woodpecker/vendor/github.com/djherbis/fscache/distrib.go
2016-04-12 17:27:24 -07:00

85 lines
1.8 KiB
Go

package fscache
import (
"bytes"
"crypto/sha1"
"encoding/binary"
"io"
)
// Distributor provides a way to partition keys into Caches.
type Distributor interface {
// GetCache will always return the same Cache for the same key.
GetCache(key string) Cache
// Clean should wipe all the caches this Distributor manages
Clean() error
}
// stdDistribution distributes the keyspace evenly.
func stdDistribution(key string, n uint64) uint64 {
h := sha1.New()
io.WriteString(h, key)
buf := bytes.NewBuffer(h.Sum(nil)[:8])
i, _ := binary.ReadUvarint(buf)
return i % n
}
// NewDistributor returns a Distributor which evenly distributes the keyspace
// into the passed caches.
func NewDistributor(caches ...Cache) Distributor {
if len(caches) == 0 {
return nil
}
return &distrib{
distribution: stdDistribution,
caches: caches,
size: uint64(len(caches)),
}
}
type distrib struct {
distribution func(key string, n uint64) uint64
caches []Cache
size uint64
}
func (d *distrib) GetCache(key string) Cache {
return d.caches[d.distribution(key, d.size)]
}
// BUG(djherbis): Return an error if cleaning fails
func (d *distrib) Clean() error {
for _, c := range d.caches {
c.Clean()
}
return nil
}
// NewPartition returns a Cache which uses the Caches defined by the passed Distributor.
func NewPartition(d Distributor) Cache {
return &partition{
distributor: d,
}
}
type partition struct {
distributor Distributor
}
func (p *partition) Get(key string) (ReadAtCloser, io.WriteCloser, error) {
return p.distributor.GetCache(key).Get(key)
}
func (p *partition) Remove(key string) error {
return p.distributor.GetCache(key).Remove(key)
}
func (p *partition) Exists(key string) bool {
return p.distributor.GetCache(key).Exists(key)
}
func (p *partition) Clean() error {
return p.distributor.Clean()
}