Thread Safe Generic Queue Class

I've been doing a lot of multi-threading work recently using the standard Thread class, the Worker Queue, and the new PLINQ (Parallel LINQ). The problem with most of the built-in generic collections (Queue<>, List<>, Dictionary<>, etc.), is that they are not thread safe.

I created a library of thread safe collections which allow me to use the standard generic collection actions (foreach, LINQ, etc.), while at the same time being thread safe.

The classes in this library inherit from the appropriate collection interface (IEnumerable, ICollection, etc.). Each class also has all the functions and properties that its original non-thread safe class has.

You can download a copy of the entire library, which includes support for a thread safe List<>, Dictionary<>, and Queue<>, here: Thread Safe Generic Collections.

TQueue<> Example

The first thing we need to do is create a container for the TQueue and a thread lock object. I generally prefer to use the ReaderWriterLockSlim because it is light weight and fast.

/// <summary> 
/// The private q which holds the actual data 
/// </summary> 
private readonly Queue<T> m_Queue; 

/// <summary> 
/// Lock for the Q 
/// </summary> 
private readonly ReaderWriterLockSlim LockQ = new ReaderWriterLockSlim(); 

Just like a standard Queue, we have three overloads for the Initialization. These overloads allow an empty Queue to be created, a Queue with a specified capacity, or a Queue with an initial IEnumerable collection to populate the Queue.

/// <summary> 
/// Initializes the Queue 
/// </summary> 
public TQueue() 
{ 
    m_Queue = new Queue<T>(); 
} 
  
/// <summary> 
/// Initializes the Queue 
/// </summary> 
/// <param name="capacity">the initial number of elements the queue can contain</param> 
public TQueue(int capacity) 
{ 
    m_Queue = new Queue<T>(capacity); 
} 

/// <summary> 
/// Initializes the Queue 
/// </summary> 
/// <param name="collection">the collection whose 
/// members are copied to the Queue</param> 
public TQueue(IEnumerable<T> collection) 
{ 
    m_Queue = new Queue<T>(collection); 
} 

This next function is probably the most important one. The GetEnumerator() is used during ForEach loops, and returns the next item in the collection. Following Microsoft's example of a thread-safe enumerator, we first get a copy of the current container Queue, then use this copy for iterating. You'll notice the use of the Read lock before acquiring the container Queue copy.

/// <summary> 
/// Returns an enumerator that enumerates through the collection 
/// </summary> 
public IEnumerator<T> GetEnumerator() 
{ 
    Queue<T> localQ; 
  
    // init enumerator 
    LockQ.EnterReadLock(); 
    try 
    { 
        // create a copy of m_TList 
        localQ = new Queue<T>(m_Queue); 
    } 
    finally 
    { 
        LockQ.ExitReadLock(); 
    } 
  
    // get the enumerator 
    foreach (T item in localQ) 
        yield return item; 
} 

A Queue must include an Enqueue and a Dequeue, used for adding and removing items from the collection. Just as in every other function, we're using the locks to protect our data access.

/// <summary> 
/// Adds an item to the queue 
/// </summary> 
/// <param name="item">the item to add to the queue</param> 
public void Enqueue(T item) 
{ 
    LockQ.EnterWriteLock(); 
    try 
    { 
        m_Queue.Enqueue(item); 
    } 
  
    finally 
    { 
        LockQ.ExitWriteLock(); 
    } 
} 
/// <summary> 
/// Removes and returns the item in the beginning of the queue 
/// </summary> 
public T Dequeue() 
{ 
    LockQ.EnterWriteLock(); 
    try 
    { 
        return m_Queue.Dequeue(); 
    } 
  
    finally 
    { 
        LockQ.ExitWriteLock(); 
    } 
} 

I found that many times, I have a need to enqueue multiple items at once. This leads to the creation of the EnqueueAll functions. You'll notice the second overload is using the thread safe List (TList).

/// <summary> 
/// Enqueues the list of items 
/// </summary> 
/// <param name="ItemsToQueue">list of items to enqueue</param> 
public void EnqueueAll(IEnumerable<T> ItemsToQueue) 
{ 
    LockQ.EnterWriteLock(); 
    try 
    { 
        // loop through and add each item 
        foreach (T item in ItemsToQueue) 
            m_Queue.Enqueue(item); 
    } 
    finally 
    { 
        LockQ.ExitWriteLock(); 
    } 
} 

/// <summary> 
/// Enqueues the list of items 
/// </summary> 
/// <param name="ItemsToQueue">list of items to enqueue</param> 
public void EnqueueAll(TList<T> ItemsToQueue) 
{ 
    LockQ.EnterWriteLock(); 
    try 
    { 
        // loop through and add each item 
        foreach (T item in ItemsToQueue) 
            m_Queue.Enqueue(item); 
    } 
  
    finally 
    { 
        LockQ.ExitWriteLock(); 
    } 
} 

And, since we have an EnqueueAll, I also found a need to dequeue everything at once. DequeueAll returns a thread safe list (TList), instead of the standard List.

/// <summary> 
/// Dequeues all the items and returns them as a thread safe list 
/// </summary> 
public TList<T> DequeueAll() 
{ 
    LockQ.EnterWriteLock(); 
    try 
    { 
        // create return object 
        TList<T> returnList = new TList<T>(); 
  
        // dequeue until everything is out 
        while (m_Queue.Count > 0) 
            returnList.Add(m_Queue.Dequeue()); 
  
        // return the list 
        return returnList; 
    } 
    finally 
    { 
        LockQ.ExitWriteLock(); 
    } 
} 

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