github.com/graemephi/kahugo@v0.62.3-0.20211121071557-d78c0423784d/common/para/para.go (about)

     1  // Copyright 2019 The Hugo Authors. All rights reserved.
     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  // http://www.apache.org/licenses/LICENSE-2.0
     7  //
     8  // Unless required by applicable law or agreed to in writing, software
     9  // distributed under the License is distributed on an "AS IS" BASIS,
    10  // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
    11  // See the License for the specific language governing permissions and
    12  // limitations under the License.
    13  
    14  // Package para implements parallel execution helpers.
    15  package para
    16  
    17  import (
    18  	"context"
    19  
    20  	"golang.org/x/sync/errgroup"
    21  )
    22  
    23  // Workers configures a task executor with the most number of tasks to be executed in parallel.
    24  type Workers struct {
    25  	sem chan struct{}
    26  }
    27  
    28  // Runner wraps the lifecycle methods of a new task set.
    29  //
    30  // Run wil block until a worker is available or the context is cancelled,
    31  // and then run the given func in a new goroutine.
    32  // Wait will wait for all the running goroutines to finish.
    33  type Runner interface {
    34  	Run(func() error)
    35  	Wait() error
    36  }
    37  
    38  type errGroupRunner struct {
    39  	*errgroup.Group
    40  	w   *Workers
    41  	ctx context.Context
    42  }
    43  
    44  func (g *errGroupRunner) Run(fn func() error) {
    45  	select {
    46  	case g.w.sem <- struct{}{}:
    47  	case <-g.ctx.Done():
    48  		return
    49  	}
    50  
    51  	g.Go(func() error {
    52  		err := fn()
    53  		<-g.w.sem
    54  		return err
    55  	})
    56  }
    57  
    58  // New creates a new Workers with the given number of workers.
    59  func New(numWorkers int) *Workers {
    60  	return &Workers{
    61  		sem: make(chan struct{}, numWorkers),
    62  	}
    63  }
    64  
    65  // Start starts a new Runner.
    66  func (w *Workers) Start(ctx context.Context) (Runner, context.Context) {
    67  	g, ctx := errgroup.WithContext(ctx)
    68  	return &errGroupRunner{
    69  		Group: g,
    70  		ctx:   ctx,
    71  		w:     w,
    72  	}, ctx
    73  }