Nasıl Yapılır: Dosya Aramak için Arka Plan İş Parçacığı Kullanma

Makale
10/18/2023

Bileşen BackgroundWorker , ad alanının yerini alır ve ad alanına işlevsellik System.Threading ekler; ancak isterseniz ad System.Threading alanı hem geriye dönük uyumluluk hem de gelecekteki kullanım için korunur. Daha fazla bilgi için bkz . BackgroundWorker Bileşenine Genel Bakış.

Windows Forms, doğal olarak apartman iş parçacıklı yerel Win32 pencerelerini temel alır çünkü Windows Forms tek iş parçacıklı daire (STA) modelini kullanır. STA modeli, herhangi bir iş parçacığında bir pencere oluşturulabileceğini, ancak oluşturulduktan sonra iş parçacıklarını değiştiremeyeceğini ve bu pencereye yapılan tüm işlev çağrılarının kendi oluşturma iş parçacığında gerçekleşmesi gerektiğini gösterir. Windows Forms dışında, .NET Framework'teki sınıflar ücretsiz iş parçacığı modelini kullanır. .NET Framework'te iş parçacığı oluşturma hakkında bilgi için bkz . İş parçacığı oluşturma.

STA modeli, denetimin oluşturma iş parçacığı dışından çağrılması gereken bir denetimdeki tüm yöntemlerin denetimin oluşturma iş parçacığına sıralanması (üzerinde yürütülmesi) gerekir. Temel sınıf Control , bu amaçla çeşitli yöntemler (Invoke, BeginInvokeve EndInvoke) sağlar. Invoke zaman uyumlu yöntem çağrıları yapar; BeginInvoke zaman uyumsuz yöntem çağrıları yapar.

Yoğun kaynak kullanan görevler için denetiminizde çok iş parçacığı kullanırsanız, yoğun kaynak kullanan bir hesaplama arka plan iş parçacığında yürütülürken kullanıcı arabirimi yanıt vermeye devam edebilir.

Aşağıdaki örnek (DirectorySearcher), belirtilen arama dizesiyle eşleşen dosyaları yinelemeli olarak aramak için arka plan iş parçacığı kullanan ve ardından bir liste kutusunu arama sonucuyla dolduran çok iş parçacıklı bir Windows Forms denetimini gösterir. Örnek tarafından gösterilen temel kavramlar aşağıdaki gibidir:

DirectorySearcher aramayı gerçekleştirmek için yeni bir iş parçacığı başlatır. İş parçacığı, gerçek aramayı yapmak ve liste kutusunu doldurmak için yardımcı RecurseDirectory yöntemini çağıran yöntemini yürütürThreadProcedure. Ancak, liste kutusunu doldurma işlemi, sonraki iki madde işaretli öğede açıklandığı gibi iş parçacıkları arası bir çağrı gerektirir.
DirectorySearcherAddFiles, liste kutusuna dosya ekleme yöntemini tanımlar; ancak yalnızca RecurseDirectory oluşturulan DirectorySearcherSTA iş parçacığında yürütülebildiğinden doğrudan çağrılamaz AddFilesAddFiles.
Çağrısının tek yoluRecurseDirectory, öğesinin oluşturma iş parçacığını çağırarak Invoke veya BeginInvoke sıralayarak AddFiles bir çapraz iş parçacığı çağrısı yapmaktırDirectorySearcher.AddFiles RecurseDirectory çağrısının zaman uyumsuz olarak yapılabilmesi için kullanılır BeginInvoke .
Bir yöntemin sıralanması, işlev işaretçisinin veya geri çağırmanın eşdeğerini gerektirir. Bu, .NET Framework'teki temsilciler kullanılarak gerçekleştirilir. BeginInvoke bağımsız değişken olarak bir temsilci alır. DirectorySearcherbu nedenle bir temsilci ()FileListDelegate tanımlar, oluşturucusunda bir örneğine FileListDelegate bağlar AddFiles ve bu temsilci örneğini öğesine BeginInvokegeçirir. DirectorySearcher ayrıca, arama tamamlandığında sıralanmış bir olay temsilcisi tanımlar.

