我已经构建了一个从互联网上下载文件的简单控制台应用程序.
因为 I had problems with WebClient我决定使用HttpClient编写我的应用程序.
因为 I had problems with WebClient我决定使用HttpClient编写我的应用程序.
基本上我正在请求读取头文件,然后使用ReadAsStreamAsync我正在获取流,我正在使用CopyToAsync复制到本地文件.
public static class StreamExtensions
{
public static async Task CopyToAsync(this Stream source,Stream destination,IProgress<long> progress,CancellationToken cancellationToken = default(CancellationToken),int bufferSize = 0x1000)
{
var buffer = new byte[bufferSize];
int bytesRead;
long totalRead = 0;
while ((bytesRead = await source.ReadAsync(buffer,buffer.Length,cancellationToken)) > 0)
{
await destination.WriteAsync(buffer,bytesRead,cancellationToken);
cancellationToken.ThrowIfCancellationRequested();
totalRead += bytesRead;
//Thread.Sleep(10);
progress.Report(totalRead);
}
}
}
我的应用程序有效,但我得到了错误的进度信息.
例如,当下载2个文件时,我在输出窗口中看到了这个：
file1.tmp 60.95% file2.tmp 98.09% file1.tmp 60.98% file2.tmp 98.21% file2.tmp 98.17% file2.tmp 98.25% file1.tmp 61.02% file2.tmp 98.41% file2.tmp downloaded file2.tmp 98.29% file2.tmp 98.37% file1.tmp 61.06% file2.tmp 89.27% file2.tmp 89.31% file2.tmp 98.33% file2.tmp 98.45% file2.tmp 98.48% file1.tmp 61.10% file1.tmp 61.14% file2.tmp 98.52% file1.tmp 61.22% file2.tmp 98.60% file2.tmp 98.56% file1.tmp 61.30% file2.tmp 98.88% file2.tmp 90.44% file1.tmp 61.53% file2.tmp 98.72% file1.tmp 61.41% file1.tmp 61.73% file2.tmp 98.80% file1.tmp 61.26% file1.tmp 61.49% file1.tmp 61.57% file1.tmp 61.69% ... file1.tmp 99.31% file1.tmp 98.84% file1.tmp 98.80% file1.tmp 99.04% file1.tmp 99.43% file1.tmp 99.12% file1.tmp 99.00% file1.tmp downloaded file1.tmp 100.00% file1.tmp 98.73% file1.tmp 98.88% file1.tmp 99.47% file1.tmp 99.98% file1.tmp 99.90% file1.tmp 98.96% file1.tmp 99.78% file1.tmp 99.99% file1.tmp 99.74% file1.tmp 99.59% file1.tmp 99.94% file1.tmp 98.49% file1.tmp 98.53% ALL FILES DOWNLOADED file1.tmp 99.55% file1.tmp 98.41% file1.tmp 99.62% file1.tmp 98.34% file1.tmp 99.66% file1.tmp 98.69% file1.tmp 98.37%
正如您所看到的,我得到了file2已下载的信息,但我仍然从CopyToAsync获取进度报告,与file1相同.
因为我有时会得到这个奇怪的控制台输出：
理想情况下,我想确定比打电话时：
await streamToReadFrom.CopyToAsync(streamToWriteTo,progress,source.Token,0x2000); Debug.WriteLine(filename+" downloaded");
在我获得调试信息后,没有报告进度(文件已下载).我认为等待将解决我的问题,但事实并非如此.
我怎样才能解决这个问题？作为临时解决方案,我在报告进度之前就将Thread.Sleep添加到CopyToAsync.
