Deadlock happens when two theads concurrently read from _cache dictionary

[Igor-Palaguta]

Hello,

Version: Vapor 2.1.2, Routing 2.0.0
Xcode 8.3.2/Debug

Very frequently deadlock happens, when two threads at same time read from _cache dictionary. Probably it is Foundation issue, as multiple reads should be allowed. Currently read and write operations for _cache are not synchronized. Probably _cache is corrupted after two threads modify it at same time.

Here is stack:

Thread 2 Queue : codes.vapor.server (concurrent)
#0	0x00000001013476f9 in specialized static String.== infix(String, String) -> Bool ()
#1	0x00000001013052c1 in protocol witness for static Equatable.== infix(A, A) -> Bool in conformance String ()
#2	0x00000001012696ff in _NativeDictionaryBuffer<A, B where ...>._find(A, startBucket : Int) -> (pos : _NativeDictionaryIndex<A, B>, found : Bool) ()
#3	0x0000000101277859 in _NativeDictionaryBuffer<A, B where ...>.maybeGet(A) -> B? ()
#4	0x0000000101265c36 in _VariantDictionaryBuffer.maybeGet(A) -> B? ()
#5	0x000000010123a4be in Dictionary.subscript.getter ()
#6	0x0000000100857662 in Router.route(Request) -> Responder? at /Users/Igor/Projects/TennisCup/.build/checkouts/routing.git-5366657101075133678/Sources/Routing/Router.swift:35
#7	0x0000000100853744 in Router.respond(to : Request) throws -> Response at /Users/Igor/Projects/TennisCup/.build/checkouts/routing.git-5366657101075133678/Sources/Routing/Router+Responder.swift:9
#8	0x000000010085501b in protocol witness for Responder.respond(to : Request) throws -> Response in conformance Router ()
#9	0x0000000100917062 in SessionsMiddleware.respond(to : Request, chainingTo : Responder) throws -> Response at /Users/Igor/Projects/TennisCup/.build/checkouts/vapor.git-5492988889259800272/Sources/Sessions/SessionsMiddleware.swift:52
#10	0x0000000100917e53 in protocol witness for Middleware.respond(to : Request, chainingTo : Responder) throws -> Response in conformance SessionsMiddleware ()
#11	0x00000001009f23a3 in Collection<A where ...>.(chain(to : Responder) -> Responder).(closure #1).(closure #1) at /Users/Igor/Projects/TennisCup/.build/checkouts/vapor.git-5492988889259800272/Sources/Vapor/Middleware/Chaining.swift:15
#12	0x0000000100597d02 in BasicResponder.respond(to : Request) throws -> Response at /Users/Igor/Projects/TennisCup/.build/checkouts/engine.git-3311994267206676365/Sources/HTTP/Responder/Responder.swift:13
#13	0x0000000100597da4 in protocol witness for Responder.respond(to : Request) throws -> Response in conformance BasicResponder ()
#14	0x00000001009ce3fe in FileMiddleware.respond(to : Request, chainingTo : Responder) throws -> Response at /Users/Igor/Projects/TennisCup/.build/checkouts/vapor.git-5492988889259800272/Sources/Vapor/File/FileMiddleware.swift:21
#15	0x00000001009cf1a3 in protocol witness for Middleware.respond(to : Request, chainingTo : Responder) throws -> Response in conformance FileMiddleware ()
#16	0x00000001009f23a3 in Collection<A where ...>.(chain(to : Responder) -> Responder).(closure #1).(closure #1) at /Users/Igor/Projects/TennisCup/.build/checkouts/vapor.git-5492988889259800272/Sources/Vapor/Middleware/Chaining.swift:15
#17	0x0000000100597d02 in BasicResponder.respond(to : Request) throws -> Response at /Users/Igor/Projects/TennisCup/.build/checkouts/engine.git-3311994267206676365/Sources/HTTP/Responder/Responder.swift:13
