forked from TrueCloudLab/distribution
80 lines
2 KiB
Go
80 lines
2 KiB
Go
package cache
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import (
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"github.com/docker/distribution/context"
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"github.com/docker/distribution/digest"
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"github.com/docker/distribution"
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)
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// Metrics is used to hold metric counters
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// related to the number of times a cache was
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// hit or missed.
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type Metrics struct {
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Requests uint64
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Hits uint64
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Misses uint64
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}
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// MetricsTracker represents a metric tracker
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// which simply counts the number of hits and misses.
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type MetricsTracker interface {
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Hit()
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Miss()
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Metrics() Metrics
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}
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type cachedBlobStatter struct {
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cache distribution.BlobDescriptorService
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backend distribution.BlobStatter
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tracker MetricsTracker
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}
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// NewCachedBlobStatter creates a new statter which prefers a cache and
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// falls back to a backend.
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func NewCachedBlobStatter(cache distribution.BlobDescriptorService, backend distribution.BlobStatter) distribution.BlobStatter {
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return &cachedBlobStatter{
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cache: cache,
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backend: backend,
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}
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}
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// NewCachedBlobStatterWithMetrics creates a new statter which prefers a cache and
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// falls back to a backend. Hits and misses will send to the tracker.
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func NewCachedBlobStatterWithMetrics(cache distribution.BlobDescriptorService, backend distribution.BlobStatter, tracker MetricsTracker) distribution.BlobStatter {
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return &cachedBlobStatter{
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cache: cache,
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backend: backend,
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tracker: tracker,
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}
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}
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func (cbds *cachedBlobStatter) Stat(ctx context.Context, dgst digest.Digest) (distribution.Descriptor, error) {
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desc, err := cbds.cache.Stat(ctx, dgst)
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if err != nil {
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if err != distribution.ErrBlobUnknown {
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context.GetLogger(ctx).Errorf("error retrieving descriptor from cache: %v", err)
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}
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goto fallback
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}
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if cbds.tracker != nil {
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cbds.tracker.Hit()
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}
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return desc, nil
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fallback:
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if cbds.tracker != nil {
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cbds.tracker.Miss()
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}
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desc, err = cbds.backend.Stat(ctx, dgst)
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if err != nil {
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return desc, err
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}
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if err := cbds.cache.SetDescriptor(ctx, dgst, desc); err != nil {
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context.GetLogger(ctx).Errorf("error adding descriptor %v to cache: %v", desc.Digest, err)
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}
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return desc, err
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}
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