Option Strict
Option Explicit

Imports System.IO
Imports System.Threading
Imports System.Windows.Forms

Namespace Microsoft.Samples.DirectorySearcher
   ' <summary>
   '      This class is a Windows Forms control that implements a simple directory searcher.
   '      You provide, through code, a search string and it will search directories on
   '      a background thread, populating its list box with matches.
   ' </summary>
   Public Class DirectorySearcher
      Inherits Control
      ' Define a special delegate that handles marshaling
      ' lists of file names from the background directory search
      ' thread to the thread that contains the list box.
      Delegate Sub FileListDelegate(files() As String, startIndex As Integer, count As Integer)

      Private _listBox As ListBox
      Private _searchCriteria As String
      Private _searching As Boolean
      Private _deferSearch As Boolean
      Private _searchThread As Thread
      Private _fileListDelegate As FileListDelegate
      Private _onSearchComplete As EventHandler

      Public Sub New()
         _listBox = New ListBox()
         _listBox.Dock = DockStyle.Fill

         Controls.Add(_listBox)

         _fileListDelegate = New FileListDelegate(AddressOf AddFiles)
         _onSearchComplete = New EventHandler(AddressOf OnSearchComplete)
      End Sub

      Public Property SearchCriteria() As String
         Get
            Return _searchCriteria
         End Get
         Set
            ' If currently searching, abort
            ' the search and restart it after
            ' setting the new criteria.
            '
            Dim wasSearching As Boolean = Searching

            If wasSearching Then
               StopSearch()
            End If

            _listBox.Items.Clear()
            _searchCriteria = value

            If wasSearching Then
               BeginSearch()
            End If
         End Set
      End Property

      Public ReadOnly Property Searching() As Boolean
         Get
            Return _searching
         End Get
      End Property

      Public Event SearchComplete As EventHandler

      ' <summary>
      ' This method is called from the background thread.  It is called through
      ' a BeginInvoke call so that it is always marshaled to the thread that
      ' owns the list box control.
      ' </summary>
      ' <param name="files"></param>
      ' <param name="startIndex"></param>
      ' <param name="count"></param>
      Private Sub AddFiles(files() As String, startIndex As Integer, count As Integer)
         While count > 0
            count -= 1
            _listBox.Items.Add(files((startIndex + count)))
         End While
      End Sub

      Public Sub BeginSearch()
         ' Create the search thread, which
         ' will begin the search.
         ' If already searching, do nothing.
         '
         If Searching Then
            Return
         End If

         ' Start the search if the handle has
         ' been created. Otherwise, defer it until the
         ' handle has been created.
         If IsHandleCreated Then
            _searchThread = New Thread(New ThreadStart(AddressOf ThreadProcedure))
            _searching = True
            _searchThread.Start()
         Else
            _deferSearch = True
         End If
      End Sub

      Protected Overrides Sub OnHandleDestroyed(e As EventArgs)
         ' If the handle is being destroyed and you are not
         ' recreating it, then abort the search.
         If Not RecreatingHandle Then
            StopSearch()
         End If
         MyBase.OnHandleDestroyed(e)
      End Sub

      Protected Overrides Sub OnHandleCreated(e As EventArgs)
         MyBase.OnHandleCreated(e)
         If _deferSearch Then
            _deferSearch = False
            BeginSearch()
         End If
      End Sub

      ' <summary>
      ' This method is called by the background thread when it has
      ' finished the search.
      ' </summary>
      ' <param name="sender"></param>
      ' <param name="e"></param>
      Private Sub OnSearchComplete(sender As Object, e As EventArgs)
         RaiseEvent SearchComplete(sender, e)
      End Sub

      Public Sub StopSearch()
         If Not _searching Then
            Return
         End If

         If _searchThread.IsAlive Then
            _searchThread.Abort()
            _searchThread.Join()
         End If

         _searchThread = Nothing
         _searching = False
      End Sub

      ' <summary>
      ' Recurses the given path, adding all files on that path to
      ' the list box. After it finishes with the files, it
      ' calls itself once for each directory on the path.
      ' </summary>
      ' <param name="searchPath"></param>
      Private Sub RecurseDirectory(searchPath As String)
         ' Split searchPath into a directory and a wildcard specification.
         '
         Dim directoryPath As String = Path.GetDirectoryName(searchPath)
         Dim search As String = Path.GetFileName(searchPath)

