Asynchronous and wait (async and await), asyncawait

Asynchronous and wait (async and await), asyncawait

In. Net 4.5, a new task-based asynchronous programming model (TAP) is introduced through the async and await keywords ). In this way, asynchronous code can be written in a similar synchronous mode, greatly simplifying the asynchronous programming model. A simple example is as follows:

static async void DownloadStringAsync2(Uri uri)    {        var webClient = new WebClient();        var result = await webClient.DownloadStringTaskAsync(uri);        Console.WriteLine(result);    }

The previous method is as follows:

static void DownloadStringAsync(Uri uri)    {        var webClient = new WebClient();        webClient.DownloadStringCompleted += (s, e) =>            {                Console.WriteLine(e.Result);            };        webClient.DownloadStringAsync(uri);    }

Perhaps the previous example is insufficient to reflect the superiority brought by async and await. The following example is much more obvious:

public void CopyToAsyncTheHardWay(Stream source, Stream destination)    {        byte[] buffer = new byte[0x1000];        Action<IAsyncResult> readWriteLoop = null;        readWriteLoop = iar =>        {            for (bool isRead = (iar == null); ; isRead = !isRead)            {                switch (isRead)                {                    case true:                        iar = source.BeginRead(buffer, 0, buffer.Length,                            readResult =>                            {                                if (readResult.CompletedSynchronously) return;                                readWriteLoop(readResult);                            }, null);                        if (!iar.CompletedSynchronously) return;                        break;                    case false:                        int numRead = source.EndRead(iar);                        if (numRead == 0)                        {                            return;                        }                        iar = destination.BeginWrite(buffer, 0, numRead,                            writeResult =>                            {                                if (writeResult.CompletedSynchronously) return;                                destination.EndWrite(writeResult);                                readWriteLoop(null);                            }, null);                        if (!iar.CompletedSynchronously) return;                        destination.EndWrite(iar);                        break;                }            }        };        readWriteLoop(null);    }    public async Task CopyToAsync(Stream source, Stream destination)    {        byte[] buffer = new byte[0x1000];        int numRead;        while ((numRead = await source.ReadAsync(buffer, 0, buffer.Length)) != 0)        {            await destination.WriteAsync(buffer, 0, numRead);        }    }

For more information, see Microsoft's official website: Visual Studio Asynchronous Programming. Its official documentation, Task-Based Asynchronous Pattern Overview, describes CSharp Language Specification in Visual Studio.

 

Source: http://blog.csdn.net/wulex/article/details/73499500