An adventure of Happy Eyeballs

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class Socket def self.tcp(host, port) # Do something end end
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class Socket def self.tcp(host, port) threads = [Socket::AF_INET6, Socket::AF_INET].map {
|family| Thread.new(...) { |...| addresses = Addrinfo.getaddrinfo(...) shared_list.concat(addresses); cond.signal } } connected_socket = loop do cond.wait(mutex) while addresses.empty? address = addresses.shift; socket = Socket.new(...) socket.connect_nonblock(address); sockets.push(socket) _, writables, = IO.select(nil, sockets, nil, 0.25) connected_socket = pick_connected_socket(...) break connected_socket if connected_socket end connected_socket end end "OEJUJTDPNQMFUFE *NQMFNFOUBUJPOPG4PDLFUUDQXJUI)&W

class Socket def self.tcp(host, port) # ... threads = [Socket::AF_INET6,
Socket::AF_INET].map { |family| args = { Thread.new(args) { |args| addresses = Addrinfo.getaddrinfo(...) sleep 0.05 if addresses.last == Socket::AF_INET args[:mutex].synchronize do args[:shared_list].concat(addresses) args[:cond].signal end } } # ... end end 5IF fi STUQBSUJTUPIBOEMFOBNFSFTPMVUJPO *UTUBSUTCZDSFBUJOHUISFBETGPSFBDIBEESFTTGBNJMZ BOETUBSUIPTUOBNFSFTPMVUJPOBTZODISPOPVTMZ XJUIJOFBDIUISFBE )PTUOBNFSFTPMVUJPO $SFBUFBUISFBE *NQMFNFOUBUJPOPG4PDLFUUDQXJUI)&W { host:, port:, family:, resolved_addresses:, mutex:, cond: }

Socket::AF_INET].map { |family| args = { Thread.new(args) { |args| addresses = Addrinfo.getaddrinfo(...) sleep 0.05 if addresses.last == Socket::AF_INET args[:mutex].synchronize do args[:resolved_addresses].concat(addresses) args[:cond].signal end } } # ... end end 0ODFOBNFSFTPMVUJPOJT fi OJTIFE BEEUIFOFXBEESFTTFTUPUIFMJTUPGSFTPMWFE *1BEESFTTFT "EEBEESFTTFTUPUIFMJTU *NQMFNFOUBUJPOPG4PDLFUUDQXJUI)&W { host:, port:, family:, resolved_addresses:, mutex:, cond: }

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Socket::AF_INET].map { |family| # ... } loop do # Do "obtaining an address", "starting a connection # and "waiting for connections" end # ... end end 6TF,FSOFMMPPQUPSFQFBUUIFTFTUFQT *NQMFNFOUBUJPOPG4PDLFUUDQXJUI)&W n attempt",

class Socket def self.tcp(host, port) # ... loop do mutex.synchronize
do cond.wait(mutex) while resolved_addresses.empty? address = resolved_addresses.shift end socket = Socket.new(...) # ... end # ... end end 6QPO fi STUFOUFSJOHUIFMPPQ UIFMJTUPGSFTPMWFE*1 BEESFTTFTJTFNQUZ8BJUVOUJMBOZDIJMEUISFBEBEET BEESFTTFT UIFOCSFBLUIFXBJUBOEPCUBJOPOFPGUIFN 8BJUGPSBEESFTTFT 0CUBJOBOBEESFTT *NQMFNFOUBUJPOPG4PDLFUUDQXJUI)&W

do cond.wait(mutex) while resolved_addresses.empty? address = resolved_addresses.shift end socket = sockets.push(Socket.new(...)).last socket.connect_nonblock(address, exception: false) # ... end # ... end end 5IFOTUBSUBDPOOFDUJPOBUUFNQU UPUIFPCUBJOFEBEESFTT *NQMFNFOUBUJPOPG4PDLFUUDQXJUI)&W 4UBSUBDPOOFDUJPOBUUFNQU

do cond.wait(mutex) while resolved_addresses.empty? address = resolved_addresses.shift end socket = sockets.push(Socket.new(...)).last socket.connect_nonblock(address, exception: false) _, writable_sockets, = IO.select(nil, sockets, nil, 0.25) connected = pick_connected_socket(writable_sockets, sockets) break connected if connected end # cleanup connected end end "GUFSTUBSUJOHUIFDPOOFDUJPO XBJUGPSNT *NQMFNFOUBUJPOPG4PDLFUUDQXJUI)&W 8BJUGPSDPOOFDUJPOT

do cond.wait(mutex) while resolved_addresses.empty? address = resolved_addresses.shift end socket = sockets.push(Socket.new(...)).last socket.connect_nonblock(address, exception: false) _, writable_sockets, = IO.select(nil, sockets, nil, 0.25) connected = pick_connected_socket(writable_sockets, sockets) break connected if connected end do_cleanup connected end end *GBDPOOFDUJPOJTFTUBCMJTIFEXJUIJOUIFUJNF FYJUUIF MPPQ"GUFSQPTUQSPDFTTJOH SFUVSOUIFDPOOFDUFE TPDLFU BOEUIFNFUIPEDPODMVEFT 0CUBJODPOOFDUFETPDLFU 3FUVSOJU *NQMFNFOUBUJPOPG4PDLFUUDQXJUI)&W

class Socket def self.tcp(host, port) # ... connected = loop
do mutex.synchronize do cond.wait(mutex) while resolved_addresses.empty? address = resolved_addresses.shift end socket = sockets.push(Socket.new(...)).last socket.connect_nonblock(address, exception: false) _, writable_sockets, = IO.select(nil, sockets, nil, 0.25) connected = pick_connected_socket(writable_sockets, sockets) break connected if connected end do_cleanup connected end end 0UIFSXJTF JUHPFTUPUIFUPQPGUIFMPPQBOESFQFBUT UIFQSPDFTTPGPCUBJOJOHBOBEESFTT TUBSUJOH BDPOOFDUJPOBUUFNQU BOEXBJUJOHGPSDPOOFDUJPOT *NQMFNFOUBUJPOPG4PDLFUUDQXJUI)&W &OUFSUIFOFYUMPPQ

class Socket def self.tcp(host, port) # ... connected = loop
do mutex.synchronize do cond.wait(mutex) while resolved_addresses.empty? address = resolved_addresses.shift end socket = sockets.push(Socket.new(...)).last socket.connect_nonblock(address, exception: false) _, writable_sockets, = IO.select(nil, sockets, nil, 0.25) connected = pick_connected_socket(writable_sockets, sockets) break connected if connected end do_cleanup connected end end 4PDLFUUDQXJUI)&WTVQQPSUFEJTOPXDPNQMFUF *NQMFNFOUBUJPOPG4PDLFUUDQXJUI)&W

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def self.tcp(host, port) # ... connected = loop do mutex.synchronize
do cond.wait(mutex) while resolved_addresses.empty? address = resolved_addresses.shift end socket = sockets.push(Socket.new(...)).last socket.connect_nonblock(address, exception: false) _, writable_sockets, = IO.select(nil, sockets, nil, 0.25) connected = pick_connected_socket(writable_sockets, sockets) break connected if connected end # ... end *TTVFTXJUIUIJTJNQMFNFOUBUJPO -FUTDPOTJEFSUIFDBTFXIFSF BGUFSTUBSUJOHB DPOOFDUJPOBUUFNQU JUIBTOPUCFFOFTUBCMJTIFE XJUIJONT BOEJUFOUFSTUIFOFYUMPPQ &OUFSUIFOFYUMPPQ

do cond.wait(mutex) while resolved_addresses.empty? address = resolved_addresses.shift end socket = sockets.push(Socket.new(...)).last socket.connect_nonblock(address, exception: false) _, writable_sockets, = IO.select(nil, sockets, nil, 0.25) connected = pick_connected_socket(writable_sockets, sockets) break connected if connected end # ... end 4VQQPTFUIFMJTUPGSFTPMWFE*1BEESFTTFTJTFNQUZ BUUIJTUJNF *GTP JUXJMMXBJUIFSFVOUJMOFXBEESFTTFTBSFBEEFE 8BJUIFSF *TTVFTXJUIUIJTJNQMFNFOUBUJPO &NQUZ

