mirror of
https://github.com/restic/restic.git
synced 2024-08-14 16:33:22 +02:00
275 lines
7.7 KiB
Go
275 lines
7.7 KiB
Go
package repository
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import (
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"context"
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"fmt"
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"sync"
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"time"
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"github.com/restic/restic/internal/backend"
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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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type lockContext struct {
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lock *restic.Lock
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cancel context.CancelFunc
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refreshWG sync.WaitGroup
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}
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type locker struct {
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retrySleepStart time.Duration
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retrySleepMax time.Duration
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refreshInterval time.Duration
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refreshabilityTimeout time.Duration
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}
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const defaultRefreshInterval = 5 * time.Minute
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var lockerInst = &locker{
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retrySleepStart: 5 * time.Second,
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retrySleepMax: 60 * time.Second,
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refreshInterval: defaultRefreshInterval,
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// consider a lock refresh failed a bit before the lock actually becomes stale
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// the difference allows to compensate for a small time drift between clients.
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refreshabilityTimeout: restic.StaleLockTimeout - defaultRefreshInterval*3/2,
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}
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func Lock(ctx context.Context, repo restic.Repository, exclusive bool, retryLock time.Duration, printRetry func(msg string), logger func(format string, args ...interface{})) (*Unlocker, context.Context, error) {
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return lockerInst.Lock(ctx, repo, exclusive, retryLock, printRetry, logger)
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}
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// Lock wraps the ctx such that it is cancelled when the repository is unlocked
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// cancelling the original context also stops the lock refresh
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func (l *locker) Lock(ctx context.Context, repo restic.Repository, exclusive bool, retryLock time.Duration, printRetry func(msg string), logger func(format string, args ...interface{})) (*Unlocker, context.Context, error) {
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lockFn := restic.NewLock
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if exclusive {
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lockFn = restic.NewExclusiveLock
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}
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var lock *restic.Lock
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var err error
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retrySleep := minDuration(l.retrySleepStart, retryLock)
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retryMessagePrinted := false
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retryTimeout := time.After(retryLock)
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retryLoop:
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for {
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lock, err = lockFn(ctx, repo)
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if err != nil && restic.IsAlreadyLocked(err) {
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if !retryMessagePrinted {
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printRetry(fmt.Sprintf("repo already locked, waiting up to %s for the lock\n", retryLock))
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retryMessagePrinted = true
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}
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debug.Log("repo already locked, retrying in %v", retrySleep)
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retrySleepCh := time.After(retrySleep)
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select {
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case <-ctx.Done():
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return nil, ctx, ctx.Err()
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case <-retryTimeout:
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debug.Log("repo already locked, timeout expired")
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// Last lock attempt
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lock, err = lockFn(ctx, repo)
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break retryLoop
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case <-retrySleepCh:
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retrySleep = minDuration(retrySleep*2, l.retrySleepMax)
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}
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} else {
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// anything else, either a successful lock or another error
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break retryLoop
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}
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}
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if restic.IsInvalidLock(err) {
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return nil, ctx, errors.Fatalf("%v\n\nthe `unlock --remove-all` command can be used to remove invalid locks. Make sure that no other restic process is accessing the repository when running the command", err)
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}
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if err != nil {
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return nil, ctx, fmt.Errorf("unable to create lock in backend: %w", err)
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}
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debug.Log("create lock %p (exclusive %v)", lock, exclusive)
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ctx, cancel := context.WithCancel(ctx)
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lockInfo := &lockContext{
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lock: lock,
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cancel: cancel,
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}
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lockInfo.refreshWG.Add(2)
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refreshChan := make(chan struct{})
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forceRefreshChan := make(chan refreshLockRequest)
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go l.refreshLocks(ctx, repo.Backend(), lockInfo, refreshChan, forceRefreshChan, logger)
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go l.monitorLockRefresh(ctx, lockInfo, refreshChan, forceRefreshChan, logger)
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return &Unlocker{lockInfo}, ctx, nil
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}
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func minDuration(a, b time.Duration) time.Duration {
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if a <= b {
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return a
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}
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return b
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}
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type refreshLockRequest struct {
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result chan bool
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}
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func (l *locker) refreshLocks(ctx context.Context, backend backend.Backend, lockInfo *lockContext, refreshed chan<- struct{}, forceRefresh <-chan refreshLockRequest, logger func(format string, args ...interface{})) {
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debug.Log("start")
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lock := lockInfo.lock
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ticker := time.NewTicker(l.refreshInterval)
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lastRefresh := lock.Time
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defer func() {
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ticker.Stop()
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// ensure that the context was cancelled before removing the lock
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lockInfo.cancel()
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// remove the lock from the repo
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debug.Log("unlocking repository with lock %v", lock)
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if err := lock.Unlock(); err != nil {
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debug.Log("error while unlocking: %v", err)
