From: Simon Krahnke <overlord@...>
Date: 2008-12-28T12:04:46+09:00
Subject: Re: Are all Ruby built-in objects thread safe?

* Robert Klemme <shortcutter@googlemail.com> (11:52) schrieb:

> On 27.12.2008 09:55, Simon Krahnke wrote:
>> * Robert Klemme <shortcutter@googlemail.com> (11:23) schrieb:
>>
>>> if hash.contains_key? k
>>>   dat = hash[k]
>>> else
>>>   dat = create_dat(k)
>>>   hash[k] = dat
>>> end
>>
>>> [...]
>>
>>> So in this case you need a lock around the _complete_ block of code.
>>> (Note, the method level lock would work if using a Hash with a default
>>> block, but this solves only a small portion of the cases.)
>>
>> If Hash had a method get_with_default that took a default value or a
>> block like initialize you could solve these cases.
>
> Please read my note: this was just an example for the class of
> synchronization problems that cannot be solved within the class.  You
> can invent arbitrary more complex scenarios that would not make any
> sense to be covered by a standard method in class Hash.

Well, my point is it's a bad example. You are asking an object questions
to base your actions on the object on. Don't ask, tell. :-)

> Put it differently: in concurrent applications there are many scenarios
> where lock granularity "method" is insufficient to guarantee correct
> code.  Instead you need explicit locking for larger portions of _client_
> code.

That might be, I'd like to see a good example.

mfg,                    simon .... i'm not killfiled?