         ' If a directory or search criteria are not specified, then return.
         '
         If directoryPath Is Nothing Or search Is Nothing Then
            Return
         End If

         Dim files() As String

         ' File systems like NTFS that have
         ' access permissions might result in exceptions
         ' when looking into directories without permission.
         ' Catch those exceptions and return.
         Try
            files = Directory.GetFiles(directoryPath, search)
         Catch e As UnauthorizedAccessException
            Return
         Catch e As DirectoryNotFoundException
            Return
         End Try

         ' Perform a BeginInvoke call to the list box
         ' in order to marshal to the correct thread. It is not
         ' very efficient to perform this marshal once for every
         ' file, so batch up multiple file calls into one
         ' marshal invocation.
         Dim startingIndex As Integer = 0
         While startingIndex < files.Length
            ' Batch up 20 files at once, unless at the
            ' end.
            '
            Dim count As Integer = 20
            If count + startingIndex >= files.Length Then
               count = files.Length - startingIndex
            End If
            ' Begin the cross-thread call. Because you are passing
            ' immutable objects into this invoke method, you do not have to
            ' wait for it to finish. If these were complex objects, you would
            ' have to either create new instances of them or
            ' wait for the thread to process this invoke before modifying
            ' the objects.
            Dim r As IAsyncResult = BeginInvoke(_fileListDelegate, New Object() {files, startingIndex, count})
            startingIndex += count
         End While
         ' Now that you have finished the files in this directory, recurse
         ' for each subdirectory.
         Dim directories As String() = Directory.GetDirectories(directoryPath)
         Dim d As String
         For Each d In  directories
            RecurseDirectory(Path.Combine(d, search))
         Next d
      End Sub

      '/ <summary>
      '/ This is the actual thread procedure. This method runs in a background
      '/ thread to scan directories. When finished, it simply exits.
      '/ </summary>
      Private Sub ThreadProcedure()
         ' Get the search string. Individual
         ' field assigns are atomic in .NET, so you do not
         ' need to use any thread synchronization to grab
         ' the string value here.
         Try
            Dim localSearch As String = SearchCriteria

            ' Now, search the file system.
            '
            RecurseDirectory(localSearch)
         Finally
            ' You are done with the search, so update.
            '
            _searching = False

            ' Raise an event that notifies the user that
            ' the search has terminated.
            ' You do not have to do this through a marshaled call, but
            ' marshaling is recommended for the following reason:
            ' Users of this control do not know that it is
            ' multithreaded, so they expect its events to
            ' come back on the same thread as the control.
            BeginInvoke(_onSearchComplete, New Object() {Me, EventArgs.Empty})
         End Try
      End Sub
   End Class
End Namespace

namespace Microsoft.Samples.DirectorySearcher
{
   using System;
   using System.IO;
   using System.Threading;
   using System.Windows.Forms;

   /// <summary>
   ///      This class is a Windows Forms control that implements a simple directory searcher.
   ///      You provide, through code, a search string and it will search directories on
   ///      a background thread, populating its list box with matches.
   /// </summary>
   public class DirectorySearcher : Control
   {
      // Define a special delegate that handles marshaling
      // lists of file names from the background directory search
      // thread to the thread that contains the list box.
      private delegate void FileListDelegate(string[] files, int startIndex, int count);

      private ListBox listBox;
      private string  searchCriteria;
      private bool searching;
      private bool deferSearch;
      private Thread searchThread;
      private FileListDelegate fileListDelegate;
      private EventHandler onSearchComplete;

      public DirectorySearcher()
      {
         listBox = new ListBox();
         listBox.Dock = DockStyle.Fill;

         Controls.Add(listBox);

         fileListDelegate = new FileListDelegate(AddFiles);
         onSearchComplete = new EventHandler(OnSearchComplete);
      }

      public string SearchCriteria
      {
         get
         {
            return searchCriteria;
         }
         set
         {
            // If currently searching, abort
            // the search and restart it after
            // setting the new criteria.
            //
            bool wasSearching = Searching;

            if (wasSearching)
            {
               StopSearch();
            }

            listBox.Items.Clear();
            searchCriteria = value;

            if (wasSearching)
            {
               BeginSearch();
            }
         }
      }

      public bool Searching
      {
         get
         {
            return searching;
         }
      }

      public event EventHandler SearchComplete;

