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
4  1973  http://msdn.microsoft.com/library/de...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:%2****************@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
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" <Ju****@games4dotnet.com> wrote in message
news:e5**************@tk2msftngp13.phx.gbl... http://msdn.microsoft.com/library/de...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:%2****************@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
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:Ob**************@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" <Ju****@games4dotnet.com> wrote in message
news:e5**************@tk2msftngp13.phx.gbl... http://msdn.microsoft.com/library/de...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:%2****************@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
Splendid explanation. That does kind of make sense, and it's a good job we
spotted it now (and didn't put it into our 'strange but true' bug file) and
not after release. My TV show "When multithreading goes bad" is coming on
leaps and bounds.
Thanks again, and I hope it's not as late where you are as it is here :-)
Steve
"Justin Rogers" <Ju****@games4dotnet.com> wrote in message
news:OC*************@TK2MSFTNGP12.phx.gbl... 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:Ob**************@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" <Ju****@games4dotnet.com> wrote in message
news:e5**************@tk2msftngp13.phx.gbl...
http://msdn.microsoft.com/library/de...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:%2****************@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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