpinLock(); //将被多线程执行的代码, //由于使用了自旋锁,可以保证被“锁定”代码一次只会被一个线程执行 public void DoWork() { bool lockTaken = false; try { _spinLock.Enter(ref lockTaken); //申请获取“锁” // 获得了锁,在此书写工作代码,这些工作代码不会同时被两个线程执行 } finally { //工作完毕,或者发生异常时,检查一下当前线程是否占有了锁 //如果占有了锁,释放它,以避免出现死锁的情况。 if (lockTaken) _spinLock.Exit(); } } }
4、实现原子操作——Interlocked类
Interlocked类是一种互锁操作,提供对多个线程共享的变量进行同步访问的方法,互锁操作具有原子性,即整个操作时不能由相同变量上的另一个互锁操作所中断的单元。
这个类提供了Increment、Decrement、Add静态方法用于对int或long型变量的递增、递减或相加操作。还提供了Exchange(为整型或引用对象赋值)、CompareExchange(比较后再对整型或引用对象赋值),用于为整型或引用类型的赋值提供原子操作。
在大多数计算机上,增加变量操作不是一个原子操作,需要执行下列步骤:
- 将实例变量中的值加载到寄存器中。
- 增加或减少该值。
- 在实例变量中存储该值。
利用Interlocked类类解决生产者-消费者关系中的竞争条件问题:(例子来自《周长发——c#面向对象编程》
- // Interlocked.cs
- // Interlocked示例
- using System;
- using System.Threading;
- class Test
- {
- private long bufferEmpty = 0;
- private string buffer = null;
- static void Main()
- {
- Test t = new Test();
- // 进行测试
- t.Go();
- }
- public void Go()
- {
- Thread t1 = new Thread(new ThreadStart(Producer));
- t1.Name = "生产者线程";
- t1.Start();
- Thread t2 = new Thread(new ThreadStart(Consumer));
- t2.Name = "消费者线程";
- t2.Start();
- // 等待两个线程结束
- t1.Join();
- t2.Join();
- }
- // 生产者方法
- public void Producer()
- {
- Console.WriteLine("{0}:开始执行", Thread.CurrentThread.Name);
- try
- {
- for (int j = 0; j < 16; ++j)
- {
- // 等待共享缓冲区为空
- while (Interlocked.Read(ref bufferEmpty) != 0)
- Thread.Sleep(100);
- // 构造共享缓冲区
- Random r = new Random();
- int bufSize = r.Next() % 64;
- char[] s = new char[bufSize];
- for (int i = 0; i < bufSize; ++i)
- {
- s[i] = (char)((int)'A' + r.Next() % 26);
- }
- buffer = new string(s);
- Console.WriteLine("{0}:{1}", Thread.CurrentThread.Name, buffer);
- // 互锁加一,成为1,标志共享缓冲区已满
- Interlocked.Increment(ref bufferEmpty);
- // 休眠,将时间片让给消费者
- Thread.Sleep(10);
- }
- Console.WriteLine("{0}:执行完毕", Thread.CurrentThread.Name);
- }
- catch (System.Threading.ThreadInterruptedException)
- {
- Console.WriteLine("{0}:被终止", Thread.CurrentThread.Name);
- }
- }
- // 消费者方法
- public void Consumer()
- {
- Console.WriteLine("{0}:开始执行", Thread.CurrentThread.Name);
- try
- {
- for (int j = 0; j < 16; ++j)
- {
- while (Interlocked.Read(ref bufferEmpty) == 0)
- Thread.Sleep(100);
- // 打印共享缓冲区
- Console.WriteLine("{0}:{1}", Thread.CurrentThread.Name, buffer);
- // 互锁减一,成为0,标志共享缓冲区已空
- Interlocked.Decrement(ref bufferEmpty);
- // 休眠,将时间片让给生产者
- Thread.Sleep(10);
- }
- Console.WriteLine("{0}:执行完毕", Thread.CurrentThread.Name);
- }
- catch (System.Threading.ThreadInterruptedException)
- {
- Console.WriteLine("{0}:被终止", Thread.CurrentThread.Name);
- }
- }
- }
- // Interlocked.cs
- // Interlocked示例
- using System;
- using System.Threading;
- class Test
- {
- private long bufferEmpty = 0;
- private string buffer = null;
- static void Main()
- {
- Test t = new Test();
- // 进行测试
- t.Go();
- }
- public void Go()
- {
- Thread t1 = new Thread(new ThreadStart(Producer));
- t1.Name = "生产者线程";
- t1.Start();
- Thread t2 = new Thread(new ThreadStart(Consumer));
- t2.Name = "消费者线程";
- t2.Start();
- // 等待两个线程结束
- t1.Join();
- t2.Join();
- }
- // 生产者方法
- public void Producer()
- {
- Console.WriteLine("{0}:开始执行", Thread.CurrentThread.Name);
- try
- {
- for (int j = 0; j < 16; ++j)
- {
- // 等待共享缓冲区为空
- while (Interlocked.Read(ref bufferEmpty) != 0)
- Thread.Sleep(100);
- // 构造共享缓冲区
- Random r = new Random();
- int bufSize = r.Next() % 64;
- char[] s = new char[bufSize];
- for (int i = 0; i < bufSize; ++i)
- {
- s[i] = (char)((int)'A' + r.Next() % 26);
- }
- buffer = new string(s);
- Console.WriteLine("{0}:{1}", Thread.CurrentThread.Name, buffer);
- // 互锁加一,成为1,标志共享缓冲区已满
- Interlocked.Increment(ref bufferEmpty);
- // 休眠,将时间片让给消费者
- Thread.Sleep(10);
- }