      /// <summary>
      /// This method is called from the background thread. It is called through
      /// a BeginInvoke call so that it is always marshaled to the thread that
      /// owns the list box control.
      /// </summary>
      /// <param name="files"></param>
      /// <param name="startIndex"></param>
      /// <param name="count"></param>
      private void AddFiles(string[] files, int startIndex, int count)
      {
         while(count-- > 0)
         {
            listBox.Items.Add(files[startIndex + count]);
         }
      }

      public void BeginSearch()
      {
         // Create the search thread, which
         // will begin the search.
         // If already searching, do nothing.
         //
         if (Searching)
         {
            return;
         }

         // Start the search if the handle has
         // been created. Otherwise, defer it until the
         // handle has been created.
         if (IsHandleCreated)
         {
            searchThread = new Thread(new ThreadStart(ThreadProcedure));
            searching = true;
            searchThread.Start();
         }
         else
         {
            deferSearch = true;
         }
      }

      protected override void OnHandleDestroyed(EventArgs e)
      {
         // If the handle is being destroyed and you are not
         // recreating it, then abort the search.
         if (!RecreatingHandle)
         {
            StopSearch();
         }
         base.OnHandleDestroyed(e);
      }

      protected override void OnHandleCreated(EventArgs e)
      {
         base.OnHandleCreated(e);
         if (deferSearch)
         {
            deferSearch = false;
            BeginSearch();
         }
      }

      /// <summary>
      /// This method is called by the background thread when it has finished
      /// the search.
      /// </summary>
      /// <param name="sender"></param>
      /// <param name="e"></param>
      private void OnSearchComplete(object sender, EventArgs e)
      {
         if (SearchComplete != null)
         {
            SearchComplete(sender, e);
         }
      }

      public void StopSearch()
      {
         if (!searching)
         {
            return;
         }

         if (searchThread.IsAlive)
         {
            searchThread.Abort();
            searchThread.Join();
         }

         searchThread = null;
         searching = false;
      }

      /// <summary>
      /// Recurses the given path, adding all files on that path to
      /// the list box. After it finishes with the files, it
      /// calls itself once for each directory on the path.
      /// </summary>
      /// <param name="searchPath"></param>
      private void RecurseDirectory(string searchPath)
      {
         // Split searchPath into a directory and a wildcard specification.
         //
         string directory = Path.GetDirectoryName(searchPath);
         string search = Path.GetFileName(searchPath);

         // If a directory or search criteria are not specified, then return.
         //
         if (directory == null || search == null)
         {
            return;
         }

         string[] files;

         // File systems like NTFS that have
         // access permissions might result in exceptions
         // when looking into directories without permission.
         // Catch those exceptions and return.
         try
         {
            files = Directory.GetFiles(directory, search);
         }
         catch(UnauthorizedAccessException)
         {
            return;
         }
         catch(DirectoryNotFoundException)
         {
            return;
         }

         // Perform a BeginInvoke call to the list box
         // in order to marshal to the correct thread. It is not
         // very efficient to perform this marshal once for every
         // file, so batch up multiple file calls into one
         // marshal invocation.
         int startingIndex = 0;

         while(startingIndex < files.Length)
         {
            // Batch up 20 files at once, unless at the
            // end.
            //
            int count = 20;
            if (count + startingIndex >= files.Length)
            {
               count = files.Length - startingIndex;
            }

            // Begin the cross-thread call. Because you are passing
            // immutable objects into this invoke method, you do not have to
            // wait for it to finish. If these were complex objects, you would
            // have to either create new instances of them or
            // wait for the thread to process this invoke before modifying
            // the objects.
            IAsyncResult r = BeginInvoke(fileListDelegate, new object[] {files, startingIndex, count});
            startingIndex += count;
         }

         // Now that you have finished the files in this directory, recurse for
         // each subdirectory.
         string[] directories = Directory.GetDirectories(directory);
         foreach(string d in directories)
         {
            RecurseDirectory(Path.Combine(d, search));
         }
      }

      /// <summary>
      /// This is the actual thread procedure. This method runs in a background
      /// thread to scan directories. When finished, it simply exits.
      /// </summary>
      private void ThreadProcedure()
      {
         // Get the search string. Individual
         // field assigns are atomic in .NET, so you do not
         // need to use any thread synchronization to grab
         // the string value here.
         try
         {
            string localSearch = SearchCriteria;

