Hashtable.IsSynchronized 属性

获取一个值，该值指示是否同步对 Hashtable 的访问（线程安全）。

**命名空间:**System.Collections
**程序集:**mscorlib（在 mscorlib.dll 中）

语法

声明
Public Overridable ReadOnly Property IsSynchronized As Boolean
用法
Dim instance As Hashtable
Dim value As Boolean

value = instance.IsSynchronized

public virtual bool IsSynchronized { get; }

public:
virtual property bool IsSynchronized {
    bool get ();
}

/** @property */
public boolean get_IsSynchronized ()

public function get IsSynchronized () : boolean

属性值

如果对 Hashtable 的访问是同步的（线程安全），则为 true；否则为 false。默认为 false。

备注

Hashtable 可以同时支持一个编写器和多个阅读器。若要支持多个编写器，所有操作必须通过由 Synchronized 方法返回的包装完成。

从头到尾对一个集合进行枚举本质上并不是一个线程安全的过程。即使一个集合已进行同步，其他线程仍可以修改该集合，这将导致枚举数引发异常。若要在枚举过程中保证线程安全，可以在整个枚举过程中锁定集合，或者捕捉由于其他线程进行的更改而引发的异常。

下面的代码示例显示如何在整个枚举过程中使用 SyncRoot 锁定集合：

Hashtable myCollection = new Hashtable();
  lock(myCollection.SyncRoot) {
  foreach (Object item in myCollection) {
  // Insert your code here.
  }
 }

Dim myCollection As New Hashtable()
 Dim item As Object
 SyncLock myCollection.SyncRoot
  For Each item In myCollection
  ' Insert your code here.
  Next item
 End SyncLock

检索此属性的值的运算复杂度为 O(1)。

示例

下面的示例演示如何同步 Hashtable、如何确定 Hashtable 是否同步以及如何使用同步的 Hashtable。

Imports System
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 Then
            msg = "synchronized"
        Else
            msg = "not synchronized"
        End If
        Console.WriteLine("myHT is {0}.", msg)
        If mySyncdHT.IsSynchronized Then
            msg = "synchronized"
        Else
            msg = "not synchronized"
        End If        
        Console.WriteLine("mySyncdHT is {0}.", msg)
    End Sub
End Class

' 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.
      Hashtable 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.
*/ 

#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.
 */

import System.*;
import System.Collections.*;

public class SamplesHashtable
{
    public static void main(String[] args)
    {
        // Creates and initializes a new Hashtable.
        Hashtable myHT = new Hashtable();

        myHT.Add(new Integer(0), "zero");
        myHT.Add(new Integer(1), "one");
        myHT.Add(new Integer(2), "two");
        myHT.Add(new Integer(3), "three");
        myHT.Add(new Integer(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.get_IsSynchronized()) ? 
            "synchronized" : "not synchronized");
        Console.WriteLine("mySyncdHT is {0}.", 
            (mySyncdHT.get_IsSynchronized()) ? 
            "synchronized" : "not synchronized");
    } //main
} //SamplesHashtable

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

import System
import System.Collections

// Creates and initializes a new Hashtable.
var myHT : Hashtable = 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.
var mySyncdHT : Hashtable = Hashtable.Synchronized(myHT)

// Displays the sychronization status of both Hashtables.
var msg : String
if(myHT.IsSynchronized)
    msg = "synchronized"
else
    msg = "not synchronized"
Console.WriteLine("myHT is {0}.", msg)
if(mySyncdHT.IsSynchronized)
    msg = "synchronized"
else
    msg = "not synchronized"
Console.WriteLine("mySyncdHT is {0}.", msg)

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

平台

Windows 98、Windows 2000 SP4、Windows CE、Windows Millennium Edition、Windows Mobile for Pocket PC、Windows Mobile for Smartphone、Windows Server 2003、Windows XP Media Center Edition、Windows XP Professional x64 Edition、Windows XP SP2、Windows XP Starter Edition

.NET Framework 并不是对每个平台的所有版本都提供支持。有关受支持版本的列表，请参见系统要求。

版本信息

.NET Framework

受以下版本支持：2.0、1.1、1.0

.NET Compact Framework

受以下版本支持：2.0、1.0

请参见

参考

Hashtable 类
Hashtable 成员
System.Collections 命名空间
Synchronized
SyncRoot