- Console.WriteLine("{0}:执行完毕", Thread.CurrentThread.Name);
- }
- catch (System.Threading.ThreadInterruptedException)
- {
- Console.WriteLine("{0}:被终止", Thread.CurrentThread.Name);
- }
- }
- // 消费者方法
- public void Consumer()
- {
- Console.WriteLine("{0}:开始执行", Thread.CurrentThread.Name);
- try
- {
- for (int j = 0; j < 16; ++j)
- {
- while (Interlocked.Read(ref bufferEmpty) == 0)
- Thread.Sleep(100);
- // 打印共享缓冲区
- Console.WriteLine("{0}:{1}", Thread.CurrentThread.Name, buffer);
- // 互锁减一,成为0,标志共享缓冲区已空
- Interlocked.Decrement(ref bufferEmpty);
- // 休眠,将时间片让给生产者
- Thread.Sleep(10);
- }
- Console.WriteLine("{0}:执行完毕", Thread.CurrentThread.Name);
- }
- catch (System.Threading.ThreadInterruptedException)
- {
- Console.WriteLine("{0}:被终止", Thread.CurrentThread.Name);
- }
- }
- }
// Interlocked.cs // Interlocked示例 using System; using System.Threading; class Test { private long bufferEmpty = 0; private string buffer = null; static void Main() { Test t = new Test(); // 进行测试 t.Go(); } public void Go() { Thread t1 = new Thread(new ThreadStart(Producer)); t1.Name = "生产者线程"; t1.Start(); Thread t2 = new Thread(new ThreadStart(Consumer)); t2.Name = "消费者线程"; t2.Start(); // 等待两个线程结束 t1.Join(); t2.Join(); } // 生产者方法 public void Producer() { Console.WriteLine("{0}:开始执行", Thread.CurrentThread.Name); try { for (int j = 0; j < 16; ++j) { // 等待共享缓冲区为空 while (Interlocked.Read(ref bufferEmpty) != 0) Thread.Sleep(100); // 构造共享缓冲区 Random r = new Random(); int bufSize = r.Next() % 64; char[] s = new char[bufSize]; for (int i = 0; i < bufSize; ++i) { s[i] = (char)((int)'A' + r.Next() % 26); } buffer = new string(s); Console.WriteLine("{0}:{1}", Thread.CurrentThread.Name, buffer); // 互锁加一,成为1,标志共享缓冲区已满 Interlocked.Increment(ref bufferEmpty); // 休眠,将时间片让给消费者 Thread.Sleep(10); } Console.WriteLine("{0}:执行完毕", Thread.CurrentThread.Name); } catch (System.Threading.ThreadInterruptedException) { Console.WriteLine("{0}:被终止", Thread.CurrentThread.Name); } } // 消费者方法 public void Consumer() { Console.WriteLine("{0}:开始执行", Thread.CurrentThread.Name); try { for (int j = 0; j < 16; ++j) { while (Interlocked.Read(ref bufferEmpty) == 0) Thread.Sleep(100); // 打印共享缓冲区 Console.WriteLine("{0}:{1}", Thread.CurrentThread.Name, buffer); // 互锁减一,成为0,标志共享缓冲区已空 Interlocked.Decrement(ref bufferEmpty); // 休眠,将时间片让给生产者 Thread.Sleep(10); } Console.WriteLine("{0}:执行完毕", Thread.CurrentThread.Name); } catch (System.Threading.ThreadInterruptedException) { Console.WriteLine("{0}:被终止", Thread.CurrentThread.Name); } } }
5、Mutex类
Mutex与Monitor类似,需要注意的是Mutex分两种:一种是本地Mutex一种是系统级Mutex,系统级Mutex可以用来进行跨进程间的线程的同步。尽管 mutex 可以用于进程内的线程同步,但是使用 Monitor 通常更为可取,因为监视器是专门为 .NET Framework 而设计的,因而它可以更好地利用资源。相比之下,Mutex 类是 Win32 构造的包装。尽管 mutex 比监视器更为强大,但是相对于 Monitor 类,它所需要的互操作转换更消耗计算资源。
一个线程要想访问共享资源,它必须调用Mutex对象的Wait系列方法之一提出申请。当申请得到批准的线程完成了对于共享资源的访问后,它调用Mutex对象的ReleaseMutex()方法释放对于共享资源的访问权。
利用多线程模拟3个人在ATM上多次提款操作:
- using System;
- using System.Collections.Generic;
- using System.Text;
- using System.Threading;
- namespace UseATM
- {
- class Program
- {
- static ATM OneATM=new ATM(); //共享资源
- static void Main(string[] args)
- {
- //向公共帐号存款2万
- Console.Write("输入公司公共帐户的金额:");
- int PublicAcountMoney =Convert.ToInt32(Console.ReadLine());
- OneATM.Deposit(PublicAcountMoney);
- Console.Write("输入ATM中的现金额:");
- int ATMLeftMoney = Convert.ToInt32(Console.ReadLine());
- OneATM.SetATMLeftMoney(ATMLeftMoney);
- System.Console.WriteLine("\n敲任意键从公共帐户中取钱,ESC键退出……\n");
- while (System.Console.ReadKey(true).Key !=ConsoleKey.Escape)
- {
- System.Console.WriteLine("");
- Thread One = new Thread(WithDrawMoney);
- Thread Two = new Thread(WithDrawMoney);
- Thread Three = new Thread(WithDrawMoney);
- //随机生成一个要提款的数额,最少100元,最高5000元
