55 lines
1.7 KiB
Go
55 lines
1.7 KiB
Go
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package state
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import (
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"sync"
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"time"
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)
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// Delay is used to mark certain locks as unacquirable. When a lock is
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// forcefully released (failing health check, destroyed session, etc.), it is
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// subject to the LockDelay impossed by the session. This prevents another
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// session from acquiring the lock for some period of time as a protection
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// against split-brains. This is inspired by the lock-delay in Chubby. Because
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// this relies on wall-time, we cannot assume all peers perceive time as flowing
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// uniformly. This means KVSLock MUST ignore lockDelay, since the lockDelay may
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// have expired on the leader, but not on the follower. Rejecting the lock could
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// result in inconsistencies in the FSMs due to the rate time progresses. Instead,
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// only the opinion of the leader is respected, and the Raft log is never
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// questioned.
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type Delay struct {
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// delay has the set of active delay expiration times, organized by key.
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delay map[string]time.Time
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// lock protects the delay map.
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lock sync.RWMutex
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}
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// NewDelay returns a new delay manager.
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func NewDelay() *Delay {
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return &Delay{delay: make(map[string]time.Time)}
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}
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// GetExpiration returns the expiration time of a key lock delay. This must be
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// checked on the leader node, and not in KVSLock due to the variability of
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// clocks.
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func (d *Delay) GetExpiration(key string) time.Time {
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d.lock.RLock()
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expires := d.delay[key]
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d.lock.RUnlock()
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return expires
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}
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// SetExpiration sets the expiration time for the lock delay to the given
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// delay from the given now time.
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func (d *Delay) SetExpiration(key string, now time.Time, delay time.Duration) {
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d.lock.Lock()
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defer d.lock.Unlock()
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d.delay[key] = now.Add(delay)
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time.AfterFunc(delay, func() {
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d.lock.Lock()
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delete(d.delay, key)
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d.lock.Unlock()
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})
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}
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