github.com/mika/distribution@v2.2.2-0.20160108133430-a75790e3d8e0+incompatible/registry/storage/cache/cachedblobdescriptorstore.go (about)

     1  package cache
     2  
     3  import (
     4  	"github.com/docker/distribution/context"
     5  	"github.com/docker/distribution/digest"
     6  
     7  	"github.com/docker/distribution"
     8  )
     9  
    10  // Metrics is used to hold metric counters
    11  // related to the number of times a cache was
    12  // hit or missed.
    13  type Metrics struct {
    14  	Requests uint64
    15  	Hits     uint64
    16  	Misses   uint64
    17  }
    18  
    19  // MetricsTracker represents a metric tracker
    20  // which simply counts the number of hits and misses.
    21  type MetricsTracker interface {
    22  	Hit()
    23  	Miss()
    24  	Metrics() Metrics
    25  }
    26  
    27  type cachedBlobStatter struct {
    28  	cache   distribution.BlobDescriptorService
    29  	backend distribution.BlobDescriptorService
    30  	tracker MetricsTracker
    31  }
    32  
    33  // NewCachedBlobStatter creates a new statter which prefers a cache and
    34  // falls back to a backend.
    35  func NewCachedBlobStatter(cache distribution.BlobDescriptorService, backend distribution.BlobDescriptorService) distribution.BlobDescriptorService {
    36  	return &cachedBlobStatter{
    37  		cache:   cache,
    38  		backend: backend,
    39  	}
    40  }
    41  
    42  // NewCachedBlobStatterWithMetrics creates a new statter which prefers a cache and
    43  // falls back to a backend. Hits and misses will send to the tracker.
    44  func NewCachedBlobStatterWithMetrics(cache distribution.BlobDescriptorService, backend distribution.BlobDescriptorService, tracker MetricsTracker) distribution.BlobStatter {
    45  	return &cachedBlobStatter{
    46  		cache:   cache,
    47  		backend: backend,
    48  		tracker: tracker,
    49  	}
    50  }
    51  
    52  func (cbds *cachedBlobStatter) Stat(ctx context.Context, dgst digest.Digest) (distribution.Descriptor, error) {
    53  	desc, err := cbds.cache.Stat(ctx, dgst)
    54  	if err != nil {
    55  		if err != distribution.ErrBlobUnknown {
    56  			context.GetLogger(ctx).Errorf("error retrieving descriptor from cache: %v", err)
    57  		}
    58  
    59  		goto fallback
    60  	}
    61  
    62  	if cbds.tracker != nil {
    63  		cbds.tracker.Hit()
    64  	}
    65  	return desc, nil
    66  fallback:
    67  	if cbds.tracker != nil {
    68  		cbds.tracker.Miss()
    69  	}
    70  	desc, err = cbds.backend.Stat(ctx, dgst)
    71  	if err != nil {
    72  		return desc, err
    73  	}
    74  
    75  	if err := cbds.cache.SetDescriptor(ctx, dgst, desc); err != nil {
    76  		context.GetLogger(ctx).Errorf("error adding descriptor %v to cache: %v", desc.Digest, err)
    77  	}
    78  
    79  	return desc, err
    80  
    81  }
    82  
    83  func (cbds *cachedBlobStatter) Clear(ctx context.Context, dgst digest.Digest) error {
    84  	err := cbds.cache.Clear(ctx, dgst)
    85  	if err != nil {
    86  		return err
    87  	}
    88  
    89  	err = cbds.backend.Clear(ctx, dgst)
    90  	if err != nil {
    91  		return err
    92  	}
    93  	return nil
    94  }
    95  
    96  func (cbds *cachedBlobStatter) SetDescriptor(ctx context.Context, dgst digest.Digest, desc distribution.Descriptor) error {
    97  	if err := cbds.cache.SetDescriptor(ctx, dgst, desc); err != nil {
    98  		context.GetLogger(ctx).Errorf("error adding descriptor %v to cache: %v", desc.Digest, err)
    99  	}
   100  	return nil
   101  }