- Random ran = new Random();
- One.Start(ran.Next(100, 5000));
- Two.Start(ran.Next(100, 5000));
- Three.Start(ran.Next(100, 5000));
- //等三人取完钱
- One.Join();
- Two.Join();
- Three.Join();
- System.Console.WriteLine("公共账号剩余{0}元,ATM中可提现金:{1}", OneATM.QueryPublicAccount(),OneATM.QueryATMLeftAccount());
- }
- }
- //线程函数
- static void WithDrawMoney(object amount)
- {
- switch(OneATM.WithDraw((int)amount))
- {
- case WithDrawState.Succeed:
- System.Console.WriteLine("成功取出{0}元。",amount );
- break;
- case WithDrawState.ATMHasNotEnoughCash:
- System.Console.WriteLine("ATM中现金不足,无法支取{0}元。", amount);
- break ;
- case WithDrawState.AccountHasNotEnoughMoney:
- System.Console.WriteLine("帐户中没钱了!无法取出{0}元",amount);
- break ;
- }
- }
- }
- //自助取款机
- class ATM
- {
- private int PublicAcountLeftMoney;//帐户剩余的钱
- private int ATMLeftMoney;//提款机剩余的钱
- //同步信息号量
- private Mutex m = new Mutex();
- //取钱
- public WithDrawState WithDraw(int amount)
- {
- m.WaitOne();
- //公共帐号钱不够
- if (PublicAcountLeftMoney < amount)
- {
- m.ReleaseMutex();
- return WithDrawState.AccountHasNotEnoughMoney;
- }
- //ATM现金不够
- if (ATMLeftMoney < amount)
- {
- m.ReleaseMutex();
- return WithDrawState.ATMHasNotEnoughCash;
- }
- //用户可以提取现金
- ATMLeftMoney -= amount;
- PublicAcountLeftMoney -= amount;
- m.ReleaseMutex();
- return WithDrawState.Succeed;
- }
- //存钱
- public void Deposit(int amount)
- {
- m.WaitOne();
- PublicAcountLeftMoney += amount;
- m.ReleaseMutex();
- }
- /// <summary>
- /// 设置ATM的现金金额
- /// </summary>
- /// <param name="amount"></param>
- public void SetATMLeftMoney(int amount)
- {
- Interlocked.Exchange(ref ATMLeftMoney, amount);
- }
- //获取还剩余多少钱
- public int QueryPublicAccount()
- {
- return PublicAcountLeftMoney;
- }
- /// <summary>
- /// 查询ATM剩余多少钱
- /// </summary>
- /// <returns></returns>
- public int QueryATMLeftAccount()
- {
- return ATMLeftMoney;
- }
- }
- //取款状态
- public enum WithDrawState
- {
- Succeed, //取钱成功
- AccountHasNotEnoughMoney, //账号中没钱了
- ATMHasNotEnoughCash //ATM中没有足够的现金
- }
- }
- using System;
- using System.Collections.Generic;
- using System.Text;
- using System.Threading;
- namespace UseATM
- {
- class Program
- {
- static ATM OneATM=new ATM(); //共享资源
- static void Main(string[] args)
- {
- //向公共帐号存款2万
- Console.Write("输入公司公共帐户的金额:");
- int PublicAcountMoney =Convert.ToInt32(Console.ReadLine());
- OneATM.Deposit(PublicAcountMoney);
- Console.Write("输入ATM中的现金额:");
- int ATMLeftMoney = Convert.ToInt32(Console.ReadLine());
- OneATM.SetATMLeftMoney(ATMLeftMoney);
- System.Console.WriteLine("\n敲任意键从公共帐户中取钱,ESC键退出……\n");
- while (System.Console.ReadKey(true).Key !=ConsoleKey.Escape)
- {
- System.Console.WriteLine("");
- Thread One = new Thread(WithDrawMoney);
- Thread Two = new Thread(WithDrawMoney);
- Thread Three = new Thread(WithDrawMoney);
- //随机生成一个要提款的数额,最少100元,最高5000元
- Random ran = new Random();
- One.Start(ran.Next(100, 5000));
- Two.Start(ran.Next(100, 5000));
- Three.Start(ran.Next(100, 5000));
- //等三人取完钱
- One.Join();
- Two.Join();
- Three.Join();
- System.Console.WriteLine("公共账号剩余{0}元,ATM中可提现金:{1}", OneATM.QueryPublicAccount(),OneATM.QueryATMLeftAccount());
- }
- }
- //线程函数
- static void WithDrawMoney(object amount)
- {
- switch(OneATM.WithDraw((int)amount))
- {
- case WithDrawState.Succeed:
- System.Console.WriteLine("成功取出{0}元。",amount );
- break;
- case WithDrawState.ATMHasNotEnoughCash:
- System.Console.WriteLine("ATM中现金不足,无法支取{0}元。", amount);
- break ;
- case WithDrawState.AccountHasNotEnoughMoney:
- System.Console.WriteLine("帐户中没钱了!无法取出{0}元",amount);
- break ;
- }
- }
- }
- //自助取款机
- class ATM
- {
- private int PublicAcountLeftMoney;//帐户剩余的钱
- private int ATMLeftMoney;//提款机剩余的钱
- //同步信息号量
