Preallocating Arrays for Deterministic Loops

When programming a deterministic, time-critical loop, avoid using any shared resources, including the memory manager, to reduce jitter. If you are using arrays in your loops, you can reduce jitter by preallocating all of your arrays before entering the loop.

Figure 1 shows an example of a method that induces jitter. Because the Build Array node inside the WHILE loop uses the memory manager, a shared resource, this example induces jitter, especially if there are parallel normal priority VIs running that also use the memory manager.


Figure 2 shows an example of a method that reduced jitter. Because the WHILE loop uses a Replace Array Subset node to create the output array, this example does not use the memory manager because the array has been preallocated.



Look inside all of the subVIs that are inside of your time-critical loop to make sure that no memory management occurs inside of them. Even if you build an array with only one element in it, the memory manager still is used. You also need to preallocate an array with only one element.

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