Re: Thread safety

Tech-Archive recommends: Fix windows errors by optimizing your registry

From: Justin Rogers (Justin_at_games4dotnet.com)
Date: 05/26/04 

Date: Wed, 26 May 2004 16:51:40 -0700

Image is abstracting you from a bunch of method calls. In GDI+ each object
is simply a pointer or handle, and you call methods to get the information from
those handles. If Image cached the values for you, then it would have a bunch
of state work to handle for things like moving to the next frame or other events
that could possibly change the height or width of the underlying image.

This generally isn't a huge problem across the framework, but is common when
API's are created that are wrapping an unmanaged API. The unmanaged API's
simply have semantics that don't translate 1 for 1 into the .NET world. 

-- 
Justin Rogers
DigiTec Web Consultants, LLC.
Blog: http://weblogs.asp.net/justin_rogers
"Steve McLellan" <sjm.NOSPAM AT fixerlabs DOT com> wrote in message
news:ObCcHt3QEHA.3528@TK2MSFTNGP09.phx.gbl...
> OK, cheers. Just the sort of thing I need to find out at 1am :-)  Is this
> common to the framework? I'm never likely to know what's cached and what
> isn't for a given property.... and surely this is unnecessary if there are
> only read operations going on? I'm still not sure why exactly that could
> ever be a problem.
>
> Steve
>
> "Justin Rogers" <Justin@games4dotnet.com> wrote in message
> news:e5ZtEn3QEHA.2400@tk2msftngp13.phx.gbl...
> >
>
http://msdn.microsoft.com/library/default.asp?url=/library/en-us/gdicpp/GDIPlus/sec_gdiplus.asp?frame=true
> >
> > Info on thread safety.  Internally Height always calls methods to get the
> height
> > and no caching is performed.  Since each call is a method, there might be
> some
> > work, the return of an ObjectBusy status, or any number of other items
> that
> > might go wrong.
> >
> >
> > -- 
> > Justin Rogers
> > DigiTec Web Consultants, LLC.
> > Blog: http://weblogs.asp.net/justin_rogers
> >
> > "Steve McLellan" <sjm.NOSPAM AT fixerlabs DOT com> wrote in message
> > news:%23jr4ci3QEHA.3532@TK2MSFTNGP12.phx.gbl...
> > > Hi,
> > >
> > > I've just discovered that accessing Image.Height (and probably other
> > > properties) in a multi-threaded environment can cause access problems
> (as a
> > > test, you can spawn a hundred threads and get them all to perform a
> couple
> > > of multiplications on an image's height and width ). I know I can
> prevent
> > > simultaneous access, but is there any reason why Image can't be accessed
> > > like this? And is this common for all .NET objects? I know the docs say
> 'not
> > > thread-safe' but not being safe for multiple reads seems bizarre.
> > >
> > > Steve
> > >
> > >
> >
> >
>
>

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