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8e1e3844aa
The SemaphoreBackend now uniformly enforces the limit of concurrent backend operations. In addition, it unifies the parameter validation. The List() methods no longer uses a semaphore. Restic already never runs multiple list operations in parallel. By managing the semaphore in a wrapper backend, the sections that hold a semaphore token grow slightly. However, the main bottleneck is IO, so this shouldn't make much of a difference. The key insight that enables the SemaphoreBackend is that all of the complex semaphore handling in `openReader()` still happens within the original call to `Load()`. Thus, getting and releasing the semaphore tokens can be refactored to happen directly in `Load()`. This eliminates the need for wrapping the reader in `openReader()` to release the token.
118 lines
3.1 KiB
Go
118 lines
3.1 KiB
Go
package backend
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import (
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"bytes"
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"context"
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"fmt"
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"io"
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"github.com/restic/restic/internal/debug"
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"github.com/restic/restic/internal/errors"
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"github.com/restic/restic/internal/restic"
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)
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// LoadAll reads all data stored in the backend for the handle into the given
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// buffer, which is truncated. If the buffer is not large enough or nil, a new
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// one is allocated.
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func LoadAll(ctx context.Context, buf []byte, be restic.Backend, h restic.Handle) ([]byte, error) {
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retriedInvalidData := false
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err := be.Load(ctx, h, 0, 0, func(rd io.Reader) error {
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// make sure this is idempotent, in case an error occurs this function may be called multiple times!
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wr := bytes.NewBuffer(buf[:0])
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_, cerr := io.Copy(wr, rd)
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if cerr != nil {
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return cerr
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}
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buf = wr.Bytes()
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// retry loading damaged data only once. If a file fails to download correctly
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// the second time, then it is likely corrupted at the backend. Return the data
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// to the caller in that case to let it decide what to do with the data.
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if !retriedInvalidData && h.Type != restic.ConfigFile {
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id, err := restic.ParseID(h.Name)
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if err == nil && !restic.Hash(buf).Equal(id) {
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debug.Log("retry loading broken blob %v", h)
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retriedInvalidData = true
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return errors.Errorf("loadAll(%v): invalid data returned", h)
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}
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}
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return nil
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})
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if err != nil {
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return nil, err
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}
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return buf, nil
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}
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// LimitedReadCloser wraps io.LimitedReader and exposes the Close() method.
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type LimitedReadCloser struct {
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io.Closer
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io.LimitedReader
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}
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// LimitReadCloser returns a new reader wraps r in an io.LimitedReader, but also
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// exposes the Close() method.
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func LimitReadCloser(r io.ReadCloser, n int64) *LimitedReadCloser {
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return &LimitedReadCloser{Closer: r, LimitedReader: io.LimitedReader{R: r, N: n}}
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}
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// DefaultLoad implements Backend.Load using lower-level openReader func
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func DefaultLoad(ctx context.Context, h restic.Handle, length int, offset int64,
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openReader func(ctx context.Context, h restic.Handle, length int, offset int64) (io.ReadCloser, error),
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fn func(rd io.Reader) error) error {
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rd, err := openReader(ctx, h, length, offset)
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if err != nil {
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return err
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}
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err = fn(rd)
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if err != nil {
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_ = rd.Close() // ignore secondary errors closing the reader
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return err
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}
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return rd.Close()
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}
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type memorizedLister struct {
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fileInfos []restic.FileInfo
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tpe restic.FileType
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}
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func (m *memorizedLister) List(ctx context.Context, t restic.FileType, fn func(restic.FileInfo) error) error {
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if t != m.tpe {
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return fmt.Errorf("filetype mismatch, expected %s got %s", m.tpe, t)
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}
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for _, fi := range m.fileInfos {
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if ctx.Err() != nil {
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break
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}
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err := fn(fi)
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if err != nil {
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return err
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}
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}
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return ctx.Err()
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}
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func MemorizeList(ctx context.Context, be restic.Lister, t restic.FileType) (restic.Lister, error) {
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if _, ok := be.(*memorizedLister); ok {
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return be, nil
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}
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var fileInfos []restic.FileInfo
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err := be.List(ctx, t, func(fi restic.FileInfo) error {
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fileInfos = append(fileInfos, fi)
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return nil
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})
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if err != nil {
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return nil, err
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}
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return &memorizedLister{
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fileInfos: fileInfos,
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tpe: t,
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}, nil
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}
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