What's the advantage of this over just iterating over the array serially using each?
Matt
On Jan 24, 2011, at 3:40 AM, Alan Skipp wrote:
> Warning, horrible hack alert!
> I'm sure there must be a far better implementation, but the idea is to have
> an array subclass which diverts all method calls through a serial dispatch
> queue, which should ensure thread safe access.
>
> Anyway, here's the horrible hack. By the way, it manages to break Enumerable,
> other than that it's perfect!
>
> class ThreadSafeArray < Array
> instance_methods.each do |meth|
> eval "
> def #{meth}(*args, &block)
> val = []
> @serial_queue.async(@group) do
> val[0] = super
> end
> @group.wait
> val[0]
> end"
> end
>
> def initialize(size=0, obj=nil)
> @serial_queue = Dispatch::Queue.new("array.serial_queue")
> @group = Dispatch::Group.new
> super
> end
> end
>
> gcdq = Dispatch::Queue.new('doc')
> @result = ThreadSafeArray.new
> gcdq.apply(5) {|i| @result[i] = i*i }
> p @result #=> [0, 1, 4, 9, 16, 25]
>
>
> Having to create an array for every method call to copy the return value into
> is terrible, is there a better way of getting a reference to the return value
> from a dispatch queue?
>
>
>
> On 22 Jan 2011, at 14:52, Ernest N. Prabhakar, Ph.D. wrote:
>
>> Hi Charles,
>>
>> On Jan 21, 2011, at 9:57 PM, Charles Oliver Nutter wrote:
>>
>>> I'm curious about this example in Queue#apply's rdoc:
>>>
>>> * gcdq = Dispatch::Queue.new('doc')
>>> * @result = []
>>> * gcdq.apply(5) {|i| @result[i] = i*i }
>>> * p @result #=> [0, 1, 4, 9, 16, 25]
>>>
>>> apply is said to issue the jobs in parallel, so this would be making
>>> concurrent updates to the @result array. Are simple arrays in MacRuby
>>> thread-safe?
>>
>> My assumption was that doing a parallel assign:
>>
>> result[i] = i*i
>>
>> would be safe, since it always accessed a unique portion of memory, but
>> doing a serial append:
>>
>> result << i*i
>>
>> would not. But that may have been a mistake on my part, since the size (at
>> least) needs to be updated. Anyone know better?
>>
>> -- Ernie P.
>>
>>
>>>
>>> - Charlie
>>> _______________________________________________
>>> MacRuby-devel mailing list
>>> MacRuby-devel@lists.macosforge.org
>>> http://lists.macosforge.org/mailman/listinfo.cgi/macruby-devel
>>
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>
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