#18	0x0000000100597da4 in protocol witness for Responder.respond(to : Request) throws -> Response in conformance BasicResponder ()
#19	0x00000001009a57bc in DateMiddleware.respond(to : Request, chainingTo : Responder) throws -> Response at /Users/Igor/Projects/TennisCup/.build/checkouts/vapor.git-5492988889259800272/Sources/Vapor/Date/DateMiddleware.swift:36
#20	0x00000001009a6e63 in protocol witness for Middleware.respond(to : Request, chainingTo : Responder) throws -> Response in conformance DateMiddleware ()
#21	0x00000001009f23a3 in Collection<A where ...>.(chain(to : Responder) -> Responder).(closure #1).(closure #1) at /Users/Igor/Projects/TennisCup/.build/checkouts/vapor.git-5492988889259800272/Sources/Vapor/Middleware/Chaining.swift:15
#22	0x0000000100597d02 in BasicResponder.respond(to : Request) throws -> Response at /Users/Igor/Projects/TennisCup/.build/checkouts/engine.git-3311994267206676365/Sources/HTTP/Responder/Responder.swift:13
#23	0x0000000100597da4 in protocol witness for Responder.respond(to : Request) throws -> Response in conformance BasicResponder ()
#24	0x00000001009bfc3b in ErrorMiddleware.respond(to : Request, chainingTo : Responder) throws -> Response at /Users/Igor/Projects/TennisCup/.build/checkouts/vapor.git-5492988889259800272/Sources/Vapor/Error/ErrorMiddleware.swift:17
#25	0x00000001009c27b3 in protocol witness for Middleware.respond(to : Request, chainingTo : Responder) throws -> Response in conformance ErrorMiddleware ()
#26	0x00000001009f23a3 in Collection<A where ...>.(chain(to : Responder) -> Responder).(closure #1).(closure #1) at /Users/Igor/Projects/TennisCup/.build/checkouts/vapor.git-5492988889259800272/Sources/Vapor/Middleware/Chaining.swift:15
#27	0x0000000100597d02 in BasicResponder.respond(to : Request) throws -> Response at /Users/Igor/Projects/TennisCup/.build/checkouts/engine.git-3311994267206676365/Sources/HTTP/Responder/Responder.swift:13
#28	0x0000000100597da4 in protocol witness for Responder.respond(to : Request) throws -> Response in conformance BasicResponder ()
#29	0x00000001009b12bb in Droplet.(init(config : Config?, router : Router?, server : ServerFactoryProtocol?, client : ClientFactoryProtocol?, middleware : [Middleware]?, console : ConsoleProtocol?, log : LogProtocol?, hash : HashProtocol?, cipher : CipherProtocol?, commands : [Command]?, view : ViewRenderer?, cache : CacheProtocol?, mail : MailProtocol?) throws -> Droplet).(closure #1) at /Users/Igor/Projects/TennisCup/.build/checkouts/vapor.git-5492988889259800272/Sources/Vapor/Droplet/Droplet.swift:146
#30	0x0000000100597d02 in BasicResponder.respond(to : Request) throws -> Response at /Users/Igor/Projects/TennisCup/.build/checkouts/engine.git-3311994267206676365/Sources/HTTP/Responder/Responder.swift:13
#31	0x0000000100597da4 in protocol witness for Responder.respond(to : Request) throws -> Response in conformance BasicResponder ()
#32	0x00000001005a56f3 in BasicServer.respond(stream : A.Client, responder : Responder) throws -> () at /Users/Igor/Projects/TennisCup/.build/checkouts/engine.git-3311994267206676365/Sources/HTTP/Server/BasicServer.swift:96
#33	0x00000001005a4f91 in BasicServer.(start(Responder, errors : (ServerError) -> ()) throws -> ()).(closure #1) at /Users/Igor/Projects/TennisCup/.build/checkouts/engine.git-3311994267206676365/Sources/HTTP/Server/BasicServer.swift:53

