[PD] another question about the threaded design in pd

[Ivica Ico Bukvic]

Hi all,

Another question regarding the threaded design (in follow-up to my earlier
posts re: disis_wiimote object. When redesigning the threaded version, what
I found out is something rather odd.

Basically, I have two threads (see my previous email from a couple days ago
for the source files). One is the main thread where all PD-related stuff
happens and another thread that deals with offending calls to wiimote (by
offending I mean they cause dropped samples in the audio thread).

The two threads do not write into each other's variable pool but rather
second thread compares its internal variables to the ones from the main
thread to figure out what needs to be done, plus usleeps in the interim.

Everything works fine and in the destructor, I set the flag for the second
thread to exit the while loop and reach pthread_exit(NULL); call. Then I do
pthread_join() call in the destructor of the main thread to allow time for
the second thread to close and that is the end of the destructor. To the
best of my knowledge this should just work. However in practice I found out
that after several connects/disconnects, the wiimote would connect but not
broadcast any data (or at least the external would not perceive any). This
was not the case with the non-threaded version so something must be amiss in
the current threaded implementation.

What perplexes me is if I add half-second usleep after pthread_join in the
*main* thread's destructor, this problem goes away making external rock
solid (same seemed to help in an earlier implementation that had more than 2
threads), almost as if Pd does not want to wait for objects whose
destructors so it makes them close prematurely. Yet, usleep seems to fix it
despite the fact that the pthread_join should wait for the completion/exit
of the other thread.

Any ideas?

Ivica Ico Bukvic, D.M.A.
Composition, Music Technology
Director, DISIS Interactive Sound & Intermedia Studio
Assistant Co-Director, CCTAD
CHCI, CS, and Art (by courtesy)
Virginia Tech
Dept. of Music - 0240
Blacksburg, VA 24061
(540) 231-6139
(540) 231-5034 (fax)
ico at vt.edu
http://www.music.vt.edu/faculty/bukvic/