do cond.wait(mutex) while resolved_addresses.empty? address = resolved_addresses.shift end socket = sockets.push(Socket.new(...)).last socket.connect_nonblock(address, exception: false) _, writable_sockets, = IO.select(nil, sockets, nil, 0.25) connected = pick_connected_socket(writable_sockets, sockets) break connected if connected end # ... end 8IBUTIPVMEJUEPJGUIFDPOOFDUJPOJTFTUBCMJTIFEJO UIFCBDLHSPVOEEVSJOHUIJTUJNF "DPOOFDUJPOJTFTUBCMJTIFE JOUIFCBDLHSPVOE *TTVFTXJUIUIJTJNQMFNFOUBUJPO 8BJUIFSF &NQUZ

do cond.wait(mutex) while resolved_addresses.empty? address = resolved_addresses.shift end socket = sockets.push(Socket.new(...)).last socket.connect_nonblock(address, exception: false) _, writable_sockets, = IO.select(nil, sockets, nil, 0.25) connected = pick_connected_socket(writable_sockets, sockets) break connected if connected end # ... end *OTVDIBDBTF UIFNFUIPETIPVMESFUVSOUIFDPOOFDUFE TPDLFUJNNFEJBUFMZ)PXFWFS JUTJNQPTTJCMFUPEFUFDUB FTUBCMJTIFEDPOOFDUJPOXIJMFBXBJUJOHBEESFTTFTDVSSFOUMZ *TTVFTXJUIUIJTJNQMFNFOUBUJPO $BOUTUPQUPXBJU &NQUZ

do cond.wait(mutex) while resolved_addresses.empty? address = resolved_addresses.shift end socket = sockets.push(Socket.new(...)).last socket.connect_nonblock(address, exception: false) _, writable_sockets, = IO.select(nil, sockets, nil, 0.25) connected = pick_connected_socket(writable_sockets, sockets) break connected if connected end # ... end 0SXIBUXPVMEIBQQFOJGUIFMJTUPGSFTPMWFE*1 BEESFTTFTJTFNQUZBOEBMMBEESFTTGBNJMJFTIBWFCFFO OBNFSFTPMWFE *TTVFTXJUIUIJTJNQMFNFOUBUJPO 8BJUIFSF &NQUZ "MMOBNFSFTPMVUJPOTIBWF BMSFBEZCFFO fi OJTIFE

do cond.wait(mutex) while resolved_addresses.empty? address = resolved_addresses.shift end socket = sockets.push(Socket.new(...)).last socket.connect_nonblock(address, exception: false) _, writable_sockets, = IO.select(nil, sockets, nil, 0.25) connected = pick_connected_socket(writable_sockets, sockets) break connected if connected end # ... end *OTVDIBDBTF OPOFXBEESFTTFTXJMMCFBEEFEUP UIFMJTU BOEUIVT UIFQSPDFTTXPVMECFQFSNBOFOUMZ TUPQQFE *TTVFTXJUIUIJTJNQMFNFOUBUJPO 8BJUIFSFGPSFWFS &NQUZ

do cond.wait(mutex) while resolved_addresses.empty? address = resolved_addresses.shift end socket = sockets.push(Socket.new(...)).last socket.connect_nonblock(address, exception: false) _, writable_sockets, = IO.select(nil, sockets, nil, 0.25) connected = pick_connected_socket(writable_sockets, sockets) break connected if connected end # ... end "MTP DPOOFDUJPOBUUFNQUTDBOGBJMXJUIJONTPGTUBSUJOH *OTVDIBDBTF JUTIPVMEXBJUGPSUIFSFNBJOEFSPGUIFNT CFGPSFFOUFSJOHUIFOFYUMPPQBOETUBSUBOFXBUUFNQU *UUVSOFEPVUUIBUBDPOOFDUJPOBUUFNQUJTGBJMFE *TTVFTXJUIUIJTJNQMFNFOUBUJPO

do cond.wait(mutex) while resolved_addresses.empty? address = resolved_addresses.shift end socket = sockets.push(Socket.new(...)).last socket.connect_nonblock(address, exception: false) _, writable_sockets, = IO.select(nil, sockets, nil, 0.25) connected = pick_connected_socket(writable_sockets, sockets) break connected if connected end # ... end #VUXJUIUIFJNQMFNFOUBUJPO JUQSPDFFETUPUIFOFYU MPPQXJUIPVUXBJUJOHGPSUIFSFNBJOEFSPGUIFUJNF JNNFEJBUFMZTUBSUJOHBOFXDPOOFDUJPOBUUFNQU &OUFSUIFOFYUMPPQXJUIPVU XBJUJOHGPSSFNBJOJOHUJNF *TTVFTXJUIUIJTJNQMFNFOUBUJPO 4UBSUBOFXDPOOFDUJPOBUUFNQU

do cond.wait(mutex) while resolved_addresses.empty? address = resolved_addresses.shift end socket = sockets.push(Socket.new(...)).last socket.connect_nonblock(address, exception: false) _, writable_sockets, = IO.select(nil, sockets, nil, 0.25) connected = pick_connected_socket(writable_sockets, sockets) sleep(remaining) if connection_failed break connected if connected end # ... end 5PBWPJEUIJT TIPVMEJUTMFFQGPSUIFSFNBJOJOHUJNF JGBOZDPOOFDUJPOTGBJM 4IPVMETMFFQ *TTVFTXJUIUIJTJNQMFNFOUBUJPO

do cond.wait(mutex) while resolved_addresses.empty? address = resolved_addresses.shift end socket = sockets.push(Socket.new(...)).last socket.connect_nonblock(address, exception: false) _, writable_sockets, = IO.select(nil, sockets, nil, 0.25) connected = pick_connected_socket(writable_sockets, sockets) sleep(remaining) if connection_failed break connected if connected end # ... end *OUIBUDBTF JGPUIFSDPOOFDUJPOTBSFJOQSPHSFTTBOE POFJTFTUBCMJTIFEXIJMFTMFFQJOHJOUIFCBDLHSPVOE JUDBOUEFUFDUUIFFTUBCMJTIFEDPOOFDUJPO $BOUEFUFDUFTUBCMJTIFEDPOOFDUJPOT *TTVFTXJUIUIJTJNQMFNFOUBUJPO "DPOOFDUJPOJTFTUBCMJTIFE JOUIFCBDLHSPVOE

do cond.wait(mutex) while resolved_addresses.empty? address = resolved_addresses.shift end socket = sockets.push(Socket.new(...)).last socket.connect_nonblock(address, exception: false) _, writable_sockets, = IO.select(nil, sockets, nil, 0.25) connected = pick_connected_socket(writable_sockets, sockets) sleep(remaining) if connection_failed break connected if connected end # ... end 0S JGUIFMJTUPGSFTPMWFE*1BEESFTTFTJTFNQUZJOUIF OFYUMPPQBGUFSXBLJOHGSPNTMFFQ JUXPVMETUBSUXBJUJOH GPSBEESFTTFTBHBJO"OETPPOBOETPGPSUI &OUFSUIFOFYUMPPQ *TTVFTXJUIUIJTJNQMFNFOUBUJPO 4UBSUUPXBJUIFSFBHBJO JGUIFMJTUJTFNQUZ &NQUZ

8IZEPFTUIFNIBQQFO def self.tcp(host, port) # ... connected = loop do
mutex.synchronize do cond.wait(mutex) while resolved_addresses.empty? address = resolved_addresses.shift end socket = sockets.push(Socket.new(...)).last socket.connect_nonblock(address, exception: false) _, writable_sockets, = IO.select(nil, sockets, nil, 0.25) connected = pick_connected_socket(writable_sockets, sockets) sleep(remaining) if connection_failed break connected if connected end # ... end -FUTSFWJTJUUIFDVSSFOUJNQMFNFOUBUJPO UPDMBSJGZUIFVOEFSMZJOHQSPCMFN

do cond.wait(mutex) while resolved_addresses.empty? address = resolved_addresses.shift end socket = sockets.push(Socket.new(...)).last socket.connect_nonblock(address, exception: false) _, writable_sockets, = IO.select(nil, sockets, nil, 0.25) connected = pick_connected_socket(writable_sockets, sockets) sleep(remaining) if connection_failed break connected if connected end # ... end 8JUIJOUIJTMPPQ GSPNUIFUPQEPXO JUTXBJUJOHGPS OBNFSFTPMVUJPOTBOEPCUBJOJOHBOBEESFTT 8IZEPFTUIFNIBQQFO 8BJUGPSOBNFSFTPMVUJPOT "DPOUJOVPVTTFRVFODFJOUIFMPPQ 0CUBJOBOBEESFTT

