docker-volume-backup/cmd/backup/lock.go

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// Copyright 2022 - Offen Authors <hioffen@posteo.de>
// SPDX-License-Identifier: MPL-2.0
package main
import (
"errors"
"fmt"
"time"
"github.com/gofrs/flock"
)
// lock opens a lockfile at the given location, keeping it locked until the
// caller invokes the returned release func. In case the lock is currently blocked
// by another execution, it will repeatedly retry until the lock is available
// or the given timeout is exceeded.
func (s *script) lock(lockfile string) (func() error, error) {
start := time.Now()
defer func() {
s.stats.LockedTime = time.Now().Sub(start)
}()
retry := time.NewTicker(5 * time.Second)
defer retry.Stop()
deadline := time.NewTimer(s.c.LockTimeout)
defer deadline.Stop()
fileLock := flock.New(lockfile)
for {
acquired, err := fileLock.TryLock()
if err != nil {
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return noop, fmt.Errorf("lock: error trying to lock: %w", err)
}
if acquired {
if s.encounteredLock {
s.logger.Info("Acquired exclusive lock on subsequent attempt, ready to continue.")
}
return fileLock.Unlock, nil
}
if !s.encounteredLock {
s.logger.Info(
fmt.Sprintf(
"Exclusive lock was not available on first attempt. Will retry until it becomes available or the timeout of %s is exceeded.",
s.c.LockTimeout,
),
)
s.encounteredLock = true
}
select {
case <-retry.C:
continue
case <-deadline.C:
return noop, errors.New("lock: timed out waiting for lockfile to become available")
}
}
}