つまらないシステム(1) Scala の Future と ExecutionContext

Scalaで詰まらないシステムを作るために覚えていてほしいこと。

Transcript

1. ͭ·Βͳ͍γεςϜ(1) - FutureͱExecutionContext -
   mashi
   
2. ૝ఆͯ͠Δಡऀ
   •  ৽ଔͷΈͳ͞Μ •  Scalaॻ͘ͷָ͕͘͠ͳ͖ͬͯͨ •  Future͍͢͝ʂָ͍͠ʂ
3. Future[T] ͱ͸
   •  ͍͔ͭT͕ฦͬͯ͘Δ •  ͍ͭʁ – Θ͔Μͳ͍
4. Future ͷ࡞Γํ
   •  Future.apply Λ࢖͏ def apply(f: => T)(implicit ec: ExecutionContext): T •  f Ͱ౉ͨؔ͠਺͸
   ec: ExecutionContext ʹ Α࣮ͬͯߦ͞ΕΔ – ͜ͷ f Λࠓ͔Β Runnable ͱݺͼ·͢ •  ͍࣮ͭߦ͞ΕΔͷ͔ – Θ͔Μͳ͍ (ExecutionContext ͕ܾΊΔ) ৄ͘͠͸
   http://mashi.hatenablog.com/entry/2014/11/24/010417 Scala ExecutionContextͬͯԿ
   / Future͸εϨου্ཱͪ͛͡Όͳ͍Α
5. ExecutionContext ͷҰൠతͳ࣮૷
   Thread 1
   Thread 2
   Thread 3
   Thread 4
   •  ༩͑ͨ Runnable Λۭ͍ͯΔεϨουͰ͍ ͍ײ͡ʹ࣮ߦ͢Δ
   Runnable 1
   Runnable 2
   Runnable 3
   Runnable n
   ۭ͖࣍ୈ࣮ߦ͢Δ
   
6. ৗʹొ৔͢ΔExecutionContext
   •  Future Λ͍͘͡Δʹ͸ৗʹ ExecutionContext ΛٻΊΒΕΔ •  ීஈॻ͍͍ͯΔίʔυ
   val dbData: Future[A] = getFromDB() val result: Future[B] = dbData.map({ e => convertToB(e) })
7. ৗʹొ৔͢ΔExecutionContext
   •  ීஈԿؾͳ͘ॻ͍͍ͯΔίʔυ΋࣮͸ implicit ͰExecutionContextΛ౉͍ͯ͠Δ •  mapʹ౉ͨؔ͠਺Λ࣮ߦ͢Δ
   ExecutionContext Λ҉໧తʹࢦఆ͍ͯ͠Δ val dbData: Future[A] = getFromDB() val result: Future[B] = dbData.map({ e => convertToB(e) })(ec: ExecutionContext)
8. ExecutionContext ͸༻్ผʹఆٛ͢΂͠
   •  ྫ) memcached ͱ MySQL Ͱ෼͚Δ •  ྫ) MySQL ͷσʔλϕʔε1 ͱ 2 Ͱ෼͚Δ •  ྫ) MySQL ͷ master ͱ slaveͰ෼͚Δ •  ͳ͔ͥʁ
9. ExecutionContext ͸٧·Δ
   •  ϒϩοΩϯά͢Δ΋ͷΛ࢖͏ͱ٧·Δ – ྫ͑͹ MySQL ͷૢ࡞͸٧·Δ ˞͜͜Ͱ͸লུ͢Δ͕ɺscala-redis-nb ͷΑ͏ͳϊϯϒϩοΩϯάͳ࣮૷ Λ࢖͏ͱجຊతʹ٧·Βͳ͍
   
10. 1つのExecutionContextΛ࢖͍·Θͨ͠৔߹
    •  ྫ͑͹MySQL ͱ
    memcached͕৐͍ͬͯΔγεςϜ •  MySQLͷԠ౴͕஗͘ͳΔͱશ෦ॏ͘ͳΔ
    Thread 1
    Thread 2
    Thread 3
    Thread 4
    MySQLૢ࡞
    MySQLૢ࡞
    MySQLૢ࡞
    1ͭͷ
    ExecutionContext Λྲྀ༻
    memcached ૢ࡞
    MySQL ૢ࡞
    MySQL ૢ࡞
    MySQL ૢ࡞
    MySQL ૢ࡞
    ͦͷଞͷ ૢ࡞
    ؔ܎ͳ͍ૢ࡞·Ͱಉ͡Ωϡʔʹ٧·ΕΔͷͰ memcached ͷૢ࡞΋ॏ͘ͳΔ
    MySQL͔Β ͷԠ౴଴ͪ…
    
11. ExecutionContextΛ༻్ผʹ෼͚ͨ৔߹
    •  ͋ΔՕॴ͕٧·ͬͯ΋ଞʹӨڹ͠ͳ͘ͳΔ
    Thread 1
    Thread 2
    MySQLૢ࡞
    MySQLૢ࡞
    MySQLૢ࡞
    memcached ૢ࡞
    MySQL ૢ࡞
    MySQL ૢ࡞
    ͦͷଞͷ ૢ࡞
    Thread 1
    Thread 2
    Thread 1
    Thread 2
    ͬͪ͜ʹ͸Өڹ͠ͳ͍
    MySQL͚͕ͩ٧·Δ
    
12. ·ͱΊ
    •  ීஈؾʹ͍ͯ͠ͳͯ͘΋implicitͰ҉໧తʹ ExecutionContextΛ౉͍ͯ͠Δ͜ͱ͕͋Δ –  'VUVSF
    ͷ
    NBQ
    ΍
    qBU.BQ
    Λ͢Δͱඞͣ౉ͯ͠ ͍Δ
    •  map ΍
    flatMap Λ͢Δͱ͖ʹࠓ͜͜Ͱ౉͍ͯ͠ ΔExecutionContextΛ٧·ΒͤΔڪΕ͕ͳ͍͔Λ ৗʹҙࣝ͢΂͠ –  ࣮૷ɾϨϏϡʔ࣌ʹΑ͘ݟ·͠ΐ͏
    •  ͪΌΜͱ࣮૷͢Ε͹
    ྫ͑͹
    ʮmemcached ͕յ Εͯ΋
    memcached ʹ͸ؔ܎ͳ͍ͱ͜Ζʹ͸Ұ ੾Өڹ͕Ͱͳ͍ʯΑ͏ͳϑΣʔϧιϑτͳγε ςϜΛ࡞Γ্͛ΒΕΔ