On 9/4/2018 8:31 AM, Craig Allen wrote:
I saw that function, but was scared off by its documentation:
Like semaphore-wait, but semaphore-try-wait? never blocks execution.
If sema’s internal counter is zero, semaphore-try-wait? returns #f
immediately without decrementing the counter. If sema’s counter is
positive, it is decremented and #t is returned.
I'm not sure why I'd want it to decrement the count, I really just
want to see if my critical section is running. I will try it though,
thanks.
'wait' takes the semaphore when it is available. 'try-wait' takes the
semaphore if possible, or fails immediately if it can't.
AFAIK there is no way to simply 'check' if the semaphore is available.
In a multithread environment, such checking doesn't do much good anyway
... a positive counter value doesn't mean you actually can take a
semaphore - some other thread(s) may beat you to it.
The canon [language independent] methods of "optimistic" locking are
either to spin until 'try' returns true, or to combine one or a few
initial probes using 'try' with a fall back to a normal wait if the
probes fail.
George
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