{"id":890,"date":"2023-03-11T18:54:31","date_gmt":"2023-03-11T11:54:31","guid":{"rendered":"https:\/\/csharptutorial.net\/?page_id=890"},"modified":"2023-03-11T19:10:25","modified_gmt":"2023-03-11T12:10:25","slug":"csharp-autoresetevent","status":"publish","type":"page","link":"https:\/\/www.csharptutorial.net\/csharp-concurrency\/csharp-autoresetevent\/","title":{"rendered":"C# AutoResetEvent"},"content":{"rendered":"\n

Summary<\/strong>: in this tutorial, you’ll learn how to use the C# AutoResetEvent<\/code> class to synchronize threads and control their executions by signaling events between them.<\/p>\n\n\n\n

Introduction to the C# AutoResetEvent class<\/h2>\n\n\n\n

The AutoResetEvent<\/code> class allows multiple threads to communicate with each other by signaling events.<\/p>\n\n\n\n

An AutoResetEvent<\/code> has two states:<\/p>\n\n\n\n

    \n
  • Signaled<\/li>\n\n\n\n
  • Non-signaled<\/li>\n<\/ul>\n\n\n\n

    When an AutoResetEvent<\/code> object is signaled, a single waiting thread will be released and continues its execution.<\/p>\n\n\n\n

    However, when an AutoResetEvent<\/code><\/code> object is Unsignaled, the waiting thread will be blocked until the AutoResetEvent<\/code><\/code> becomes signaled again.<\/p>\n\n\n\n

    The AutoResetEvent<\/code> object has two main methods that control its state: Waitone()<\/code> and Set()<\/code>:<\/p>\n\n\n\n

      \n
    • The WaitOne()<\/code> method blocks the current thread until the AutoResetEvent<\/code> is signaled or a timeout interval has elapsed.<\/li>\n\n\n\n
    • The Set()<\/code> method changed the state of the AutoResetEvent<\/code> to non-signaled and releases a single waiting thread.<\/li>\n<\/ul>\n\n\n\n

      In practice, you use the AutoResetEvent<\/code> in multithreaded applications where one thread needs to wait for another thread to complete its work before continuing.<\/p>\n\n\n\n

      For example, in a producer-consumer scenario, the consumer thread may wait for the producer thread to produce the data before the consumer thread can consume the data.<\/p>\n\n\n\n

      To use the AutoResetEvent<\/code> class, you can follow these steps:<\/p>\n\n\n\n

