github.com/livekit/protocol@v1.16.1-0.20240517185851-47e4c6bba773/rpc/race.go (about) 1 // Copyright 2023 LiveKit, Inc. 2 // 3 // Licensed under the Apache License, Version 2.0 (the "License"); 4 // you may not use this file except in compliance with the License. 5 // You may obtain a copy of the License at 6 // 7 // http://www.apache.org/licenses/LICENSE-2.0 8 // 9 // Unless required by applicable law or agreed to in writing, software 10 // distributed under the License is distributed on an "AS IS" BASIS, 11 // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 12 // See the License for the specific language governing permissions and 13 // limitations under the License. 14 15 package rpc 16 17 import ( 18 "context" 19 "sync" 20 ) 21 22 type raceResult[T any] struct { 23 i int 24 val *T 25 err error 26 } 27 28 type Race[T any] struct { 29 ctx context.Context 30 cancel context.CancelFunc 31 nextIndex int 32 33 resultLock sync.Mutex 34 result *raceResult[T] 35 } 36 37 // NewRace creates a race to yield the result from one or more candidate 38 // functions 39 func NewRace[T any](ctx context.Context) *Race[T] { 40 ctx, cancel := context.WithCancel(ctx) 41 return &Race[T]{ 42 ctx: ctx, 43 cancel: cancel, 44 } 45 } 46 47 // Go adds a candidate function to the race by running it in a new goroutine 48 func (r *Race[T]) Go(fn func(ctx context.Context) (*T, error)) { 49 i := r.nextIndex 50 r.nextIndex++ 51 52 go func() { 53 val, err := fn(r.ctx) 54 55 r.resultLock.Lock() 56 if r.result == nil { 57 r.result = &raceResult[T]{i, val, err} 58 } 59 r.resultLock.Unlock() 60 61 r.cancel() 62 }() 63 } 64 65 // Wait awaits the first complete function and returns the index and results 66 // or -1 if the context is cancelled before any candidate finishes. 67 func (r *Race[T]) Wait() (int, *T, error) { 68 <-r.ctx.Done() 69 70 r.resultLock.Lock() 71 res := r.result 72 r.resultLock.Unlock() 73 if res != nil { 74 return res.i, res.val, res.err 75 } 76 return -1, nil, r.ctx.Err() 77 }