Question

ASP.NET 3.5 VB.NET

我有代码，我想从10个不同的URL中获取PNG图像。

我发现获取每个PNG最多可能需要2-3秒才能认为最好同时获取所有PNG。

有人可以通过调整下面的代码为每个PNG抓取制作一个线程来帮助我吗？在尝试一小时左右之前和之后我没有做过很多线程的东西我希望得到一些帮助。 TIA

Imports Microsoft.VisualBasic
Imports System.Collections.Generic
Imports System.Drawing
Imports System.Drawing.Drawing2D


Public Class TestImageSuggestionsCreate

    Dim intClsWidthMaximumAllowed As Integer = 600
    Dim intClsHeightMaximumAllowed As Integer = 400
    Dim intClsWidthMinimumAllowed As Integer = 200
    Dim intClsHeightMinimumAllowed As Integer = 200

    Dim strClsImageOriginalURL As String = ""
    Dim lstClsWebsitesImageURLs As New List(Of String)


    Public Function fWebsitesImageSuggestionsCreate() As Boolean

        'Load URLS strings into class List variable: lstClsWebsitesImageURLs
        fWebsitesImageURLSuggestionsGet()

        'Go through each URL and download image to disk
        For Each strURL1 As String In lstClsWebsitesImageURLs

            'This needs to be done in a separate thread 
            '(Up to 10 threads):

            fAddImageIfSuitable(strURL1)

        Next

    End Function

    Private Function fWebsitesImageURLSuggestionsGet() As Boolean

        Dim strURL As String = ""

        strURL = "https://upload.wikimedia.org/wikipedia/en/thumb/f/f7/Sheraton_Hotels.svg/1231px-Sheraton_Hotels.svg.png"
        lstClsWebsitesImageURLs.Add(strURL)

        strURL = "http://wall--art.com/wp-content/uploads/2014/10/sheraton-logo-png.png"
        lstClsWebsitesImageURLs.Add(strURL)

        'Up to 10 strURL items
        '.............

    End Function

    Private Function fAddImageIfSuitable(ByVal strImageURL As String) As Boolean

        'Get bitmap from URL
        Dim btmImage1 As Bitmap = New Bitmap(fGetStreamBitmap(strImageURL))

        'Don't add if image too small
        If btmImage1.Width < intClsWidthMinimumAllowed Or _
            btmImage1.Height < intClsHeightMinimumAllowed Then
            Exit Function
        End If

        'Save image to disk here
        '..............

    End Function

    Private Function fGetStreamBitmap(ByVal strURL As String) As Bitmap

        Try
            Dim request As System.Net.WebRequest = System.Net.WebRequest.Create(strURL)
            Dim response As System.Net.WebResponse = request.GetResponse()
            Dim responseStream As System.IO.Stream = response.GetResponseStream()
            Dim btmBitmap1 As New Bitmap(responseStream)

            Return btmBitmap1

        Finally
        End Try

    End Function

End Class

Answer 1

使用Parallel.ForEach进行简化线程。

How to: Write a Simple Parallel.ForEach Loop

您可以使用MaxDegreeOfParallelism限制主题数。

Parallel.ForEach(
    lstClsWebsitesImageURLs,
    new ParallelOptions { MaxDegreeOfParallelism = 10 },
    strURL1 => { fAddImageIfSuitable(strURL1); }
);

Answer 2

在每个Task上创建10个任务，任务数组调用异步方法（处理URL以将图像下载到磁盘的方法相同）等待所有线程返回

var tasks = new List<Task>();
foreach(task in tasks){
task[0] = GetImageAsync();}

Task.WaitAll(tasks.ToArray());

使用参数进行ASP.NET线程化？

2 个答案: