context.Context is not just for cancelation

Presented on Go(Un)Conference 3kg
https://gounconference.connpass.com/event/92794/

nrutil & nrsql : https://github.com/izumin5210/newrelic-contrib-go

Transcript

1. context.Context is not just for cancelation Go(Un)Conference 3kg @izumin5210
2. izumin5210 Engineer at Wantedly, Inc. Wantedly People ‣ Web Application Engineer - Server-side : Golang, Ruby, etc. - Web Frontend ‣ Interests in developer productivity on microservices ‣ I'll talk on builderscon Tokyo 2018 :)
3. * https://golang.org/pkg/context/ Package context defines the Context type, which carries deadlines, cancelation signals, and other request-scoped values across API boundaries and between processes.* context.Context
4. * https://golang.org/pkg/context/ Package context defines the Context type, which carries deadlines, cancelation signals, and other request-scoped values across API boundaries and between processes.* context.Context
5. carries deadlines
6. * https://golang.org/pkg/context/ Package context defines the Context type, which carries deadlines, cancelation signals, and other request-scoped values across API boundaries and between processes.* context.Context
7. carries cancelation signals
8. `context.Context`
   
   Usecases ‣
   λΠϜΞ΢τ 
   FH
   ଞͷαʔό΁ͷϦΫΤετΛ౤͚͛ͨͲɼ஗͘ͳ͍ͬͯΔ৔߹͸ఘΊ͍ͨ ‣
   Ωϟϯηϧͷ఻ൖ 
   FH
   Ϩεϙϯε͸ฦ͠ऴΘͬͯΔͷʹ
   HPSPVUJOF
   ͕ࢮͳͣಈ͖ଓ͚͍ͯΔͷ͸ࠔΔ
9. Cancelation ‣
   ద੾ͳ
   DBODFM
   ॲཧ͸લఏ 
   ӈͷ͸ద౰͚ͩͲ ‣
   ඪ४ύοέʔδͰ΋ଟ͘Ͱ࣮૷ࡁΈ 
   `database/sql`
   ͱ͔
   `net/http`
   ͱ͔
10. ࠷ߴʹศར
    ͔͍͖ͭͬͯ·͠ΐ͏
11. &/%
12. &/%
13. ࢖͍ॴ͕Θ͔Βͳ͍
    ๨ΕΒΕ͕ͪͳ ΋͏Ұͭͷػೳ
14. * https://golang.org/pkg/context/ Package context defines the Context type, which carries deadlines, cancelation signals, and other request-scoped values across API boundaries and between processes.* context.Context
15. func WithValue(parent Context, key, val interface{}) Context func (Context) Value(key interface{}) interface{}
16. ͳΜͰ΋͸͍ͬͯศརʢʁʣ ctx := context.TODO() ctx = context.WithValue(ctx, "ctxkey1", 100) ctx = context.WithValue(ctx, "ctxkey2", "foobar") // Output: // 100 foobar fmt.Println(ctx.Value("ctxkey1"), ctx.Value("ctxkey2"))
17. func WithValue(parent Context, key, val interface{}) Context func (Context) Value(key interface{}) interface{}
18. TFUUFS
    
    HFUUFS
    Ͱʢ͋Δఔ౓ʣܕΛकΖ͏ func GetFoo(ctx context.Context) string { if v, ok := ctx.Value("foo").(string); ok { return v } return "" } func SetFoo(ctx context.Context, v string) context.Context { return context.WithValue(ctx, "foo", v) }
19. func GetFoo(ctx context.Context) string { if v, ok := ctx.Value("foo").(string); ok { return v } return "" } func SetFoo(ctx context.Context, v string) context.Context { return context.WithValue(ctx, "foo", v) }
20. type ctxKeyFoo struct {} func GetFoo(ctx context.Context) string { if v, ok := ctx.Value(ctxKeyFoo{}).(string); ok { return v } return "" } func SetFoo(ctx context.Context, v string) context.Context { return context.WithValue(ctx, ctxKeyFoo{}, v) } LFZ
    ͷॏෳΛ๷͝͏
21. Ͱɼ
22. ԿΛೖΕΔ͔ Կʹ࢖͏͔
23. ! Bad pattern " ϩδοΫʢυϝΠϯ
    ӬଓԽϩδοΫʣʹؔΘΔ΋ͷΛೖΕͳ͍ type PostStore interface { Create(ctx context.Context) error } func (s *postStoreImpl) Create(ctx context.Context) error { title := GetPostTitleFromContext(ctx) body := GetPostBodyFromContext(ctx) // snip. }
24. ! Bad pattern " JOUFSGBDF
    ఆ͚ٛͩͰ͸ύϥϝλʹԿ͕ඞཁ͔Θ͔Βͳ͍
    
