PropertyCollection.ICollection.SyncRoot Property


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

property System::Object ^ System::Collections::ICollection::SyncRoot { System::Object ^ get(); };
object System.Collections.ICollection.SyncRoot { get; }
 ReadOnly Property SyncRoot As Object Implements ICollection.SyncRoot

Property Value

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



For collections whose underlying store is not publicly available, the expected implementation is to return the current instance. Note that the pointer to the current instance might not be sufficient for collections that wrap other collections; those should return the underlying collection's SyncRoot property.

Most collection classes in the System.Collections namespace also implement a Synchronized method, which provides a synchronized wrapper around the underlying collection. However, derived classes can provide their own synchronized version of the collection using the SyncRoot property. The synchronizing code must perform operations on the SyncRoot of the collection, not directly on the collection. 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 collection instance.

In the absence of a Synchronized method on a collection, the expected usage for SyncRoot looks like this:

ICollection MyCollection =...  
 lock(MyCollection.SyncRoot) {  
  // Some operation on the collection, which is now thread safe.  
Dim myCollection as New ICollection()  
 SyncLock myCollection.SyncRoot  
  ' Some operation on the collection, which is now thread safe.  
 End SyncLock  

Enumerating through a collection is intrinsically not a thread safe procedure. Even when a collection is synchronized, other threads can 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:

ICollection myCollection = new ICollection();  
 lock(myCollection.SyncRoot) {  
  foreach (Object item in myCollection) {  
  // Insert your code here.  
Dim myCollection As New ICollection()  
 Dim item As Object  
 SyncLock myCollection.SyncRoot  
  For Each item In myCollection  
  ' Insert your code here.  
  Next item  
 End SyncLock  

Applies to

See also