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/*
Copyright 2011 Google Inc.
Licensed under the Apache License, Version 2.0 (the "License");
you may not use this file except in compliance with the License.
You may obtain a copy of the License at
http://www.apache.org/licenses/LICENSE-2.0
Unless required by applicable law or agreed to in writing, software
distributed under the License is distributed on an "AS IS" BASIS,
WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
See the License for the specific language governing permissions and
limitations under the License.
*/
package blobserver
import (
"camlistore.org/pkg/blob"
"golang.org/x/net/context"
)
const buffered = 8
// MergedEnumerate implements the BlobEnumerator interface by
// merge-joining 0 or more sources.
func MergedEnumerate(ctx context.Context, dest chan<- blob.SizedRef, sources []BlobEnumerator, after string, limit int) error {
return mergedEnumerate(ctx, dest, len(sources), func(i int) BlobEnumerator { return sources[i] }, after, limit)
}
// MergedEnumerateStorage implements the BlobEnumerator interface by
// merge-joining 0 or more sources.
//
// In this version, the sources implement the Storage interface, even
// though only the BlobEnumerator interface is used.
func MergedEnumerateStorage(ctx context.Context, dest chan<- blob.SizedRef, sources []Storage, after string, limit int) error {
return mergedEnumerate(ctx, dest, len(sources), func(i int) BlobEnumerator { return sources[i] }, after, limit)
}
func mergedEnumerate(ctx context.Context, dest chan<- blob.SizedRef, nsrc int, getSource func(int) BlobEnumerator, after string, limit int) error {
defer close(dest)
subctx, cancel := context.WithCancel(ctx)
defer cancel()
errch := make(chan error, nsrc+1) // +1 for nil
startEnum := func(source BlobEnumerator) *blob.ChanPeeker {
ch := make(chan blob.SizedRef, buffered)
go func() {
err := source.EnumerateBlobs(subctx, ch, after, limit)
if err != nil {
errch <- err
}
}()
return &blob.ChanPeeker{Ch: ch}
}
peekers := make([]*blob.ChanPeeker, 0, nsrc)
for i := 0; i < nsrc; i++ {
peekers = append(peekers, startEnum(getSource(i)))
}
nSent := 0
var lastSent blob.Ref
tooLow := func(br blob.Ref) bool { return lastSent.Valid() && (br == lastSent || br.Less(lastSent)) }
for nSent < limit {
lowestIdx := -1
var lowest blob.SizedRef
for idx, peeker := range peekers {
for !peeker.Closed() && tooLow(peeker.MustPeek().Ref) {
peeker.Take()
}
if peeker.Closed() {
continue
}
sb := peeker.MustPeek() // can't be nil if not Closed
if lowestIdx == -1 || sb.Ref.Less(lowest.Ref) {
lowestIdx = idx
lowest = sb
}
}
if lowestIdx == -1 {
// all closed
break
}
select {
case dest <- lowest:
nSent++
lastSent = lowest.Ref
case <-ctx.Done():
return ctx.Err()
case err := <-errch:
return err
}
}
// If any part returns an error, we return an error.
errch <- nil
return <-errch
}
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