pthread_spinlock_t & intrspin_t

QNX DEVELOPERS Realtime and Embedded
1

Hi

Does any one know what is the significance of pthread_spinlock_t & intrspin_t (spinlock)?..or what sort of exclusion do they provide?

2

spinlocks are like mutex’s except that they can work in interrupt handlers where no OS calls are allowed. This is necessary when you have multiple processors.

3

Actually spinlocks (the pthread_spin_lock call) are not interrupt safe (from the doc’s).

The InterruptLock call (with the intrspin_t variable) is what you want to use with multiple processors / interrupt handlers.

I recall from a few years ago using 6.3.0 that one downside to spinlocks was that they didn’t trigger priority inversion processing in the kernel. What I discovered was that a high priority task that called spinlock waited infinitely spinning in a tight loop for the lock to be released by a lower priority task that never got any CPU to run. Hence, I avoid spinlock like the plague.

Tim

4

I guess I’m confused. I wasn’t thinking of a function that calls the OS like pthread_…

I thought there was some call that provided mutex like behavior at the hardware level.

5

yeah…there are sleepon locks and condvar locks…they are very suitable i guess…but i need to evaluate them…

thanks tim & maschoen