do cond.wait(mutex) while resolved_addresses.empty? address = resolved_addresses.shift end socket = sockets.push(Socket.new(...)).last socket.connect_nonblock(address, exception: false) _, writable_sockets, = IO.select(nil, sockets, nil, 0.25) connected = pick_connected_socket(writable_sockets, sockets) sleep(remaining) if connection_failed break connected if connected end # ... end TUBSUJOHBDPOOFDUJPOBUUFNQU 8IZEPFTUIFNIBQQFO "DPOUJOVPVTTFRVFODFJOUIFMPPQ 4UBSUBDPOOFDUJPOBUUFNQU

do cond.wait(mutex) while resolved_addresses.empty? address = resolved_addresses.shift end socket = sockets.push(Socket.new(...)).last socket.connect_nonblock(address, exception: false) _, writable_sockets, = IO.select(nil, sockets, nil, 0.25) connected = pick_connected_socket(writable_sockets, sockets) sleep(remaining) if connection_failed break connected if connected end # ... end BOEXBJUJOHGPSUIPTFDPOOFDUJPOT BTBDPOUJOVPVTTFRVFODF 8IZEPFTUIFNIBQQFO 8BJUGPSDPOOFDUJPOT "DPOUJOVPVTTFRVFODFJOUIFMPPQ

do cond.wait(mutex) while resolved_addresses.empty? address = resolved_addresses.shift end socket = sockets.push(Socket.new(...)).last socket.connect_nonblock(address, exception: false) _, writable_sockets, = IO.select(nil, sockets, nil, 0.25) connected = pick_connected_socket(writable_sockets, sockets) sleep(remaining) if connection_failed break connected if connected end # ... end 8IZEPFTUIFNIBQQFO )PXFWFS EFQFOEJOHPOUIFTUBUVTPGUIFMJTUPG SFTPMWFE*1BEESFTTFTBOEUIFDPOOFDUJOHTPDLFUT VOOFDFTTBSZEFMBZTDBOPDDVSXJUIJOUIFMPPQ 6OOFDFTTBSZEFMBZTDBOPDDVS "DPOUJOVPVTTFRVFODFJOUIFMPPQ

do cond.wait(mutex) while resolved_addresses.empty? address = resolved_addresses.shift end socket = sockets.push(Socket.new(...)).last socket.connect_nonblock(address, exception: false) _, writable_sockets, = IO.select(nil, sockets, nil, 0.25) connected = pick_connected_socket(writable_sockets, sockets) sleep(remaining) if connection_failed break connected if connected end # ... end 8IZEPFTUIFNIBQQFO 5IFQSPDFTTUIBUTIPVMECFFYFDVUFEJOUIFMPPQTFFNT UPCFEJ ff FSFOUFBDIUJNF EFQFOEJOHPOUIFTUBUVT PGUIFMJTUPGBEESFTTFTBOEUIFDPOOFDUJOHTPDLFUT "DPOUJOVPVTTFRVFODFJOUIFMPPQ

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start to - v6c - v4w - failure - timeout do Thread.new { IPv6 Addrinfo.getaddrinfo } Thread.new { IPv4 Addrinfo.getaddrinfo } Until the next state is determined select([Hostname resolution rpipe], Resolv timeout expires at) case IPv6 resolved Selectable addrinfo = Hostname resolution queue.pop Selectable addrinfos.push Selectable addrinfo -> v6c "OFYBNQMFPGUIFQTFVEPDPEF

