如何控制好多个线程相互之间的联系,不产生冲突和重复,这需要用到互斥对象,即:System.Threading 命名空间中的 Mutex 类。
我们可以把Mutex看作一个出租车,乘客看作线程。乘客首先等车,然后上车,最后下车。当一个乘客在车上时,其他乘客就只有等他下车以后才可以上车。而线程与Mutex对象的关系也正是如此,线程使用Mutex.WaitOne()方法等待Mutex对象被释放,如果它等待的Mutex对象被释放了,它就自动拥有这个对象,直到它调用Mutex.ReleaseMutex()方法释放这个对象,而在此期间,其他想要获取这个Mutex对象的线程都只有等待。
下面这个例子使用了Mutex对象来同步四个线程,主线程等待四个线程的结束,而这四个线程的运行又是与两个Mutex对象相关联的。
其中还用到AutoResetEvent类的对象,可以把它理解为一个信号灯。这里用它的有信号状态来表示一个线程的结束。
// AutoResetEvent.Set()方法设置它为有信号状态
// AutoResetEvent.Reset()方法设置它为无信号状态
Mutex 类的程序示例:
using
System;
using System.Threading;
namespace ThreadExample
{
public class MutexSample
{
static Mutex gM1;
static Mutex gM2;
const int ITERS = 100 ;
static AutoResetEvent Event1 = new AutoResetEvent( false );
static AutoResetEvent Event2 = new AutoResetEvent( false );
static AutoResetEvent Event3 = new AutoResetEvent( false );
static AutoResetEvent Event4 = new AutoResetEvent( false );
public static void Main(String[] args)
{
Console.WriteLine( " Mutex Sample " );
// 创建一个Mutex对象,并且命名为MyMutex
gM1 = new Mutex( true , " MyMutex " );
// 创建一个未命名的Mutex 对象.
gM2 = new Mutex( true );
Console.WriteLine( " - Main Owns gM1 and gM2 " );
AutoResetEvent[] evs = new AutoResetEvent[ 4 ];
evs[ 0 ] = Event1; // 为后面的线程t1,t2,t3,t4定义AutoResetEvent对象
evs[ 1 ] = Event2;
evs[ 2 ] = Event3;
evs[ 3 ] = Event4;
MutexSample tm = new MutexSample( );
Thread t1 = new Thread( new ThreadStart(tm.t1Start));
Thread t2 = new Thread( new ThreadStart(tm.t2Start));
Thread t3 = new Thread( new ThreadStart(tm.t3Start));
Thread t4 = new Thread( new ThreadStart(tm.t4Start));
t1.Start( ); // 使用Mutex.WaitAll()方法等待一个Mutex数组中的对象全部被释放
t2.Start( ); // 使用Mutex.WaitOne()方法等待gM1的释放
t3.Start( ); // 使用Mutex.WaitAny()方法等待一个Mutex数组中任意一个对象被释放
t4.Start( ); // 使用Mutex.WaitOne()方法等待gM2的释放
Thread.Sleep( 2000 );
Console.WriteLine( " - Main releases gM1 " );
gM1.ReleaseMutex( ); // 线程t2,t3结束条件满足
Thread.Sleep( 1000 );
Console.WriteLine( " - Main releases gM2 " );
gM2.ReleaseMutex( ); // 线程t1,t4结束条件满足
// 等待所有四个线程结束
WaitHandle.WaitAll(evs);
Console.WriteLine( " Mutex Sample " );
Console.ReadLine();
}
public void t1Start( )
{
Console.WriteLine( " t1Start started, Mutex.WaitAll(Mutex[]) " );
Mutex[] gMs = new Mutex[ 2 ];
gMs[ 0 ] = gM1; // 创建一个Mutex数组作为Mutex.WaitAll()方法的参数
gMs[ 1 ] = gM2;
Mutex.WaitAll(gMs); // 等待gM1和gM2都被释放
Thread.Sleep( 2000 );
Console.WriteLine( " t1Start finished, Mutex.WaitAll(Mutex[]) satisfied " );
Event1.Set( ); // 线程结束,将Event1设置为有信号状态
}
public void t2Start( )
{
Console.WriteLine( " t2Start started, gM1.WaitOne( ) " );
gM1.WaitOne( ); // 等待gM1的释放
Console.WriteLine( " t2Start finished, gM1.WaitOne( ) satisfied " );
Event2.Set( ); // 线程结束,将Event2设置为有信号状态
}
public void t3Start( )
{
Console.WriteLine( " t3Start started, Mutex.WaitAny(Mutex[]) " );
Mutex[] gMs = new Mutex[ 2 ];
gMs[ 0 ] = gM1; // 创建一个Mutex数组作为Mutex.WaitAny()方法的参数
gMs[ 1 ] = gM2;
Mutex.WaitAny(gMs); // 等待数组中任意一个Mutex对象被释放
Console.WriteLine( " t3Start finished, Mutex.WaitAny(Mutex[]) " );
Event3.Set( ); // 线程结束,将Event3设置为有信号状态
}
public void t4Start( )
{
Console.WriteLine( " t4Start started, gM2.WaitOne( ) " );
gM2.WaitOne( ); // 等待gM2被释放
Console.WriteLine( " t4Start finished, gM2.WaitOne( ) " );
Event4.Set( ); // 线程结束,将Event4设置为有信号状态
}
}
}
using System.Threading;
namespace ThreadExample
{
public class MutexSample
{
static Mutex gM1;
static Mutex gM2;
const int ITERS = 100 ;
static AutoResetEvent Event1 = new AutoResetEvent( false );
static AutoResetEvent Event2 = new AutoResetEvent( false );
static AutoResetEvent Event3 = new AutoResetEvent( false );
static AutoResetEvent Event4 = new AutoResetEvent( false );
public static void Main(String[] args)
{
Console.WriteLine( " Mutex Sample " );
// 创建一个Mutex对象,并且命名为MyMutex
gM1 = new Mutex( true , " MyMutex " );
// 创建一个未命名的Mutex 对象.
