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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 utils
import (
"context"
"errors"
"time"
"go.uber.org/multierr"
)
var ErrMaxAttemptsReached = errors.New("max attempts reached")
type HedgeParams[T any] struct {
Timeout time.Duration
RetryDelay time.Duration
MaxAttempts int
IsRecoverable func(err error) bool
Func func(context.Context) (T, error)
}
// race retries if the function takes too long to return
// |---------------- attempt 1 ----------------|
// | delay |--------- attempt 2 ---------|
//
// If an attempt fails while no others are in flight, the next attempt
// starts immediately rather than waiting out RetryDelay:
// |-- attempt 1 --X|-- attempt 2 ----------|
func HedgeCall[T any](ctx context.Context, params HedgeParams[T]) (v T, err error) {
ctx, cancel := context.WithTimeout(ctx, params.Timeout)
defer cancel()
type result struct {
value T
err error
}
ch := make(chan result, params.MaxAttempts)
race := func() {
value, err := params.Func(ctx)
ch <- result{value, err}
}
var attempt, done int
delay := time.NewTimer(0)
defer delay.Stop()
for {
select {
case <-delay.C:
go race()
if attempt++; attempt < params.MaxAttempts {
delay.Reset(params.RetryDelay)
}
case res := <-ch:
if res.err == nil {
return res.value, nil
}
err = multierr.Append(err, res.err)
if params.IsRecoverable != nil && !params.IsRecoverable(res.err) {
return
}
if done++; done == params.MaxAttempts {
err = multierr.Append(err, ErrMaxAttemptsReached)
return
}
// No attempts are currently in flight — skip the remaining
// RetryDelay so the next attempt fires on the next iteration.
if attempt == done && attempt < params.MaxAttempts {
delay.Reset(0)
}
case <-ctx.Done():
err = multierr.Append(err, ctx.Err())
return
}
}
}