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- timeout do Local addrinfos = Addrinfo.getaddrinfo case ϦϞʔτϗετ·ͨ͸ϩʔΧϧϗετ͕IPΞυϨε addrinfo = Addrinfo.getaddrinfo Selectable addrinfos.push Selectable addrinfo case IPv6 addrinfo -> v6c case IPv4 addrinfo -> v4c case ϦϞʔτϗετͱϩʔΧϧϗετ͕υϝΠϯ໊ Thread.new { IPv6 Addrinfo.getaddrinfo } Thread.new { IPv4 Addrinfo.getaddrinfo } while ࣍ͷstate͕ܾఆ͢Δ·Ͱ select([Hostname resolution rpipe], Resolv timeout expires at) case Resolv timeout expires at ௒ա -> timeout case v6໊લղܾ Selectable addrinfo = Hostname resolution queue.pop Selectable addrinfos.push Selectable addrinfo -> v6c case v4໊લղܾ Selectable addrinfo = Hostname resolution queue.pop Selectable addrinfos.push Selectable addrinfo -> v4w case ໊લղܾΤϥʔ case retryable: true retry case retryable: false Last error = Τϥʔ -> failure case v4w from - start condition - selectͷฦΓ஋: - Resolution delay expires at ௒ա - v6໊લղܾ - ໊લղܾΤϥʔ to - v4c - v46c do select([Hostname resolution rpipe], Resolution delay expires at) case Resolution delay expires at ௒ա -> v4c case v6ΞυϨεղܾ Selectable addrinfo = Hostname resolution queue.pop Selectable addrinfos.push Selectable addrinfo -> v46c case ໊લղܾΤϥʔ -> v46c case v6c, v4c, v46c from - start - v4w - v46w to - v46c - v46w - success - failure do Connecting addrinfo = Selectable addrinfos.pop Connecting socket = Socket.new(Connecting addrinfo) case Local addrinfos: any case Connecting addrinfoͱಉ͡ΞυϨεϑΝϛϦͷLocal addrinfo͕͋Δ Local addrinfo = Local addrinfos.pick Connecting socket.bind Local addrinfo ҎԼ΁ਐΉ case Connecting addrinfoͱಉ͡ΞυϨεϑΝϛϦͷLocal addrinfo͕ͳ͍ case Selectable addrinfos: any && Connecting sockets: any && Hostname resolution queue: opened # ࣍ͷϧʔϓͰผͷSelectable addrinfoΛࢼ͢ -> v46c case Selectable addrinfos: any && Connecting sockets: any && Hostname resolution queue: closed # ࣍ͷϧʔϓͰผͷSelectable addrinfoΛࢼ͢ -> v46c case Selectable addrinfos: any && Connecting sockets: empty && Hostname resolution queue: opened # ࣍ͷϧʔϓͰผͷSelectable addrinfoΛࢼ͢ -> v46c case Selectable addrinfos: any && Connecting sockets: empty && Hostname resolution queue: closed # ࣍ͷϧʔϓͰผͷSelectable addrinfoΛࢼ͢ -> v46c case Selectable addrinfos: empty && Connecting sockets: any && Hostname resolution queue: opened # ࣍ͷϧʔϓͰ઀ଓ໊͔લղܾΛ଴ͭ # Connecting sockets͕͋Δ͏ͪ͸Resolv timeout expires at ͸ߟྀ͠ͳ͍ Connection attempt delay expires at = nil -> v46w case Selectable addrinfos: empty && Connecting sockets: any && Hostname resolution queue: closed # ࣍ͷϧʔϓͰ઀ଓΛ଴ͭ Connection attempt delay expires at = nil -> v46w case Selectable addrinfos: empty && Connecting sockets: empty && Hostname resolution queue: opened case Resolv timeout expires at: ઃఆ͋Γ && Resolv timeout expires at ௒ա -> timeout case ͦΕҎ֎ # ࣍ͷϧʔϓͰ໊લղܾΛ଴ͭ Connection attempt delay expires at = nil -> v46w case Selectable addrinfos: empty && Connecting sockets: empty && Hostname resolution queue: closed -> failure case Local addrinfos: empty ҎԼ΁ਐΉ Connection attempt delay expires at = ݱࡏͷΫϩοΫ࣌ؒ + Connection Attempt Delay case Selectable addrinfos: empty && Connecting sockets: empty && Hostname resolution queue: closed connect case ͦΕҎ֎ connect_nonblock ҎԼ΁ਐΉ case ઀ଓʹ੒ޭ -> success case ઀ଓத Connecting sockets.add Connecting socket -> v46w case SystemCallError Last error = SystemCallError case Selectable addrinfos: any && Connecting Sockets: any && Hostname resolution queue: opened # ࣍ͷϧʔϓͰผͷSelectable addrinfoΛࢼ͢ -> v46c case Selectable addrinfos: any && Connecting Sockets: any && Hostname resolution queue: closed # ࣍ͷϧʔϓͰผͷSelectable addrinfoΛࢼ͢ -> v46c case Selectable addrinfos: any && Connecting Sockets: empty && Hostname resolution queue: opened # ࣍ͷϧʔϓͰผͷSelectable addrinfoΛࢼ͢ -> v46c case Selectable addrinfos: any && Connecting Sockets: empty && Hostname resolution queue: closed # ࣍ͷϧʔϓͰผͷSelectable addrinfoΛࢼ͢ -> v46c case Selectable addrinfos: empty && Connecting Sockets: any && Hostname resolution queue: opened # ࣍ͷϧʔϓͰ໊લղܾ͔઀ଓΛ଴ͭɻ໊લղܾͨ͠৔߹͸͞Βʹ࣍ͷϧʔϓͰv46c΁ɺ઀ଓͨ͠৔߹͸͞Βʹ࣍ͷϧʔϓͰsuccess΁ Connection attempt delay expires at = nil -> v46w case Selectable addrinfos: empty && Connecting Sockets: any && Hostname resolution queue: closed # ࣍ͷϧʔϓͰ઀ଓΛ଴ͭ Connection attempt delay expires at = nil -> v46w case Selectable addrinfos: empty && Connecting Sockets: empty && Hostname resolution queue: opened case Resolv timeout expires at: ઃఆ͋Γ && Resolv timeout expires at ௒ա -> timeout case ͦΕҎ֎ # ࣍ͷϧʔϓͰ໊લղܾΛ଴ͭ Connection attempt delay expires at = nil -> v46w case Selectable addrinfos: empty && Connecting Sockets: empty && Hostname resolution queue: closed -> failure case v46w from - v6c - v4c - v46c - v46w to - v46c - v46w - success - timeout do case Connect timeout expires at ௒ա -> timeoeut case Connect timeout expires at ௒աͰ͸ͳ͍ ҎԼ΁ਐΉ select([Hostname resolution rpipe], Connecting sockets, Connection attempt delay expires at) case Connectable sockets: any while (Connectable socket = Connectable sockets.pop) Connecting sockets.remove Connectable socket getsockopt(<઀ଓΤϥʔͷ֬ೝ>) case Τϥʔͳ͠ Connected socket = Connectable socket -> success case Τϥʔ͋Γ case Connectable sockets: any retry case Connectable sockets: empty ҎԼʹਐΉ case Selectable addrinfos: any && Connecting sockets: any && Hostname resolution queue: opened # ࣍ͷϧʔϓͰConnection attempt delay expires atΛ௒ա͢Δ·Ͱ઀ଓ໊͔લղܾΛ଴ͭ # ઀ଓ͠ͳ͔ͬͨ৔߹ɺ໊લղܾͯ͠΋͠ͳͯ͘΋͞Βʹ࣍ͷϧʔϓͰv46c΁ -> v46w case Selectable addrinfos: any && Connecting sockets: any && Hostname resolution queue: closed # ࣍ͷϧʔϓͰConnection attempt delay expires atΛ௒ա͢Δ·Ͱ઀ଓΛ଴ͭ # ઀ଓ͠ͳ͔ͬͨ৔߹͸͞Βʹ࣍ͷϧʔϓͰv46c΁ -> v46w case Selectable addrinfos: any && Connecting sockets: empty && Hostname resolution queue: opened # ࣍ͷϧʔϓͰConnection attempt delay expires atΛ௒ա͢Δ·Ͱ໊લղܾΛ଴ͭ # ໊લղܾͯ͠΋͠ͳͯ͘΋͞Βʹ࣍ͷϧʔϓͰv46c΁ -> v46w case Selectable addrinfos: any && Connecting sockets: empty && Hostname resolution queue: closed # ࣍ͷϧʔϓͰConnection attempt delay expires atΛ௒ա͢Δ·Ͱ໊લղܾΛ଴ͭ # ͞Βʹ࣍ͷϧʔϓͰv46c΁ -> v46w case Selectable addrinfos: empty && Connecting sockets: any && Hostname resolution queue: opened # ͋ͱ͸઀ଓ໊͔લղܾΛͻͨ͢Β଴ͭ͜ͱ͔͠Ͱ͖ͳ͍ # Connecting sockets͕͋Δ͏ͪ͸Resolv timeout expires at ͸ߟྀ͠ͳ͍ -> v46w case Selectable addrinfos: empty && Connecting sockets: any && Hostname resolution queue: closed # ͋ͱ͸઀ଓΛͻͨ͢Β଴ͭ͜ͱ͔͠Ͱ͖ͳ͍ Connection attempt delay expires at = nil -> v46w case Selectable addrinfos: empty && Connecting sockets: empty && Hostname resolution queue: opened case Resolv timeout expires at: ઃఆ͋Γ && Resolv timeout expires at ௒ա -> timeout case ͦΕҎ֎ # ͋ͱ͸໊લղܾΛͻͨ͢Β଴ͭ͜ͱ͔͠Ͱ͖ͳ͍ Connection attempt delay expires at = nil -> v46w case Selectable addrinfos: empty && Connecting sockets: empty && Hostname resolution queue: closed -> failure case ໊લղܾ Selectable addrinfo = Hostname resolution queue.pop Selectable addrinfos.push Selectable addrinfo # ࣍ͷϧʔϓͰConnection attempt delay expires atΛ௒ա͢Δ·Ͱ଴ͪɺ͞Βʹ࣍ͷϧʔϓͰv46c΁ -> v46w case ໊લղܾΤϥʔ # ࣍ͷϧʔϓͰConnection attempt delay expires atΛ௒ա͢Δ·Ͱ଴ͪɺ͞Βʹ࣍ͷϧʔϓͰϦιʔεͷঢ়ଶʹΑͬͯ෼ذ -> v46w case Connection attempt delay expires at ௒ա case Selectable addrinfos: any && Connecting sockets: any && Hostname resolution queue: opened -> v46c case Selectable addrinfos: any && Connecting sockets: empty && Hostname resolution queue: opened -> v46c case Selectable addrinfos: any && Connecting sockets: empty && Hostname resolution queue: opened -> v46c case Selectable addrinfos: any && Connecting sockets: empty && Hostname resolution queue: closed -> v46c case Selectable addrinfos: empty && Connecting sockets: any && Hostname resolution queue: opened # ͋ͱ͸઀ଓ໊͔લղܾΛͻͨ͢Β଴ͭ͜ͱ͔͠Ͱ͖ͳ͍ # Connecting sockets͕͋Δ͏ͪ͸Resolv timeout expires at ͸ߟྀ͠ͳ͍ Connection attempt delay expires at = nil -> v46w case Selectable addrinfos: empty && Connecting sockets: empty && Hostname resolution queue: opened case Resolv timeout expires at: ઃఆ͋Γ && Resolv timeout expires at ௒ա -> timeout case ͦΕҎ֎ # ͋ͱ͸໊લղܾΛͻͨ͢Β଴ͭ͜ͱ͔͠Ͱ͖ͳ͍ Connection attempt delay expires at = nil -> v46w case Selectable addrinfos: empty && Connecting sockets: any && Hostname resolution queue: closed # ͋ͱ͸઀ଓΛͻͨ͢Β଴ͭ͜ͱ͔͠Ͱ͖ͳ͍ Connection attempt delay expires at = nil -> v46w case Selectable addrinfos: empty && Connecting sockets: empty && Hostname resolution queue: closed -> failure case success from - 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def self.tcp(host, port, ...) # Do something ensure # ...
end /PX MFUNFCSJF fl ZJOUSPEVDF UIFBDUVBMDPEFGPS4PDLFUUDQ *NQMFNFOUBUJPOPG4PDLFUUDQXJUI)&W

def self.tcp(host, port, ...) # ... loop do case state
when :start # ... end end ensure # ... end *OUIJTJNQMFNFOUBUJPO VTF,FSOFMMPPQBOEDBTFTUBUFNFOUTUPQFSGPSN BQQSPQSJBUFBDUJPOTGPSFBDITUBUF *NQMFNFOUBUJPOPG4PDLFUUDQXJUI)&W ,FSOFMMPPQ DBTFTUBUFNFOUT

def self.tcp(host, port, ...) # ... state = :start loop
do case state when :start # ... end end ensure # ... end 'JSTU TFUDVSSFOUTUBUFUPTUBSUBTBOJOJUJBMTUBUF CFGPSFTUBSUJOHUIFMPPQ *NQMFNFOUBUJPOPG4PDLFUUDQXJUI)&W *OJUJBMJ[FTUBUF