gM2 = new Mutex( true );
Console.WriteLine( " - Main Owns gM1 and gM2 " );
AutoResetEvent[] evs = new AutoResetEvent[ 4 ];
evs[ 0 ] = Event1; // 为后面的线程t1,t2,t3,t4定义AutoResetEvent对象
evs[ 1 ] = Event2;
evs[ 2 ] = Event3;
evs[ 3 ] = Event4;
MutexSample tm = new MutexSample( );
Thread t1 = new Thread( new ThreadStart(tm.t1Start));
Thread t2 = new Thread( new ThreadStart(tm.t2Start));
Thread t3 = new Thread( new ThreadStart(tm.t3Start));
Thread t4 = new Thread( new ThreadStart(tm.t4Start));
t1.Start( ); // 使用Mutex.WaitAll()方法等待一个Mutex数组中的对象全部被释放
t2.Start( ); // 使用Mutex.WaitOne()方法等待gM1的释放
t3.Start( ); // 使用Mutex.WaitAny()方法等待一个Mutex数组中任意一个对象被释放
t4.Start( ); // 使用Mutex.WaitOne()方法等待gM2的释放
Thread.Sleep( 2000 );
Console.WriteLine( " - Main releases gM1 " );
gM1.ReleaseMutex( ); // 线程t2,t3结束条件满足
Thread.Sleep( 1000 );
Console.WriteLine( " - Main releases gM2 " );
gM2.ReleaseMutex( ); // 线程t1,t4结束条件满足
// 等待所有四个线程结束
WaitHandle.WaitAll(evs);
Console.WriteLine( " Mutex Sample " );
Console.ReadLine();
}
public void t1Start( )
{
Console.WriteLine( " t1Start started, Mutex.WaitAll(Mutex[]) " );
Mutex[] gMs = new Mutex[ 2 ];
gMs[ 0 ] = gM1; // 创建一个Mutex数组作为Mutex.WaitAll()方法的参数
gMs[ 1 ] = gM2;
Mutex.WaitAll(gMs); // 等待gM1和gM2都被释放
Thread.Sleep( 2000 );
Console.WriteLine( " t1Start finished, Mutex.WaitAll(Mutex[]) satisfied " );
Event1.Set( ); // 线程结束,将Event1设置为有信号状态
}
public void t2Start( )
{
Console.WriteLine( " t2Start started, gM1.WaitOne( ) " );
gM1.WaitOne( ); // 等待gM1的释放
Console.WriteLine( " t2Start finished, gM1.WaitOne( ) satisfied " );
Event2.Set( ); // 线程结束,将Event2设置为有信号状态
}
public void t3Start( )
{
Console.WriteLine( " t3Start started, Mutex.WaitAny(Mutex[]) " );
Mutex[] gMs = new Mutex[ 2 ];
gMs[ 0 ] = gM1; // 创建一个Mutex数组作为Mutex.WaitAny()方法的参数
gMs[ 1 ] = gM2;
Mutex.WaitAny(gMs); // 等待数组中任意一个Mutex对象被释放
Console.WriteLine( " t3Start finished, Mutex.WaitAny(Mutex[]) " );
Event3.Set( ); // 线程结束,将Event3设置为有信号状态
}
public void t4Start( )
{
Console.WriteLine( " t4Start started, gM2.WaitOne( ) " );
gM2.WaitOne( ); // 等待gM2被释放
Console.WriteLine( " t4Start finished, gM2.WaitOne( ) " );
Event4.Set( ); // 线程结束,将Event4设置为有信号状态
}
}
}
程序的输出结果:
Mutex Sample
- Main Owns gM1 and gM2
t1Start started, Mutex.WaitAll(Mutex[])
t2Start started, gM1.WaitOne( )
t3Start started, Mutex.WaitAny(Mutex[])
t4Start started, gM2.WaitOne( )
- Main releases gM1
t2Start finished, gM1.WaitOne( ) satisfied
t3Start finished, Mutex.WaitAny(Mutex[])
- Main releases gM2
t1Start finished, Mutex.WaitAll(Mutex[]) satisfied
t4Start finished, gM2.WaitOne( )
Mutex Sample
- Main Owns gM1 and gM2
t1Start started, Mutex.WaitAll(Mutex[])
t2Start started, gM1.WaitOne( )
t3Start started, Mutex.WaitAny(Mutex[])
t4Start started, gM2.WaitOne( )
- Main releases gM1
t2Start finished, gM1.WaitOne( ) satisfied
t3Start finished, Mutex.WaitAny(Mutex[])
- Main releases gM2
t1Start finished, Mutex.WaitAll(Mutex[]) satisfied
t4Start finished, gM2.WaitOne( )
Mutex Sample
从执行结果可以很清楚地看到,线程t2,t3的运行是以gM1的释放为条件的,而t4在gM2释放后开始执行,t1则在gM1和gM2都被释放了之后才执行。Main()函数最后,使用WaitHandle等待所有的AutoResetEvent对象的信号,这些对象的信号代表相应线程的结束。
本文转自钢钢博客园博客,原文链接:http://www.cnblogs.com/xugang/archive/2008/03/23/1118530.html,如需转载请自行联系原作者