    DBMMFS
    ͕಺෦࣮૷ʹґଘͯ͠͠·͏ type PostStore interface { Create(ctx context.Context) error } func (s *postStoreImpl) Create(ctx context.Context) error { title := GetPostTitleFromContext(ctx) body := GetPostBodyFromContext(ctx) // snip. }
25. ܕ͕མͪΔ
    ! JOUFSGBDF
    ͕Θ͔ΓͮΒ͘ͳΔ!
26. Կʹ࢖͑Δͷ͔
    !
27. Idea - υϝΠϯͱؔ܎ͳ͍ϝλσʔλΛೖΕΔ ‣
    ʢυϝΠϯɾӬଓԽɾFUDʣϩδοΫͰ࢖ΘΕͳ͍΋ͷͳΒྑ͍ 
    ͦͷσʔλ͕ͳͯ͘΋ϩδοΫʹ͸Өڹ͕ग़ͳ͍
    ΋ͷ 
    ͦͷϩδοΫͱ͸ຊ࣭తʹؔ܎ͳ͍΋ͷ 
    JOUFSGBDF
    ʹυϝΠϯͱؔ܎ͳ͍΋ͷ͕͋Δͱ
    DPOGVTJOH
    !
28. ϩδοΫͰ࢖ΘΕͳ͍΋ͷʁ ‣
    ͳΜΒ͔ͷܭଌɾσʔλऩूʹ༻͍ΒΕΔ΋ͷ 
    FH 
    ϝτϦΫεऩू 
    αʔϏεؒ௨৴ͷτϨʔγϯά 
    ΤϥʔϨϙʔςΟϯά
29. e.g. New Relic ʢϝτϦΫεऩूʣ
    ‣
    αʔόͷϦΫΤετίϯςΩετ఻ൖ 
    `sql.DB.QueryContext`
    ͳͲΛ
    XSBQ
    ͯ͠ɼͦͷதͰ
    TFHNFOU
    Λ࡞ΕΕ͹ྑ͍
    
    ϦΫΤετΛड͚Δͱ͜Ζ
    ˠ
    ΫΤϦ౤͛Δͱ͜Ζ·Ͱ
    DPOUFYU
    ఻ൖͤ͞Δ
30. e.g. New Relic `context.Context`
    ʹ
    `newrelic.Transaction`
    Λ֨ೲ͓ͯ͘͠ ʢNJEEMFXBSF
    `http.Handler`
    ΍
    H31$
    ͷ
    JOUFSDFQUPS
    Ͱ΍Ε͹0,ʣ // SetTransaction stores newrelic transaction object into given context. func SetTransaction(ctx context.Context, txn newrelic.Transaction) context.Context { return context.WithValue(ctx, txnKey, txn) } https://godoc.org/github.com/izumin5210/newrelic-contrib-go/nrutil
31. e.g. New Relic + DB `sql.DB` Λ
    XSBQ
    ͯ͠ɼDPOUFYU
    ͔Β
    5SBOTBDUJPO
    ΛऔΓग़͠
    TFHNFOU
    Λ࡞Δ func (w *dbWrapper) QueryContext(ctx context.Context, q string, args ...interface{}) (*sql.Rows, error) { var ( rows *sql.Rows err error ) w.segment(ctx, q, args, func() { rows, err = w.original.QueryContext(ctx, q, args...) }) return rows, err } https://godoc.org/github.com/izumin5210/newrelic-contrib-go/nrsql
32. Point ‣
    ͋ΒΏΔ
    ϦΫΤετ
    ʹ͸ඞͣ
    DPOUFYU
    Λ౉͓ͯ͘͠ 
    
    Ͳ͏ͤλΠϜΞ΢τͱ͔ߟ͑ͳ͍ͱ͍͚ͳ͘ͳΔ 
    
    ͱΓ͋͑ͣ౉͠ͱ͚͹ɼ৽͘͠ͳΜ͔ܭଌ͍ͨ͠ͱ͖ͱ͔ศར type PostStore interface { Create(ctx context.Context, title, body string, userID UserID) error }
33. ‣
    `context.Context`
    ͸ΩϟϯηϧɾλΠϜΞ΢τͷͨΊͷϧʔϧ 
    ͋Δఔ౓Ҏ্େ͖ͳαʔϏεͩͱඞཁෆՄܽͳػೳ 
    ͚ͩͲɼͦΕ͚ͩ͡Όͳ͍ ‣
    ϦΫΤετͷϝλ৘ใΛ͓࣋ͨͤͯ͘ͱ͍Ζ͍Ζܭଌ͢Δͱ͖ศར 
    3FRVFTU
    *%
    ΍
    USBDJOH
    ʹඞཁͳ৘ใॾʑɼϝτϦΫεऩूΦϒδΣΫτͳͲΛͬͦ͜Γ࣋ͪճͤΔ ‣
    ϦΫΤετ
    ͬΆ͍ؔ਺ʹ͸
    `context.Context`
    Λඞͣ౉͢Α͏ʹ͢Δ 
    Ͳ͏ͤ͋ͱ͔Βཉ͘͠ͳΔͷͰɼ͍·͙͢࢖Θͳͯ͘΋࠷ॳ͔Β౉͓ͯ͜͠͏ 
    ͋ͱ͔Β௥Ճ͢Δͷ͸୯७ʹखؒʹͳΔ
34. https://www.wantedly.com/projects/223823