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Re: [simspark-devel] about multi-thread implementation
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From: Hedayat V. <hed...@ai...> - 2008-03-08 17:42:04
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<span>Hi Yuan,<br>
<br>
<style type="text/css">blockquote {color: navy !important; background-color: RGB(245,245,245) !important; padding: 0 15 10 15 !important; margin: 15 0 0 0; border-left: #1010ff 2px solid;} blockquote blockquote {color: maroon !important; background-color: RGB(235,235,235) !important; border-left-color:maroon !important} blockquote blockquote blockquote {color: green !important; background-color: RGB(225,225,225) !important; border-left-color:teal !important} blockquote blockquote blockquote blockquote {color: purple !important; background-color: RGB(215,215,215) !important; border-left-color: purple !important} blockquote blockquote blockquote blockquote blockquote {color: teal !important; background-color: RGB(205,205,205) !important; border-left-color: green !important}</style><i><b>"Yuan
Xu" <a class="moz-txt-link-rfc2396E" href="mailto:xuy...@gm..."><xuy...@gm...></a></b></i> wrote on 03/08/2008 08:27:05 AM:</span><br>
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<pre wrap="">Hi Hedayat,
Thanks for your reply.
[...]
GameControlServer should be updated after the PostPhysicsUpdate.
So the loop of the main thread should be:
mSceneServer->PrePhysicsUpdate
mSceneServer->PhysicsUpdate
mSceneServer->PostPhysicsUpdate
GameControlServer->Update
</pre>
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Done. Thanks! <br>
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<pre wrap=""> I'm using Mesa 7.0.1 with nvidia binary driver 169.09 and the problem still
exists.
Yes, the main reason was rendering, but there is another problem too. FRP
sensor calls dJointGetFeedback(). ODE is not thread safe and this call will
generate segmentation faults some times. Also, this call should happen
before next physics update since the feedback information will not be
available then (I think!).
</pre>
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<pre wrap=""><!---->
Bad news, the OpenGL should be thread-safe.
</pre>
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Yes :(. But Mesa might be thread safe now. Since I've installed nvidia
binary drivers, simspark uses nvidia OpenGL libraries instead of using
Mesa. So, I can't say anything about mesa, but nvidia opengl is not
thread safe.<br>
<br>
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<pre wrap="">
You can call dJointGetFeedback() in PostPhysicsUpdateInternal(), and
cache the feedback information.
It just likes cache the actions and realize them in PrePhysicsUpdateInternal().
</pre>
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<br>
Good suggestion. I never liked creating feedback structs using new, and
I've changed the code so the dJointFeedbacks are now stored inside
ForceResistancePerceptor and no ODE calls are necessary anymore. It
solved the problem.<br>
<br>
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<pre wrap=""><!---->
Ah, I see! It is OK, and much simpler and clear than the old code, great job!
</pre>
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Thanks! :)<br>
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<pre wrap="">But there may be a small problem in current code:
The scene tree should not be accessed by the main thread and
SimCtrThreads at the same time.
(May be the problem will come after you remove the Step().)
So when call the follow functions, the SimCtrThreads should be blocked.
mSceneServer->PrePhysicsUpdate
mSceneServer->PostPhysicsUpdate
GameControlServer->Update
So the lines in RunMultiThreaded() needs adjustment, I think it is easy for you.
</pre>
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I thought that I can call mSceneServer->PrePhysicsUpdate() in
parallel :(. This is really bad! This function should be called after
EndCycle() functions which run in parallel now. So, protecting
mSceneServer->PrePhysicsUpdate() needs two more wait() calls. I
wonder if this can be worse than calling EndCycle() and
mSceneServer->PrePhysicsUpdate() functions in the main thread!<br>
<br>
The interesting (not much!) point is that I have not encountered any
problems by calling mSceneServer->PrePhysicsUpdate() in parallel
till now! Is there any conflicts between
mSceneServer->PrePhysicsUpdate() and EndCycle() functions in the
current code?! <br>
<br>
I've committed my changes. Any suggestions/comments are highly
appreciated!<br>
<br>
Thanks,<br>
Hedayat<br>
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