Why is While Loop in the Producer Consumer Queue?

Question

4.00/5 (1 vote)

See more:

Hi everyone,

I'm not fully understanding the EventWaitHandle class and the while() within the producer consumer queue:

C#

Queue<string> que = new Queue<string>();
EventWaitHandle wh = new AutoResetEvent(false);
object sync = new object();

private void job(string task)
{
  lock(sync)
  {
    queue.Enqueue(task);
  }
  wh.Set();
}

private void worker()
{
  while(true)
  {
     string copyTask = "";

     lock(sync)
     {
       if(queue.Count > 0)
       {
         copyTask = queue.Dequeue();
       }
       
      if(copyTask != "")
      {
          // process data...
      }
      else
        wh.WaitOne();
  }
}
</string></string>

My question is: "if" the wh.WaitOne() sends a signal to wh.Set() notifying job() that it's ready to process data why is the while() necessary? Does the wh.WaitOne() stop the while() loop and put it to sleep? Or does it put the Thread that worker() is running on to sleep?

I've read and done a few tutorials on this and I'm still not clearly understanding what's going on. Can someone please explain to me what's happening here?

Thank in advance!
-Donald

Posted 18-Mar-11 15:37pm

d.allen101

Updated 18-Mar-11 20:08pm

Sandeep Mewara

v2

Add a Solution

1 solution

Add a Solution

Add your solution here

Treat my content as plain text, not as HTML

Preview 0

…

Existing Members

Sign in to your account

...or Join us

Download, Vote, Comment, Publish.

Your Email
Password
Forgot your password?

Your Email
This email is in use. Do you need your password?
Optional Password

I have read and agree to the Terms of Service and Privacy Policy
Please subscribe me to the CodeProject newsletters

When answering a question please:

Read the question carefully.
Understand that English isn't everyone's first language so be lenient of bad spelling and grammar.
If a question is poorly phrased then either ask for clarification, ignore it, or edit the question and fix the problem. Insults are not welcome.
Don't tell someone to read the manual. Chances are they have and don't get it. Provide an answer or move on to the next question.

Let's work to help developers, not make them feel stupid.

This content, along with any associated source code and files, is licensed under The Code Project Open License (CPOL)

Sergey Alexandrovich Kryukov · Answer 1 · 2011-03-18T15:58:00

See the full source code and explanation in my Tips/Tricks article: Simple Blocking Queue for Thread Communication and Inter-thread Invocation[^]. It solves exactly the same problem, only in a cultured way, using generics.

You're very confused with threading, not just WaitOne. When a thread is calling a blocking code such as WaitOne it is "sleeping" using zero CPU time. The thread simply switched of and never scheduled for execution again until it is "waken up". EventWaitHandle.Set of the same instance makes the thread in wait state wake up. There is no loop at all. That you probably have in mind is called "spin-wait" and is the absolute evil.

—SA