[PD] xrun-free file i/o using the coll external (SOLVED)

[Ivica Ico Bukvic]

In hope to answer some of the questions I presented on the pd-list the
other day, attached is the patch (diff -u against pd-extended svn
0.42.5) that converts miXed/cyclone/coll.c object into a threaded
version which in turn does not trigger xruns every time one tries to
open or save a file at runtime. This is particularly apparent when
opening/closing large files using low latency audio buffers. This
problem is also apparent in other similar objects (e.g. msgfile) and
should be ostensibly solvable using the same principle.

Additional lessons I learned from this exercise and am sharing them here
in hope others may benefit from them as well are as follows:

1) Spawning a secondary thread within an external (detached or not)
should in principle never result in an xrun, except in the coll object I
discovered that always the first thread creation did result in an xrun
which is why the code also does a bogus thread immediately following the
creation time using clock_delay. I am not sure whether this is
atom-CPU-specific or more widespread and/or whether this has to do with
the way PD is designed. Any thoughts are most appreciated here.

2) Triggering clock_delay from a separate thread works fine and should
be always used (rather than dealing with the outlet traffic directly) to
prevent out-of-sync gui operations which may result in gui
freezing/crashing.

Cheers!

Ico

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