Problems with Sleep() in thread

[S Douglas]

acerunner316 wrote:

but 6ms delay is still way too slow

To get an understanding of how time works read Time is the Simplest Thing[^]

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I'd love to help, but unfortunatley I have prior commitments monitoring the length of my grass. :Andrew Bleakley:

[Jorgen Sigvardsson]

So.. uh, the system timer resolution is too low? Lucky me that I don't have to do anything multimedia related, because I was under the impression that a timer which is given the attribute system would be the most accurate one. Thanks for the heads up - who knows? I might have to deal with issues like this some day...

-- Verletzen zerfetzen zersetzen zerstören Doch es darf nicht mir gehören Ich muss zerstören

[Chris Losinger]

it's updated every ~15ms to 50ms (depending on the version of Windows). so, it is measuring time in the ms range, but the difference between two consecutive calls will never be less than ~15ms. QueryPerformanceCounter is much more accurate.

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[acerunner316]

I don't know if it takes 0ms, but there is nothing else to my code other than repeatedly posting messages. UINT CNOx1000MonitorDlg::FThreadLoop (LPVOID PptrToClass) { CMainWindowDlg *LptrClass = static_cast(PptrToClass); HWND *ptrWindowHandle = new HWND; *ptrWindowHandle = LptrClass->GetSafeHwnd(); while(LptrClass->mbolThreadExecute) { ::PostMessage(*ptrWindowHandle, WM_UPDATE_CONTROLS, 0, 0); ::Sleep(10); } delete ptrWindowHandle; return 0; }

[acerunner316]

How will I use QueryPerformanceCounter as a way of sampling data? I will still need a thread to loop a function call. And in that function will check QueryPerformanceCounter. But if posting a message takes longer than 6ms. Then QueryPerformanceCounter can only be as accurate as that. Can you provide a code sample? Im fairly new to windows programming. I am basically learning from sample code that I find online. Thanks.

[Chris Losinger]

acerunner316 wrote:

I will still need a thread to loop a function call. And in that function will check QueryPerformanceCounter.

right

acerunner316 wrote:

But if posting a message takes longer than 6ms. Then QueryPerformanceCounter can only be as accurate as that.

right maybe this article can help... scroll down to the bottom for a message-loop / QueryPerfCounter sample.

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[acerunner316]

sorry, i'm still having trouble understanding. In code sample at the link you gave, I can see that the function is monitoring for any messages and checking for the time. But there is the message being generated from, and how?

[Chris Losinger]

acerunner316 wrote:

But there is the message being generated from, and how?

the message comes from code outside the loop. this is pretty close to an old-style C Windows message loop. Windows is passing messages (button down, repaint, keydown, etc) to the application, which the app grabs, when it sees one, and starts processing with that Peek/Translate/DispathMessage bit - other code is responsible for handling the specific msgs. otherwise, every 40ms, the app does a run through its Render/Move/etc stuff, then goes back to looking for messages.

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[acerunner316]

Isn't this similar to what I'm already doing, posting messages every 10ms? Because what I'm doing is posting the message repeatedly in a loop every 10ms. And then I have a function mapped to handle that message ON_MESSAGE(WM_UPDATE_DATA, OnUpdateData). So the only difference I see is instead of using ON_MESSAGE, I will have my own function that loops to check for the message posted an respond to it. Is this right? Will this make the difference of the 6ms delay? Would I have to post this message like every 1ms in order to get the 1ms resolution?

[Chris Losinger]

acerunner316 wrote:

Isn't this similar to what I'm already doing, posting messages every 10ms?

pretty much. but Sleep simply isn't that accurate. Sleep uses the system clock, which has a resolution closer to 15ms per tick in most modern versions of Windows. and, it's entirely possible for your sleeping thread to get preempted by another thread, further delaying its awakening. i'm not sure what the overhead in PostMessage / ON_MESSAGE amounts to. but they're asynchronous anyway; apps respond to messages when they get around to it, not the instant they appear in their message. the time from PostMessage to the actual response is (i believe) indeterminate.

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[acerunner316]

Chris Losinger wrote:

pretty much. but Sleep simply isn't that accurate. Sleep uses the system clock, which has a resolution closer to 15ms per tick in most modern versions of Windows. and, it's entirely possible for your sleeping thread to get preempted by another thread, further delaying its awakening.

In that case, what do I use to loop posting of a message?

[Chris Losinger]

honestly, i don't know. Windows really isn't a real-time OS, and as far as I know, there's not a lot of high-level support for the kind of timing precision you seem to want. maybe you could check an open source game or audio application (ex. Audacity) that you could plunder for ideas.

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