Re: take vs. takeIfExists

Richard Dallaway wrote:
> On 18 Nov 2008, at 08:24, Asaf Lahav wrote:
>> What is the difference between using take vs. takeIfExists in the 
>> following cases:
>>
>> entry = space.takeIfExists(tmpl, null, 0);
>> vs.
>> entry = space.take (tmpl, null, 0);
>
> I'd be interested to know the answer too.
>
> My understanding is that it makes no difference unless you're in a 
> transaction (which of course you're not).  From p. 245 of JavaSpaces 
> Principles, Patterns  and Practice I see: "In effect, a readIfExists 
> is able to 'peak inside' transactions: if a matching entry exists 
> within a transaction, then readIfExists will wait up until its timeout 
> value for a transaction to complete before it returns".  (surely take 
> and read will behave the same way in this situation).
It doesn't matter if the query is under a transaction or not - it 
matters if the space is a participant in any active transactions.

All queries on a space will return without blocking if there is an 
available (available == not locked by an active transaction) entry that 
matches.

If there is no available matching entry then read and take will block 
for up to their timeout, or until a matching entry becomes available, 
which ever comes first.

The ifExists queries will always return immediately (even if the timeout 
is non-zero)  if there are no matching entires in the space they will 
only block if there is an entry in the space that is not available - 
that is the entry is locked by a conflicting transaction - in such cases 
they will wait for up to the timeout for a matching entry to become 
available or until there are no matching entries in the space.

read and talk obey the ACID properties, the ifExists queries break 
isolation.

Does that help?

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