case state when :start # ... h hostname_resolution_threads.concat( resolving_family_names.map {
|family| thread_args = [family, *hostname_resolution_args] thread = Thread.new(*thread_args) { |*thread_args| hostname_resolution(*thread_args) } Thread.pass thread } ) # ... 5IJTJTTUBSU $SFBUFUISFBETGPSFBDIBEESFTTGBNJMZBOE TUBSUOBNFSFTPMVUJPOXJUIJOFBDIUISFBE *NQMFNFOUBUJPOPG4PDLFUUDQXJUI)&WTUBSU hostname_resolution_args = [host, port, hostname_resolution_queue] $SFBUFUISFBETGPSFBDIBEESFTTGBNJMZ &YFDVUFOBNFSFTPMVUJPONFUIPE

case state when :start # ... hostname_resolution_queue = HostnameResolutionQueue.new(...) hostname_resolution_waiting
= h # ... remaining = resolv_timeout ? second_to_timeout(...) : nil hostname_resolved, _, = IO.select( # ... 5IFO XBJUGPSFJUIFS*1WPS*1WOBNFSFTPMVUJPO UP fi OJTI)FSF VTF*0TFMFDUUPXBJUGPSOBNF SFTPMVUJPO5IFSFBTPOGPSUIJTXJMMCFFYQMBJOFEMBUFS *NQMFNFOUBUJPOPG4PDLFUUDQXJUI)&WTUBSU (hostname_resolution_waiting, nil, nil, remaining) hostname_resolution_queue.waiting_pipe 8BJUGPSOBNFSFTPMVUJPOUP fi OJTI

case state when :start # ... family_name, res = hostname_resolution_queue.get
if res.is_a? Exception # ... else state = case family_name when :ipv6 then :v6c when :ipv4 then <resolution completed?> ? :v4c : :v4w end selectable_addrinfos.add(family_name, res) # ... end # ... next # ... 0ODFOBNFSFTPMVUJPOJT fi OJTIFE BEEUIFPCUBJOFE BEESFTTFTUPUIFMJTUPGSFTPMWFE*1BEESFTTFT *NQMFNFOUBUJPOPG4PDLFUUDQXJUI)&WTUBSU "EEUIFPCUBJOFEBEESFTTFT 5IFMJTUPGSFTPMWFE*1BEESFTTFT

case state when :start # ... family_name, res = hostname_resolution_queue.get
if res.is_a? Exception # ... else state = case family_name when :ipv6 then :v6c when :ipv4 then < end selectable_addrinfos.add(family_name, res) # ... end # ... next # ... %FUFSNJOFUIFOFYUTUBUFCBTFEPOUIFPCUBJOFE BEESFTT BOEUIFOFOUFSUIFOFYUMPPQ *NQMFNFOUBUJPOPG4PDLFUUDQXJUI)&WTUBSU %FUFSNJOFUIFOFYUTUBUF ⬅︎ All name resolutions are finished?> ? :v4c : :v4w

case state when :v4w ipv6_resolved, _, = IO.select( # ...
5IJTJTWX *0TFMFDUJTVTFEBHBJOUP XBJUGPS*1WOBNFSFTPMVUJPOGPSNT *NQMFNFOUBUJPOPG4PDLFUUDQXJUI)&WWX (hostname_resolution_waiting, nil, nil, RESOLUTION_DELAY) 8BJUGPSOBNFSFTPMVUJPOUP fi OJTI 3&40-65*0/@%&-":NT

case state when :v4w ipv6_resolved, _, = IO.select( if ipv6_resolved
family_name, res = hostname_resolution_queue.get selectable_addrinfos.add(family_name, res) unless res.is_a? E # ... else # ... end # ... *GUIFOBNFSFTPMVUJPOJT fi OJTIFEXJUIJONT BEEUIFOFXMZPCUBJOFEBEESFTTFTUPUIFMJTUPG SFTPMWFE*1BEESFTTFT *NQMFNFOUBUJPOPG4PDLFUUDQXJUI)&WWX Exception (hostname_resolution_waiting, nil, nil, RESOLUTION_DELAY) "EEUIFPCUBJOFEBEESFTTFT 5IFMJTUPGSFTPMWFE*1BEESFTTFT

case state when :v4w ipv6_resolved, _, = IO.select( if ipv6_resolved
family_name, res = hostname_resolution_queue.get selectable_addrinfos.add(family_name, res) unless res.is_a? E state = :v46c else state = :v4c end next # ... %FUFSNJOFUIFOFYUCBTFEPOXIFUIFSUIFOBNF SFTPMVUJPOXBT fi OJTIFEXJUIJOUIFBMMPUUFEUJNF BOEUIFOFOUFSUIFOFYUMPPQ *NQMFNFOUBUJPOPG4PDLFUUDQXJUI)&WWX Exception (hostname_resolution_waiting, nil, nil, RESOLUTION_DELAY) %FUFSNJOFUIFOFYUTUBUF ⬅︎

case state when :v6c, :v4c, v46c # ... WD WD
BOEWDBSFEJ ff FSFOUTUBUFT CVUTJODF UIFDPEFTGPSFBDIJTFYBDUMZUIFTBNF UIFZBSFHSPVQFEUPHFUIFSBTBTJOHMFDBTF *NQMFNFOUBUJPOPG4PDLFUUDQXJUI)&WWDWDWD

case state when :v6c, :v4c, v46c # ... addrinfo =
selectable_addrinfos.get # ... connection_attempt_delay_expires_at = current_clocktime + CONNECTION_ATTEMPT_DELAY # ... socket = Socket.new( socket.bind(local_addrinfo) if local_addrinfo result = socket.connect_nonblock(addrinfo, exception: false) # ... )FSF fi STUPCUBJOBOBEESFTTGSPNUIFMJTUPGSFTPMWFE *1BEESFTTFTBOEUIFOTUBSUBDPOOFDUJPOBUUFNQU *NQMFNFOUBUJPOPG4PDLFUUDQXJUI)&WWDWDWD (addrinfo.pfamily, addrinfo.socktype, addrinfo.protocol) 0CUBJOBOBEESFTT 4UBSUBDPOOFDUJPOBUUFNQU 5IFMJTUPGSFTPMWFE*1BEESFTTFT 0CUBJOUJNFPVUQFSJPE

case state when :v6c, :v4c, v46c # ... addrinfo =
selectable_addrinfos.get # ... 1FSUIF3'$ BEESFTTFTTIPVMECFTPSUFECFGPSF DPOOFDUJOH5IJTJNQMFNFOUBUJPOTJNQMJ fi FTUIFQSPDFTT CZBMUFSOBUJOHCFUXFFO*1WBOE*1WBEESFTTFT *NQMFNFOUBUJPOPG4PDLFUUDQXJUI)&WWDWDWD precedences = case @last_family when :ipv4, nil then [:ipv6, :ipv4] when :ipv6 then [:ipv4, :ipv6] end precedences.each do |family_name| addrinfo = @addrinfo_dict[family_name]&.shift next unless addrinfo @last_family = family_name return addrinfo end 0CUBJOBOBEESFTT GSPNBEJ ff FSFOUBEESFTTGBNJMZ UIBOQSFWJPVTMZTFMFDUFE QSJPSJUJ[JOH*1WJOJUJBMMZ

case state when :v6c, :v4c, v46c # ... case result
when 0 connected_socket = socket state = :success when Socket connected_socket = result state = :success when :wait_writable connecting_sockets.add(socket, addrinfo) state = :v46w end # ... next "GUFSTUBSUJOHUIFDPOOFDUJPOBUUFNQU EFUFSNJOFUIF OFYUTUBUFCBTFEPOXIFUIFSUIFDPOOFDUJPOXBTNBEF JNNFEJBUFMZ BOEUIFOFOUFSUIFOFYUMPPQ *NQMFNFOUBUJPOPG4PDLFUUDQXJUI)&WWDWDWD %FUFSNJOFUIFOFYUTUBUF ⬅︎

case state when :v6c, :v4c, v46c # ... case result
when 0 connected_socket = socket state = :success when Socket connected_socket = result state = :success when :wait_writable connecting_sockets.add(socket, addrinfo) state = :v46w end # ... next *GUIFDPOOFDUJPODBOUCFFTUBCMJTIFEJNNFEJBUFMZ BEEUIFTPDLFUVTFEGPSUIFBUUFNQUUPUIFMJTUPG DPOOFDUJOHTPDLFUTCFGPSFEFUFSNJOJOHUIFOFYUTUBUF *NQMFNFOUBUJPOPG4PDLFUUDQXJUI)&WWDWDWD "EEUIFTPDLFUVTFE 5IFMJTUPGDPOOFDUJOHTPDLFUT

case state when :v46w # ... *NQMFNFOUBUJPOPG4PDLFUUDQXJUI)&WWX 5IJTJTWX )FSF JUOFFETUPTJNVMUBOFPVTMZXBJUGPSFJUIFS
FTUBCMJTINFOUTPGDPOOFDUJPOTPS fi OJTIPGUIF OBNFSFTPMVUJPO

case state when :v46w # ... ...tname_resolved, ...nectable_sockets, = IO.select(
# ... *NQMFNFOUBUJPOPG4PDLFUUDQXJUI)&WWX *0TFMFDUJTVTFEIFSFBHBJOGPSUIJTQVSQPTF (...tname_resolution_waiting, ...necting_sockets.all, ..., ...aining) *0TFMFDUJTDBMMFE

