/
election.go
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/
election.go
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// Copyright 2018 Google LLC. All Rights Reserved.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
// Package testonly contains an Election implementation for testing.
package testonly
import (
"context"
"sync"
"github.com/google/trillian/util/election2"
)
// Factory allows creating Election instances for testing.
var Factory factory
// Election implements election2.Election interface for testing.
type Election struct {
isMaster bool
revision int
mu sync.Mutex
cond *sync.Cond
}
// NewElection returns a new initialized Election for testing.
func NewElection() *Election {
e := &Election{}
e.cond = sync.NewCond(&e.mu)
return e
}
// update updates this instance's mastership status. Must be called under lock.
func (e *Election) update(isMaster bool) {
e.isMaster = isMaster
e.revision++
e.cond.Broadcast()
}
// Await sets this instance to be the master. It always succeeds. To imitate
// errors and/or blocking behavior use the Decorator type.
func (e *Election) Await(ctx context.Context) error {
e.mu.Lock()
defer e.mu.Unlock()
if !e.isMaster {
e.update(true)
}
return nil
}
// WithMastership returns mastership context, which gets canceled if / when
// this instance is not / stops being the master.
func (e *Election) WithMastership(ctx context.Context) (context.Context, error) {
e.mu.Lock()
defer e.mu.Unlock()
if !e.isMaster {
cctx, cancel := context.WithCancel(ctx)
cancel()
return cctx, nil
}
cctx, cancel := watchContext(ctx, &e.mu, e.cond) // Notify e.cond on ctx cancelation.
rev := e.revision
go func() { // Watch mastership and the context in the background.
defer cancel()
e.mu.Lock()
defer e.mu.Unlock()
for e.isMaster && e.revision == rev && ctx.Err() == nil {
e.cond.Wait()
}
}()
return cctx, nil
}
// Resign resets mastership.
func (e *Election) Resign(ctx context.Context) error {
e.mu.Lock()
defer e.mu.Unlock()
e.update(false)
return nil
}
// Close resets mastership permanently.
func (e *Election) Close(ctx context.Context) error {
return e.Resign(ctx)
}
func watchContext(ctx context.Context, l sync.Locker, cond *sync.Cond) (context.Context, context.CancelFunc) {
cctx, cancel := context.WithCancel(ctx)
go func() {
defer cancel()
<-cctx.Done()
l.Lock() // Avoid racing with cond waiters on ctx status.
defer l.Unlock()
cond.Broadcast()
}()
return cctx, cancel
}
// factory allows creating Election instances.
type factory struct{}
// NewElection creates a new Election instance.
// TODO(pavelkalinnikov): Use resourceID in tests with multiple resources.
func (f factory) NewElection(ctx context.Context, resourceID string) (election2.Election, error) {
return NewElection(), nil
}