Hello Weiyu,
Weiyu Yi wrote:
> I have some problems when I add some multithreading functionality to a
> project.
>
> ******************************************************************************************************
>
>
> First I think I should describe the project a bit:
[SNIP - project description]
thanks for providing the background info.
> ******************************************************************************************************
> Now is my error:
>
> By single-thread there is no error, but my multithreading, this means 2
> threads, one is for collision detection and the other is the movem, the
> user phase application.
>
> Errors like this:
> =========================================
> Program received signal SIGSEGV, Segmentation fault.
> [Switching to Thread 0xb4d9eb90 (LWP 18751)]
> 0xb72f7cd5 in osg::PThreadBase::getAspect () at
> /home/weiyu/Projects/OpenSG/Source/System/FieldContainer/OSGThread.cpp:142
> 142 return *pUint;
it looks like you are accessing OpenSG objects from a thread OpenSG does
not know anything about. see below for more details.
> =========================================
> I imagine that, there are 2 probabilities for the errors?
>
> 1: the the opensg's function is called in the scope of callback(), which
> is called by the thread collision detection not the movem, although it's
> compiled and linked in movem. But collision detection library doesn't
> recoginize the opensg, then error happens
>
> 2 the opensg's data types are thread-safe, this means all the data type
> like osg::Node are protected by some mechanism like mutex or something
> else. when the thread initialized by boost or direct by system accesses
> these data, error happens.
OpenSG uses very few locks/mutexes etc. internally and none of the
objects you normally find in a scene are protected in this way. Instead
in OpenSG every thread is associated with an aspect (essentially a copy
of the scene), so that threads on different aspects can make changes to
the scene without interfering with each other. All modified fields that
are modified are recorded in the threads changelist which the
application can then apply whenever it is convenient to merge changes
from one aspect to another.
> If I am right, How can I resolve it?
as I mentioned you are probably accessing OpenSG from a thread the
system does not know about - probably because you create a boost thread
instead of an OpenSG thread. The result is that the system does not know
which OpenSG aspect the thread is supposed to operate on. Anyway, the
solution is to tell OpenSG about your thread like this:
At the beginning of the thread function:
OSG::UInt32 aspectId = 0;
OSG::ExternalThread::get(0)->initialize(aspectId);
This will make the thread use aspect 0 (which is also the aspect used by
the thread of the main function of your program).
Cheers,
Carsten
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