Hi all,
What's the best way to queue up and wait for number of threads to complete.
This problem was trivial in VC++ 6 but I'm finding it rather hard to solve
in VB.NET. My calculations run about 2 mins each (on a 2.8 Ghz Xeon and the
server range from 2 to 8 processors) (give or take about 15 secs). I have 8
sets of calculations to do (in another app I have 121) all the same calc
just different data. But the rest of the processing cannot continue until
ALL of the calculations are done.
so here's the algorithm I want to use (written from the C++ implentation
standpoint) {for ease of reading i have left out any/all discussion about
the queue ops used to schedule the runs which can change to what ever is
appropriate}
------------------------------------------------------------------
get user pref on number of concurrent threads...
for loop (to number of concurrent threads)
start a thread (with data)
add to wait list
while true
WaitForMultiple Objects(...thre ads...)
if more threads to process
launch thread with data
add to wait list
else if all threads finished
break
------------------------------------------------------------------
The problem I'm having is finding the .NET equivalent to
WaitForMultiple Objects. The threads might not complete in order or might
complete at the same time. I was toying with the idea of a delegate that
would basically have the functionality of the while loop, but seemed like
spaghetti coding to me.
Any ideas or examples you can think of would be greatly appreciated.
Thanks in advance,
Mike
----------------------------------------------------------
Mike Elledge
Jul 21 '05
10  3073 
MikeE,
Why not use two queues?
One queue for the questions (requests) to the N threads in the pool and a
second queue for the answers (to the main thread). The main thread can
simply wait for answers on the second queue, once it has all the answers it
can figure the final result.
Hope this helps
Jay
"MikeE" <mikeDOTelledge ATattbiDOTcom> wrote in message
news:e4******** ******@TK2MSFTN GP15.phx.gbl... Jon,
Thanks, I'll look into the single monitor option... seems promising.
One clarification though.. I HAVE to wait for all the threads to finish,
not because I want to reuse the thread, but because I need the "ANSWER". A
math problem is not finished until all the parts are there. In our program
the final result can NOT be calculated until ALL the threads have
returned.
Thanks again,
ME
"Jon Skeet [C# MVP]" <sk***@pobox.co m> wrote in message
news:MP******** *************** *@msnews.micros oft.com... <"Mike E" <mikeDOTelledge ATattbiDOTcom>> wrote: Yes! what I want is so close to the threadpool that it is irritating.
The
ONE MAJOR missing part for a thread pool is the MAX number of threads.
See,
this processing is some rather lengthy numerical calculations, VERY CPU
intensive. We do not run it on any machine that does not have at least 2
processors (or one hyper threaded one, and then just for testing).
Otherwise it locks the system up. But we have some servers that have up
to
8 CPUs in them. So we need the number of concurrent threads to be
variable.
If we just lanched them all at once, we would QUICKLY run out of cpu
bandwith for the calcs and the system. (back to locked systems). we
just
have to be able to control the number of "active" threads at one time.
What would your thoughts/feelings be towards using
"WaitForMultipl eObjects".
We of course could import it (which ive done) but having trouble
setting up
the array of Thread handles to be watched. Any ideas? (just a
reminder...i
kinda need this in vb.net)
Well, you don't really want to wait for other threads to actually
finish, because you can't reuse them. Doing a thread pool of *some*
description (which could just be several threads with a
producer/consumer queue - see
http://www.pobox.com/~skeet/csharp/t...eadlocks.shtml for some
sample code) is a much better answer here.
Alternatively, using Auto/ManualResetEven ts, one per thread, would
allow you to wait for any of the threads to finish without being too
hard. Or just have a single monitor which the main thread waits on and
which other threads pulse.
On another note.. since i do have to get something working soon.. i've
started down the spaghetti code method, where the threads fire events to
which i have a re-enterable function that can access the remaining
queue,
and when finally empty and done fires another event that is handled by a
delegate that does "the rest of the stuff" Unfortunatly this is looking
REALLY ugly, so i'm trying to come up with a class to wrap the thread
and
that contains a wait handle which is montitored.. but still trying to
flush
this out.
Again, what gets me, is that this takes less than 50 lines of code in
VC++,
with error checking, and was rock solid. I'm really having a tough time
coming to grips with the fact that we can't do it EVEN EASIER in .NET
like
so many of our other upgrades.
You may well find it's easier in .NET, once you change the approach
slightly. There are lots of things which are hard to do if you try
using the "old" approach, but for which there are new approaches which
make things easier.
--
Jon Skeet - <sk***@pobox.co m>
http://www.pobox.com/~skeet
If replying to the group, please do not mail me too
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sets of calculations to do (in another app I have 121) all the same calc
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