      First, create an AutoResetEvent<\/code> object:<\/p>\n\n\n

      var<\/span> autoResetEvent = new<\/span> AutoResetEvent(false<\/span>);<\/code><\/span>Code language:<\/span> C#<\/span> (<\/span>cs<\/span>)<\/span><\/small><\/pre>\n\n\n
      The parameter false sets the state of the AutoResetEvent<\/code> object to Unsignaled.<\/p>\n\n\n\n
      Second, create one thread that waits for the event to be signaled:<\/p>\n\n\n
      var<\/span> t = new<\/span> Thread(() =>\n{\n    \/\/ do some work<\/span>\n    \/\/ ...<\/span>\n    \/\/ wait for the event to be signaled<\/span>\n    autoResetEvent.WaitOne(); \n    \n    \/\/ continue execution after the event is signaled<\/span>\n    \/\/ do something else<\/span>\n});<\/code><\/span>Code language:<\/span> C#<\/span> (<\/span>cs<\/span>)<\/span><\/small><\/pre>\n\n\n
      Third, starts the thread:<\/p>\n\n\n
      t.Start();<\/code><\/span>Code language:<\/span> C#<\/span> (<\/span>cs<\/span>)<\/span><\/small><\/pre>\n\n\n
      Fourth, do some operations before the thread can continue to execute and signal the AutoResetEvent<\/code> by calling the Set()<\/code> method:<\/p>\n\n\n
      autoResetEvent.Set();<\/code><\/span>Code language:<\/span> C#<\/span> (<\/span>cs<\/span>)<\/span><\/small><\/pre>\n\n\n
      The Set()<\/code> method changes the state of the AutoResetEvent<\/code> to signaled. As the result, the waiting thread (t) is released and continues the execution until the next call of the WaitOne()<\/code> method.  <\/p>\n\n\n\n
      Once the thread is released, the AutoResetEvent<\/code> is automatically reset to the Non-signaled state.<\/p>\n\n\n\n
      Notice that the AutoResetEvent<\/code> will be reset automatically after releasing a single waiting thread. To release multiple waiting threads, you need to call the Set()<\/code> method for each waiting thread or use the ManualResetEvent<\/code> class instead.<\/p>\n\n\n\n
      C# AutoResetEvent class example<\/h2>\n\n\n\n
      The following program demonstrates how the AutoResetEvent<\/code> works:<\/p>\n\n\n
      using<\/span> static<\/span> System.Console;\n\nvar<\/span> autoResetEvent = new<\/span> AutoResetEvent(false<\/span>);\n\nvoid<\/span> DoWork<\/span>(<\/span>)<\/span>\n{\n    WriteLine($\"Thread {Thread.CurrentThread.ManagedThreadId}<\/span> is waiting for the event to be signaled...\"<\/span>);\n\n    \/\/ Wait for the event to be signaled<\/span>\n    autoResetEvent.WaitOne();\n\n    WriteLine($\"Thread {Thread.CurrentThread.ManagedThreadId}<\/span> has been signaled and has resumed execution.\"<\/span>);\n}\n\n\/\/ Create a thread that wait for the event to be signaled and start it<\/span>\nvar<\/span> t = new<\/span> Thread(() => DoWork());\nt.Start();\n\n\/\/ Wait for 1s to let the thread runs for a while <\/span>\nThread.Sleep(1000<\/span>);\n\n\/\/ Wait for 2s before signaling the event<\/span>\nWriteLine(\"Waiting for 2 seconds before signaling the event...\"<\/span>);\nThread.Sleep(2000<\/span>);\n\n\n\/\/ Signal the event<\/span>\nautoResetEvent.Set();\n\n\/\/ Wait for the threads to finish<\/span>\nt.Join();\n\nWriteLine(\"Press any key to exit.\"<\/span>);\nReadKey();<\/code><\/span>Code language:<\/span> C#<\/span> (<\/span>cs<\/span>)<\/span><\/small><\/pre>\n\n\n
      How it works.<\/p>\n\n\n\n
      First, create a new AutoResetEvent<\/code> object and initialize it with false, denoting that the event is not signaled initially:<\/p>\n\n\n
      var<\/span> autoResetEvent = new<\/span> AutoResetEvent(false<\/span>);<\/code><\/span>Code language:<\/span> C#<\/span> (<\/span>cs<\/span>)<\/span><\/small><\/pre>\n\n\n
      Second, define the DoWork()<\/code> method that represents the operation that a thread will perform:<\/p>\n\n\n
      void<\/span> DoWork<\/span>(<\/span>)<\/span>\n{\n    WriteLine($\"Thread {Thread.CurrentThread.ManagedThreadId}<\/span> is waiting for the event to be signaled...\"<\/span>);\n\n    \/\/ Wait for the event to be signaled<\/span>\n    autoResetEvent.WaitOne();\n\n    WriteLine($\"Thread {Thread.CurrentThread.ManagedThreadId}<\/span> has been signaled and has resumed execution.\"<\/span>);\n}<\/code><\/span>Code language:<\/span> C#<\/span> (<\/span>cs<\/span>)<\/span><\/small><\/pre>\n\n\n
      The DoWork()<\/code> method writes a message to the console indicating that the thread is waiting for the event to be signaled. It then calls the WaitOne()<\/code> method of the AutoResetEvent<\/code> object to wait for the event to be signaled. <\/p>\n\n\n\n
      The WaitOne()<\/code> method blocks the thread that executes the DoWork()<\/code> method until the AutoResetEvent<\/code> object becomes signaled.<\/p>\n\n\n\n
      When the AutoResetEvent<\/code> is signaled, the method resumes its execution that writes another message to the console.<\/p>\n\n\n\n
      Third, create and start a new thread that executes the DoWork()<\/code> method:<\/p>\n\n\n
      var<\/span> t = new<\/span> Thread(() => DoWork());\nt.Start();<\/code><\/span>Code language:<\/span> C#<\/span> (<\/span>cs<\/span>)<\/span><\/small><\/pre>\n\n\n
      Fourth, wait for one second to leave enough time for the thread t to run until the WaitOne()<\/code> method is called:<\/p>\n\n\n
      Thread.Sleep(1000<\/span>);<\/code><\/span>Code language:<\/span> C#<\/span> (<\/span>cs<\/span>)<\/span><\/small><\/pre>\n\n\n
      Fifth, write a message to the console and wait for two seconds before signaling the event: <\/p>\n\n\n
      WriteLine(\"Waiting for 2 seconds before signaling the event...\"<\/span>);\nThread.Sleep(2000<\/span>);<\/code><\/span>Code language:<\/span> C#<\/span> (<\/span>cs<\/span>)<\/span><\/small><\/pre>\n\n\n
      Sixth, change the state of the AutoResetEvent<\/code><\/code> object to be signaled by calling the Set()<\/code> method of the AutoResetEvent<\/code><\/code> object:<\/p>\n\n\n
      autoResetEvent.Set();<\/code><\/span>Code language:<\/span> C#<\/span> (<\/span>cs<\/span>)<\/span><\/small><\/pre>\n\n\n
      At this moment, the thread that executes the DoWork<\/code> resumes its execution and displays a message to the console.<\/p>\n\n\n\n
      Seventh, wait for the thread to complete by calling the Join()<\/code> method of the Thread class:<\/p>\n\n\n
      t.Join();<\/code><\/span>Code language:<\/span> C#<\/span> (<\/span>cs<\/span>)<\/span><\/small><\/pre>\n\n\n
      Finally, wait for the user to press any key to exit the program:<\/p>\n\n\n
      WriteLine(\"Press any key to exit.\"<\/span>);\nReadKey();<\/code><\/span>Code language:<\/span> C#<\/span> (<\/span>cs<\/span>)<\/span><\/small><\/pre>\n\n\n
      The following example shows the output of the program:<\/p>\n\n\n
      Thread 9<\/span> is<\/span> waiting for<\/span> the event<\/span> to be signaled...\nWaiting for<\/span> 2<\/span> seconds before signaling the event<\/span>...\nThread 9<\/span> has been signaled and has resumed execution.\nPress any key to exit.<\/code><\/span>Code language:<\/span> C#<\/span> (<\/span>cs<\/span>)<\/span><\/small><\/pre>\n\n\n
      Summary<\/h2>\n\n\n\n
        \n
      • Use the C# AutoResetEvent<\/code> class to synchronize threads and control their executions by signaling events between them.<\/li>\n<\/ul>\n
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