*0TFMFDUJTBNFUIPEUIBUXBJUTGPSSFBEJOFTTPG*0 PCKFDUT *UUBLFT*0PCKFDUTXBJUJOHGPSSFBEJOHBOE *0PCKFDUTXBJUJOHGPSXSJUJOHBTBSHVNFOUT 5IFNFUIPEXBJUTVOUJMBUMFBTUPOFPGUIFTFPCKFDUT CFDPNFTSFBEZGPSSFBEJOHPSXSJUJOH *0TFMFDU "OBSSBZPG*0PCKFDUTXBJUJOHGPSSFBEJOH "OBSSBZPG*0PCKFDUTXBJUJOHGPSXSJUJOH IO.select(readfds,
writefds, nil, timeout)

5IJTNFUIPEBMTPBMMPXTTQFDJGZJOHBUJNFPVUQFSJPEBT BOBSHVNFOU *USFMFBTFTUIFXBJUFWFOJGUIFSFBSFOPPCKFDUTSFBEZGPS SFBEJOHPSXSJUJOHJGJUUJNFTPVU *0TFMFDU IO.select(readfds, writefds, nil, timeout) "UJNFPVUQFSJPE

5IFSFUVSOWBMVFJTTPNFBSSBZTPG*0PCKFDUTUIBUIBWF CFDPNFSFBEZGPSSFBEJOHPSXSJUJOH *GJUUJNFTPVU JUSFUVSOTOJM *0TFMFDU rs, ws, _ = IO.select(readfds,
writefds, nil, timeout) [[<readable IO object>, ...], [<writable IO object>, ...], ...]

case state when :v46w # ... ...tname_resolved, ...nectable_sockets, = IO.select(
# ... *NQMFNFOUBUJPOPG4PDLFUUDQXJUI)&WWX 4JODFUIF4PDLFUGBNJMZPGDMBTTFTJOIFSJUTGSPN*0 DMBTT *0TFMFDUDBOBMTPXBJUGPS4PDLFUPCKFDUT 6UJMJ[JOHUIJT JOWX UIFDPOOFDUJOHTPDLFUTBSF QBTTFEUPUIJTNFUIPEBT*0PCKFDUTXBJUJOHGPSXSJUJOH (...tname_resolution_waiting, connecting_sockets.all, nil, ...aining) $POOFDUJOHTPDLFUTBTXSJUJOH*0PCKFDUT Socket.ancestors => [Socket, BasicSocket, IO, # ... BasicObject]

case state when :v46w # ... ...tname_resolved, connectable_sockets, = IO.select(
# ... *NQMFNFOUBUJPOPG4PDLFUUDQXJUI)&WWX 8IFOBDPOOFDUJPOJTFTUBCMJTIFEPSGBJMTPOBOZPG UIFTPDLFUTQBTTFEBTBSHVNFOUT *0TFMFDUDPOTJEFST UIFTFUPCFXSJUBCMF*0PCKFDUT 5IFO*0TFMFDUSFMFBTFTUIFXBJU BOESFUVSOTBOBSSBZ PGUIFSFMFWBOUTPDLFUTBTXSJUBCMF*0PCKFDUT (...tname_resolution_waiting, connecting_sockets.all, nil, ...aining) 4PDLFUTBTXSJUBCMF*0PCKFDUT

# ... *NQMFNFOUBUJPOPG4PDLFUUDQXJUI)&WWX 5IJTBMMPXTVTUPXBJUGPSUIFFTUBCMJTINFOUPG DPOOFDUJPOT4P IPXTIPVMEXFXBJUGPSUIF fi OJTIPGUIFOBNFSFTPMVUJPO (...tname_resolution_waiting, connecting_sockets.all, nil, ...aining)

# ... (<IO objectsca?n be passed >, connecting_sockets.all, nil, ...aining) *NQMFNFOUBUJPOPG4PDLFUUDQXJUI)&WWX 5IFEJ ff i DVMUZJTUIBU UIFOBNFSFTPMVUJPOUISFBETBSFOPU*0PCKFDUTBOE DBOOPUCFXBJUFEGPSJO*0TFMFDU $BOUQBTTOBNFSFTPMVUJPOUISFBET

# ... *NQMFNFOUBUJPOPG4PDLFUUDQXJUI)&WWX 5PSFTPMWFUIJT VTF*0QJQF (...tname_resolution_waiting, connecting_sockets.all, nil, ...aining)

*0QJQFSFUVSOTUXPJOUFSDPOOFDUFE*0PCKFDUT 0OFPGUIFTFJTGPSSFBEJOHBOEUIFPUIFSJTGPSXSJUJOH *0QJQF rpipe, wpipe = IO.pipe "O*0PCKFDUGPSSFBEJOH "O*0PCKFDUGPSXSJUJOH

*0QJQF 8IFOZPVXSJUFUPUIFXSJUJOH*0PCKFDU ZPVDBOSFBEUIBUGSPNUIFSFBEJOH*0PCKFDU rpipe, wpipe = IO.pipe Thread.new(wpipe) do
|w| w.puts "foo" w.close end p rpipe.gets # => "foo" 8SJUFUIFXSJUJOH*0PCKFDU 5IFOUIFSFBEJOH*0PCKFDUDBOCFSFBE

case state when :start # ... hostname_resolution_queue = HostnameResolutionQueue.new(...) #
... *NQMFNFOUBUJPOPG4PDLFUUDQXJUI)&WWX *OUIJTJNQMFNFOUBUJPO *0QJQFXBTDBMMFEBUTUBSUUP DSFBUFBQBJSPG*0PCKFDUT class HostnameResolutionQueue def initialize(size) # ... @rpipe, @wpipe = IO.pipe end # ... $SFBUFBQBJSPG*0PCKFDUT

case state when :start # ... hostname_resolution_queue = HostnameResolutionQueue.new(...) #
... *0QJQF 0GUIFTFUXP*0PCKFDUT UIFPOFGPSXSJUJOHJT class HostnameResolutionQueue # ... def waiting_pipe [@wpipe] end # ... hostname_resolution_waiting = hostname_resolution_queue.waiting_pipe hostname_resolution_args = [host, port, hostname_resolution_queue] 5IFXSJUJOH*0PCKFDU 5IFXSJUJOH*0PCKFDU BOEPUIFSBSHVNFOUT

case state when :start # ... hostname_resolution_queue = HostnameResolutionQueue.new(...) hostname_resolution_threads.concat(
resolving_family_names.map { |family| thread_args = [family, *hostname_resolution_args] thread = Thread.new(*thread_args) { |*thread_args| hostname_resolution(*thread_args) } Thread.pass thread } ) # ... *0QJQF QBTTFEBTBOBSHVNFOUUPUIFOBNFSFTPMVUJPO UISFBET hostname_resolution_waiting = hostname_resolution_queue.waiting_pipe hostname_resolution_args = [host, port, hostname_resolution_queue] 1BTTUIFBSHTJODMVEJOHUIFXSJUJOH*0PCKFDU

case state when :start # ... thread = Thread.new(*thread_args) {
|*thread_args| hostname_resolution(*thread_args) } *0QJQF 0ODFOBNFSFTPMVUJPOJT fi OJTIFEJOUIFUISFBE JUXSJUFTUPUIFXSJUJOH*0PCKFDUUPOPUJGZDPNQMFUJPO def self.hostname_resolution(family, ..., hostname_resolution_queue) resolved_addrinfos = Addrinfo.getaddrinfo(...) hostname_resolution_queue.add_resolved(family, resolved_addrinfos) # ... def add_resolved(family, resolved_addrinfos) @mutex.synchronize do @queue.push [family, resolved_addrinfos] @wpipe.putc HOSTNAME_RESOLUTION_QUEUE_UPDATED # ... 8SJUFUPUIFXSJUJOH*0PCKFDU

