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barrier.go
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barrier.go
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package recipe
import (
"context"
v3 "github.com/oldnicke/etcd/clientv3"
"github.com/oldnicke/etcd/mvcc/mvccpb"
)
// Barrier creates a key in etcd to block processes, then deletes the key to
// release all blocked processes.
type Barrier struct {
client *v3.Client
ctx context.Context
key string
}
func NewBarrier(client *v3.Client, key string) *Barrier {
return &Barrier{client, context.TODO(), key}
}
// Hold creates the barrier key causing processes to block on Wait.
func (b *Barrier) Hold() error {
_, err := newKey(b.client, b.key, v3.NoLease)
return err
}
// Release deletes the barrier key to unblock all waiting processes.
func (b *Barrier) Release() error {
_, err := b.client.Delete(b.ctx, b.key)
return err
}
// Wait blocks on the barrier key until it is deleted. If there is no key, Wait
// assumes Release has already been called and returns immediately.
func (b *Barrier) Wait() error {
resp, err := b.client.Get(b.ctx, b.key, v3.WithFirstKey()...)
if err != nil {
return err
}
if len(resp.Kvs) == 0 {
// key already removed
return nil
}
_, err = WaitEvents(
b.client,
b.key,
resp.Header.Revision,
[]mvccpb.Event_EventType{mvccpb.PUT, mvccpb.DELETE})
return err
}