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swift backend: fix premature release of semaphore in Load() & document

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concurrency issue in List().

refactor wrapReader from b2 -> semaphore so it can be used elsewhere.

As per discussion in PR #1399.
This commit is contained in:
George Armhold 2017-11-02 12:38:17 -04:00
parent 99ac0da4bc
commit 8515d093e0
3 changed files with 49 additions and 48 deletions
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12
internal/backend/swift/swift.go
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@ -129,11 +129,6 @@ func (be *beSwift) Load(ctx context.Context, h restic.Handle, length int, offset
objName := be.Filename(h)
be.sem.GetToken()
defer func() {
be.sem.ReleaseToken()
}()
headers := swift.Headers{}
if offset > 0 {
headers["Range"] = fmt.Sprintf("bytes=%d-", offset)
@ -147,13 +142,15 @@ func (be *beSwift) Load(ctx context.Context, h restic.Handle, length int, offset
debug.Log("Load(%v) send range %v", h, headers["Range"])
}
be.sem.GetToken()
obj, _, err := be.conn.ObjectOpen(be.container, objName, false, headers)
if err != nil {
debug.Log(" err %v", err)
be.sem.ReleaseToken()
return nil, errors.Wrap(err, "conn.ObjectOpen")
}
return obj, nil
return be.sem.ReleaseTokenOnClose(obj, nil), nil
}
// Save stores data in the backend at the handle.
@ -243,6 +240,9 @@ func (be *beSwift) List(ctx context.Context, t restic.FileType) <-chan string {
go func() {
defer close(ch)
// NB: unfortunately we can't protect this with be.sem.GetToken() here.
// Doing so would enable a deadlock situation (PR: gh-1399), as ObjectsWalk()
// starts its own goroutine and returns results via a channel.
err := be.conn.ObjectsWalk(be.container, &swift.ObjectsOpts{Prefix: prefix},
func(opts *swift.ObjectsOpts) (interface{}, error) {
newObjects, err := be.conn.ObjectNames(be.container, opts)