My latest iteration has brought me to this:
https://github.com/jimpil/bankio/blob/master/src/bankio/core.clj
If anyone can think of a more evident and safe approach for
demonstration purposes, by all means, shout out. After consulting the
Clojure Programming book, I decided to use commute for simply depositing
in to an account. There are still 2 fns that use dosync but only modify
a single identity, namely deposit! & withdraw!. I don't see how else
this can be done since they are refs. I would appreciate feedback for
this (hopefully) last version...
many thanks in advance :)
Jim
On 21/11/13 13:19, John D. Hume wrote:
If you want to demonstrate STM with the deposit-withdraw-transfer
example, you definitely need a ref for each account.
I'd suggest an atom for the account-num->balance-ref map ("the bank")
and an atom for the account-num-generator, but you say coordination is
necessary for opening and closing accounts. What coordination do you
have in mind?
On Nov 21, 2013 5:27 AM, "Jim - FooBar();" <jimpil1...@gmail.com
<mailto:jimpil1...@gmail.com>> wrote:
also I forgot to add that having the bank in some reference type
allows opening/closing new accounts, an operation that at least to
me sounds like it needs coordination...
So which way is preferred? map-ref that stores values, map that
stores refs or map-ref that stores refs?
Jim
On 21/11/13 10:58, Jim - FooBar(); wrote:
Hi Stefan,
thanks for your interest. let me explain further...
1. I did start with a design that involved a map (the bank)
full of agents (accounts). Then I switched to a map full of
atoms thinking that I don't really need asynchronous
operations. I settled to the single ref approach because it
seemed like an overkill to have all these refs inside. Your
comment however does make sense...Since there is a single
identity, perhaps STM is an overkill...
2. can you ellaborate why you think this is debatable? All the
ref-managing fns return the in-transaction value of the ref
(i.e. 'alter'). My problem was with 'doseq' which returns nil
so I followed the general approach of returning the
in-transaction value of the ref after it commits.
3. As I understand it these 2 transactions will be
composed/merged into a single transaction. Again, originally I
had a bare 'alter' (no dosync) on the private fn transfer1
simply because it is hidden and not supposed to be
used...think of it as a helper fn for 'transfer'. but then I
read somewhere that transaction can be nested without a
problem so I thought it is safer to include 'dosync' in
tranfer1 as well...
I'm not getting you wrong, don't worry...this is the reason I
started this thread - need some answers /feedback :)
Jim
On 21/11/13 10:42, Stefan Kamphausen wrote:
Hi,
I may be missing something here, since this thread leaves
me a bit confused.
1. Why are you using a Ref for the bank in the first
place? It is a single identity and thus should be an
atom, because you do not need to coordinate changes of at
least two identities.
If I am not mistaken, the generic bank transfer example is
to have a Ref for each of the accounts and to make sure,
that there is never a state of the world in which the
money is missing or is available twice.
2. "Even our side-effecting fns return something (per
alter) which is good." -> That seems debatable to me.
3. Why do you nest transactions on the same Ref in
transfer1 and transfer?
Don't get me wrong, what you're doing may be fine. In
that case, I just don't get it. Which, in turn, may be a
relevant feedback to you, since this is to be educational :-)
Kind regards,
Stefan
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