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// Copyright 2019 The Hugo Authors. All rights reserved.
//
// 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 para implements parallel execution helpers.
package para
import (
"context"
"golang.org/x/sync/errgroup"
)
// Workers configures a task executor with the most number of tasks to be executed in parallel.
type Workers struct {
sem chan struct{}
}
// Runner wraps the lifecycle methods of a new task set.
//
// Run wil block until a worker is available or the context is cancelled,
// and then run the given func in a new goroutine.
// Wait will wait for all the running goroutines to finish.
type Runner interface {
Run(func() error)
Wait() error
}
type errGroupRunner struct {
*errgroup.Group
w *Workers
ctx context.Context
}
func (g *errGroupRunner) Run(fn func() error) {
select {
case g.w.sem <- struct{}{}:
case <-g.ctx.Done():
return
}
g.Go(func() error {
err := fn()
<-g.w.sem
return err
})
}
// New creates a new Workers with the given number of workers.
func New(numWorkers int) *Workers {
return &Workers{
sem: make(chan struct{}, numWorkers),
}
}
// Start starts a new Runner.
func (w *Workers) Start(ctx context.Context) (Runner, context.Context) {
g, ctx := errgroup.WithContext(ctx)
return &errGroupRunner{
Group: g,
ctx: ctx,
w: w,
}, ctx
}
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