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POMouse jiggling / message processing loop
 

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  1. POMouse jiggling / message processing loop
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    <p>I have written a multithreaded program which does some thinking and prints out some diagnostics along the way. I have noticed that if I jiggle the mouse while the program is running then the program runs quicker. Now I could go in to detail here about how exactly I'm printing... but I will hold off just for now because I've noticed that in many other programs, things happen faster if the mouse is jiggled, I wonder if there is some classic error that many people have made in which the message loop is somehow slowed down by a non-moving mouse.</p> <p>EDIT: My method of "printing" is as follows... I have a rich edit control window to display text. When I want to print something, I append the new text on to the existing text within the window and then redraw the window with SendMessage(,WM_PAINT,0,0).</p> <p>Actually its a bit more complicated, I have multiple rich edit control windows, one for each thread (4 threads on my 4-core PC). A rough outline of my "my_printf()" is as follows:</p> <pre><code>void _cdecl my_printf(char *the_text_to_add) { EnterCriticalSection(&amp;my_printf_critsec); GetWindowText(...); // get the existing text SetWindowText(...); // append the_text_to_add SendMessage(...WM_PAINT...); LeaveCriticalSection(&amp;my_printf_critsec); } </code></pre> <p>I should point out that I have been using this method of printing for years in a non-multithreaded program without even noticing any interaction with mouse-jiggling.</p> <p>EDIT: Ok, here's my entire messageloop that runs on the root thread while the child threads do their work. The child threads call my_printf() to report on their progress.</p> <pre><code>for(;;) { DWORD dwWake; MSG msg; dwWake = MsgWaitForMultipleObjects( current_size_of_handle_list, hThrd, FALSE, INFINITE, QS_ALLEVENTS); if (dwWake &gt;= WAIT_OBJECT_0 &amp;&amp; dwWake &lt; (WAIT_OBJECT_0 + current_size_of_handle_list)) { int index; index = dwWake - WAIT_OBJECT_0; int j; for (j = index+1;j &lt; current_size_of_handle_list;j++) { hThrd[j-1] = hThrd[j]; } current_size_of_handle_list--; if (current_size_of_handle_list == 0) { break; } } else if (dwWake == (WAIT_OBJECT_0 + current_size_of_handle_list)) { while (PeekMessage(&amp;msg, NULL, 0, 0, PM_REMOVE)) { TranslateMessage(&amp;msg); DispatchMessage(&amp;msg); } } else if (dwWake == WAIT_TIMEOUT) { printmessage("TIMEOUT!"); } else { printmessage("Goof!"); } } </code></pre> <p>EDIT: Solved! This may be an ugly solution - but I just changed the timeout from infinite to 20ms, then in the if (dwWake == WAIT_TIMEOUT) section I swapped printmessage("TIMEOUT!"); for:</p> <pre><code>while (PeekMessage(&amp;msg, NULL, 0, 0, PM_REMOVE)) { TranslateMessage(&amp;msg); DispatchMessage(&amp;msg); } </code></pre> <p>I'm not closing this question yet because I'd still like to know why the original code did not work all by itself.</p>
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    1. USMick
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      1. POMouse jiggling / message processing loop
      1. USMick
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      1. VTUpMod
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    1. CODo you have any benchmarks to show this? The popular JiggleMark 2009 is good, I hear.
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      1. USBen James
    2. CODon't close it. It could be useful for the next guy with a similar problem.
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      1. USKelly S. French
 

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