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ArrayList.SyncRoot Property

Gets an object that can be used to synchronize access to the ArrayList.

[Visual Basic]
Public Overridable ReadOnly Property SyncRoot As Object  Implements _
   ICollection.SyncRoot
[C#]
public virtual object SyncRoot {get;}
[C++]
public: __property virtual Object* get_SyncRoot();
[JScript]
public function get SyncRoot() : Object;

Property Value

An object that can be used to synchronize access to the ArrayList.

Implements

ICollection.SyncRoot

Remarks

To create a synchronized version of the ArrayList, use the Synchronized method. However, derived classes can provide their own synchronized version of the ArrayList using the SyncRoot property. The synchronizing code must perform operations on the SyncRoot of the ArrayList, not directly on the ArrayList. This ensures proper operation of collections that are derived from other objects. Specifically, it maintains proper synchronization with other threads that might be simultaneously modifying the ArrayList object.

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

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 | IsSynchronized | Synchronized

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