Problem:
I have a ref representing a queue of people in line.
I add a watch to the ref to print out the contents of the queue whenever it
changes.
Naturally, and expected, the following can happen if queuing happens in
rapid succession:
Queue: []
console: "Queue is Mike, John"
console: "Queu
Code? It's hard to debug if we can't see what's going on.
On Wed, Jul 31, 2013 at 9:00 AM, Michael Drogalis wrote:
> Problem:
>
> I have a ref representing a queue of people in line.
> I add a watch to the ref to print out the contents of the queue whenever
> it changes.
> Naturally, and expecte
A watcher fn has 4 parameters: key, reference, old-state, new-state
If you use old-state and new-state rather than the reference, you should
not see your problem.
--Aaron
On Wed, Jul 31, 2013 at 11:00 AM, Michael Drogalis wrote:
> Problem:
>
> I have a ref representing a queue of people in lin
Aaron: Yep, I'm aware - and am using the value provided by the last
parameter.
This is going to be tough to show the problem without bringing more details
of my concurrency set up.
I'm not sure if this will exhibit the problem, but this is what it boils
down to:
https://gist.github.com/Michael
I can precisely exemplify the behavior here:
https://gist.github.com/MichaelDrogalis/6123177
On Wednesday, July 31, 2013 11:13:17 AM UTC-4, Michael Drogalis wrote:
>
> Aaron: Yep, I'm aware - and am using the value provided by the last
> parameter.
>
> This is going to be tough to show the probl
The answer is here:
https://github.com/clojure/clojure/blob/master/src/jvm/clojure/lang/LockingTransaction.java#L361
Agents and watches are dispatched outside of the transaction locking. This
means that multiple transactions could be executing watches in parallel,
and hence execute out of order.
Thanks for the link. :) I understand that the behavior I'm seeing is
correct. Any idea how to achieve the desired behavior, though?
On Wed, Jul 31, 2013 at 12:06 PM, Timothy Baldridge wrote:
> The answer is here:
>
>
> https://github.com/clojure/clojure/blob/master/src/jvm/clojure/lang/LockingTr
You might want to consider switching to agents (or something else) I don't
think it's possible to do what you want with refs.
Timothy Baldridge
On Wed, Jul 31, 2013 at 10:08 AM, Mike Drogalis wrote:
> Thanks for the link. :) I understand that the behavior I'm seeing is
> correct. Any idea how t
I'll play around with agents for this when I get some more free time.
I find it odd that, as the sole perceiver of an indentity, events are
capable of being perceived out of order.
If I were watching a line queue up in person, events are obviously
"dispatched" in order through my visual perception
Deadlocks? Imagine a watch that ended up running a transaction against the
ref it was triggered from. Sounds insane, but it could be fairly easy to do
in a situation like this:
ref -> calls watchers -> calls fn1 -> calls fn 2 -> calls fn3 -> starts
transaction on ref
Since watchers are notified o
Good reasoning; that makes a lot of sense -- even if intuitively it doesn't
follow through.
I'll do some more thinking about my concurrency needs and come back with a
follow up question later. Thanks man!
On Wed, Jul 31, 2013 at 12:51 PM, Timothy Baldridge wrote:
> Deadlocks? Imagine a watch th
Try using an agent send from inside a transaction. Such sends are only
dispatched if the transaction commits, and successive sends to the same
agent from a single thread are run by the agent in the same order the
thread sent them.
On Wed, Jul 31, 2013 at 1:12 PM, Mike Drogalis wrote:
> Good rea
Cedric: Will agents give me the guarantee that if I have something in Agent
A, and I want to move it to agent B, and I do this inside a transaction:
- perceivers will see it in A at read point
- perceivers will see it in B at write point
- perceivers will never see it in neither nor both?
If that'
"Try using an agent send from inside a transaction. Such sends are only
dispatched if the transaction commits, and successive sends to the same
agent from a single thread are run by the agent in the same order the
thread sent them."
That's not the problem. The problem is that agent sends (just lik
Unfortunately, my problem is not one where the operation is communitive. To
be concrete,
I am dealing with multiple threads plucking elements off the top of many
different queues, and
putting them into a new queue. So adding element A, then B results in line
[A, B], whereas
adding element B, then A
Ding! You said the magic words! For queues, can I recommend one of the
following?
http://docs.oracle.com/javase/6/docs/api/java/util/concurrent/BlockingQueue.html
According to Rich "why doesn't Clojure provide queues? The Java ones are
just fine! Use them"
Also, if you have a large number of que
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