Jesus. You have no idea how much did you help me! That's exactly where the
bug was.
Now I made it work, but I simply did not expect it to be so friggin slow.
As you could see, I hardcoded the paramethers in the "boss" function,
because all I wanted, for now, is to make it work correctly.
I left it running for half a hour circa, and I obtained, like ~330
different board configurations and still counting, since there were, like,
other ~400 still to be processed.
I simply did not believe that I'd spend THAT much of time to calculate a
tree where the absolute maximum of times I would have to launch a worker
would be about 16!/9! .
Now, I reduced the board to a 3x3 one with only 3 chess pieces. It's absurd
that it has to take this much.
And my assignment was to calculate the whole tree of possibilities given a
7x7 board with 7 chesspieces...
Since I believe that I'm doing something wrong, is there some jvm profiling
instrument that's compatible with clojure code? Maybe I'm parrallelizing in
a wrong way...
On Monday, April 25, 2016 at 4:44:10 AM UTC+2, James Reeves wrote:
>
> It's hard to tell for sure from your code sample, because you don't
> include "place" or "get-free-squares", but it's possible your error is in
> the reducing function here:
>
> (reduce #(when (not (keyword? %2))
> (conj! %1
> (if nxt
> {:board %2 :pawns (update pwns nxt dec)}
> brd)))
> (transient [])
> (map #(place nxt (first %) (last %) brd)
> (get-free-squares brd)))
>
> In your reducing function, if %2 is not a keyword, then you return nil.
> This means that the next %1 will be nil, and you'll end up with a null
> pointer exception.
>
> I wonder if you meant instead to write:
>
> (reduce #(if (not (keyword? %2))
> (conj! %1
> (if nxt
> {:board %2 :pawns (update pwns nxt dec)}
> brd))
> %1)
> (transient [])
> (map #(place nxt (first %) (last %) brd)
> (get-free-squares brd)))
>
> - James
>
>
> On 25 April 2016 at 01:26, Vandr0iy <vandr0iy...@gmail.com <javascript:>>
> wrote:
>
>> Hi, Clojurists!
>>
>> I'm writing some clojure in these days, and I stumbled upon an error that
>> I'm unable to easily understand.
>> My goal is to asynchronously process a 2D vector in order to solve a
>> parametric version of the 8 chess queens problem (where the parameters are:
>> the board's dimensions and the chess pieces to be put on the board).
>> My solution mainly consists in two functions: the worker and the boss.
>> The worker takes in input a board (2d array) and yields a collection of
>> boards that contain another chess piece placed in a certain way. This means
>> that I:
>> > take all of the free squares from the board
>> > try to place the chesspiece on every one of them
>> > if I succeed (do not hit other pieces) - it goes to the output.
>>
>> Until I use the version without the transients - it appears to be
>> working.
>> But I wanted to optimize my code, because the last time I solved it using
>> recursive pmap - when I gave it an output that's a bit larger - it went
>> into a bats**t crazy heap overflow. So I tried to use a transient
>> collection.
>> And here my problems began. When I try to execute this code it dies after
>> just a couple of moves processed, giving me a nullpointer on the row where
>> conj! is situated:
>>
>> NullPointerException clojure.core/conj! (core.clj:3257)
>>
>> What a hellish issue may it be? Clojure is not helping - its error
>> messages are always cryptic, and really hard to understand.
>>
>> Here is my code. It's not complete though - some functions are omitted,
>> for the sake of brevity. Please, help me to understand what am I missing
>> here...
>>
>> Thank you.
>> (def fw (agent {}))
>>
>> (defn worker [subj]
>> (let [{brd :board pwns :pawns} subj
>> nxt (get-next-pawn pwns)]
>> (when (map? subj)
>> (when (and brd pwns)
>> (into #{}
>> (persistent!
>> (reduce #(when (not (keyword? %2))
>> (conj! %1
>> (if nxt
>> {:board %2 :pawns (update pwns nxt
>> dec)}
>> brd)))
>> (transient [])
>> (map #(place nxt (first %) (last %) brd)
>> (get-free-squares brd)))))))))
>> (defn boss []
>>
>> (send fw
>> #(into {} %2)
>> {:complete 0
>> :coll
>> #{{:board (blank-board 4 4)
>> :pawns
>> {:rook 1
>> :knight 3
>> :bishop 2
>> }}}})
>> (loop []
>> (await fw)
>> @fw
>> (let [{done :complete col :coll} @fw]
>> (if (= done (count col))
>> col
>> (do (send-off fw
>> #(identity {:complete (+ (:complete %1)
>> (count (filter
>> vector? %2)))
>> :coll (into (:coll %1) %2)})
>> (reduce #(into %1 %2)
>> #{}
>> (pmap #(worker %) col)))
>> (recur))))))
>>
>>
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