Patricia Shanahan wrote:
On 7/5/2010 8:39 PM, Peter Firmstone wrote:
Patricia Shanahan wrote:
Peter Firmstone wrote:
...
This is where you have to be careful of Distributed computing, I
think you'd have to branch out in both directions, checking older and
younger tasks as the tasks arrival may be a combination of processing
remote and local calls. In fact a task might arrive so far out of
sequence that it could be at the opposite end of the queue.
...
So what happens if Task x arrives so late that we have already done
the runAfter tests for Task y, but y should run after x?
Patricia
Hmm, yes I was just thinking that, need to look at the implementations
again...
I've checked both the comments and the code. The TaskManager class
Javadoc comment talks about "not required to run after any of the
tasks that precede it in the queue", and I believe that is the way it
is implemented. For example, takeTask sets the size to i in the
runAfter call for a candidate at index i in the list.
It seems to be the caller's responsibility to make sure that a task is
not added to a TaskManager until after any task it needs to run after.
Patricia
Hmm, yes you have a point, that is the current behaviour.
It'll be interesting to see if we can simulate RemoteEvent's arriving
out of order with a time delay between them. I suspect that the state
would just get muddled without any complaint, we'd need to test that
with a current implementation, then decide which party should be
responsible.
I'm interested in getting River to run on the Internet, currently River
/ Jini is at home on local intranet's where there is probably a very low
likelyhood that RemoteEvents will be received out of order. I suspect
this behaviour was overlooked or missed by the designer, the caller
cannot always know, if it did, I wouldn't need a TaskManager that
manages dependencies, just a fifo queue. But I could be wrong. It's a
pity the original author isn't around to comment. I find my
understanding improves as I implement things, we don't have to know the
right answer up front, so experiment away, I'm confident you'll work out
what's right, based on your comments to date.
Cheers,
Peter.
