ArrayList::Synchronized Method (ArrayList^)


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Returns an ArrayList wrapper that is synchronized (thread safe).

Namespace:   System.Collections
Assembly:  mscorlib (in mscorlib.dll)

[HostProtectionAttribute(SecurityAction::LinkDemand, Synchronization = true)]
static ArrayList^ Synchronized(
	ArrayList^ list


Type: System.Collections::ArrayList^

The ArrayList to synchronize.

Return Value

Type: System.Collections::ArrayList^

An ArrayList wrapper that is synchronized (thread safe).

Exception Condition

list is null.

To guarantee the thread safety of the ArrayList, all operations must be done through this wrapper.

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.

The following code example shows how to lock the collection using the SyncRoot during the entire enumeration.

ArrayList^ myCollection = gcnew ArrayList();
bool lockTaken = false;
    Monitor::Enter(myCollection->SyncRoot, lockTaken);
    for each (Object^ item in myCollection);
        // Insert your code here.
    if (lockTaken)

This method is an O(1) operation.

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

using namespace System;
using namespace System::Collections;
int main()

   // Creates and initializes a new ArrayList instance.
   ArrayList^ myAL = gcnew 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.
   String^ szRes = myAL->IsSynchronized ?  (String^)"synchronized" :  "not synchronized";
   Console::WriteLine(  "myAL is {0}.", szRes );
   String^ szSyncRes = mySyncdAL->IsSynchronized ?  (String^)"synchronized" :  "not synchronized";
   Console::WriteLine(  "mySyncdAL is {0}.", szSyncRes );

 This code produces the following output.

 myAL is not synchronized.
 mySyncdAL is synchronized.

Universal Windows Platform
Available since 10
.NET Framework
Available since 1.1
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