jack_recompute_total_latencies() is called in the process callback

[drobilla]

... which is not allowed. See discussion at sjaehn/BSchaffl#17

Original code from cebeaf2.

This event will need to be shunted to the UI thread and dealt with later somehow, though I don't know exactly how to do this correctly (or if it's even possible to do correctly, for some sufficiently pedantic definition of "correctly").

[x42]

Ardour starts a background thread for interacting with jack1. Its only job is to make or break connections and send latency-callbacks.

[drobilla]

yaaaay :/