Help with ManualResetEvent signalling...

Question

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Hi guys!
I'm creating a chat program using XML Web Services..
Now currently on chat client...
I have a question about client side message validating...
I use ManualResetEvent object to set event for another validating thread to filter a user message before sending to Web Service..
I plan this:
I process KeyPressed event of a TextBox component to
marshal text validation to another thread...
I use this thread to validate client messages (remove any offesnsive words like
f***, sh*t, bullshit, c*** due to signalling of ManualResetEvent object...

Pseudo - Code:

private Thread m_ValidationThread = new Thread(DoTextProcessing);

private ManualResetEvent m_KeyPressedEvent = new ManualResetEvent(false);

private void txtMessageOnKeyPress(object sender, KeyPressEventArgs arg) {
  //blah-blah-blah

 m_KeyPressedEvent.Set( );
}

private void DoTextProcessing( ) {

 while(true) {
 m_KeyPressedEvent.WaitOne( );

lock( m_TextToSend) {
string[ ] words = m_TextToSend.Split( new char[ ] { ' ' });
  foreach(string word in words)
   if ( m_ForbiddenWords.Contains(word))
     NotifyClient("Be a good guy!");
 } // end lock

  m_KeyPressedEvent.Reset( );
 } // end while
}

What if a user types another char and thus m_KeyPressedEvent would call its
<bold>Set( ) method again!!!!!
So a SIGNALLED m_KeyPressedEvent would signal again
without being reset (by validation thread)....what's the next???
Is it okay???

Posted 22-Mar-11 9:32am

Nick Reshetinsky

Updated 22-Mar-11 10:00am

v3

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2 solutions

Solution 1

Why not just wait to validate the string until the user presses the enter key, and then make the validation part of the send thread processing? I think you're making it more difficult than it needs to be...

Posted 22-Mar-11 10:13am

#realJSOP

Comments

Sergey Alexandrovich Kryukov 22-Mar-11 17:25pm

Sorry, not quite agree. This is not too complex and makes sense, only OP is confused about wait. See my Answer is you wish.
--SA

Albin Abel 22-Mar-11 22:52pm

Conceptually I agree with this. Not sure how to implement in .Net. May be SAKryukov's answer helps. My 5

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Sergey Alexandrovich Kryukov · Accepted Answer · 2011-03-22T11:20:00

I see. To use manual reset, you need to call m_KeyPressedEvent.Reset in the blocked thread right after return from m_KeyPressedEvent.Wait. Just do

C#

m_KeyPressedEvent.Wait();
m_KeyPressedEvent.Reset();

Alternatively, use auto-reset.

[EDIT]
Remove that wait(true), immediately, never do it again, ever!
This is not a spin wait! Never use spin wait!
EventWaitHandle.Wait is blocking. The thread is switched off by OS and put to a wait state using zero CPU time. In other words, OS never schedule this thread for executions until it is awaken by Set.

—SA