/// <summary>
/// 开始下载文件
/// </summary>
/// <returns></returns>
public async Task DownloadFile()
{
_logger.LogInformation($"Start download Url={Url} File={File.FullName}");
var(response, contentLength) = await GetContentLength();
FileStream = File.Create();
FileStream.SetLength(contentLength);
FileWriter = new RandomFileWriter(FileStream);
SegmentManager = new SegmentManager(contentLength);
_progress.Report(new DownloadProgress($"file length = {contentLength}", SegmentManager));
var downloadSegment = SegmentManager.GetNewDownloadSegment();
// 下载第一段
Download(response, downloadSegment);
var supportSegment = await TryDownloadLast(contentLength);
var threadCount = 1;
if (supportSegment)
{
// 多创建几个线程下载
threadCount = 10;
for (var i = 0; i < threadCount; i++)
{
Download(SegmentManager.GetNewDownloadSegment());
}
}
for (var i = 0; i < threadCount; i++)
{
_ = Task.Run(DownloadTask);
}
await FileDownloadTask.Task;
}
/// <summary>
/// 网速控制开关
/// </summary>
/// <returns></returns>
private async void ControlSwitch()
{
// 使用独立的线程的优势在于不需要等待下载就能进入方法
// 可以干掉 LastTime 属性，因此定时是 3 秒
await Task.Delay(ControlDelayTime);
while (!SegmentManager.IsFinished())
{
LogDebugInternal("Start ControlSwitch");
var(segment, runCount, maxReportTime) = SegmentManager.GetDownloadSegmentStatus();
int waitCount = DownloadDataList.Count;
LogDebugInternal("ControlSwitch 当前等待数量：{0},待命最大响应时间：{1},运行数量：{2},运行线程{3}", waitCount, maxReportTime, runCount, _threadCount);
if (maxReportTime > TimeSpan.FromSeconds(10) && segment != null && runCount > 1)
{
// 此时速度太慢
segment.LoadingState = DownloadingState.Pause;
LogDebugInternal("ControlSwitch slowly pause segment={0}", segment.Number);
}
else if (maxReportTime < TimeSpan.FromMilliseconds(600) && waitCount > 0 || runCount < 1)
{
// 速度非常快，尝试再开线程，或者当前没有在进行的任务
// 如果此时是刚好全部完成了，而 runCount 是 0 进入 StartDownloadTask 也将会啥都不做
LogDebugInternal("ControlSwitch StartDownloadTask");
// 这里不需要线程安全，如果刚好全部线程都在退出，等待 ControlDelayTime 再次创建
if (_threadCount < MaxThreadCount)
{
StartDownloadTask();
}
}
LogDebugInternal("Finish ControlSwitch");
//变速器3秒为一周期
await Task.Delay(ControlDelayTime);
}
}
/// <summary>
/// 开始下载文件
/// </summary>
/// <returns></returns>
public async Task DownloadFileAsync()
{
_logger.LogInformation($"Start download Url={Url} File={File.FullName}");
var(response, contentLength) = await GetContentLength();
_logger.LogInformation($"ContentLength={contentLength}");
if (contentLength < 0)
{
// contentLength == -1
// 当前非下载内容，没有存在长度
// 可测试使用的链接是 https://dotnet.microsoft.com/download/dotnet/thank-you/sdk-5.0.100-preview.7-windows-x64-installer
_logger.LogWarning($"Can not download file. ContentLength={contentLength}");
return;
}
FileStream = File.Create();
FileStream.SetLength(contentLength);
FileWriter = new RandomFileWriterWithOrderFirst(FileStream);
FileWriter.StepWriteFinished += (sender, args) => SharedArrayPool.Return(args.Data);
SegmentManager = new SegmentManager(contentLength);
_progress.Report(new DownloadProgress($"file length = {contentLength}", SegmentManager));
var downloadSegment = SegmentManager.GetNewDownloadSegment();
// 下载第一段
Download(response, downloadSegment !);
var supportSegment = await TryDownloadLast(contentLength);
int threadCount;
if (supportSegment)
{
// 先根据文件的大小，大概是 1M 让一个线程下载，至少需要开两个线程，最多是 10 个线程
threadCount = Math.Max(Math.Min(2, (int)(contentLength / 1024 / 1024)), MaxThreadCount);
}
else
{
// 不支持分段下载下，多个线程也没啥用
threadCount = 1;
}
if (supportSegment)
{
// 多创建几个线程下载
for (var i = 0; i < threadCount; i++)
{
Download(SegmentManager.GetNewDownloadSegment());
}
//控制开关，如果下载阻塞就先暂停
ControlSwitch();
}
// 一开始就创建足够量的线程尝试下载
for (var i = 0; i < threadCount; i++)
{
StartDownloadTask();
}
await FileDownloadTask.Task;
}
public DownloadProgress(string message, SegmentManager segmentManager)
{
Message = message;
SegmentManager = segmentManager;
}
public DownloadProgress(SegmentManager segmentManager)
{
SegmentManager = segmentManager;
}