*NQMFNFOUBUJPOPG4PDLFUUDQXJUI)&WWX case state when :v46w # ... ...tname_resolved, connectable_sockets, =
IO.select( # ... .FBOXIJMF UIFSFBEJOH*0PCKFDUDSFBUFEXJUI*0QJQF JTQBTTFEUP*0TFMFDUJONBJOUISFBE (hostname_resolution_waiting, connecting_sockets.all, nil, ...aining) 5IFSFBEJOH*0PCKFDU

*NQMFNFOUBUJPOPG4PDLFUUDQXJUI)&WWX case state when :v46w # ... hostname_resolved, connectable_sockets, =
IO.select( # ... 5IJT*0PCKFDUXJMMCFSFBEBCMFPODFOBNFSFTPMVUJPO JT fi OJTIFEJOUIFDIJMEUISFBET 5IFO*0TFMFDUXJMMSFMFBTFUIFXBJUBOESFUVSOUIJT SFBEJOH*0PCKFDU (hostname_resolution_waiting, connecting_sockets.all, nil, ...aining) 5IFSFBEJOH*0PCKFDU 3FBEBCMF*0PCKFDUT

*NQMFNFOUBUJPOPG4PDLFUUDQXJUI)&WWX case state when :v46w # ... hostname_resolved, connectable_sockets, =
IO.select( # ... 5IJTJTUIFUSJDLUPBMMPXGPSXBJUJOHGPSCPUI UIFDPNQMFUJPOPGDPOOFDUJPOTBOEOBNFSFTPMVUJPO (hostname_resolution_waiting, connecting_sockets.all, nil, ...aining) #PUIDPOOFDUJPOTBOEOBNFSFTPMVUJPODBOCFXBJU

case state when :start # ... hostname_resolution_queue = HostnameResolutionQueue.new(...) hostname_resolution_waiting
= h # ... hostname_resolved, _, = IO.select( # ... when :v4w ipv6_resolved, _, = IO.select( # ... (hostname_resolution_waiting, nil, nil, remaining) hostname_resolution_queue.waiting_pipe *NQMFNFOUBUJPOPG4PDLFUUDQXJUI)&WTUBSUWX "OEJUJTUIFSFBTPOXIZTUBSUBOEWXVTFE*0TFMFDU UPXBJUGPSOBNFSFTPMVUJPO (hostname_resolution_waiting, nil, nil, RESOLUTION_DELAY) 8BJUXJUIUIFSFBEJOH*0PCKFDU 8BJUXJUIUIFSFBEJOH*0PCKFDU

*NQMFNFOUBUJPOPG4PDLFUUDQXJUI)&WWX case state when :v46w # ... remaining = s
hostname_resolved, connectable_sockets, = IO.select( # ... -FUTSFUVSOUPWX 4FUUIFUJNFPVUCZQBTTJOH*0TFMFDUUIFUJNFUPXBJU GPSDPOOFDUJPOT (hostname_resolution_waiting, connecting_sockets.all, nil, remaining) second_to_timeout(connection_attempt_delay_expires_at) 4FUUJNFPVU $BMDVMBUFSFNBJOJOHUJNFGSPNUIFUJNFPVUQFSJPE

case state when :v46w # ... hostname_resolved, connectable_sockets, = IO.select(
# ... if connectable_sockets&.any? # ... elsif hostname_resolved&.any? # ... else # ... end # ... next (hostname_resolution_waiting, connecting_sockets.all, nil, remaining) *G*0TFMFDUSFUVSOTBXSJUBCMF*0PCKFDUXJUIJOUIF XBJUJOHQFSJPE JUNFBOTUIBUBTJUVBUJPOIBTBSJTFO XIFSFTPDLFUTIBWFFJUIFSTVDDFTTGVMMZDPOOFDUFEPS GBJMFEUPDPOOFDU *NQMFNFOUBUJPOPG4PDLFUUDQXJUI)&WWX 8IFO*0TFMFDUSFUVSOTXSJUBCMF*0PCKFDUT 3FBDIUIJTCMPDL

case state when :v46w # ... if connectable_sockets&.any? while (connectable_socket
= connectable_sockets.pop) # ... sockopt = c is_connected = sockopt.int.zero? # ... if is_connected # ... else # ... end # ... next *OUIJTDBTF EFUFSNJOFUIFOFYUTUBUFCBTFEPO XIFUIFSUIFTPDLFUTXFSFDPOOFDUFEPSOPU BOEUIFOFOUFSUIFOFYUMPPQ *NQMFNFOUBUJPOPG4PDLFUUDQXJUI)&WWX connectable_socket.getsockopt(Socket::SOL_SOCKET, Socket::SO_ERROR) %FUFSNJOFUIFOFYUTUBUF $IFDLUIFDPOOFDUJPOTUBUVT ⬅︎

# ... if connectable_sockets&.any? # ... elsif hostname_resolved&.any? # ... else # ... end # ... next 0SJG*0TFMFDUSFUVSOTSFBEBCMF*0PCKFDUTXJUIJOUIF XBJUJOHQFSJPE JUNFBOTUIBUOBNFSFTPMVUJPOJT fi OJTIFE *NQMFNFOUBUJPOPG4PDLFUUDQXJUI)&WWX (hostname_resolution_waiting, connecting_sockets.all, nil, remaining) 8IFO*0TFMFDUSFUVSOTSFBEBCMF*0PCKFDUT 3FBDIUIJTCMPDL

# ... if connectable_sockets&.any? # ... elsif hostname_resolved&.any? family_name, res = hostname_resolution_queue.get selectable_addrinfos.add(family_name, res) unless res.is_a? E else # ... end # ... next *OUIJTDBTF BEEUIFPCUBJOFEBEESFTTFTUPUIFMJTUPG SFTPMWFE*1BEESFTTFT *NQMFNFOUBUJPOPG4PDLFUUDQXJUI)&WWX Exception (hostname_resolution_waiting, connecting_sockets.all, nil, remaining) "EEUIFPCUBJOFEBEESFTTFT 5IFMJTUPGSFTPMWFE*1BEESFTTFT

# ... if connectable_sockets&.any? # ... elsif hostname_resolved&.any? family_name, res = hostname_resolution_queue.get selectable_addrinfos.add(family_name, res) unless res.is_a? E else # ... end # ... next 5PXBJUGPSUIFSFNBJOJOHUJNF LFFQUIFDVSSFOUTUBUF BUWX BOEFOUFSUIFOFYUMPPQ *NQMFNFOUBUJPOPG4PDLFUUDQXJUI)&WWX (hostname_resolution_waiting, connecting_sockets.all, nil, remaining) &OUFSUIFOFYUMPPQXJUIWXTUBUF Exception

# ... if connectable_sockets&.any? # ... elsif hostname_resolved&.any? family_name, res = hostname_resolution_queue.get selectable_addrinfos.add(family_name, res) unless res.is_a? E else # ... end # ... next 0SJG*0TFMFDUUJNFTPVUBOESFUVSOTOJM JUNFBOTUIBU OFJUIFSBDPOOFDUJPOOPSUIFOBNFSFTPMVUJPOXFSF fi OJTIFEXJUIJOUIFBMMPUUFEUJNF *NQMFNFOUBUJPOPG4PDLFUUDQXJUI)&WWX (hostname_resolution_waiting, connecting_sockets.all, nil, remaining) 8IFO*0TFMFDUSFUVSOTOJM 3FBDIUIJTCMPDL Exception

