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To create an
AutoResetEvent event use a command like:
Dim mySyncdQEvent As New AutoResetEvent(False)
This will create an
AutoResetEvent event called
mySyncdQEvent with the initial value of
False . When your code writes to a queue you can use the
Set method to signal to the reader thread that something is on the queue. The reader thread can use the
WaitOne method to wait to be signaled. The code for the writer thread to put something on the queue and then signal the event is:
mySyncdQ.Enqueue(Something)
mySyncdQEvent.Set()
The reader thread can use code like:
mySyncdQEvent.WaitOne()
While mySyncdQ.CountConsole.WriteLine(mySyncdQ.Dequeue())
End While
This will wait until something is available on the queue and then take all the items in the queue off and print the contents. This assumes that there is only one reader for the queue. If you have more than one reader for the queue you will need to lock the resource before using it. This is not explained here.
This example starts with a VB Form application that contains one TextBox named
TextBox1 . Double clicking on the TextBox will open the code view and make a
TextBox1_TextChanged method. As you type into the TextBox this method will be executed for each character that changes.
The example has one queue called
myQ and is used as a synchronized queue with
mySyncdQ . There is also a thread named
thread1 that is started that runs the method
ThreadMethodReceive . This method will remove items from the queue and print them to the console.
Every time the text changes in the TextBox the
TextBox1_TextChanged method puts the contents of the TextBox onto the queue and signals a
AutoResetEvent named
mySyncdQEvent . The thread
thread1 calls the method
WaitOne for the
AutoResetEvent event. This will cause the thread to block until there is something on the queue.
Imports System.Threading
Public Class Form1' Thread that will receive the messages that are put on the queue
Dim thread1 As New Thread(AddressOf ThreadMethodReceive)' Queue where message will be stored
Dim myQ As New Queue' Thread safe queue that will be used
Dim mySyncdQ As Queue = Queue.Synchronized(myQ)' Event used to syncronize the TextBox putting items on the queue and the thread
Dim mySyncdQEvent As New AutoResetEvent(False)' Method executed when the form is loadedPrivate Sub Form1_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load' Make this a background thread so it automatically
' aborts when the main program stops.thread1.IsBackground = True
' Set the thread priority to lowestthread1.Priority = ThreadPriority.Lowest
' Start the threadthread1.Start()
End Sub' Thread that runs seperate from the Form1 threadPrivate Sub ThreadMethodReceive()
' Loop foreverWhile 1
' Half second pause before checking the sync eventThread.Sleep(500)
' Wait on the sync event. If something has been put on' the queue there will be an event.
mySyncdQEvent.WaitOne()' Continue removing items from the queue until it is empty
While mySyncdQ.Count' Print the items removed from the queue
Console.WriteLine(mySyncdQ.Dequeue())End WhileEnd WhileEnd SubPrivate Sub TextBox1_TextChanged(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles TextBox1.TextChanged
' Put the content of the text box on the queuemySyncdQ.Enqueue(TextBox1.Text)
' Signal that something has been added to the queue.mySyncdQEvent.Set()End Sub
End Class
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