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restic/internal/restorer/fileswriter.go
Igor Fedorenko f17ffa0283 restorer: Allow writing target file blobs out of order
Much simpler implementation that guarantees each required pack
is downloaded only once (and hence does not need to manage
pack cache). Also improves large file restore performance.

Signed-off-by: Igor Fedorenko <igor@ifedorenko.com>
2020-02-26 16:14:45 +01:00

93 lines
1.8 KiB
Go

package restorer
import (
"os"
"sync"
"github.com/cespare/xxhash"
)
// writes blobs to target files.
// multiple files can be written to concurrently.
// multiple blobs can be concurrently written to the same file.
// TODO I am not 100% convinced this is necessary, i.e. it may be okay
// to use multiple os.File to write to the same target file
type filesWriter struct {
buckets []filesWriterBucket
}
type filesWriterBucket struct {
lock sync.Mutex
files map[string]*os.File
users map[string]int
}
func newFilesWriter(count int) *filesWriter {
buckets := make([]filesWriterBucket, count)
for b := 0; b < count; b++ {
buckets[b].files = make(map[string]*os.File)
buckets[b].users = make(map[string]int)
}
return &filesWriter{
buckets: buckets,
}
}
func (w *filesWriter) writeToFile(path string, blob []byte, offset int64, create bool) error {
bucket := &w.buckets[uint(xxhash.Sum64String(path))%uint(len(w.buckets))]
acquireWriter := func() (*os.File, error) {
bucket.lock.Lock()
defer bucket.lock.Unlock()
if wr, ok := bucket.files[path]; ok {
bucket.users[path]++
return wr, nil
}
var flags int
if create {
flags = os.O_CREATE | os.O_TRUNC | os.O_WRONLY
} else {
flags = os.O_WRONLY
}
wr, err := os.OpenFile(path, flags, 0600)
if err != nil {
return nil, err
}
bucket.files[path] = wr
bucket.users[path] = 1
return wr, nil
}
releaseWriter := func(wr *os.File) error {
bucket.lock.Lock()
defer bucket.lock.Unlock()
if bucket.users[path] == 1 {
delete(bucket.files, path)
delete(bucket.users, path)
return wr.Close()
}
bucket.users[path]--
return nil
}
wr, err := acquireWriter()
if err != nil {
return err
}
_, err = wr.WriteAt(blob, offset)
if err != nil {
releaseWriter(wr)
return err
}
return releaseWriter(wr)
}