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转发自：http://www.cnblogs.com/HouZhiHouJueBlogs/p/3945195.html 互斥量是一个内核对象，它用来确保一个线程独占一个资源的访问，并且互斥量可以用于不同进程中的线程互斥访问资源。 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C# Mutex对象的关系也正是如此，线程使用Mutex.WaitOne()方法等待C# Mutex对象被释放，如果它等待的C# Mutex对象被释放了，或者它没有被任何对象有用，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C# Mutex对象的线程都只有等待。 Msdn地址：http://msdn.microsoft.com/en-us/library/system.threading.mutex(v=vs.110).aspx 举MSDN上的例子说明： using System;
using System.Threading;
class Example
{
// Create a new Mutex. The creating thread does not own the mutex.
private static Mutex mut = new Mutex();
private const int numIterations = 1;
private const int numThreads = 3;
static void Main()
{
// Create the threads that will use the protected resource.
for(int i = 0; i < numThreads; i++)
{
Thread newThread = new Thread(new ThreadStart(ThreadProc));
newThread.Name = String.Format("Thread{0}", i + 1);
newThread.Start();
}
// The main thread exits, but the application continues to
// run until all foreground threads have exited.
}
private static void ThreadProc()
{
for(int i = 0; i < numIterations; i++)
{
UseResource();
}
}
// This method represents a resource that must be synchronized
// so that only one thread at a time can enter.
private static void UseResource()
{
// Wait until it is safe to enter, and do not enter if the request times out.
Console.WriteLine("{0} is requesting the mutex", Thread.CurrentThread.Name);
if (mut.WaitOne(1000)) {
Console.WriteLine("{0} has entered the protected area",
Thread.CurrentThread.Name);
// Place code to access non-reentrant resources here.
// Simulate some work.
Thread.Sleep(5000);
Console.WriteLine("{0} is leaving the protected area",
Thread.CurrentThread.Name);
// Release the Mutex.
mut.ReleaseMutex();
Console.WriteLine("{0} has released the mutex",
Thread.CurrentThread.Name);
}
else {
Console.WriteLine("{0} will not acquire the mutex",
Thread.CurrentThread.Name);
}
}
}
// The example displays output like the following:
// Thread1 is requesting the mutex
// Thread1 has entered the protected area
// Thread2 is requesting the mutex
// Thread3 is requesting the mutex
// Thread2 will not acquire the mutex
// Thread3 will not acquire the mutex
// Thread1 is leaving the protected area
// Thread1 has released the mutex
当一个线程占有Mutex后，代码就可以这样写： mutex.WaitOne(); mutex.WaitOne(); mutex.WaitOne(); mutex.WaitOne(); 。。 。。 WaitOne这个方法被调用时 系统检查发现mutex没有被任何线程使用 故而将mutex分配给当前线程 所以不能这样写： mutex.ReleaseMutex();//如果已经占有 那么OK mutex.ReleaseMutex();//调用第二次直接异常 Mutex是一个内核对象，所以，它是可以用作跨进程线程同步的。 A进程可以如此写： Mutex mutex = new Mutex(true,"mutex1"); B进程则可以如此写： Mutex mutex = Mutex.OpenExisting("mutex1")
OpenExisting这个方法签名我们后面也可以经常看到，作用就是获取一个已经存在的内核对象。 完毕。 |
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