以下是我目前的代码：
using System;
using System.Collections.Generic;
using System.Diagnostics;
using System.IO;
using System.Linq;
using System.Net.Http;
using System.Threading;
using System.Threading.Tasks;
namespace AsyncDownloadTest
{
class Program
{
private const string LocalPath = @"D:\TEMP";
static void Main()
{
try
{
var filesToDownlad = new List<Tuple<string,string>>
{
new Tuple<string,string>("file1.tmp","http://ipv4.download.thinkbroadband.com/10MB.zip"),new Tuple<string,string>("file2.tmp","http://ipv4.download.thinkbroadband.com/10MB.zip")
};
_consolePosition = -1;
Console.CursorVisible = false;
Parallel.ForEach(filesToDownlad,new ParallelOptions { MaxDegreeOfParallelism = 4 },doc =>
{
DownloadFile(doc.Item2,doc.Item1).Wait();
});
Debug.WriteLine("ALL FILES DOWNLOADED");
Console.CursorVisible = true;
}
catch (Exception e)
{
Console.WriteLine(e);
Console.ReadLine();
}
}
private static readonly object ConsoleLock = new object();
private static int _consolePosition;
static readonly CancellationTokenSource source = new CancellationTokenSource();
private static async Task DownloadFile(string url,string filename)
{
int currenctLineNumber = 0;
int currectProgress = 0;
try
{
lock (ConsoleLock)
{
_consolePosition++;
currenctLineNumber = _consolePosition;
}
long fileSize = -1;
IProgress<long> progress = new Progress<long>(value =>
{
decimal tmp = (decimal)(value * 100) / fileSize;
if (tmp != currectProgress && tmp > currectProgress)
{
lock (ConsoleLock)
{
currectProgress = (int)tmp;
Console.CursorTop = currenctLineNumber;
Console.CursorLeft = 0;
Console.Write("{0,10} - {2,11} - {1,6:N2}%",filename,tmp,"DOWNLOADING");
}
Debug.WriteLine("{1} {0:N2}%",filename);
}
});
using (HttpClient client = new HttpClient())
{
using (HttpResponseMessage response = await client.GetAsync(url,HttpCompletionOption.ResponseHeadersRead,source.Token))
{
response.EnsureSuccessStatusCode();
if (response.Content.Headers.ContentLength.HasValue) fileSize = response.Content.Headers.ContentLength.Value;
if (response.Content.Headers.ContentDisposition != null)
{
var tmp = response.Content.Headers.ContentDisposition.FileName.Replace("\"","");
Debug.WriteLine("Real name: {0}",tmp);
}
using (Stream streamToReadFrom = await response.Content.ReadAsStreamAsync())
{
using (Stream streamToWriteTo = File.Open(Path.Combine(LocalPath,filename),FileMode.Create,FileAccess.Write))
{
await streamToReadFrom.CopyToAsync(streamToWriteTo,0x2000);
Debug.WriteLine(filename+" downloaded");
lock (ConsoleLock)
{
Console.CursorTop = currenctLineNumber;
Console.CursorLeft = 0;
var oldColor = Console.ForegroundColor;
Console.ForegroundColor = ConsoleColor.Green;
Console.Write("{0,100,"SUCCESS");
Console.ForegroundColor = oldColor;
}
}
}
}
}
}
catch (Exception e)
{
Debug.WriteLine(e.Message);
lock (ConsoleLock)
{
Console.CursorTop = currenctLineNumber;
Console.CursorLeft = 0;
var oldColor = Console.ForegroundColor;
Console.ForegroundColor = ConsoleColor.Red;
Console.Write("{0,currectProgress,"ERROR");
Console.ForegroundColor = oldColor;
}
}
}
}
public static class StreamExtensions
{
public static async Task CopyToAsync(this Stream source,int bufferSize = 0x1000)
{
var buffer = new byte[bufferSize];
int bytesRead;
long totalRead = 0;
while ((bytesRead = await source.ReadAsync(buffer,cancellationToken)) > 0)
{
await destination.WriteAsync(buffer,cancellationToken);
cancellationToken.ThrowIfCancellationRequested();
totalRead += bytesRead;
Thread.Sleep(10);
progress.Report(totalRead);
}
}
}
}
解决方法
你的问题实际上在这里：
new Progress<long>
进展< T> class always invokes its callbacks in a SynchronizationContext – 在本例中是线程池SynchronizationContext.这意味着当进度报告代码调用Report时,它只是将回调排队到线程池.因此,可能会看到它们出现故障(或者在下载实际完成后仍然会出现这种情况).
要解决此问题,您可以创建自己的IProgress< T>自定义实现：
//C#6.0
public sealed class SynchronousProgress<T> : IProgress<T>
{
private readonly Action<T> _callback;
public SynchronousProgress(Action<T> callback) { _callback = callback; }
void IProgress<T>.Report(T data) => _callback(data);
}
//older version
public sealed class SynchronousProgress<T> : IProgress<T>
{
private readonly Action<T> _callback;
public SynchronousProgress(Action<T> callback)
{
_callback = callback;
}
void IProgress<T>.Report(T data)
{
_callback(data);
}
}
然后更换线
IProgress<long> progress = new Progress<long>(value =>
同
IProgress<long> progress = new SynchronousProgress<long>(value =>
