There is no real answer as this is probably totally dependent on the rest of your code.
Now, if you can reproduce the problem in a simple sketch you can show to us, perhaps we can take a look.

Also, take a look at the last example in the following post link:
http://forum.processing.org/topic/threading-background-threads-inherently-slower-than-animation-thread

Having extra threads drawing to canvas at the same time makes whole screen blink or worse!
Use separate PGraphics objects to try to avoid such bugs!

I'm only drawing to the screen in the main thread, the other thread is just processing some data and returning that to the main thread