problem with locks

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Greg Newton (gregn++at++cc.gatech.edu)
Wed, 9 Oct 1996 12:08:46 -0400

I am having a problem trying to use shared arena locks within a Performer
program. I'm using Performer 2.0 and have run into this problem on an IR, a
Max Impact and on a Solid Impact, all running IRIX 6.2.

I have a fastrak class that sprocs off a reader process to read the data from
the serial port. The class has a lock that I want to use to ensure mutual
exclusion when updating or reading some member variables that contain the
position and rotation info.

Here's how I allocate the lock :

// =========================================

void* semaArena = pfGetSemaArena();
if (!arena)
  return 0;

mutex = usnewlock(arena);
if (!mutex)
  return 0;

usinitlock(mutex);

// =========================================

It is always allocated and initialized okay.

When I'm ready to write to the member variables, I make the following call :

ussetlock(mutex);

I've checked the return value for ussetlock and it's always 1, indicating that
the lock was acquired.

I then write to a few variables and make the following call to unlock the lock
:

usunsetlock(mutex);

Here's where the problem arises. My program core dumps when the usunsetlock
function is called. According to cvd, it dies at
_r4kup_unsetlock()["r4k.s":243, 0x0fa3cce4]

The lock is valid and was acquired so I don't understand what could be causing
this. I use the same locking/unlocking methods in other programs that don't
use Performer and never have any problems.

Anybody have any suggestions?

Thanks,
Greg

-- 


_______________________________________________________________________________
Greg Newton                          Graphics, Visualization & Usability Center
M.S. Student                                               College of Computing
gregn++at++cc.gatech.edu                             Georgia Institute of Technology
http://www.cc.gatech.edu/people/home/gregn                       (404) 894-9635


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