Dynamically-Launched VIs and Context Switching

I'm working on a project that dynamically calls instances of a reentrant VI, which I assume is a pretty common practice. Everything works pretty well, until the number of calls to this dynamic VI gets pretty large--on the order of 1000 or more--at which point, we begin to see performance degradation. My guess is that we are taking hits due to context switching, since the number of threads far exceeds the number of logical processor cores available.
A little more background:
The dynamic VIs being called effectively run as daemons, each running a while loop and waiting on a dedicated input queue to receive data and save it to disk. All are stopped via a globally shared stop notifier (passed as a ControlValue.Set method argument at launch). Each is waiting on its respective queue with a 1 second timeout so that the stop notifier can be polled. Under normal operating conditions, each one will run at some rate between 0.1Hz and 25Hz (the various rates are a large driving factor for separating them and needing to spawn them dynamically).
So, this leads me to the following questions:
Am I correct that the context switching is the likely culprit in the performance degradation?
If so, is there a fundamental difference in how LabVIEW handles multithreading with dynamic VI calls versus explicitly drawing separate while loops on a block diagram, or dropping multiple instances of a reentrant VI directly on the block diagram?
Is it likely that reducing the number of dynamic clones to equal the number of available processor cores would improve performance? (the scope of each clone would grow, as it would have to maintain the state information that was original distributed across multiple clones)
I realize that this question is pretty vague without concrete examples, but I'm hoping someone (AQ? Ben? Any of you NI gurus?) out there could provide some general insight into what's going on under the hood without needing to get too specific.

TurboPhil wrote:
Each is waiting on its respective queue with a 1 second timeout so that the stop notifier can be polled.
There is one relatively easy fix you can probably make here - set the timeout to -1 and destroy the queues to stop the loop (destroying the queue will output an error from the wait primitive). This should at least stop all the code from running all the time, although I'm still not sure how the threading of the different VIs will play with each other. This might be an issue if the queue is only created in the VI, but I'm assuming it isn't.
Try to take over the world!

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wfarid wrote:
I already used occurrences for Thread1 to execute before Thread2. Does occurrences guarantee that Labview will switch the context to Thread2, as soon as the context is fired ?
-- Walid
NO!
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Asking this question just out of curiosity to know the internal concepts.
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ranit B wrote:
Hi Experts,
Asking this question just out of curiosity to know the internal concepts.
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Wrote file afiedt.buf
1 declare
2 v_sysdate DATE;
3 begin
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10 LOOP
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12 END LOOP;
13 DBMS_OUTPUT.PUT_LINE('Multi Transaction: Time Taken: '||ROUND(((SYSDATE-v_sysdate)*(24*60*60)),0));
14 EXECUTE IMMEDIATE 'TRUNCATE TABLE mytable';
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Multi Transaction: Time Taken: 37
PL/SQL procedure successfully completed.
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>
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Hello !
The following program is for 3 Threads which do
context switching.
Often we get '0' zero for the low priority thread when
we run this program.
MY QUESTION IS WHY DO WE GET ZERO ?Presumably because the low priority thread gets no CPU time.
>
As far as my understanding is concerned; even if
preemptive multitasking is done by the threads,
the low priority thread should have run through few
iterations and thus giving some value other
than zero '0'.You can't make ANY assumptions about when or how much CPU time a given thread will get. Why don't you let your main thread sleep longer--a minute or 5 or ten--and see if LO gets some cycles then.
Secondly most of the time we get negative values for
the high priority thread. Why is that ?count = Integer.MAX_VALUE;
count++; // --> Integer.MIN_VALUE (-2^31)
I guess 10 seconds is enough time for a thread in a tight loop to count to 2 billion.
Is it because of the fact that volatile sets the
variable 'running' to some different value ?Volatile does nothing of the sort, and, in any case, isn't even in your code.
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FORALL context switching .. how it works ?

hi guys,
in the asktom link over here
http://asktom.oracle.com/pls/asktom/f?p=100:11:0::::P11_QUESTION_ID:17483288166654#17514276298239 
it was said that

forall i in 1 .. z_tab.count
insert
does this:
a) gather up inpus to insert (the entire z_tab)
b) perform context switch from PLSQL to SQL
c) execute insert N-times
d) perform context switch back from SQL to PLSQL

my question is does FORALL statement loops ?
does it do this ?
Example 1
loop 1
gather data to insert
loop 2
gather data to insert
loop 3
gather data to insert
loop finish
context switch to sql engine
perform insert 1 by 1
or
Example 2
loop 1 or no loop at all
gather all data required for insert
loop finish
context switch to sql engine
perform insert 1 by 1
my guess is example 1 is the correct answer
Advices gurus ?
Regards,
Noob

At what level are you asking the question?
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Justin

Thread context switching.

Since I'm working with some real-time applications I'm interested in the thread switching mechanisms of Java ME.
So my question is when does the context switching take place?
If a thread A changes the priority of thread B to higher than its own priority will thread B preempt A instantly or is it neccessary to cause the current thread to interrupt?
How do same priority threads preempt each other?
What priority is given to the garbage collector?
Mikael

Hi Mikael,
I'm not a ME VM expert, so do not have the deep knowledge. But from what I know:
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Regards,
Andrey

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