Hashtable.IsSynchronized 屬性

定義

取得值,該值指出是否同步存取 Hashtable (安全執行緒)。Gets a value indicating whether access to the Hashtable is synchronized (thread safe).

public:
 virtual property bool IsSynchronized { bool get(); };
public virtual bool IsSynchronized { get; }
member this.IsSynchronized : bool
Public Overridable ReadOnly Property IsSynchronized As Boolean

屬性值

如果 true 的存取為同步 (安全執行緒),則為 Hashtable,否則為 falsetrue if access to the Hashtable is synchronized (thread safe); otherwise, false. 預設為 falseThe default is false.

實作

範例

下列範例示範如何同步處理 Hashtable、判斷 Hashtable 是否同步,以及是否使用同步處理的 HashtableThe following example shows how to synchronize a Hashtable, determine if a Hashtable is synchronized, and use a synchronized Hashtable.

#using <system.dll>

using namespace System;
using namespace System::Collections;
void main()
{
   
   // Creates and initializes a new Hashtable.
   Hashtable^ myHT = gcnew Hashtable;
   myHT->Add( (int^)0, "zero" );
   myHT->Add( 1, "one" );
   myHT->Add( 2, "two" );
   myHT->Add( 3, "three" );
   myHT->Add( 4, "four" );
   
   // Creates a synchronized wrapper around the Hashtable.
   Hashtable^ mySyncdHT = Hashtable::Synchronized( myHT );
   
   // Displays the sychronization status of both Hashtables.
   Console::WriteLine( "myHT is {0}.", myHT->IsSynchronized ? (String^)"synchronized" : "not synchronized" );
   Console::WriteLine( "mySyncdHT is {0}.", mySyncdHT->IsSynchronized ? (String^)"synchronized" : "not synchronized" );
}

/*
 This code produces the following output.

 myHT is not synchronized.
 mySyncdHT is synchronized.
 */
using System;
using System.Collections;
public class SamplesHashtable
{

   public static void Main()
   {
      // Creates and initializes a new Hashtable.
      var myHT = new Hashtable();
      myHT.Add(0, "zero");
      myHT.Add(1, "one");
      myHT.Add(2, "two");
      myHT.Add(3, "three");
      myHT.Add(4, "four");

      // Creates a synchronized wrapper around the Hashtable.
      Hashtable mySyncdHT = Hashtable.Synchronized(myHT);

      // Displays the sychronization status of both Hashtables.
      Console.WriteLine("myHT is {0}.", myHT.IsSynchronized ? "synchronized" : "not synchronized" );
      Console.WriteLine("mySyncdHT is {0}.", mySyncdHT.IsSynchronized ? "synchronized" : "not synchronized");
   }
}
/* 
This code produces the following output.

myHT is not synchronized.
mySyncdHT is synchronized.
*/ 
Imports System.Collections

Public Class SamplesHashtable    
    
    Public Shared Sub Main()
        
        ' Creates and initializes a new Hashtable.
        Dim myHT As New Hashtable()
        myHT.Add(0, "zero")
        myHT.Add(1, "one")
        myHT.Add(2, "two")
        myHT.Add(3, "three")
        myHT.Add(4, "four")
        
        ' Creates a synchronized wrapper around the Hashtable.
        Dim mySyncdHT As Hashtable = Hashtable.Synchronized(myHT)
        
        ' Displays the sychronization status of both Hashtables.
        Dim msg As String = If(myHT.IsSynchronized, "synchronized", "not synchronized")
        Console.WriteLine($"myHT is {msg}.")
        msg = If(mySyncdHT.IsSynchronized, "synchronized", "not synchronized")
        Console.WriteLine($"mySyncdHT is {msg}.")
    End Sub
End Class

' This code produces the following output.
' 
' myHT is not synchronized.
' mySyncdHT is synchronized. 

備註

Hashtable 可以同時支援一個寫入器和多個讀取器。A Hashtable can support one writer and multiple readers concurrently. 若要支援多個寫入器,所有作業都必須透過 Synchronized 方法所傳回的包裝函式來完成。To support multiple writers, all operations must be done through the wrapper returned by the Synchronized method.

透過集合進行列舉,本質上並不是安全線程的程式。Enumerating through a collection is intrinsically not a thread safe procedure. 即使集合經過同步化,其他的執行緒仍可修改該集合,使列舉值擲回例外狀況。Even when a collection is synchronized, other threads can still modify the collection, which causes the enumerator to throw an exception. 若要保證列舉過程的執行緒安全,您可以在整個列舉過程中鎖定集合,或攔截由其他執行緒的變更所造成的例外狀況。To guarantee thread safety during enumeration, you can either lock the collection during the entire enumeration or catch the exceptions resulting from changes made by other threads.

下列程式碼範例示範如何使用整個列舉期間的 SyncRoot 來鎖定集合:The following code example shows how to lock the collection using the SyncRoot during the entire enumeration:

Hashtable^ myCollection = gcnew Hashtable();
bool lockTaken = false;

try
{
    Monitor::Enter(myCollection->SyncRoot, lockTaken);
    for each (Object^ item in myCollection)
    {
        // Insert your code here.
    }
}
finally
{
    if (lockTaken)
    {
        Monitor::Exit(myCollection->SyncRoot);
    }
}
var myCollection = new Hashtable();
lock (myCollection.SyncRoot)
{
    foreach (object item in myCollection)
    {
        // Insert your code here.
    }
}
Dim myCollection As New Hashtable()
SyncLock myCollection.SyncRoot
    For Each item In myCollection
        ' Insert your code here.
    Next
End SyncLock

適用於

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