- private Mutex m = new Mutex();
- //取钱
- public WithDrawState WithDraw(int amount)
- {
- m.WaitOne();
- //公共帐号钱不够
- if (PublicAcountLeftMoney < amount)
- {
- m.ReleaseMutex();
- return WithDrawState.AccountHasNotEnoughMoney;
- }
- //ATM现金不够
- if (ATMLeftMoney < amount)
- {
- m.ReleaseMutex();
- return WithDrawState.ATMHasNotEnoughCash;
- }
- //用户可以提取现金
- ATMLeftMoney -= amount;
- PublicAcountLeftMoney -= amount;
- m.ReleaseMutex();
- return WithDrawState.Succeed;
- }
- //存钱
- public void Deposit(int amount)
- {
- m.WaitOne();
- PublicAcountLeftMoney += amount;
- m.ReleaseMutex();
- }
- /// <summary>
- /// 设置ATM的现金金额
- /// </summary>
- /// <param name="amount"></param>
- public void SetATMLeftMoney(int amount)
- {
- Interlocked.Exchange(ref ATMLeftMoney, amount);
- }
- //获取还剩余多少钱
- public int QueryPublicAccount()
- {
- return PublicAcountLeftMoney;
- }
- /// <summary>
- /// 查询ATM剩余多少钱
- /// </summary>
- /// <returns></returns>
- public int QueryATMLeftAccount()
- {
- return ATMLeftMoney;
- }
- }
- //取款状态
- public enum WithDrawState
- {
- Succeed, //取钱成功
- AccountHasNotEnoughMoney, //账号中没钱了
- ATMHasNotEnoughCash //ATM中没有足够的现金
- }
- }
using System; using System.Collections.Generic; using System.Text; using System.Threading; namespace UseATM { class Program { static ATM OneATM=new ATM(); //共享资源 static void Main(string[] args) { //向公共帐号存款2万 Console.Write("输入公司公共帐户的金额:"); int PublicAcountMoney =Convert.ToInt32(Console.ReadLine()); OneATM.Deposit(PublicAcountMoney); Console.Write("输入ATM中的现金额:"); int ATMLeftMoney = Convert.ToInt32(Console.ReadLine()); OneATM.SetATMLeftMoney(ATMLeftMoney); System.Console.WriteLine("\n敲任意键从公共帐户中取钱,ESC键退出……\n"); while (System.Console.ReadKey(true).Key !=ConsoleKey.Escape) { System.Console.WriteLine(""); Thread One = new Thread(WithDrawMoney); Thread Two = new Thread(WithDrawMoney); Thread Three = new Thread(WithDrawMoney); //随机生成一个要提款的数额,最少100元,最高5000元 Random ran = new Random(); One.Start(ran.Next(100, 5000)); Two.Start(ran.Next(100, 5000)); Three.Start(ran.Next(100, 5000)); //等三人取完钱 One.Join(); Two.Join(); Three.Join(); System.Console.WriteLine("公共账号剩余{0}元,ATM中可提现金:{1}", OneATM.QueryPublicAccount(),OneATM.QueryATMLeftAccount()); } } //线程函数 static void WithDrawMoney(object amount) { switch(OneATM.WithDraw((int)amount)) { case WithDrawState.Succeed: System.Console.WriteLine("成功取出{0}元。",amount ); break; case WithDrawState.ATMHasNotEnoughCash: System.Console.WriteLine("ATM中现金不足,无法支取{0}元。", amount); break ; case WithDrawState.AccountHasNotEnoughMoney: System.Console.WriteLine("帐户中没钱了!无法取出{0}元",amount); break ; } } } //自助取款机 class ATM { private int PublicAcountLeftMoney;//帐户剩余的钱 private int ATMLeftMoney;//提款机剩余的钱 //同步信息号量 private Mutex m = new Mutex(); //取钱 public WithDrawState WithDraw(int amount) { m.WaitOne(); //公共帐号钱不够 if (PublicAcountLeftMoney < amount) { m.ReleaseMutex(); return WithDrawState.AccountHasNotEnoughMoney; } //ATM现金不够 if (ATMLeftMoney < amount) { m.ReleaseMutex(); return WithDrawState.ATMHasNotEnoughCash; } //用户可以提取现金 ATMLeftMoney -= amount; PublicAcountLeftMoney -= amount; m.ReleaseMutex(); return WithDrawState.Succeed; } //存钱 public void Deposit(int amount) { m.WaitOne(); PublicAcountLeftMoney += amount; m.ReleaseMutex(); } /// <summary> /// 设置ATM的现金金额 /// </summary> /// <param name="amount"></param> public void SetATMLeftMoney(int amount) { Interlocked.Exchange(ref ATMLeftMoney, amount); } //获取还剩余多少钱 public int QueryPublicAccount() { return PublicAcountLeftMoney; } /// <summary> /// 查询ATM剩余多少钱 /// </summary> /// <returns></returns> public int QueryATMLeftAccount() { return ATMLeftMoney; } } //取款状态 public enum WithDrawState { Succeed, //取钱成功 AccountHasNotEnoughMoney, //账号中没钱了 ATMHasNotEnoughCash //ATM中没有足够的现金 } }可能的运行结果:
- 输入公司公共帐户的金额:200000
- 输入ATM中的现金额:6000000
- 敲任意键从公共帐户中取钱,ESC键退出……
- 成功取出1249元。
- 成功取出643元。
- 成功取出4958元。
- 公共账号剩余193150元,ATM中可提现金:5993150
- 成功取出1168元。
- 成功取出3650元。
- 成功取出2707元。
- 公共账号剩余185625元,ATM中可提现金:5985625
- 成功取出3866元。
- 成功取出402元。
- 成功取出2397元。
- 公共账号剩余178960元,ATM中可提现金:5978960
- 成功取出4485元。
- 成功取出1701元。
- 成功取出3354元。
- 公共账号剩余169420元,ATM中可提现金:5969420
- 输入公司公共帐户的金额:200000
- 输入ATM中的现金额:6000000
- 敲任意键从公共帐户中取钱,ESC键退出……
- 成功取出1249元。
- 成功取出643元。
- 成功取出4958元。
- 公共账号剩余193150元,ATM中可提现金:5993150
- 成功取出1168元。
- 成功取出3650元。
- 成功取出2707元。
- 公共账号剩余185625元,ATM中可提现金:5985625
- 成功取出3866元。
- 成功取出402元。
- 成功取出2397元。
- 公共账号剩余178960元,ATM中可提现金:5978960
- 成功取出4485元。
- 成功取出1701元。
- 成功取出3354元。
- 公共账号剩余169420元,ATM中可提现金:5969420
输入公司公共帐户的金额:200000 输入ATM中的现金额:6000000 敲任意键从公共帐户中取钱,ESC键退出…… 成功取出1249元。 成功取出643元。 成功取出4958元。 公共账号剩余193150元,ATM中可提现金:5993150 成功取出1168元。 成功取出3650元。 成功取出2707元。 公共账号剩余185625元,ATM中可提现金:5985625 成功取出3866元。 成功取出402元。 成功取出2397元。 公共账号剩余178960元,ATM中可提现金:5978960 成功取出4485元。 成功取出1701元。 成功取出3354元。 公共账号剩余169420元,ATM中可提现金:5969420
Mustex与Monitor有一个很大的区别:
Mutex可以用来同步属于不同应用程序或者进程的线程,而Monitor没有这个能力。
为了说明这个区别,我们将生产者和消费者线程分别放在两个应用程序中,在两个应用程序中都各自创建一个同名的Mutex对象,并利用他们来对生产者和消费者线程同步:
生产者线程所在应用程序代码:
- // Mutex1.cs
- // Mutex1示例
- using System;
- using System.IO;
- using System.Threading;
- using System.Diagnostics;
- class Test
- {
- static void Main()
- {
- Test t = new Test();
- // 进行测试
- t.Go();
- }
- public void Go()
- {
- // 创建并启动线程
- Thread t1 = new Thread(new ThreadStart(Producer));
- t1.Name = "生产者线程";
- t1.Start();
- // 等待线程结束
- t1.Join();
- Console.WriteLine("按Enter键退出...");
- Console.Read();
- }
- // 生产者方法
- public void Producer()
- {
- Console.WriteLine("{0}:开始执行", Thread.CurrentThread.Name);
- // 创建互斥体
- Mutex mutex = new Mutex(false, "CSharp_Mutex_test");
- // 启动消费者进程
- Process.Start("Mutex2.exe");
- for (int j = 0; j < 16; ++j)
- {
- try
- {
- // 进入互斥体
- mutex.WaitOne();
- FileStream fs = new FileStream(@"d:\text.txt", FileMode.OpenOrCreate, FileAccess.Write);
- StreamWriter sw = new StreamWriter(fs);
- // 构造字符串
- Random r = new Random();
- int bufSize = r.Next() % 64;
- char[] s = new char[bufSize];
- for (int i = 0; i < bufSize; ++i)
- {
- s[i] = (char)((int)'A' + r.Next() % 26);
- }
- string str = new string(s);
- // 将字符串写入文件
- sw.WriteLine(str);
- sw.Close();
- Console.WriteLine("{0}:{1}", Thread.CurrentThread.Name, str);
- }
- catch (System.Threading.ThreadInterruptedException)
- {
- Console.WriteLine("{0}:被终止", Thread.CurrentThread.Name);
- break;
- }
- finally
- {
- // 退出互斥体
- mutex.ReleaseMutex();
- }
- // 休眠,将时间片让给消费者
- Thread.Sleep(1000);
- }
- // 关闭互斥体
- mutex.Close();
- Console.WriteLine("{0}:执行完毕", Thread.CurrentThread.Name);
- }
- }
- // Mutex1.cs
- // Mutex1示例
- using System;
- using System.IO;
- using System.Threading;
- using System.Diagnostics;
- class Test
- {
- static void Main()
- {
- Test t = new Test();
- // 进行测试
- t.Go();
- }
- public void Go()
- {
- // 创建并启动线程
- Thread t1 = new Thread(new ThreadStart(Producer));
- t1.Name = "生产者线程";
- t1.Start();
- // 等待线程结束
- t1.Join();
- Console.WriteLine("按Enter键退出...");
- Console.Read();
- }
- // 生产者方法
- public void Producer()
- {
- Console.WriteLine("{0}:开始执行", Thread.CurrentThread.Name);
- // 创建互斥体
- Mutex mutex = new Mutex(false, "CSharp_Mutex_test");
- // 启动消费者进程
- Process.Start("Mutex2.exe");
- for (int j = 0; j < 16; ++j)
- {
- try
- {
- // 进入互斥体
- mutex.WaitOne();
- FileStream fs = new FileStream(@"d:\text.txt", FileMode.OpenOrCreate, FileAccess.Write);
- StreamWriter sw = new StreamWriter(fs);
- // 构造字符串
- Random r = new Random();
- int bufSize = r.Next() % 64;
- char[] s = new char[bufSize];
