thread priority

[Hooovahh]

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@jyang72211 wrote:

The loop doesn't have to be syn, but they all need to start ASAP.  i see that one loop is delayed by 1s.  

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You will not get the loop times you want while in Windows, period.

You are at the mercy of Windows and having a 1ms loop rate is not going to be something that can be achived for any length of time.  The jitter along is probably on the order of a few milliseconds.  What if Windows downloads an update?  Runs anti-virus?  Performs a cache memory to disk? etc.

If you are trying to have anything happen at 1ms timing, you want hardware timed loops.  This means FPGA, real-time, or some kind of embedded device.

[jyang72211]

dont' really  need the 1ms timing.  It believe it is put there to indicate high priority.

[nathand]

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@jyang72211 wrote:

The loop doesn't have to be syn, but they all need to start ASAP.  i see that one loop is delayed by 1s.  

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Is it always exactly 1 second, or it varies from run to run? How are you measuring that delay? Are all the loops in one VI, or separate VIs? If you separate them into different VIs and put them in different execution subsystems, does it make a difference? Are you doing any operations that would cause a switch to the user interface thread - for example, using front-panel property nodes - which could force portions of the loops to execute serially rather than in parallel?

[nathand]

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@jyang72211 wrote:

dont' really  need the 1ms timing.  It believe it is put there to indicate high priority.

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That's not how thread priority works at all. The wait functions (Wait (ms), Dequeue, etc) wait until at least that amount of time has passed; in no way does it guarantee that execution will resume after exactly that amount of time has passed. If you want a high priority loop, do it properly: move it to a separate VI and set the priority, or use a Timed Loop (which runs in its own thread at a high priority).

[jyang72211]

I don't really care about the loop rate.  I just care about the start time of the loop.  

[chipsahoying]

Hello jyang72211,

There is a very good chance that you are already familiar with this concept, but have you looked into using Wait Until Next ms Multiple?

http://digital.ni.com/public.nsf/allkb/12B2EA9AD5B265AD86256257004DD8E2

http://zone.ni.com/reference/en-XX/help/371361K-01/glang/wait_till_next_ms_multiple/

Here is an example:

https://decibel.ni.com/content/docs/DOC-14149

It may assist in at least getting loops to synchronously start, though again, it may still be susceptable to software timing issues.

[billko]

I think we are trying to provide a solution for a problem that hasn't really been defined.  What happens in the loop that is "late"?  Does it do hardware initialization, are you reading or writing some equipment?  Are you building some kind af array?

I think this is one of those times where we should pull back and ask you why it is so critical that they all start at the same time and what this code is supposed to accomplish.  Maybe there's an easy solution that doesn't involve loop timing at all.