Very strange, your example works for me in irb too. Irb must do something odd
with locals. Have you tried this outside of irb, though? If you wrap with a
method def'n in irb, it behaves differently, and the fact that locals are
copied has been discussed lots on the list. But Laurent (I think) said this
will likely change, has it already? I'm on 0.10
$ macirb --noprompt
def check
print "can I change a local scalar? "
maybe = "nope"
$q.sync do
maybe = "yep"
end
puts maybe
end
=> nil
def check_p
print "can I assign to a pointer? "
maybe_p = Pointer.new(:id)
maybe_p.assign "nope"
$q.sync do
maybe_p.assign "yep"
end
puts maybe_p[0]
end
=> nil
def check_w
print "can I assign to a wrapper attr? "
maybe = ResultWrapper.new("nope")
$q.sync do
maybe.value = "yep"
end
puts maybe.value
end
=> nil
ResultWrapper = Struct.new(:value)
=> ResultWrapper
$q= Dispatch::Queue.new('q')
=> q
check
can I change a local scalar? nope
=> nil
# but using a pointer works:
=> nil
check_p
can I assign to a pointer? yep
=> nil
# or a wrapper (but more expensive for tight loops):
=> nil
check_w
can I assign to a wrapper attr? yep
=> nil
$q= Dispatch::Queue.concurrent
=> com.apple.root.default-priority
# double-checking it isn't different for the parallel queues:
=> nil
check
can I change a local scalar? nope
=> nil
check_p
can I assign to a pointer? yep
=> nil
check_w
can I assign to a wrapper attr? yep
=> nil
Cheerio,
Michael Johnston
lastobe...@mac.com
On 2011-10-22, at 12:32 AM, Joshua Ballanco wrote:
> On Saturday, October 22, 2011 at 1:35 AM, Michael Johnston wrote:
>> When I need to get a queue-protected result into a local in code that is
>> concurrent (so I can't use an ivar) is a pointer the best (only) way to get
>> the result of a sync block? Assuming I don't want to factor out a method
>> object.
>>
>>
>> ex:
>>
>> result_p = Pointer.new(:id)
>> some_queue.sync do
>> result_p.assign(value_protected_by_queue)
>> end
>> result = result_p[0]
>>
>> it's not very ruby-ish...
>
> There's no restriction on not using ivars in block. Indeed, even locals are
> in scope in a block (and with a #sync dispatched block such as the one you
> provided, there aren't even any threading issues):
>
> result = nil
> Dispatch::Queue.concurrent.sync do
> result = true
> end
> p result #=> true
> _______________________________________________
> MacRuby-devel mailing list
> MacRuby-devel@lists.macosforge.org
> http://lists.macosforge.org/mailman/listinfo.cgi/macruby-devel
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