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つまらないシステム(1) Scala の Future と ExecutionContext
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mashijp
November 13, 2015
Programming
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2k
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。
mashijp
November 13, 2015
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Transcript
ͭ·Βͳ͍γεςϜ(1) - FutureͱExecutionContext - mashi
ఆͯ͠Δಡऀ • ৽ଔͷΈͳ͞Μ • Scalaॻ͘ͷָ͕͘͠ͳ͖ͬͯͨ • Future͍͢͝ʂָ͍͠ʂ
Future[T] ͱ • ͍͔ͭT͕ฦͬͯ͘Δ • ͍ͭʁ – Θ͔Μͳ͍
Future ͷ࡞Γํ • Future.apply Λ͏ def apply(f: => T)(implicit ec:
ExecutionContext): T • f Ͱͨؔ͠ec: ExecutionContext ʹ Α࣮ͬͯߦ͞ΕΔ – ͜ͷ f Λࠓ͔Β Runnable ͱݺͼ·͢ • ͍࣮ͭߦ͞ΕΔͷ͔ – Θ͔Μͳ͍ (ExecutionContext ͕ܾΊΔ) ৄ͘͠http://mashi.hatenablog.com/entry/2014/11/24/010417 Scala ExecutionContextͬͯԿ/ FutureεϨου্ཱͪ͛͡Όͳ͍Α
ExecutionContext ͷҰൠతͳ࣮ Thread 1 Thread 2 Thread 3 Thread 4
• ༩͑ͨ Runnable Λۭ͍ͯΔεϨουͰ͍ ͍ײ͡ʹ࣮ߦ͢Δ Runnable 1 Runnable 2 Runnable 3 Runnable n ۭ͖࣍ୈ࣮ߦ͢Δ
ৗʹొ͢ΔExecutionContext • Future Λ͍͘͡Δʹৗʹ ExecutionContext ΛٻΊΒΕΔ • ීஈॻ͍͍ͯΔίʔυ val dbData:
Future[A] = getFromDB() val result: Future[B] = dbData.map({ e => convertToB(e) })
ৗʹొ͢ΔExecutionContext • ීஈԿؾͳ͘ॻ͍͍ͯΔίʔυ࣮ implicit ͰExecutionContextΛ͍ͯ͠Δ • mapʹͨؔ͠Λ࣮ߦ͢Δ ExecutionContext Λ҉తʹࢦఆ͍ͯ͠Δ val
dbData: Future[A] = getFromDB() val result: Future[B] = dbData.map({ e => convertToB(e) })(ec: ExecutionContext)
ExecutionContext ༻్ผʹఆٛ͢͠ • ྫ) memcached ͱ MySQL Ͱ͚Δ • ྫ)
MySQL ͷσʔλϕʔε1 ͱ 2 Ͱ͚Δ • ྫ) MySQL ͷ master ͱ slaveͰ͚Δ • ͳ͔ͥʁ
ExecutionContext ٧·Δ • ϒϩοΩϯά͢ΔͷΛ͏ͱ٧·Δ – ྫ͑ MySQL ͷૢ࡞٧·Δ ˞͜͜Ͱলུ͢Δ͕ɺscala-redis-nb ͷΑ͏ͳϊϯϒϩοΩϯάͳ࣮ Λ͏ͱجຊతʹ٧·Βͳ͍
1つのExecutionContextΛ͍·Θͨ͠߹ • ྫ͑MySQL ͱmemcached͕͍ͬͯΔγεςϜ • MySQLͷԠ͕͘ͳΔͱશ෦ॏ͘ͳΔ Thread 1 Thread 2
Thread 3 Thread 4 MySQLૢ࡞ MySQLૢ࡞ MySQLૢ࡞ 1ͭͷExecutionContext Λྲྀ༻ memcached ૢ࡞ MySQL ૢ࡞ MySQL ૢ࡞ MySQL ૢ࡞ MySQL ૢ࡞ ͦͷଞͷ ૢ࡞ ؔͳ͍ૢ࡞·Ͱಉ͡Ωϡʔʹ٧·ΕΔͷͰ memcached ͷૢ࡞ॏ͘ͳΔ MySQL͔Β ͷԠͪ…
ExecutionContextΛ༻్ผʹ͚ͨ߹ • ͋ΔՕॴ͕٧·ͬͯଞʹӨڹ͠ͳ͘ͳΔ Thread 1 Thread 2 MySQLૢ࡞ MySQLૢ࡞ MySQLૢ࡞
memcached ૢ࡞ MySQL ૢ࡞ MySQL ૢ࡞ ͦͷଞͷ ૢ࡞ Thread 1 Thread 2 Thread 1 Thread 2 ͬͪ͜ʹӨڹ͠ͳ͍ MySQL͚͕ͩ٧·Δ
·ͱΊ • ීஈؾʹ͍ͯ͠ͳͯ͘implicitͰ҉తʹ ExecutionContextΛ͍ͯ͠Δ͜ͱ͕͋Δ – 'VUVSFͷNBQqBU.BQΛ͢Δͱඞͣͯ͠ ͍Δ • map flatMap
Λ͢Δͱ͖ʹࠓ͜͜Ͱ͍ͯ͠ ΔExecutionContextΛ٧·ΒͤΔڪΕ͕ͳ͍͔Λ ৗʹҙࣝ͢͠ – ࣮ɾϨϏϡʔ࣌ʹΑ͘ݟ·͠ΐ͏ • ͪΌΜͱ࣮͢Εྫ͑ʮmemcached ͕յ Εͯmemcached ʹؔͳ͍ͱ͜ΖʹҰ Өڹ͕Ͱͳ͍ʯΑ͏ͳϑΣʔϧιϑτͳγε ςϜΛ࡞Γ্͛ΒΕΔ