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logger("error while unlocking: %v", err)
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}
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lockInfo.refreshWG.Done()
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}()
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for {
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select {
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case <-ctx.Done():
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debug.Log("terminate")
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return
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case req := <-forceRefresh:
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debug.Log("trying to refresh stale lock")
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// keep on going if our current lock still exists
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success := tryRefreshStaleLock(ctx, backend, lock, lockInfo.cancel, logger)
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// inform refresh goroutine about forced refresh
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select {
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case <-ctx.Done():
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case req.result <- success:
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}
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if success {
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// update lock refresh time
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lastRefresh = lock.Time
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}
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case <-ticker.C:
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if time.Since(lastRefresh) > l.refreshabilityTimeout {
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// the lock is too old, wait until the expiry monitor cancels the context
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continue
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}
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debug.Log("refreshing locks")
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err := lock.Refresh(context.TODO())
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if err != nil {
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logger("unable to refresh lock: %v\n", err)
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} else {
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lastRefresh = lock.Time
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// inform monitor goroutine about successful refresh
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select {
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case <-ctx.Done():
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case refreshed <- struct{}{}:
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}
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}
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}
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}
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}
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func (l *locker) monitorLockRefresh(ctx context.Context, lockInfo *lockContext, refreshed <-chan struct{}, forceRefresh chan<- refreshLockRequest, logger func(format string, args ...interface{})) {
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// time.Now() might use a monotonic timer which is paused during standby
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// convert to unix time to ensure we compare real time values
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lastRefresh := time.Now().UnixNano()
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pollDuration := 1 * time.Second
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if l.refreshInterval < pollDuration {
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// required for TestLockFailedRefresh
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pollDuration = l.refreshInterval / 5
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}
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// timers are paused during standby, which is a problem as the refresh timeout
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// _must_ expire if the host was too long in standby. Thus fall back to periodic checks
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// https://github.com/golang/go/issues/35012
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ticker := time.NewTicker(pollDuration)
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defer func() {
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ticker.Stop()
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lockInfo.cancel()
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lockInfo.refreshWG.Done()
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}()
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var refreshStaleLockResult chan bool
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for {
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select {
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case <-ctx.Done():
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debug.Log("terminate expiry monitoring")
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return
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case <-refreshed:
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if refreshStaleLockResult != nil {
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// ignore delayed refresh notifications while the stale lock is refreshed
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continue
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}
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lastRefresh = time.Now().UnixNano()
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case <-ticker.C:
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if time.Now().UnixNano()-lastRefresh < l.refreshabilityTimeout.Nanoseconds() || refreshStaleLockResult != nil {
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continue
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}
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debug.Log("trying to refreshStaleLock")
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// keep on going if our current lock still exists
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refreshReq := refreshLockRequest{
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result: make(chan bool),
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}
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refreshStaleLockResult = refreshReq.result
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// inform refresh goroutine about forced refresh
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select {
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case <-ctx.Done():
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case forceRefresh <- refreshReq:
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}
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case success := <-refreshStaleLockResult:
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if success {
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lastRefresh = time.Now().UnixNano()
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refreshStaleLockResult = nil
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continue
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}
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logger("Fatal: failed to refresh lock in time\n")
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return
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}
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}
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}
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func tryRefreshStaleLock(ctx context.Context, be backend.Backend, lock *restic.Lock, cancel context.CancelFunc, logger func(format string, args ...interface{})) bool {
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freeze := backend.AsBackend[backend.FreezeBackend](be)
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if freeze != nil {
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debug.Log("freezing backend")
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freeze.Freeze()
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defer freeze.Unfreeze()
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}
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err := lock.RefreshStaleLock(ctx)
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if err != nil {
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logger("failed to refresh stale lock: %v\n", err)
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// cancel context while the backend is still frozen to prevent accidental modifications
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cancel()
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return false
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}
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return true
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}
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type Unlocker struct {
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info *lockContext
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}
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func (l *Unlocker) Unlock() {
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l.info.cancel()
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l.info.refreshWG.Wait()
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}
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