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lock.go
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lock.go
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package drivers
import (
"context"
"errors"
"math/rand"
"time"
)
const (
// MutexTableName is the name being used for the mutex table
MutexTableName = "db_lock"
// minWaitInterval is the minimum amount of time to wait between locking attempts
minWaitInterval = 1 * time.Second
// maxWaitInterval is the maximum amount of time to wait between locking attempts
maxWaitInterval = 5 * time.Minute
// pollWaitInterval is the usual time to wait between unsuccessful locking attempts
pollWaitInterval = 1 * time.Second
// jitterWaitInterval is the amount of jitter to add when waiting to avoid thundering herds
jitterWaitInterval = minWaitInterval / 2
// TTL is the interval after which a locked mutex will expire unless refreshed
TTL = time.Second * 15
// RefreshInterval is the interval on which the mutex will be refreshed when locked
RefreshInterval = TTL / 2
)
// MakeLockKey returns the prefixed key used to namespace mutex keys.
func MakeLockKey(key string) (string, error) {
if key == "" {
return "", errors.New("must specify valid mutex key")
}
return key, nil
}
// NextWaitInterval determines how long to wait until the next lock retry.
func NextWaitInterval(lastWaitInterval time.Duration, err error) time.Duration {
nextWaitInterval := lastWaitInterval
if nextWaitInterval <= 0 {
nextWaitInterval = minWaitInterval
}
if err != nil {
nextWaitInterval *= 2
if nextWaitInterval > maxWaitInterval {
nextWaitInterval = maxWaitInterval
}
} else {
nextWaitInterval = pollWaitInterval
}
// Add some jitter to avoid unnecessary collision between competing other instances.
nextWaitInterval -= time.Duration(rand.Int63n(int64(jitterWaitInterval) / 2))
return nextWaitInterval
}
type Locker interface {
// Lock locks m unless the context is canceled. If the mutex is already locked by any other
// instance, including the current one, the calling goroutine blocks until the mutex can be locked,
// or the context is canceled.
//
// The mutex is locked only if a nil error is returned.
Lock(ctx context.Context) error
Unlock() error
}
type Lockable interface {
DriverName() string
}
// IsLockable returns whether the given instance satisfies
// drivers.Lockable or not.
func IsLockable(x interface{}) bool {
_, ok := x.(Lockable)
return ok
}