C# 4 and .NET 4

238 ❘ ChaPTer 10 cOllectiOns
The DocumentManager class is a thin layer around the Queue < T > class. The class DocumentManager defi nes
how to handle documents: adding documents to the queue with the AddDocument() method, and getting
documents from the queue with the GetDocument() method.
Inside the AddDocument() method, the document is added to the end of the queue by using the Enqueue()
method. The fi rst document from the queue is read with the Dequeue() method inside GetDocument() .
Because multiple threads can access the DocumentManager concurrently, access to the queue is locked with
the lock statement.
Threading and the lock statement are discussed in Chapter 20, “ Threads, Tasks, and
Synchronization.”
IsDocumentAvailable is a read - only Boolean property that returns true if there are documents in the
queue, and false if not:
public class DocumentManager
{
private readonly Queue < Document > documentQueue = new Queue < Document > ();
public void AddDocument(Document doc)
{
lock (this)
{
documentQueue.Enqueue(doc);
}
}
public Document GetDocument()
{
Document doc = null;
lock (this)
{
doc = documentQueue.Dequeue();
}
return doc;
}
}
public bool IsDocumentAvailable
{
get
{
return documentQueue.Count > 0;
}
}
code snippet QueueSample/DocumentManager.cs
The class ProcessDocuments processes documents from the queue in a separate thread. The only
method that can be accessed from the outside is Start() . In the Start() method, a new thread is
instantiated. A ProcessDocuments object is created for starting the thread, and the Run() method
is defi ned as the start method of the thread. ThreadStart is a delegate that references the method to
be started by the thread. After creating the Thread object, the thread is started by calling the method
Thread.Start() .
With the Run() method of the ProcessDocuments class, an endless loop is defi ned. Within this loop, the
property IsDocumentAvailable is used to see if there is a document in the queue. If there is a document in the
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