            // Now, search the file system.
            //
            RecurseDirectory(localSearch);
         }
         finally
         {
            // You are done with the search, so update.
            //
            searching = false;

            // Raise an event that notifies the user that
            // the search has terminated.
            // You do not have to do this through a marshaled call, but
            // marshaling is recommended for the following reason:
            // Users of this control do not know that it is
            // multithreaded, so they expect its events to
            // come back on the same thread as the control.
            BeginInvoke(onSearchComplete, new object[] {this, EventArgs.Empty});
         }
      }
   }
}

Bir Formda Çok İş Parçacıklı Denetimi Kullanma

Aşağıdaki örnek, çok iş parçacıklı DirectorySearcher denetimin formda nasıl kullanılabileceğini gösterir.

Option Explicit
Option Strict

Imports System.Collections
Imports System.ComponentModel
Imports System.Data
Imports System.Drawing
Imports System.Windows.Forms
Imports Microsoft.Samples.DirectorySearcher

Namespace SampleUsage

   ' <summary>
   '      Summary description for Form1.
   ' </summary>
   Public Class Form1
      Inherits System.Windows.Forms.Form
      Private WithEvents directorySearcher As DirectorySearcher
      Private searchText As System.Windows.Forms.TextBox
      Private searchLabel As System.Windows.Forms.Label
      Private WithEvents searchButton As System.Windows.Forms.Button

      Public Sub New()
         '
         ' Required for Windows Forms designer support.
         '
         InitializeComponent()
         '
         ' Add any constructor code after InitializeComponent call here.
         '
      End Sub

      #Region "Windows Form Designer generated code"
      ' <summary>
      '      Required method for designer support. Do not modify
      '      the contents of this method with the code editor.
      ' </summary>
      Private Sub InitializeComponent()
         Me.directorySearcher = New Microsoft.Samples.DirectorySearcher.DirectorySearcher()
         Me.searchButton = New System.Windows.Forms.Button()
         Me.searchText = New System.Windows.Forms.TextBox()
         Me.searchLabel = New System.Windows.Forms.Label()
         Me.directorySearcher.Anchor = System.Windows.Forms.AnchorStyles.Top Or System.Windows.Forms.AnchorStyles.Bottom Or System.Windows.Forms.AnchorStyles.Left Or System.Windows.Forms.AnchorStyles.Right
         Me.directorySearcher.Location = New System.Drawing.Point(8, 72)
         Me.directorySearcher.SearchCriteria = Nothing
         Me.directorySearcher.Size = New System.Drawing.Size(271, 173)
         Me.directorySearcher.TabIndex = 2
         Me.searchButton.Location = New System.Drawing.Point(8, 16)
         Me.searchButton.Size = New System.Drawing.Size(88, 40)
         Me.searchButton.TabIndex = 0
         Me.searchButton.Text = "&Search"
         Me.searchText.Anchor = System.Windows.Forms.AnchorStyles.Top Or System.Windows.Forms.AnchorStyles.Left Or System.Windows.Forms.AnchorStyles.Right
         Me.searchText.Location = New System.Drawing.Point(104, 24)
         Me.searchText.Size = New System.Drawing.Size(175, 20)
         Me.searchText.TabIndex = 1
         Me.searchText.Text = "c:\*.cs"
         Me.searchLabel.ForeColor = System.Drawing.Color.Red
         Me.searchLabel.Location = New System.Drawing.Point(104, 48)
         Me.searchLabel.Size = New System.Drawing.Size(176, 16)
         Me.searchLabel.TabIndex = 3
         Me.ClientSize = New System.Drawing.Size(291, 264)
         Me.Controls.AddRange(New System.Windows.Forms.Control() {Me.searchLabel, Me.directorySearcher, Me.searchText, Me.searchButton})
         Me.Text = "Search Directories"
      End Sub
      #End Region

      ' <summary>
      '    The main entry point for the application.
      ' </summary>
      <STAThread()> _
      Shared Sub Main()
         Application.Run(New Form1())
      End Sub

      Private Sub searchButton_Click(sender As Object, e As System.EventArgs) Handles searchButton.Click
         directorySearcher.SearchCriteria = searchText.Text
         searchLabel.Text = "Searching..."
         directorySearcher.BeginSearch()
      End Sub