- for (int i = 0; i < bufSize; ++i)
- {
- s[i] = (char)((int)'A' + r.Next() % 26);
- }
- string str = new string(s);
- // 将字符串写入文件
- sw.WriteLine(str);
- sw.Close();
- Console.WriteLine("{0}:{1}", Thread.CurrentThread.Name, str);
- }
- catch (System.Threading.ThreadInterruptedException)
- {
- Console.WriteLine("{0}:被终止", Thread.CurrentThread.Name);
- break;
- }
- finally
- {
- // 退出互斥体
- mutex.ReleaseMutex();
- }
- // 休眠,将时间片让给消费者
- Thread.Sleep(1000);
- }
- // 关闭互斥体
- mutex.Close();
- Console.WriteLine("{0}:执行完毕", Thread.CurrentThread.Name);
- }
- }
// Mutex1.cs // Mutex1示例 using System; using System.IO; using System.Threading; using System.Diagnostics; class Test { static void Main() { Test t = new Test(); // 进行测试 t.Go(); } public void Go() { // 创建并启动线程 Thread t1 = new Thread(new ThreadStart(Producer)); t1.Name = "生产者线程"; t1.Start(); // 等待线程结束 t1.Join(); Console.WriteLine("按Enter键退出..."); Console.Read(); } // 生产者方法 public void Producer() { Console.WriteLine("{0}:开始执行", Thread.CurrentThread.Name); // 创建互斥体 Mutex mutex = new Mutex(false, "CSharp_Mutex_test"); // 启动消费者进程 Process.Start("Mutex2.exe"); for (int j = 0; j < 16; ++j) { try { // 进入互斥体 mutex.WaitOne(); FileStream fs = new FileStream(@"d:\text.txt", FileMode.OpenOrCreate, FileAccess.Write); StreamWriter sw = new StreamWriter(fs); // 构造字符串 Random r = new Random(); int bufSize = r.Next() % 64; char[] s = new char[bufSize]; for (int i = 0; i < bufSize; ++i) { s[i] = (char)((int)'A' + r.Next() % 26); } string str = new string(s); // 将字符串写入文件 sw.WriteLine(str); sw.Close(); Console.WriteLine("{0}:{1}", Thread.CurrentThread.Name, str); } catch (System.Threading.ThreadInterruptedException) { Console.WriteLine("{0}:被终止", Thread.CurrentThread.Name); break; } finally { // 退出互斥体 mutex.ReleaseMutex(); } // 休眠,将时间片让给消费者 Thread.Sleep(1000); } // 关闭互斥体 mutex.Close(); Console.WriteLine("{0}:执行完毕", Thread.CurrentThread.Name); } }消费者线程所在应用程序代码:
- // Mutex2.cs
- // Mutex2示例
- using System;
- using System.IO;
- using System.Threading;
- class Test
- {
- static void Main()
- {
- Test t = new Test();
- // 进行测试
- t.Go();
- }
- public void Go()
- {
- // 创建并启动线程
- Thread t2 = new Thread(new ThreadStart(Consumer));
- t2.Name = "消费者线程";
- t2.Start();
- // 等待线程结束
- t2.Join();
- Console.WriteLine("按Enter键退出...");
- Console.Read();
- }
- // 消费者方法
- public void Consumer()
- {
- Console.WriteLine("{0}:开始执行", Thread.CurrentThread.Name);
- // 创建互斥体
- Mutex mutex = new Mutex(false, "CSharp_Mutex_test");
- for (int j = 0; j < 16; ++j)
- {
- try
- {
- // 进入互斥体
- mutex.WaitOne();
- StreamReader sr = new StreamReader(@"d:\text.txt");
- string s = sr.ReadLine();
- sr.Close();
- // 显示字符串的值
- Console.WriteLine("{0}:{1}", Thread.CurrentThread.Name, s);
- }
- catch (System.Threading.ThreadInterruptedException)
- {
- Console.WriteLine("{0}:被终止", Thread.CurrentThread.Name);
- break;
- }
- finally
- {
- // 退出互斥体
- mutex.ReleaseMutex();
- }
- // 休眠,将时间片让给消费者
- Thread.Sleep(1000);
- }
- // 关闭互斥体
- mutex.Close();
- Console.WriteLine("{0}:执行完毕", Thread.CurrentThread.Name);
- }
- }
- // Mutex2.cs
- // Mutex2示例
- using System;
- using System.IO;
- using System.Threading;
- class Test
- {
- static void Main()
- {
- Test t = new Test();
- // 进行测试
- t.Go();
- }
- public void Go()
- {
- // 创建并启动线程
- Thread t2 = new Thread(new ThreadStart(Consumer));
- t2.Name = "消费者线程";
- t2.Start();
- // 等待线程结束
- t2.Join();
- Console.WriteLine("按Enter键退出...");
- Console.Read();
- }
- // 消费者方法
- public void Consumer()
- {
- Console.WriteLine("{0}:开始执行", Thread.CurrentThread.Name);
- // 创建互斥体
- Mutex mutex = new Mutex(false, "CSharp_Mutex_test");
- for (int j = 0; j < 16; ++j)
- {
- try
- {
- // 进入互斥体
- mutex.WaitOne();
