异步等待前线程屈服

然而,在很多方面 Asynchronous Programming Model (APM) 是这种类型的 异步

使用IAsyncResult设计模式的异步操作是 BeginOperationName 和 EndOperationName 开始和结束 异步操作 OperationName 分别。例如 FileStream 类提供 BeginRead EndRead 方法 异步 从文件读取字节 文件。这些方法实现了读取的异步版本 方法。

因为当CPU分配时间给这个线程时,线程处于空闲状态 等待响应,那会浪费CPU时间,对吧?

这有很多工作原理,但是这里可以看到一个示例用法

private static void TestWrite()
{ 
   // Must specify FileOptions.Asynchronous otherwise the BeginXxx/EndXxx methods are
   // handled synchronously.
   FileStream fs = new FileStream(Program.FilePath, FileMode.OpenOrCreate,
      FileAccess.Write, FileShare.None, 8, FileOptions.Asynchronous);

   string content = "A quick brown fox jumps over the lazy dog";
   byte[] data = Encoding.Unicode.GetBytes(content);

   // Begins to write content to the file stream.
   Console.WriteLine("Begin to write");
   fs.BeginWrite(data, 0, data.Length, Program.OnWriteCompleted, fs);
   Console.WriteLine("Write queued");
}

private static void OnWriteCompleted(IAsyncResult asyncResult)
{ 
   // End the async operation.
   FileStream fs = (FileStream)asyncResult.AsyncState;
   fs.EndWrite(asyncResult);

   // Close the file stream.
   fs.Close();
   Console.WriteLine("Write completed");

   // Test async read bytes from the file stream.
   Program.TestRead();
}