pkg/blobserver/enumerate.go

/*
Copyright 2013 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 (
	"sync"

	"camlistore.org/pkg/blobref"
)

// EnumerateAll runs fn for each blob in src.
// If fn returns an error, iteration stops and fn isn't called again.
// EnumerateAll will not return concurrently with fn.
func EnumerateAll(src BlobEnumerator, fn func(blobref.SizedBlobRef) error) error {
	const batchSize = 1000
	var mu sync.Mutex // protects returning with an error while fn is still running
	after := ""
	errc := make(chan error, 1)
	for {
		ch := make(chan blobref.SizedBlobRef, 16)
		n := 0
		go func() {
			var err error
			for sb := range ch {
				if err != nil {
					continue
				}
				mu.Lock()
				err = fn(sb)
				mu.Unlock()
				after = sb.BlobRef.String()
				n++
			}
			errc <- err
		}()
		err := src.EnumerateBlobs(ch, after, batchSize, 0)
		if err != nil {
			mu.Lock() // make sure fn callback finished; no need to unlock
			return err
		}
		if err := <-errc; err != nil {
			return err
		}
		if n == 0 {
			return nil
		}
	}
}