在看微軟的ASP.NET - 將 ASP.NET 用作高性能文件下載器?示例里面用到了IO?線程，以前打算自己擼的，這里貼出來?已標記一下：

////// A delegate's BeginInvoke runs on a "worker thread" inside the CLR ThreadPool.// This allows you to run a delegate on a "completion port thread" inside the CLR ThreadPool// instead of a "worker thread" by calling IOBeginInvoke instead of BeginInvoke.// In a nut shell, this mechanism basically skips the actual system I/O and simply posts a// completion delegate to the completion port queue so the completion delegate will be // executed by a "completion port thread" that is working the completion port queue.//// Example:// delegate.BeginInvoke => executes delegate on "worker thread".// delegate.IOBeginInvoke => executes delegate on "completion port thread".// //// Extremely simplified explanation://// CLR ThreadPool is made up of two pools of threads: "worker threads" and "completion port threads".//// Basically you can either queue a user work item which runs the delegate on a "worker thread",// or queue a native overlapped item which runs the completion delegate on a "completion port thread".// ThreadPool.QueueUserWorkItem (and delegate.BeginInvoke) => executes delegate on "worker thread".// ThreadPool.UnsafeQueueNativeOverlapped => executes completion delegate on "completion port thread".//// (CLR ThreadPool)// / \// [worker threads] [completion port threads]//// o o oo o oo _____________post to queue using ThreadPool.UnsafeQueueNativeOverlapped// o o oo o o | (i.e. PostQueuedCompletionStatus)// o o o o o v// oo o oo o o | |// o oo oo o | | <----------completion port queue (one per process)// |__|// ^ oo o// | o o oo <---------completion port threads (work the completion port queue)// | (cpu)(cpu)(cpu)(cpu) (i.e. GetQueuedCompletionStatus in loop)// | // | ^// | |// | |// | |// | |// | Each individual completion delegate is given to the completion port queue to execute,// | and the "completion port threads" working the completion port queue execute the delegate.// | (This has much less risk of thread explosion because each delegate just gets posted to the// | completion port queue, instead of being given to its own individual thread. Basically// | the queue grows, not the threads.)// |// | The completion delegate is supplied in the overlapped structure that is posted to the// | completion port queue.// |// | Posting to queue (PostQueuedCompletionStatus) => done by ThreadPool.UnsafeQueueNativeOverlapped.// | Working queue (GetQueuedCompletionStatus in loop) => done by "completion port thread" working queue.// |// |// Each individual delegate is given to its own individual "worker thread" to execute,// and the OS schedules the "worker thread" to run on a cpu.// (This has the risk of thread explosion because each new delegate executes on its own// individual "worker thread". If the number of threads grows to large the entire OS can// grind to a hault, with all the memory used and the cpu's spending all their time// just trying to schedule the threads to run but not actually doing any work.)// ////public static class IOThread{public delegate void ProcessRequestDelegate(HttpContext context);public class IOAsyncResult : IAsyncResult{public object AsyncState { get; set; }public WaitHandle AsyncWaitHandle { get; set; }public Delegate AsyncDelegate { get; set; }public bool CompletedSynchronously { get; set; }public bool IsCompleted { get; set; }public Exception Exception { get; set; }}unsafe public static IAsyncResult IOBeginInvoke(this ProcessRequestDelegate value, HttpContext context, AsyncCallback callback, object data){ManualResetEvent evt = new ManualResetEvent(false);IOAsyncResult ar = new IOAsyncResult();ar.AsyncState = new object[] { context, callback, data };ar.AsyncDelegate = value;ar.AsyncWaitHandle = evt;Overlapped o = new Overlapped(0, 0, IntPtr.Zero, ar);NativeOverlapped* no = o.Pack(new IOCompletionCallback(ProcessRequestCompletionCallback), data);ThreadPool.UnsafeQueueNativeOverlapped(no);return ar;}unsafe private static void ProcessRequestCompletionCallback(uint errorCode, uint numBytes, NativeOverlapped* no){try{Overlapped o = Overlapped.Unpack(no);ProcessRequestDelegate d = (ProcessRequestDelegate)((IOAsyncResult)o.AsyncResult).AsyncDelegate;object[] state = (object[])o.AsyncResult.AsyncState;HttpContext context = (HttpContext)state[0];AsyncCallback callback = (AsyncCallback)state[1];object data = state[2];try{d(context);}catch(Exception ex){((IOAsyncResult)o.AsyncResult).Exception = ex;}((IOAsyncResult)o.AsyncResult).IsCompleted = true;((ManualResetEvent)o.AsyncResult.AsyncWaitHandle).Set();if (callback != null)callback(o.AsyncResult);}finally{Overlapped.Free(no);}}unsafe public static void IOEndInvoke(this ProcessRequestDelegate value, IAsyncResult result){IOAsyncResult ar = (IOAsyncResult)result;ar.AsyncWaitHandle.WaitOne(Timeout.Infinite);if (ar.Exception != null)throw ar.Exception;}}

