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lock.go
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lock.go
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package main
import (
"time"
log "github.com/Sirupsen/logrus"
"github.com/hashicorp/consul/api"
)
const lockWaitTime = 15 * time.Second
// LockHelper is a struct to help with acquiring and holding a Consul lock
type LockHelper struct {
// The name of the service/node being fought over for the lock
target string
// Consul client object to use for making lock API calls
client *api.Client
// The Lock object to use for acquisition
lock *api.Lock
// A channel used for interrupting the start() loop
stopCh chan struct{}
// A channel used for interrupting the lock acquisition
lockCh chan struct{}
// A function to be run after acquiring the lock
callback func()
// Indicates whether we currently hold the lock
acquired bool
}
// Try to acquire the lock if we don't have it, and then block until we lose it
func (l *LockHelper) start() {
shutdown := false
for !shutdown {
select {
case <-l.stopCh:
shutdown = true
default:
log.Debugf("Waiting to acquire lock on %s...", l.target)
// Lock() returns an interrupt channel on success that can be used to block until we lose the lock
intChan, err := l.lock.Lock(l.lockCh)
if intChan != nil {
// Run the callback to update check states before setting acquired to true
l.callback()
l.acquired = true
log.Infof("Acquired lock for %s", l.target)
<-intChan
l.acquired = false
log.Infof("Lost lock for %s", l.target)
l.lock.Unlock()
l.lock.Destroy()
} else {
if err != nil {
log.Warnf("Error getting lock for %s: %s", l.target, err)
}
time.Sleep(lockWaitTime)
}
}
}
}
// Shut down the lock acquisition loop, which will cause the lock to get released if it's currently acquired
func (l *LockHelper) stop() {
l.stopCh <- struct{}{}
l.lockCh <- struct{}{}
l.lock.Unlock()
l.lock.Destroy()
l.acquired = false
}