/// <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>
/// 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;
}