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書名： Multithreading in C# 5.0 Cookbook
作者名： Eugene Agafonov
本章字?jǐn)?shù)： 317字
更新時(shí)間： 2021-07-21 18:10:01

Using the Mutex construct

This recipe will describe how to synchronize two separate programs using a Mutex construct. Mutex is a primitive synchronization that grants exclusive access of the shared resource to only one thread.

Getting ready

To step through this recipe, you will need Visual Studio 2012. There are no other prerequisites. The source code for this recipe could be found at 7644_Code\Chapter2\Recipe2.

How to do it...

To understand the synchronization of two separate programs using the Mutex construct, perform the following steps:

Start Visual Studio 2012. Create a new C# Console Application project.
In the Program.cs file, add the following using directives:
```
using System;
using System.Threading;
```

Inside the Main method, add the following code snippet:

const string MutexName = "CSharpThreadingCookbook";

using (var m = new Mutex(false, MutexName))
{
  if (!m.WaitOne(TimeSpan.FromSeconds(5), false))
  {
    Console.WriteLine("Second instance is running!");
  }
  else
  {
    Console.WriteLine("Running!");
    Console.ReadLine();
    m.ReleaseMutex();
  }
}

Run the program.

How it works...

When the main program starts, it defines a mutex with a specific name, providing the initialOwner flag as false. This allows the program to acquire a mutex if it is already created. Then, if no mutex was acquired, the program simply displays Running, and waits for any key to be pressed to release the mutex and exit.

If we start a second copy of the program, it will wait for 5 seconds, trying to acquire the mutex. If we press any key in the first copy of a program, the second one will start executing. However, if we keep waiting for 5 seconds, the second copy of the program will fail to acquire the mutex.

Tip

Please note that a named mutex is a global operating system object! Always close the mutex properly; the best choice is to wrap a mutex object using a block.

This makes it possible to synchronize threads in different programs, which could be useful in a large number of scenarios.

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Multithreading in C# 5.0 Cookbook

Using the Mutex construct

Getting ready

How to do it...

How it works...

Tip