github.com/opcr-io/oras-go/v2@v2.0.0-20231122155130-eb4260d8a0ae/internal/syncutil/limit.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  	"golang.org/x/sync/semaphore"
    23  )
    24  
    25  // LimitedRegion provides a way to bound concurrent access to a code block.
    26  type LimitedRegion struct {
    27  	ctx     context.Context
    28  	limiter *semaphore.Weighted
    29  	ended   bool
    30  }
    31  
    32  // LimitRegion creates a new LimitedRegion.
    33  func LimitRegion(ctx context.Context, limiter *semaphore.Weighted) *LimitedRegion {
    34  	if limiter == nil {
    35  		return nil
    36  	}
    37  	return &LimitedRegion{
    38  		ctx:     ctx,
    39  		limiter: limiter,
    40  		ended:   true,
    41  	}
    42  }
    43  
    44  // Start starts the region with concurrency limit.
    45  func (lr *LimitedRegion) Start() error {
    46  	if lr == nil || !lr.ended {
    47  		return nil
    48  	}
    49  	if err := lr.limiter.Acquire(lr.ctx, 1); err != nil {
    50  		return err
    51  	}
    52  	lr.ended = false
    53  	return nil
    54  }
    55  
    56  // End ends the region with concurrency limit.
    57  func (lr *LimitedRegion) End() {
    58  	if lr == nil || lr.ended {
    59  		return
    60  	}
    61  	lr.limiter.Release(1)
    62  	lr.ended = true
    63  }
    64  
    65  // GoFunc represents a function that can be invoked by Go.
    66  type GoFunc[T any] func(ctx context.Context, region *LimitedRegion, t T) error
    67  
    68  // Go concurrently invokes fn on items.
    69  func Go[T any](ctx context.Context, limiter *semaphore.Weighted, fn GoFunc[T], items ...T) error {
    70  	eg, egCtx := errgroup.WithContext(ctx)
    71  	for _, item := range items {
    72  		region := LimitRegion(ctx, limiter)
    73  		if err := region.Start(); err != nil {
    74  			return err
    75  		}
    76  		eg.Go(func(t T) func() error {
    77  			return func() error {
    78  				defer region.End()
    79  				return fn(egCtx, region, t)
    80  			}
    81  		}(item))
    82  	}
    83  	return eg.Wait()
    84  }