Thread 4 Queue : codes.vapor.server (concurrent)
#0	0x000000010140bb4a in _swift_retain_ ()
#1	0x00000001013c5704 in initializeWithCopy for String ()
#2	0x00000001012696da in _NativeDictionaryBuffer<A, B where ...>._find(A, startBucket : Int) -> (pos : _NativeDictionaryIndex<A, B>, found : Bool) ()
#3	0x0000000101277859 in _NativeDictionaryBuffer<A, B where ...>.maybeGet(A) -> B? ()
#4	0x0000000101265c36 in _VariantDictionaryBuffer.maybeGet(A) -> B? ()
#5	0x000000010123a4be in Dictionary.subscript.getter ()
#6	0x0000000100857662 in Router.route(Request) -> Responder? at /Users/Igor/Projects/TennisCup/.build/checkouts/routing.git-5366657101075133678/Sources/Routing/Router.swift:35
#7	0x0000000100853744 in Router.respond(to : Request) throws -> Response at /Users/Igor/Projects/TennisCup/.build/checkouts/routing.git-5366657101075133678/Sources/Routing/Router+Responder.swift:9
#8	0x000000010085501b in protocol witness for Responder.respond(to : Request) throws -> Response in conformance Router ()
#9	0x0000000100917062 in SessionsMiddleware.respond(to : Request, chainingTo : Responder) throws -> Response at /Users/Igor/Projects/TennisCup/.build/checkouts/vapor.git-5492988889259800272/Sources/Sessions/SessionsMiddleware.swift:52
#10	0x0000000100917e53 in protocol witness for Middleware.respond(to : Request, chainingTo : Responder) throws -> Response in conformance SessionsMiddleware ()
#11	0x00000001009f23a3 in Collection<A where ...>.(chain(to : Responder) -> Responder).(closure #1).(closure #1) at /Users/Igor/Projects/TennisCup/.build/checkouts/vapor.git-5492988889259800272/Sources/Vapor/Middleware/Chaining.swift:15
#12	0x0000000100597d02 in BasicResponder.respond(to : Request) throws -> Response at /Users/Igor/Projects/TennisCup/.build/checkouts/engine.git-3311994267206676365/Sources/HTTP/Responder/Responder.swift:13
#13	0x0000000100597da4 in protocol witness for Responder.respond(to : Request) throws -> Response in conformance BasicResponder ()
#14	0x00000001009ce3fe in FileMiddleware.respond(to : Request, chainingTo : Responder) throws -> Response at /Users/Igor/Projects/TennisCup/.build/checkouts/vapor.git-5492988889259800272/Sources/Vapor/File/FileMiddleware.swift:21
#15	0x00000001009cf1a3 in protocol witness for Middleware.respond(to : Request, chainingTo : Responder) throws -> Response in conformance FileMiddleware ()
#16	0x00000001009f23a3 in Collection<A where ...>.(chain(to : Responder) -> Responder).(closure #1).(closure #1) at /Users/Igor/Projects/TennisCup/.build/checkouts/vapor.git-5492988889259800272/Sources/Vapor/Middleware/Chaining.swift:15
#17	0x0000000100597d02 in BasicResponder.respond(to : Request) throws -> Response at /Users/Igor/Projects/TennisCup/.build/checkouts/engine.git-3311994267206676365/Sources/HTTP/Responder/Responder.swift:13
#18	0x0000000100597da4 in protocol witness for Responder.respond(to : Request) throws -> Response in conformance BasicResponder ()
#19	0x00000001009a57bc in DateMiddleware.respond(to : Request, chainingTo : Responder) throws -> Response at /Users/Igor/Projects/TennisCup/.build/checkouts/vapor.git-5492988889259800272/Sources/Vapor/Date/DateMiddleware.swift:36
#20	0x00000001009a6e63 in protocol witness for Middleware.respond(to : Request, chainingTo : Responder) throws -> Response in conformance DateMiddleware ()
#21	0x00000001009f23a3 in Collection<A where ...>.(chain(to : Responder) -> Responder).(closure #1).(closure #1) at /Users/Igor/Projects/TennisCup/.build/checkouts/vapor.git-5492988889259800272/Sources/Vapor/Middleware/Chaining.swift:15
#22	0x0000000100597d02 in BasicResponder.respond(to : Request) throws -> Response at /Users/Igor/Projects/TennisCup/.build/checkouts/engine.git-3311994267206676365/Sources/HTTP/Responder/Responder.swift:13
#23	0x0000000100597da4 in protocol witness for Responder.respond(to : Request) throws -> Response in conformance BasicResponder ()
#24	0x00000001009bfc3b in ErrorMiddleware.respond(to : Request, chainingTo : Responder) throws -> Response at /Users/Igor/Projects/TennisCup/.build/checkouts/vapor.git-5492988889259800272/Sources/Vapor/Error/ErrorMiddleware.swift:17
#25	0x00000001009c27b3 in protocol witness for Middleware.respond(to : Request, chainingTo : Responder) throws -> Response in conformance ErrorMiddleware ()
#26	0x00000001009f23a3 in Collection<A where ...>.(chain(to : Responder) -> Responder).(closure #1).(closure #1) at /Users/Igor/Projects/TennisCup/.build/checkouts/vapor.git-5492988889259800272/Sources/Vapor/Middleware/Chaining.swift:15
#27	0x0000000100597d02 in BasicResponder.respond(to : Request) throws -> Response at /Users/Igor/Projects/TennisCup/.build/checkouts/engine.git-3311994267206676365/Sources/HTTP/Responder/Responder.swift:13
#28	0x0000000100597da4 in protocol witness for Responder.respond(to : Request) throws -> Response in conformance BasicResponder ()
#29	0x00000001009b12bb in Droplet.(init(config : Config?, router : Router?, server : ServerFactoryProtocol?, client : ClientFactoryProtocol?, middleware : [Middleware]?, console : ConsoleProtocol?, log : LogProtocol?, hash : HashProtocol?, cipher : CipherProtocol?, commands : [Command]?, view : ViewRenderer?, cache : CacheProtocol?, mail : MailProtocol?) throws -> Droplet).(closure #1) at /Users/Igor/Projects/TennisCup/.build/checkouts/vapor.git-5492988889259800272/Sources/Vapor/Droplet/Droplet.swift:146
#30	0x0000000100597d02 in BasicResponder.respond(to : Request) throws -> Response at /Users/Igor/Projects/TennisCup/.build/checkouts/engine.git-3311994267206676365/Sources/HTTP/Responder/Responder.swift:13
#31	0x0000000100597da4 in protocol witness for Responder.respond(to : Request) throws -> Response in conformance BasicResponder ()
#32	0x00000001005a56f3 in BasicServer.respond(stream : A.Client, responder : Responder) throws -> () at /Users/Igor/Projects/TennisCup/.build/checkouts/engine.git-3311994267206676365/Sources/HTTP/Server/BasicServer.swift:96
#33	0x00000001005a4f91 in BasicServer.(start(Responder, errors : (ServerError) -> ()) throws -> ()).(closure #1) at /Users/Igor/Projects/TennisCup/.build/checkouts/engine.git-3311994267206676365/Sources/HTTP/Server/BasicServer.swift:53