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backend: factor out connection limiting and parameter validation

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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.
This commit is contained in:
Michael Eischer
2023-04-07 23:02:35 +02:00
parent 8b5ab5b59f
commit 8e1e3844aa
13 changed files with 126 additions and 384 deletions
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44
internal/backend/rest/rest.go
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@@ -12,12 +12,9 @@ import (
"strings"
"github.com/restic/restic/internal/backend/layout"
"github.com/restic/restic/internal/backend/sema"
"github.com/restic/restic/internal/debug"
"github.com/restic/restic/internal/errors"
"github.com/restic/restic/internal/restic"
"github.com/cenkalti/backoff/v4"
)
// make sure the rest backend implements restic.Backend
@@ -27,7 +24,6 @@ var _ restic.Backend = &Backend{}
type Backend struct {
url *url.URL
connections uint
sem sema.Semaphore
client http.Client
layout.Layout
}
@@ -40,11 +36,6 @@ const (
// Open opens the REST backend with the given config.
func Open(cfg Config, rt http.RoundTripper) (*Backend, error) {
sem, err := sema.New(cfg.Connections)
if err != nil {
return nil, err
}
// use url without trailing slash for layout
url := cfg.URL.String()
if url[len(url)-1] == '/' {
@@ -56,7 +47,6 @@ func Open(cfg Config, rt http.RoundTripper) (*Backend, error) {
client: http.Client{Transport: rt},
Layout: &layout.RESTLayout{URL: url, Join: path.Join},
connections: cfg.Connections,
sem: sem,
}
return be, nil
@@ -123,10 +113,6 @@ func (b *Backend) HasAtomicReplace() bool {
// Save stores data in the backend at the handle.
func (b *Backend) Save(ctx context.Context, h restic.Handle, rd restic.RewindReader) error {
if err := h.Valid(); err != nil {
return backoff.Permanent(err)
}
ctx, cancel := context.WithCancel(ctx)
defer cancel()
@@ -143,9 +129,7 @@ func (b *Backend) Save(ctx context.Context, h restic.Handle, rd restic.RewindRea
// let's the server know what's coming.
req.ContentLength = rd.Length()
b.sem.GetToken()
resp, err := b.client.Do(req)
b.sem.ReleaseToken()
var cerr error
if resp != nil {
@@ -212,18 +196,6 @@ func (b *Backend) Load(ctx context.Context, h restic.Handle, length int, offset
}
func (b *Backend) openReader(ctx context.Context, h restic.Handle, length int, offset int64) (io.ReadCloser, error) {
if err := h.Valid(); err != nil {
return nil, backoff.Permanent(err)
}
if offset < 0 {
return nil, errors.New("offset is negative")
}
if length < 0 {
return nil, errors.Errorf("invalid length %d", length)
}
req, err := http.NewRequestWithContext(ctx, "GET", b.Filename(h), nil)
if err != nil {
return nil, errors.WithStack(err)
@@ -237,9 +209,7 @@ func (b *Backend) openReader(ctx context.Context, h restic.Handle, length int, o
req.Header.Set("Accept", ContentTypeV2)
debug.Log("Load(%v) send range %v", h, byteRange)
b.sem.GetToken()
resp, err := b.client.Do(req)
b.sem.ReleaseToken()
if err != nil {
if resp != nil {
@@ -264,19 +234,13 @@ func (b *Backend) openReader(ctx context.Context, h restic.Handle, length int, o
// Stat returns information about a blob.
func (b *Backend) Stat(ctx context.Context, h restic.Handle) (restic.FileInfo, error) {
if err := h.Valid(); err != nil {
return restic.FileInfo{}, backoff.Permanent(err)
}
req, err := http.NewRequestWithContext(ctx, http.MethodHead, b.Filename(h), nil)
if err != nil {
return restic.FileInfo{}, errors.WithStack(err)
}
req.Header.Set("Accept", ContentTypeV2)
b.sem.GetToken()
resp, err := b.client.Do(req)
b.sem.ReleaseToken()
if err != nil {
return restic.FileInfo{}, errors.WithStack(err)
}
@@ -309,19 +273,13 @@ func (b *Backend) Stat(ctx context.Context, h restic.Handle) (restic.FileInfo, e
// Remove removes the blob with the given name and type.
func (b *Backend) Remove(ctx context.Context, h restic.Handle) error {
if err := h.Valid(); err != nil {
return backoff.Permanent(err)
}
req, err := http.NewRequestWithContext(ctx, "DELETE", b.Filename(h), nil)
if err != nil {
return errors.WithStack(err)
}
req.Header.Set("Accept", ContentTypeV2)
b.sem.GetToken()
resp, err := b.client.Do(req)
b.sem.ReleaseToken()
if err != nil {
return errors.Wrap(err, "client.Do")
@@ -358,9 +316,7 @@ func (b *Backend) List(ctx context.Context, t restic.FileType, fn func(restic.Fi
}
req.Header.Set("Accept", ContentTypeV2)
b.sem.GetToken()
resp, err := b.client.Do(req)
b.sem.ReleaseToken()
if err != nil {
return errors.Wrap(err, "List")