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ArrayList.IsSynchronized Property

Gets a value indicating whether access to the ArrayList is synchronized (thread-safe).

[Visual Basic]
Public Overridable ReadOnly Property IsSynchronized As Boolean  _
   Implements ICollection.IsSynchronized
[C#]
public virtual bool IsSynchronized {get;}
[C++]
public: __property virtual bool get_IsSynchronized();
[JScript]
public function get IsSynchronized() : Boolean;

Property Value

true if access to the ArrayList is synchronized (thread-safe); otherwise, false. The default is false.

Implements

ICollection.IsSynchronized

Remarks

To guarantee the thread safety of the ArrayList, all operations must be done through the wrapper returned by the Synchronized method.

Enumerating through a collection is intrinsically not a thread-safe procedure. Even when a collection is synchronized, other threads could still modify the collection, which causes the enumerator to throw an exception. 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.

[Visual Basic, C#] The following code example shows how to lock the collection using the SyncRoot during the entire enumeration:

[C#] 
ArrayList myCollection = new ArrayList();
 lock( myCollection.SyncRoot ) {
 foreach ( Object item in myCollection ) {
 // Insert your code here.
 }
}
[Visual Basic] 
Dim myCollection As New ArrayList()
Dim item As Object
SyncLock myCollection.SyncRoot
 For Each item In myCollection
 ' Insert your code here.
 Next item
End SyncLock

Example

The following example shows how to synchronize an ArrayList, determine if an ArrayList is synchronized and use a synchronized ArrayList.

[Visual Basic] 
Imports System
Imports System.Collections

Public Class SamplesArrayList
    
    
    Public Shared Sub Main()
        
        ' Creates and initializes a new ArrayList.
        Dim myAL As New ArrayList()
        myAL.Add("The")
        myAL.Add("quick")
        myAL.Add("brown")
        myAL.Add("fox")
        
        ' Creates a synchronized wrapper around the ArrayList.
        Dim mySyncdAL As ArrayList = ArrayList.Synchronized(myAL)
        
        ' Displays the sychronization status of both ArrayLists.
        Dim str As String
        If myAL.IsSynchronized Then
            str = "synchronized"
        Else
            str = "not synchronized"
        End If
        Console.WriteLine("myAL is {0}.", str)
        If mySyncdAL.IsSynchronized Then
            str = "synchronized"
        Else
            str = "not synchronized"
        End If
        Console.WriteLine("mySyncdAL is {0}.", str)
    End Sub
End Class

' This code produces the following output.
' 
' myAL is not synchronized.
' mySyncdAL is synchronized. 

[C#] 
using System;
using System.Collections;
public class SamplesArrayList  {

   public static void Main()  {

      // Creates and initializes a new ArrayList.
      ArrayList myAL = new ArrayList();
      myAL.Add( "The" );
      myAL.Add( "quick" );
      myAL.Add( "brown" );
      myAL.Add( "fox" );

      // Creates a synchronized wrapper around the ArrayList.
      ArrayList mySyncdAL = ArrayList.Synchronized( myAL );

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

myAL is not synchronized.
mySyncdAL is synchronized.
*/ 

[C++] 
#using <mscorlib.dll>
using namespace System;
using namespace System::Collections;


int main()  {
 
       // Creates and initializes a new ArrayList instance.
       ArrayList* myAL = new ArrayList();
       myAL->Add( S"The" );
       myAL->Add( S"quick" );
       myAL->Add( S"brown" );
       myAL->Add( S"fox" );
 
       // Creates a synchronized wrapper around the ArrayList.
       ArrayList* mySyncdAL = ArrayList::Synchronized( myAL );
 
       // Displays the sychronization status of both ArrayLists.
       String* szRes = myAL->IsSynchronized ? "synchronized" : "not synchronized";
       Console::WriteLine( "myAL is {0}.", szRes );

       String* szSyncRes = mySyncdAL->IsSynchronized ? "synchronized" : "not synchronized";
       Console::WriteLine( "mySyncdAL is {0}.", szSyncRes );
    }

 /* 
 This code produces the following output.
 
 myAL is not synchronized.
 mySyncdAL is synchronized.
 */ 

[JScript] 
import System;
import System.Collections;

// Creates and initializes a new ArrayList.
var myAL : ArrayList = new ArrayList();
myAL.Add( "The" );
myAL.Add( "quick" );
myAL.Add( "brown" );
myAL.Add( "fox" );

// Creates a synchronized wrapper around the ArrayList.
var mySyncdAL : ArrayList  = ArrayList.Synchronized( myAL );

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

Requirements

Platforms: Windows 98, Windows NT 4.0, Windows Millennium Edition, Windows 2000, Windows XP Home Edition, Windows XP Professional, Windows Server 2003 family, .NET Compact Framework, Common Language Infrastructure (CLI) Standard

See Also

ArrayList Class | ArrayList Members | System.Collections Namespace | SyncRoot | Synchronized

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