- StreamReader sr = new StreamReader(@"d:\text.txt");
- string s = sr.ReadLine();
- sr.Close();
- // 显示字符串的值
- Console.WriteLine("{0}:{1}", Thread.CurrentThread.Name, s);
- }
- catch (System.Threading.ThreadInterruptedException)
- {
- Console.WriteLine("{0}:被终止", Thread.CurrentThread.Name);
- break;
- }
- finally
- {
- // 退出互斥体
- mutex.ReleaseMutex();
- }
- // 休眠,将时间片让给消费者
- Thread.Sleep(1000);
- }
- // 关闭互斥体
- mutex.Close();
- Console.WriteLine("{0}:执行完毕", Thread.CurrentThread.Name);
- }
- }
// Mutex2.cs // Mutex2示例 using System; using System.IO; using System.Threading; class Test { static void Main() { Test t = new Test(); // 进行测试 t.Go(); } public void Go() { // 创建并启动线程 Thread t2 = new Thread(new ThreadStart(Consumer)); t2.Name = "消费者线程"; t2.Start(); // 等待线程结束 t2.Join(); Console.WriteLine("按Enter键退出..."); Console.Read(); } // 消费者方法 public void Consumer() { Console.WriteLine("{0}:开始执行", Thread.CurrentThread.Name); // 创建互斥体 Mutex mutex = new Mutex(false, "CSharp_Mutex_test"); for (int j = 0; j < 16; ++j) { try { // 进入互斥体 mutex.WaitOne(); StreamReader sr = new StreamReader(@"d:\text.txt"); string s = sr.ReadLine(); sr.Close(); // 显示字符串的值 Console.WriteLine("{0}:{1}", Thread.CurrentThread.Name, s); } catch (System.Threading.ThreadInterruptedException) { Console.WriteLine("{0}:被终止", Thread.CurrentThread.Name); break; } finally { // 退出互斥体 mutex.ReleaseMutex(); } // 休眠,将时间片让给消费者 Thread.Sleep(1000); } // 关闭互斥体 mutex.Close(); Console.WriteLine("{0}:执行完毕", Thread.CurrentThread.Name); } }
我们分别编译这两个文件,然后运行Mutex1,他会在另一个窗口中启动Mutex2,可能的结果如下:
![](http://my.csdn.net/uploads/201205/31/1338475000_7086.png)
6、Semaphore
Semaphore可以限制可同时访问某一资源或资源池的线程数。
Semaphore类在内部维护一个计数器,当一个线程调用Semaphore对象的Wait系列方法时,此计数器减一,只要计数器还是一个正数,线程就不会阻塞。当计数器减到0时,再调用Semaphore对象Wait系列方法的线程将被阻塞,直到有线程调用Semaphore对象的Release()方法增加计数器值时,才有可能解除阻塞状态。
示例说明:
图书馆都配备有若干台公用计算机供读者查询信息,当某日读者比较多时,必须排队等候。UseLibraryComputer实例用多线程模拟了多人使用多台计算机的过程
图书馆都配备有若干台公用计算机供读者查询信息,当某日读者比较多时,必须排队等候。UseLibraryComputer实例用多线程模拟了多人使用多台计算机的过程
- using System;
- using System.Collections.Generic;
- using System.Text;
- using System.Threading;
- namespace UseLibraryComputer
- {
- class Program
- {
- //图书馆拥有的公用计算机
- private const int ComputerNum = 3;
- private static Computer[] LibraryComputers;
- //同步信号量
- public static Semaphore sp = new Semaphore( ComputerNum, ComputerNum);
- static void Main(string[] args)
- {
- //图书馆拥有ComputerNum台电脑
- LibraryComputers = new Computer[ComputerNum];
- for (int i = 0; i <ComputerNum; i++)
- LibraryComputers[i] = new Computer("Computer"+(i+1).ToString());
- int peopleNum = 0;
- Random ran=new Random();
- Thread user;
- System.Console.WriteLine("敲任意键模拟一批批的人排队使用{0}台计算机,ESC键结束模拟……" ,ComputerNum);
- //每次创建若干个线程,模拟人排队使用计算机
- while (System.Console.ReadKey().Key != ConsoleKey.Escape)
- {
- peopleNum = ran.Next(0, 10);
- System.Console.WriteLine("\n有{0}人在等待使用计算机。",peopleNum );
- for (int i = 1; i <= peopleNum; i++)
- {
- user = new Thread(UseComputer);
- user.Start("User" + i.ToString());
- }
- }
- }
- //线程函数
- static void UseComputer(Object UserName)
- {
- sp.WaitOne();//等待计算机可用
- //查找可用的计算机
- Computer cp=null;
- for (int i = 0; i < ComputerNum; i++)
- if (LibraryComputers[i].IsOccupied == false)
- {
- cp = LibraryComputers[i];
- break;
- }
- //使用计算机工作
- cp.Use(UserName.ToString());
- //不再使用计算机,让出来给其他人使用
- sp.Release();
- }
- }
- class Computer
- {
- public readonly string ComputerName = "";
- public Computer(string Name)
- {
- ComputerName = Name;
- }
- //是否被占用
- public bool IsOccupied = false;
- //人在使用计算机
- public void Use(String userName)
- {
- System.Console.WriteLine("{0}开始使用计算机{1}", userName,ComputerName);
- IsOccupied = true;
- Thread.Sleep(new Random().Next(1, 2000)); //随机休眠,以模拟人使用计算机
