SynchronousQueue

[Alan Bateman]

On 09/02/2019 12:33, Arkadiusz Gasiński wrote:
> :
> I assumed (as SynchronousQueue has no capacity) that the output would be
> more like:
>
> Produder.offer
> Consumer.take
> Producer.offer
> Consumer.tak
>
> And so on. But in the actual output almost each time 2 tasks are actually
> offered and then 2 tasks are taken. Do you have any idea why this happens?
I briefly looked at your test and the producer and consumer (sharing one 
thread) are running in lockstep, I think it's just the trace messages 
that are a bit misleading. The producer prints the "Offering" message 
before queue.put. The put doesn't need to block/park when the consumer 
is parked/waiting for an element N so it will continue on and print 
"Offering" message for element N+1 before it blocks/parks in queue.put. 
On the consumer side, it prints "Processing" after queue.take has been 
used to remove element N. The producer offering element N+1 has released 
the thread to allow the consumer to continue so it will process element 
N and continue to take element N+1. If you update the test to print a 
trace message before and after both queue.put and queue.take then I 
think it will be a bit clearer.

(On a side point, I regret using SQ in the demo as it's not really 
suited for fibers at this time. It's really good for transfers between 
threads where there is a lot of contention of course. TBD on what should 
be done for fibers in this area).

-Alan