github.com/opcr-io/oras-go/v2@v2.0.0-20231122155130-eb4260d8a0ae/internal/syncutil/limitgroup.go (about)

     1  /*
     2  Copyright The ORAS Authors.
     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  
    16  package syncutil
    17  
    18  import (
    19  	"context"
    20  
    21  	"golang.org/x/sync/errgroup"
    22  )
    23  
    24  // A LimitedGroup is a collection of goroutines working on subtasks that are part of
    25  // the same overall task.
    26  type LimitedGroup struct {
    27  	grp *errgroup.Group
    28  	ctx context.Context
    29  }
    30  
    31  // LimitGroup returns a new LimitedGroup and an associated Context derived from ctx.
    32  //
    33  // The number of active goroutines in this group is limited to the given limit.
    34  // A negative value indicates no limit.
    35  //
    36  // The derived Context is canceled the first time a function passed to Go
    37  // returns a non-nil error or the first time Wait returns, whichever occurs
    38  // first.
    39  func LimitGroup(ctx context.Context, limit int) (*LimitedGroup, context.Context) {
    40  	grp, ctx := errgroup.WithContext(ctx)
    41  	grp.SetLimit(limit)
    42  	return &LimitedGroup{grp: grp, ctx: ctx}, ctx
    43  }
    44  
    45  // Go calls the given function in a new goroutine.
    46  // It blocks until the new goroutine can be added without the number of
    47  // active goroutines in the group exceeding the configured limit.
    48  //
    49  // The first call to return a non-nil error cancels the group's context.
    50  // After which, any subsequent calls to Go will not execute their given function.
    51  // The error will be returned by Wait.
    52  func (g *LimitedGroup) Go(f func() error) {
    53  	g.grp.Go(func() error {
    54  		select {
    55  		case <-g.ctx.Done():
    56  			return g.ctx.Err()
    57  		default:
    58  			return f()
    59  		}
    60  	})
    61  }
    62  
    63  // Wait blocks until all function calls from the Go method have returned, then
    64  // returns the first non-nil error (if any) from them.
    65  func (g *LimitedGroup) Wait() error {
    66  	return g.grp.Wait()
    67  }