Is it possible to change the length of a writable array according to tempo/bpm? I want to be able to set the sample loop recording time to a particular number of bars so that it will automatically sync in with the current tempo, or is it easier just to adjust the playback chunk size automatically?

What techniques do others use?

i would probably go with option 2, but if you set the length properly at first this does have the advantage that you can just copy the array to a sound file and not have to trim it first.

if you want to resize arrays, it's not hard... i think you just do:

[resize
|

where x is the array size in samples, and array-name is the name of the array.

the maths to calculate x from bpm and number of loops is easy peasy japanesey.