RE: [GD-Windows] TryEnterCriticalSection

[Brian S. <bs...@mi...>]

There's also all the Interlocked* functions, like
InterlockedCompareExchange, for those who have a hard time remembering
x86 asm instructions.  And for those, like myself, who never knew the
instructions :). =20

I've used mutexes (mutices?) a lot, for instance when walking common
data structures like network message queues (receive messages on worker
thread, process messages on main thread). My usage has typically been
with 2 threads going.  I've never sensed a problem.  I don't know what
the internal implementation is like, but I would guess that lots of time
has been spent making sync primitives as efficient as possible. =20

If you're worried about the cost of wait objects vs. critical sections,
then I guess one question you could ask yourself is, does the time
required for WaitForSingleObject(0) compare at all to the time that your
thread would just sit there if you just used EnterCritSection instead of
TryEnterCritSection?  How long do the threads typically hold the
critical section?  Is your goal to actually avoid having multiple
threads execute through the guarded section in close temporal sequence,
or are you just worried about having other threads waiting idle while
one thread goes through it?

Maybe more details about how many threads you have going, what they're
doing, how many different places the critical section is currently being
used, etc. would help get answers that are more useful to you.

--brian

-----Original Message-----
From: Andy Glaister [mailto:an...@mi...]=20
Sent: Thursday, January 03, 2002 11:42 AM
To: gam...@li...
Subject: RE: [GD-Windows] TryEnterCriticalSection

There is a good performance comparison of different sync objects found
at=20

http://www.usenix.org/publications/library/proceedings/usenix-nt98/full_
papers/zabatta/zabatta_html/zabatta.html

It depends upon what you are trying to do and how often you will
check/set/block in your code. Personally I would write my own sync
object using _asm lock cmpxchg - then it would run on all CPUs 486 and
above...

There are very neat sync objects in the later OS's - SLIST for example
is very clever, but only in XP and above (of course, you could implement
it yourself without too much trouble) - also spin locks may be useful if
you only lock the resource very briefly.

Andy Glaister.

-----Original Message-----
From: Brian Hook [mailto:bri...@py...]=20
Sent: Thursday, January 03, 2002 11:18 AM
To: gam...@li...
Subject: [GD-Windows] TryEnterCriticalSection


It looks like TryEnterCriticalSection is only available on >=3D NT4 (and
according to the docs, it's not available on Win9x at all).  To get
around this I'm thinking that I could switch to using a mutex and
WaitForSingleObject with a timeout of 0 milliseconds, but mutexes are
heavier weight than critical sections (I'm not sure how bad this is in
practice though).

Any opinions, comments or shared experiences with this?

Brian


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