使用示例：

////// Example URLs to call download handler and download a file://// https://localhost/DownloadPortal/Download?file=file.txt// https://localhost/DownloadPortal/Download?file=file.txt&chunksize=1000000// https://localhost/DownloadPortal/Download?file=customer1/file.txt// https://localhost/DownloadPortal/Download?file=customer1/file.txt&chunksize=1000000//// Important!!! Must replace 'localhost' in URL with actual machine name or SSL certificate will fail.//// Can either include the 'Range' HTTP request header in the HTTP web request OR// supply the 'chunksize' parameter in the URL. If include the 'Range' HTTP request header,// it will transmit back that portion of the file identified by the 'Range'. If supply the// 'chunksize' parameter, it will transmit back the entire file in separate pieces the size of// 'chunksize'. If supply both, 'Range' will be used. If supply neither, it will transmit back// the entire file in one piece.//// Web.config on IIS 7.0:// <system.webServer>// <handlers>// <add name="Download" verb="*" path="Download" type="DownloadHandlers.DownloadHandler" />// </handlers>// </system.webServer>//// Put DownloadHandler.dll and IOThreads.dll in the /bin directory of the virtual directory on IIS.//// Put files to be downloaded into virtual directory or sub directory under virtual directory.//// To debug:// Debug \ Attach to Process \ w3wp.exe//// Note: Make sure the IIS virtual directory is using an AppPool that is using .NET Framework 4.0.// Define a new AppPool using .NET Framework 4.0, if no other AppPool exists that is using .NET Framework 4.0.////public class DownloadHandler : IHttpAsyncHandler{public IAsyncResult BeginProcessRequest(HttpContext context, AsyncCallback cb, object extraData){//Offloads to "completion port threads" inside CLR ThreadPool//instead of "worker threads" inside CLR ThreadPool, so that our//work doesn't use up the "worker threads" that are needed for the//IIS server's request processing. (see comment section at top of//IOThread class for more details)IOThread.ProcessRequestDelegate d = ProcessRequest;return d.IOBeginInvoke(context, cb, extraData);}public void EndProcessRequest(IAsyncResult result){IOThread.IOAsyncResult ar = (IOThread.IOAsyncResult)result;IOThread.ProcessRequestDelegate d = (IOThread.ProcessRequestDelegate)ar.AsyncDelegate;d.IOEndInvoke(result);}public void ProcessRequest(HttpContext context){try{string file = context.Request.QueryString["File"];if (string.IsNullOrEmpty(file))throw new Exception("Must specify file in query string. (Example: Download?File=your file)");string fileName = Path.GetFileName(file);if (string.IsNullOrEmpty(fileName))throw new Exception("File name '" + fileName + "' is not valid.");long chunkSize = 0;if (!string.IsNullOrEmpty(context.Request.QueryString["ChunkSize"]))if (context.Request.QueryString["ChunkSize"].Trim().Length > 0)chunkSize = long.Parse(context.Request.QueryString["ChunkSize"]);FileInfo fi = new FileInfo(context.Server.MapPath(file));long fileLength = fi.Length;if (chunkSize > 0 && chunkSize > fileLength)throw new Exception("ChunkSize is greater than file length.");context.Response.ClearHeaders();context.Response.ClearContent();context.Response.Clear();//request is just checking file lengthif (context.Request.HttpMethod == "HEAD"){context.Response.AddHeader("content-length", fileLength.ToString());context.Response.AddHeader("accept-ranges", "bytes");context.Response.Flush();return;}//file savecontext.Response.ContentEncoding = Encoding.UTF8;context.Response.AddHeader("content-disposition", "attachment;filename=\"" + fileName + "\"");//context.Response.AddHeader("content-disposition", "attachment;filename=\"" + HttpUtility.UrlEncode(fileName) + "\"");context.Response.ContentType = "application/octet-stream";context.Response.AddHeader("cache-control", "no-store, no-cache");context.Response.ExpiresAbsolute = DateTime.Now.Subtract(new TimeSpan(1, 0, 0, 0));context.Response.Expires = -1;context.Response.AddHeader("Connection", "Keep-Alive");context.Response.AddHeader("accept-ranges", "bytes");//request is for byte rangeif (!string.IsNullOrEmpty(context.Request.Headers["Range"]) && context.Request.Headers["Range"].Trim().Length > 0){string range = context.Request.Headers["Range"];range = range.Replace(" ", "");string[] parts = range.Split(new char[] { '=', '-' });long contentLength = long.Parse(parts[2]) - long.Parse(parts[1]);context.Response.AddHeader("content-length", contentLength.ToString());string contentRange = string.Format("bytes {0}-{1}/{2}", parts[1], parts[2], fileLength.ToString());context.Response.AddHeader("content-range", contentRange);context.Response.AddHeader("last-modified", DateTime.Now.ToString("ddd, dd MMM yyyy hh:mm:ss") + " GMT");byte[] bytes = Encoding.ASCII.GetBytes(string.Format("{0} : {1}", fi.Name, fi.LastAccessTimeUtc));string eTag = Convert.ToBase64String(MD5CryptoServiceProvider.Create().ComputeHash(bytes));context.Response.AddHeader("ETag", string.Format("\"{0}\"", eTag));context.Response.StatusCode = 206; //partial content context.Response.TransmitFile(file, long.Parse(parts[1]), contentLength);context.Response.Flush();}else //request is not for byte range {context.Response.AddHeader("content-length", fileLength.ToString());if (chunkSize <= 0){context.Response.TransmitFile(file);context.Response.Flush();}else{long index = 0;while (true){if (index >= fileLength)break;if (index < fileLength && index + chunkSize > fileLength){context.Response.TransmitFile(file, index, fileLength - index);context.Response.Flush();break;}context.Response.TransmitFile(file, index, chunkSize);context.Response.Flush();index += chunkSize;}}}}catch (Exception ex){context.Response.ClearHeaders();context.Response.ClearContent();context.Response.Clear();context.Response.StatusCode = 500;context.Response.Write("Download Error: " + ex.GetBaseException().Message);context.Response.Flush();//throw ex; }finally{context.Response.End();//context.ApplicationInstance.CompleteRequest(); }}public bool IsReusable{get { return false; }}}

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轉載于:https://www.cnblogs.com/majiang/p/7954868.html

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