Wait until x==true

This is a discussion on Wait until x==true within the C# Programming forums, part of the General Programming Boards category; Hello, this problem is more exotic than you think. i'm using 2 threads to draw pixels on the screen like ...

  1. #1
    Registered User Devils Child's Avatar
    Join Date
    Jan 2008
    Posts
    244

    Wait until x==true

    Hello,
    this problem is more exotic than you think. i'm using 2 threads to draw pixels on the screen like this:
    Code:
    // draw upper half here
    ThreadPool.QueueUserWorkItem(delegate
                    {
    // draw pixels here
    }, null);
    
    // draw lower half here
    ThreadPool.QueueUserWorkItem(delegate
                    {
    // draw pixels here
    }, null);
    and after that piece of code i need to pause the main thread UNTIL the both threads above have finished. of course the simplest thing would be to just set two variables and do this:
    Code:
    while(!thread1_finished || !thread2_finished) Thread.Sleep(1);
    but that is bad, because the operations above take far less then 1 millisecond. so how do i run these two operations simultaneously and wait for both to finish?

    any help appreciated. thanks.

  2. #2
    Registered User
    Join Date
    Aug 2003
    Posts
    1,205
    This article might contain info you are interested in (mainly the WaitHandle part)
    C# Tutorial - Using The ThreadPool | Switch on the Code

  3. #3
    Registered User C_ntua's Avatar
    Join Date
    Jun 2008
    Posts
    1,853
    Why make it sleep? If it takes less than 1ms just make it wait.
    The most optimized way is probably using a signal of some sort. For example you can use a semaphore. The main threads waits until the semaphore is released. Well, until its inner count is zero in other words, where it will start at 2 and decrease each time one operation is done.

    Sleep is NEVER the best solution. When dealing with threads try always to find a logical solution independent of timing. The Sleep() is not a good practice and not guaranteed to work. Except if you have no other solution or you don't want to lose to much time to find one.

  4. #4
    Gawking at stupidity
    Join Date
    Jul 2004
    Location
    Oregon, USA
    Posts
    3,164
    Do you have to use the threadpool? What about something like this?
    Code:
            static void Main(string[] args)
            {
                Thread thread1 = new Thread(DrawTopPixels);
                Thread thread2 = new Thread(DrawBottomPixels);
    
                thread1.Start();
                thread2.Start();
    
                thread1.Join();
                thread2.Join();
    
                Console.WriteLine("Both threads have terminated.");
            }
    
            private static void DrawTopPixels(object obj)
            {
                // Code to draw pixels
            }
    
            private static void DrawBottomPixels(object obj)
            {
                // Code to draw pixels
            }
        }
    If you understand what you're doing, you're not learning anything.

  5. #5
    Registered User Devils Child's Avatar
    Join Date
    Jan 2008
    Posts
    244
    Code:
                ManualResetEvent[] resetEvents = new ManualResetEvent[2];
                resetEvents[0] = new ManualResetEvent(false);
                resetEvents[1] = new ManualResetEvent(false);
                ThreadPool.QueueUserWorkItem(delegate
                {
                    //draw
                    resetEvents[0].Set();
                }, null);
                ThreadPool.QueueUserWorkItem(delegate
                {
                    //draw
                    resetEvents[1].Set();
                }, null);
                WaitHandle.WaitAll(resetEvents);
    this is what i came up with so far and it's actually slower than using just a single thread.

  6. #6
    Gawking at stupidity
    Join Date
    Jul 2004
    Location
    Oregon, USA
    Posts
    3,164
    Quote Originally Posted by Devils Child View Post
    this is what i came up with so far and it's actually slower than using just a single thread.
    Okay...? And what about the suggestion that I gave? Did you try it? Did you answer the question I asked?

    Are you saying you're fine with your solution even though it's slower or that you're giving up or what?
    If you understand what you're doing, you're not learning anything.

  7. #7
    Anti-Poster
    Join Date
    Feb 2002
    Posts
    1,399
    Alternately, if both methods are so fast and the main thread must wait for them anyway, why not use blocking calls?
    If I did your homework for you, then you might pass your class without learning how to write a program like this. Then you might graduate and get your degree without learning how to write a program like this. You might become a professional programmer without knowing how to write a program like this. Someday you might work on a project with me without knowing how to write a program like this. Then I would have to do you serious bodily harm. - Jack Klein

  8. #8
    Cat
    Cat is offline
    Registered User
    Join Date
    May 2003
    Posts
    1,571
    Quote Originally Posted by Devils Child View Post
    this is what i came up with so far and it's actually slower than using just a single thread.
    It looks like you're trying to do a multithreaded rendering loop, and you're now seeing why games don't do it -- the thread synchronization makes it slower to use multithreading than single threading.

    For a very quick operation, threading is just not worth it because of the time lost to synchronizing the threads and the overhead (thread pools reduce overhead but don't eliminate it), and trying to split a single viewport's rendering loop across multiple threads without trying to synchronize them would cause a lot of artifacts as different parts of the screen are drawn at different times.
    Last edited by Cat; 11-07-2010 at 02:35 PM.
    You ever try a pink golf ball, Wally? Why, the wind shear on a pink ball alone can take the head clean off a 90 pound midget at 300 yards.

  9. #9
    Registered User Devils Child's Avatar
    Join Date
    Jan 2008
    Posts
    244
    @itsme86: i did try your method and it is much slower than thread pools because we would need to create new threads for that. don't get so angry about that. and no, i'm not giving up.

    @pianorain i'll try that when i'm home

    @Cat: i guess you're right. synchronization takes more time then time i would save.

    i think i need to think of other ways. thanks guys.

Popular pages Recent additions subscribe to a feed

Similar Threads

  1. Why wait cursor still turning on?
    By Opariti in forum Windows Programming
    Replies: 0
    Last Post: 05-22-2009, 02:28 AM
  2. Replies: 3
    Last Post: 10-15-2008, 09:24 AM
  3. Signals, fork(), wait() and exec()
    By DJTurboToJo in forum C Programming
    Replies: 7
    Last Post: 03-18-2008, 09:14 AM
  4. Boom, Headoshot!!
    By mrafcho001 in forum A Brief History of Cprogramming.com
    Replies: 50
    Last Post: 07-21-2005, 08:28 PM
  5. anybody with experience using the wait() function?
    By flawildcat in forum C Programming
    Replies: 7
    Last Post: 04-22-2002, 02:43 PM

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21