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// Copyright 2023 LiveKit, Inc.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
package rpc
import (
"context"
"sync"
)
type raceResult[T any] struct {
i int
val *T
err error
}
type Race[T any] struct {
ctx context.Context
cancel context.CancelFunc
nextIndex int
resultLock sync.Mutex
result *raceResult[T]
}
// NewRace creates a race to yield the result from one or more candidate
// functions
func NewRace[T any](ctx context.Context) *Race[T] {
ctx, cancel := context.WithCancel(ctx)
return &Race[T]{
ctx: ctx,
cancel: cancel,
}
}
// Go adds a candidate function to the race by running it in a new goroutine
func (r *Race[T]) Go(fn func(ctx context.Context) (*T, error)) {
i := r.nextIndex
r.nextIndex++
go func() {
val, err := fn(r.ctx)
r.resultLock.Lock()
if r.result == nil {
r.result = &raceResult[T]{i, val, err}
}
r.resultLock.Unlock()
r.cancel()
}()
}
// Wait awaits the first complete function and returns the index and results
// or -1 if the context is cancelled before any candidate finishes.
func (r *Race[T]) Wait() (int, *T, error) {
<-r.ctx.Done()
r.resultLock.Lock()
res := r.result
r.resultLock.Unlock()
if res != nil {
return res.i, res.val, res.err
}
return -1, nil, r.ctx.Err()
}