mono/netcore/System.Private.CoreLib/shared/System/Collections/ICollection.cs

// Licensed to the .NET Foundation under one or more agreements.
// The .NET Foundation licenses this file to you under the MIT license.
// See the LICENSE file in the project root for more information.

namespace System.Collections
{
    // Base interface for all collections, defining enumerators, size, and
    // synchronization methods.
    public interface ICollection : IEnumerable
    {
        // Interfaces are not serializable
        // CopyTo copies a collection into an Array, starting at a particular
        // index into the array.
        //
        void CopyTo(Array array, int index);

        // Number of items in the collections.
        int Count
        { get; }


        // SyncRoot will return an Object to use for synchronization
        // (thread safety).  You can use this object in your code to take a
        // lock on the collection, even if this collection is a wrapper around
        // another collection.  The intent is to tunnel through to a real
        // implementation of a collection, and use one of the internal objects
        // found in that code.
        //
        // In the absence of a static Synchronized method on a collection,
        // the expected usage for SyncRoot would look like this:
        //
        // ICollection col = ...
        // lock (col.SyncRoot) {
        //     // Some operation on the collection, which is now thread safe.
        //     // This may include multiple operations.
        // }
        //
        //
        // The system-provided collections have a static method called
        // Synchronized which will create a thread-safe wrapper around the
        // collection.  All access to the collection that you want to be
        // thread-safe should go through that wrapper collection.  However, if
        // you need to do multiple calls on that collection (such as retrieving
        // two items, or checking the count then doing something), you should
        // NOT use our thread-safe wrapper since it only takes a lock for the
        // duration of a single method call.  Instead, use Monitor.Enter/Exit
        // or your language's equivalent to the C# lock keyword as mentioned
        // above.
        //
        // For collections with no publicly available underlying store, the
        // expected implementation is to simply return the this pointer.  Note
        // that the this pointer may not be sufficient for collections that
        // wrap other collections;  those should return the underlying
        // collection's SyncRoot property.
        object SyncRoot
        { get; }

        // Is this collection synchronized (i.e., thread-safe)?  If you want a
        // thread-safe collection, you can use SyncRoot as an object to
        // synchronize your collection with.  If you're using one of the
        // collections in System.Collections, you could call the static
        // Synchronized method to get a thread-safe wrapper around the
        // underlying collection.
        bool IsSynchronized
        { get; }
    }
}