# ... if connectable_sockets&.any? # ... elsif hostname_resolved&.any? family_name, res = hostname_resolution_queue.get selectable_addrinfos.add(family_name, res) unless res.is_a? E else # ... end # ... next *OUIJTDBTF EFUFSNJOFUIFOFYUTUBUFCBTFEPOUIF DVSSFOUSFTPVSDFTTUBUVT BOEUIFOFOUFSUIFOFYUMPPQ *NQMFNFOUBUJPOPG4PDLFUUDQXJUI)&WWX (hostname_resolution_waiting, connecting_sockets.all, nil, remaining) %FUFSNJOFUIFOFYUTUBUF ⬅︎ Exception

*NQMFNFOUBUJPOPG4PDLFUUDQXJUI)&WGBJMVSF ret = loop do case state # ... when
:success # ... when :failure raise last_error when :timeout # ... end end 5IFTUBUFTJOUSPEVDFEIFSFBGUFSBMMSFQSFTFOUUIF DPNQMFUJPOPGTUBUFUSBOTJUJPOT GBJMVSFXIJDIJTSFBDIFEJGBMMOBNFSFTPMVUJPOTPS BMMDPOOFDUJPOBUUFNQUTGBJM SBJTFBOFYDFQUJPO XJUIUIFMBTUDBQUVSFEFSSPS 3BJTFBOFYDFQUJPO

*NQMFNFOUBUJPOPG4PDLFUUDQXJUI)&WUJNFPVU ret = loop do case state # ... when
:success # ... when :failure raise last_error when :timeout raise Errno::ETIMEDOUT, "user specified timeout" end end *GBVTFSTQFDJ fi FEUJNFPVUPDDVST SFBDIUJNFPVU BOESBJTFBOFYDFQUJPOJOEJDBUJOHJU 3BJTFBOFYDFQUJPO

*NQMFNFOUBUJPOPG4PDLFUUDQXJUI)&WTVDDFTT ret = loop do case state # ... when
:success break connected_socket when :failure raise last_error when :timeout raise Errno::ETIMEDOUT, "user specified timeout" end end TVDDFTTXIJDIJTSFBDIFEXIFOPOFPGUIFDPOOFDUJPOT JTFTUBCMJTIFE JTIFSF #SFBLUIFMPPQXJUIUIFDPOOFDUFETPDLFU #SFBLUIFMPPQ

*NQMFNFOUBUJPOPG4PDLFUUDQXJUI)&WDMFBOVQ def self.tcp(host, port, ...) # ... ret = loop
do # ... end # ... ensure # ... hostname_resolution_threads.each do |thread| thread&.exit end hostname_resolution_queue&.close_all connecting_sockets.each do |connecting_socket| connecting_socket.close unless connecting_socket.closed? end end "GUFSCSFBLJOHPVUPGUIFMPPQ DMFBOVQUISFBET QJQFT BOEPUIFSTPDLFUTJOFBDIDPOOFDUJPOBUUFNQUT $MFBOVQ

*NQMFNFOUBUJPOPG4PDLFUUDQXJUI)&WFYJU def self.tcp(host, port, ...) # ... ret = loop
do # ... end if block_given? begin yield ret ensure ret.close end else ret end ensure # ... end SFUVSOUIFDPOOFDUFETPDLFUBOEUIFNFUIPEFYJUT &YFDVUFCMPDLXJUIUIFDPOOFDUFETPDLFU 3FUVSOUIFDPOOFDUFETPDLFU

4PGBS UIFLFZBTQFDUTPGUIF)&WJNQMFNFOUBUJPO PG4PDLFUUDQIBWFCFFOJOUSPEVDFE )PXFWFS GSPNBQSBDUJDBMTUBOEQPJOU UIFSFBSFTPNFBEEJUJPOBMDPOTJEFSBUJPOT UIBUOFFEUPCFBEESFTTFE

"EEJUJPOBMDPOTJEFSBUJPOT 'JSTUPGBMM EVSJOHUIFJNQMFNFOUBUJPO *EJTDPWFSFEBDBTFUIBU XBTOPUDPWFSFECZUIFFBSMJFSTUBUFUSBOTJUJPOEJBHSBN WD GBJMVSF WX WD
WD TUBSU WX TVDDFTT UJNFPVU

"EEJUJPOBMDPOTJEFSBUJPOT WX "O*1WBEESFTTSFTPMWFE 4FSWFS %/44FSWFS -FUTDPOTJEFSUIFTJUVBUJPOMJLFUIJT &JUIFS*1WPS*1WOBNFSFTPMVUJPOIBTCFFO fi
OJTIFE POFPSUIFPUIFS 3FTPVSDFT $POOFDUJOHTPDLFUT 3FTPMWFE*1BEESFTTFT *1WJTTUJMMSFTPMWJOH &NQUZ "EE ➡︎

"EEJUJPOBMDPOTJEFSBUJPOT WX %/44FSWFS $POOFDUJPOBUUFNQUTIBWFCFFOTUBSUFEUP BMMSFTPMWFE*1BEESFTTFTTPGBS 4UBSUBDPOOFDUJPOUPUIF*1WBEESFTT 3FTPVSDFT $POOFDUJOHTPDLFUT 3FTPMWFE*1BEESFTTFT
*1WJTTUJMMSFTPMWJOH &NQUZ 4FSWFS 0CUBJO ⬅︎

"EEJUJPOBMDPOTJEFSBUJPOT WX %/44FSWFS 4VCTFRVFOUMZ BMMPGUIPTFBUUFNQUTIBWFGBJMFE $POOFDUJPOTGBJM 3FTPVSDFT $POOFDUJOHTPDLFUT 3FTPMWFE*1BEESFTTFT
&NQUZ *1WJTTUJMMSFTPMWJOH &NQUZ 4FSWFS

"EEJUJPOBMDPOTJEFSBUJPOT WX %/44FSWFS *OUIJTTDFOBSJP UIFGPMMPXJOHTJUVBUJPOPDDVS ɾ5IFMJTUPGSFTPMWFE*1BEESFTTFTBOE ɾUIFMJTUPGDPOOFDUJOHTPDLFUTBSFFNQUZ ɾ"OBNFSFTPMVUJPOGPSUIFPUIFSBEESFTTGBNJMZJT ɾTUJMMJOQSPHSFTTJOUIFCBDLHSPVOE
3FTPVSDFT $POOFDUJOHTPDLFUT 3FTPMWFE*1BEESFTTFT &NQUZ *1WJTTUJMMSFTPMWJOH &NQUZ 4FSWFS

*OUIJTDBTF TIPVMEJUUSBOTJUJPOUPGBJMVSFCFDBVTFUIF SFTPVSDFTBSFOPXFNQUZ 0STIPVMEJUUSBOTJUJPOUPWXUPXBJUGPSUIFSFTPMVUJPOPGUIF PUIFSBEESFTTGBNJMZ "EEJUJPOBMDPOTJEFSBUJPOT WD GBJMVSF
WX WD WD TUBSU WX TVDDFTT UJNFPVU

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x.report do 100.times { Socket.tcp("localhost", 9292).close } end end #FGPSF 3VCZ "GUFS *OMPDBMFOWJSPONFOU "QQMF..BY

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class << self attr_accessor :tcp_fast_fallback end def self.tcp(host, port, local_host = nil, local_port = nil, connect_timeout: nil, resolv_timeout: nil, fast_fallback: tcp_fast_fallback, &block) &OBCMFPSEJTBCMF)&W

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$PEFTGPSEFNP $MJFOU require "socket" HOSTNAME = "localhost" PORT = 4567
Socket.tcp(HOSTNAME, PORT) do |socket| socket.write "Hi\r\n" print socket.read end 5IJTCMPDLXPVMECFFYFDVUFE PODFBDPOOFDUJPOJTFTUBCMJTIFE 4UBOEBSEPVUQVUUIFSFTQPOTFSFUVSOFEGSPNUIFUBSHFUTFSWFS &YFDVUF4PDLFUUDQ

$PEFTGPSEFNP 4FSWFS require "socket" require "optparse" class Server ADDRESS_FAMILIES =
{ IPv6: [Socket::AF_INET6, "::1"], IPv4: [Socket::AF_INET, "127.0.0.1"], } #... def accept_loop # ... end end if child_pid = fork Server.new(:IPv6).accept_loop Process.waitpid(child_pid) else Server.new(:IPv4).accept_loop end 4UBSUUXPQSPDFTTFTUPIBOEMFSFRVFTUT UPCPUI*1WBOE*1WBEESFTTFT )BOEMFSFRVFTUTXJUIUIJTNFUIPE

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An adventure of Happy Eyeballs

An adventure of Happy Eyeballs

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