From: Simon Krahnke <overlord@...>
Date: 2008-12-28T12:04:45+09:00
Subject: Re: Are all Ruby built-in objects thread safe?

* Robert Dober <robert.dober@gmail.com> (11:08) schrieb:

> On Sat, Dec 27, 2008 at 10:04 AM, Simon Krahnke <overlord@gmx.li> 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
> I believe you mean
>    "get and assign with default"
> because IIRC there is a get_with_default, it is simply called
>     Hash#fetch

You are right. There is a little difference: fetch doesn't pass the hash
to its block. But one can "abuse" both with an assignment in the block:

| dat = hash.fetch(k) { | key | hash[key] = create_dat(key) }

mfg,                   simon .... l