- System.Console.WriteLine("{0}结束使用计算机{1}", userName,ComputerName);
- IsOccupied = false;
- }
- }
- }
- using System;
- using System.Collections.Generic;
- using System.Text;
- using System.Threading;
- namespace UseLibraryComputer
- {
- class Program
- {
- //图书馆拥有的公用计算机
- private const int ComputerNum = 3;
- private static Computer[] LibraryComputers;
- //同步信号量
- public static Semaphore sp = new Semaphore( ComputerNum, ComputerNum);
- static void Main(string[] args)
- {
- //图书馆拥有ComputerNum台电脑
- LibraryComputers = new Computer[ComputerNum];
- for (int i = 0; i <ComputerNum; i++)
- LibraryComputers[i] = new Computer("Computer"+(i+1).ToString());
- int peopleNum = 0;
- Random ran=new Random();
- Thread user;
- System.Console.WriteLine("敲任意键模拟一批批的人排队使用{0}台计算机,ESC键结束模拟……" ,ComputerNum);
- //每次创建若干个线程,模拟人排队使用计算机
- while (System.Console.ReadKey().Key != ConsoleKey.Escape)
- {
- peopleNum = ran.Next(0, 10);
- System.Console.WriteLine("\n有{0}人在等待使用计算机。",peopleNum );
- for (int i = 1; i <= peopleNum; i++)
- {
- user = new Thread(UseComputer);
- user.Start("User" + i.ToString());
- }
- }
- }
- //线程函数
- static void UseComputer(Object UserName)
- {
- sp.WaitOne();//等待计算机可用
- //查找可用的计算机
- Computer cp=null;
- for (int i = 0; i < ComputerNum; i++)
- if (LibraryComputers[i].IsOccupied == false)
- {
- cp = LibraryComputers[i];
- break;
- }
- //使用计算机工作
- cp.Use(UserName.ToString());
- //不再使用计算机,让出来给其他人使用
- sp.Release();
- }
- }
- class Computer
- {
- public readonly string ComputerName = "";
- public Computer(string Name)
- {
- ComputerName = Name;
- }
- //是否被占用
- public bool IsOccupied = false;
- //人在使用计算机
- public void Use(String userName)
- {
- System.Console.WriteLine("{0}开始使用计算机{1}", userName,ComputerName);
- IsOccupied = true;
- Thread.Sleep(new Random().Next(1, 2000)); //随机休眠,以模拟人使用计算机
- System.Console.WriteLine("{0}结束使用计算机{1}", userName,ComputerName);
- IsOccupied = false;
- }
- }
- }
using System; using System.Collections.Generic; using System.Text; using System.Threading; namespace UseLibraryComputer { class Program { //图书馆拥有的公用计算机 private const int ComputerNum = 3; private static Computer[] LibraryComputers; //同步信号量 public static Semaphore sp = new Semaphore( ComputerNum, ComputerNum); static void Main(string[] args) { //图书馆拥有ComputerNum台电脑 LibraryComputers = new Computer[ComputerNum]; for (int i = 0; i <ComputerNum; i++) LibraryComputers[i] = new Computer("Computer"+(i+1).ToString()); int peopleNum = 0; Random ran=new Random(); Thread user; System.Console.WriteLine("敲任意键模拟一批批的人排队使用{0}台计算机,ESC键结束模拟……" ,ComputerNum); //每次创建若干个线程,模拟人排队使用计算机 while (System.Console.ReadKey().Key != ConsoleKey.Escape) { peopleNum = ran.Next(0, 10); System.Console.WriteLine("\n有{0}人在等待使用计算机。",peopleNum ); for (int i = 1; i <= peopleNum; i++) { user = new Thread(UseComputer); user.Start("User" + i.ToString()); } } } //线程函数 static void UseComputer(Object UserName) { sp.WaitOne();//等待计算机可用 //查找可用的计算机 Computer cp=null; for (int i = 0; i < ComputerNum; i++) if (LibraryComputers[i].IsOccupied == false) { cp = LibraryComputers[i]; break; } //使用计算机工作 cp.Use(UserName.ToString()); //不再使用计算机,让出来给其他人使用 sp.Release(); } } class Computer { public readonly string ComputerName = ""; public Computer(string Name) { ComputerName = Name; } //是否被占用 public bool IsOccupied = false; //人在使用计算机 public void Use(String userName) { System.Console.WriteLine("{0}开始使用计算机{1}", userName,ComputerName); IsOccupied = true; Thread.Sleep(new Random().Next(1, 2000)); //随机休眠,以模拟人使用计算机 System.Console.WriteLine("{0}结束使用计算机{1}", userName,ComputerName); IsOccupied = false; } } }可能的运行结果:
![](http://my.csdn.net/uploads/201205/31/1338475845_2844.jpg)