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ruuuui
September 14, 2017
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It’s been a while.
ruuuui
September 14, 2017
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Transcript
ڞ༗ࢿݯʹؔ͢Δ ށݐɹߥҪ ྨ
ϨʔείϯσΟγϣϯ
Race Condition(ڝ߹ঢ়ଶ)ͷ੬ऑੑ ✦ ֓ཁ • ڞ༗ࢿݯͱ ෳͷϓϩηοα͔Βʰಉ࣌ʱʹར༻͍ͯ͠Δ มɾڞ༗ϝϞϦɾDBɾϑΝΠϧͷ͜ͱ ڞ༗ࢿݯʹର͢Δഉଞ੍ޚ͕ෆेͳ߹ ڝ߹ঢ়ଶͷݪҼͱͳΔ
Race Conditionͷදྫ • ผਓͷݸਓใͳͲ͕දࣔ͞ΕΔ • DBͷෆ߹ • ϑΝΠϧ༰ͷഁյ
Πϯελϯεมͱ • ΦϒδΣΫτͷதͰΛอଘ͓ͯͨ͘͠Ίͷར༻͞ΕΔͷ͕ ʮΠϯελϯεมʯͰ͢ɻ • ΠϯελϯεมΫϥεͰશϝιουͰڞ௨ͯ͠༻͢Δ͜ͱ ͕ग़དྷ·͢ɻ • ࠷ॳʹͲ͔͜ͷϝιουͰ༻͞Εͨ࣌ͰΠϯελϯεม࡞ ͞ΕɺҰ࡞͞ΕͨΠϯελϯεมଞͷϝιουͰΛऔ
Γग़ͨ͠Γ֨ೲͨ͠Γ͢Δ͜ͱ͕ग़དྷΔΑ͏ʹͳΓ·͢ɻ
߈ܸख๏ͱӨڹ ӈͷϓϩάϥϜnameจࣈྻΛड͚औͬͯ Πϯελϯεมnameʹೖ͠ɺ̏ඵ·͔ͬͯΒɺ ΠϯελϯεมΛදࣔ͢ΔϓϩάϥϜ
߈ܸख๏ͱӨڹ
• มnameڞ༗ม • ڞ༗มnameͷഉଞ੍ޚΛ͍ͯ͠ͳ͍ ੬ऑੑ͕ੜ·ΕΔݪҼ αʔϒϨοτΫϥεͷΠϯελϯεม͕ ڞ༗ࢿݯͰ͋Δ͜ͱΛΒͳ͍ͱɺىͯ͜͠͠·͏
• ՄೳͰ͋Εڞ༗ࢿݯΛ༻͠ͳ͍ ex. String name = req.getParameter(“name”); • ڞ༗ࢿݯʹରͯ͠ഉଞ੍ޚΛߦ͏ synchronizedจsynchronisedϝιουΛར༻
ରࡦ
yamadaॲཧ tanakaॲཧ 1sec name=“yamada”; ༷ʑͳॲཧ(̏ඵ) nameදࣔ(yamada) SynchronisedʹΑΓػ (̎ඵ) name=“tanaka”; ༷ʑͳॲཧ(̏ඵ)
nameදࣔ(tanaka) 0sec 2sec 3sec 4sec 5sec 6sec
·ͱΊ • ڞ༗ࢿݯͰ͖Δ͚ͩΘͳ͍ • ഉଞॲཧΛ͗ͯ͢͠DoS੬ऑੑΛ࢈ΜͰ͠·͏ͷͰɺ ฒߦॲཧɾϚϧνεϨουϓϩάϥϛϯάΛߦ͏