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//------------------------------------------------------------------------------
// <copyright file="SubscriptionQueue.cs" company="Microsoft">
// Copyright (c) Microsoft Corporation. All rights reserved.
// </copyright>
//------------------------------------------------------------------------------
namespace System.Web.Util {
using System;
using System.Collections.Generic;
using System.Web;
// Similar to a Queue<T>, but allows unsubscribing from the underlying queue.
//
// !! WARNING !!
// Mutable struct for performance reasons; optimized for case where Enqueue is never called.
// Be careful with usage, e.g. no readonly declarations of this type.
//
// Type is not thread safe.
internal struct SubscriptionQueue<T> {
private LinkedList<T> _list;
public bool IsEmpty {
get { return (_list == null || _list.Count == 0); }
}
public ISubscriptionToken Enqueue(T value) {
if (_list == null) {
// lazily instantiate the list
_list = new LinkedList<T>();
}
LinkedListNode<T> node = _list.AddLast(value);
return new SubscriptionToken(node);
}
public void FireAndComplete(Action<T> action) {
try {
T value;
// Use a while loop instead of a foreach since the list might be changing
while (TryDequeue(out value)) {
action(value);
}
}
finally {
_list = null;
}
}
private bool TryDequeue(out T result) {
if (_list != null && _list.First != null) {
LinkedListNode<T> theNode = _list.First;
_list.RemoveFirst(); // also marks the SubscriptionToken as inactive
result = theNode.Value;
theNode.Value = default(T); // unroot the value in case it's large
return true;
}
else {
result = default(T); // unroot the value in case it's large
return false;
}
}
private sealed class SubscriptionToken : ISubscriptionToken {
private readonly LinkedListNode<T> _node;
public SubscriptionToken(LinkedListNode<T> node) {
_node = node;
}
public bool IsActive {
get { return (_node.List != null); }
}
public void Unsubscribe() {
if (IsActive) {
_node.List.Remove(_node);
_node.Value = default(T); // unroot the value in case it's large
}
}
}
}
}
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