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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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34
internal/backend/local/local.go
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@@ -10,7 +10,6 @@ import (
"github.com/restic/restic/internal/backend"
"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/fs"
@@ -22,7 +21,6 @@ import (
// Local is a backend in a local directory.
type Local struct {
Config
sem sema.Semaphore
layout.Layout
backend.Modes
}
@@ -38,11 +36,6 @@ func open(ctx context.Context, cfg Config) (*Local, error) {
return nil, err
}
sem, err := sema.New(cfg.Connections)
if err != nil {
return nil, err
}
fi, err := fs.Stat(l.Filename(restic.Handle{Type: restic.ConfigFile}))
m := backend.DeriveModesFromFileInfo(fi, err)
debug.Log("using (%03O file, %03O dir) permissions", m.File, m.Dir)
@@ -50,7 +43,6 @@ func open(ctx context.Context, cfg Config) (*Local, error) {
return &Local{
Config: cfg,
Layout: l,
sem: sem,
Modes: m,
}, nil
}
@@ -114,10 +106,6 @@ func (b *Local) IsNotExist(err error) bool {
// Save stores data in the backend at the handle.
func (b *Local) Save(ctx context.Context, h restic.Handle, rd restic.RewindReader) (err error) {
if err := h.Valid(); err != nil {
return backoff.Permanent(err)
}
finalname := b.Filename(h)
dir := filepath.Dir(finalname)
@@ -128,9 +116,6 @@ func (b *Local) Save(ctx context.Context, h restic.Handle, rd restic.RewindReade
}
}()
b.sem.GetToken()
defer b.sem.ReleaseToken()
// Create new file with a temporary name.
tmpname := filepath.Base(finalname) + "-tmp-"
f, err := tempFile(dir, tmpname)
@@ -216,40 +201,28 @@ func (b *Local) Load(ctx context.Context, h restic.Handle, length int, offset in
}
func (b *Local) openReader(ctx context.Context, h restic.Handle, length int, offset int64) (io.ReadCloser, error) {
b.sem.GetToken()
f, err := fs.Open(b.Filename(h))
if err != nil {
b.sem.ReleaseToken()
return nil, err
}
if offset > 0 {
_, err = f.Seek(offset, 0)
if err != nil {
b.sem.ReleaseToken()
_ = f.Close()
return nil, err
}
}
r := b.sem.ReleaseTokenOnClose(f, nil)
if length > 0 {
return backend.LimitReadCloser(r, int64(length)), nil
return backend.LimitReadCloser(f, int64(length)), nil
}
return r, nil
return f, nil
}
// Stat returns information about a blob.
func (b *Local) Stat(ctx context.Context, h restic.Handle) (restic.FileInfo, error) {
if err := h.Valid(); err != nil {
return restic.FileInfo{}, backoff.Permanent(err)
}
b.sem.GetToken()
defer b.sem.ReleaseToken()
fi, err := fs.Stat(b.Filename(h))
if err != nil {
return restic.FileInfo{}, errors.WithStack(err)
@@ -262,9 +235,6 @@ func (b *Local) Stat(ctx context.Context, h restic.Handle) (restic.FileInfo, err
func (b *Local) Remove(ctx context.Context, h restic.Handle) error {
fn := b.Filename(h)
b.sem.GetToken()
defer b.sem.ReleaseToken()
// reset read-only flag
err := fs.Chmod(fn, 0666)
if err != nil && !os.IsPermission(err) {