      Private Sub directorySearcher_SearchComplete(sender As Object, e As System.EventArgs) Handles directorySearcher.SearchComplete
         searchLabel.Text = String.Empty
      End Sub
   End Class
End Namespace

namespace SampleUsage
{
   using System;
   using System.Collections;
   using System.ComponentModel;
   using System.Data;
   using System.Drawing;
   using System.Windows.Forms;
   using Microsoft.Samples.DirectorySearcher;

   /// <summary>
   ///      Summary description for Form1.
   /// </summary>
   public class Form1 : System.Windows.Forms.Form
   {
      private DirectorySearcher directorySearcher;
      private System.Windows.Forms.TextBox searchText;
      private System.Windows.Forms.Label searchLabel;
      private System.Windows.Forms.Button searchButton;

      public Form1()
      {
         //
         // Required for Windows Forms designer support.
         //
         InitializeComponent();

         //
         // Add any constructor code after InitializeComponent call here.
         //
      }

      #region Windows Form Designer generated code
      /// <summary>
      ///      Required method for designer support. Do not modify
      ///      the contents of this method with the code editor.
      /// </summary>
      private void InitializeComponent()
      {
         this.directorySearcher = new Microsoft.Samples.DirectorySearcher.DirectorySearcher();
         this.searchButton = new System.Windows.Forms.Button();
         this.searchText = new System.Windows.Forms.TextBox();
         this.searchLabel = new System.Windows.Forms.Label();
         this.directorySearcher.Anchor = (((System.Windows.Forms.AnchorStyles.Top | System.Windows.Forms.AnchorStyles.Bottom)
            | System.Windows.Forms.AnchorStyles.Left)
            | System.Windows.Forms.AnchorStyles.Right);
         this.directorySearcher.Location = new System.Drawing.Point(8, 72);
         this.directorySearcher.SearchCriteria = null;
         this.directorySearcher.Size = new System.Drawing.Size(271, 173);
         this.directorySearcher.TabIndex = 2;
         this.directorySearcher.SearchComplete += new System.EventHandler(this.directorySearcher_SearchComplete);
         this.searchButton.Location = new System.Drawing.Point(8, 16);
         this.searchButton.Size = new System.Drawing.Size(88, 40);
         this.searchButton.TabIndex = 0;
         this.searchButton.Text = "&Search";
         this.searchButton.Click += new System.EventHandler(this.searchButton_Click);
         this.searchText.Anchor = ((System.Windows.Forms.AnchorStyles.Top | System.Windows.Forms.AnchorStyles.Left)
            | System.Windows.Forms.AnchorStyles.Right);
         this.searchText.Location = new System.Drawing.Point(104, 24);
         this.searchText.Size = new System.Drawing.Size(175, 20);
         this.searchText.TabIndex = 1;
         this.searchText.Text = "c:\\*.cs";
         this.searchLabel.ForeColor = System.Drawing.Color.Red;
         this.searchLabel.Location = new System.Drawing.Point(104, 48);
         this.searchLabel.Size = new System.Drawing.Size(176, 16);
         this.searchLabel.TabIndex = 3;
         this.ClientSize = new System.Drawing.Size(291, 264);
         this.Controls.AddRange(new System.Windows.Forms.Control[] {this.searchLabel,
                                                        this.directorySearcher,
                                                        this.searchText,
                                                        this.searchButton});
         this.Text = "Search Directories";

      }
      #endregion

      /// <summary>
      ///    The main entry point for the application.
      /// </summary>
      [STAThread]
      static void Main()
      {
         Application.Run(new Form1());
      }

      private void searchButton_Click(object sender, System.EventArgs e)
      {
         directorySearcher.SearchCriteria = searchText.Text;
         searchLabel.Text = "Searching...";
         directorySearcher.BeginSearch();
      }

      private void directorySearcher_SearchComplete(object sender, System.EventArgs e)
      {
         searchLabel.Text = string.Empty;
      }
   }
}

Aracılığıyla paylaş

Nasıl Yapılır: Dosya Aramak için Arka Plan İş Parçacığı Kullanma

Bir Formda Çok İş Parçacıklı Denetimi Kullanma

Ayrıca bkz.

Ek kaynaklar