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subscriptions.go
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subscriptions.go
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// Copyright 2017 Monax Industries Limited
//
// 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 rpc
import (
"context"
"fmt"
"sync"
"time"
"github.com/hyperledger/burrow/event"
)
var (
reaperPeriod = 5 * time.Second
reaperThreshold = 20 * time.Second
)
// Catches events that callers subscribe to and adds them to an array ready to be polled.
type Subscriptions struct {
mtx *sync.RWMutex
service *Service
subs map[string]*SubscriptionsCache
reap bool
}
type SubscriptionsCache struct {
mtx *sync.Mutex
events []interface{}
ts time.Time
subID string
}
func NewSubscriptions(service *Service) *Subscriptions {
es := &Subscriptions{
mtx: &sync.RWMutex{},
service: service,
subs: make(map[string]*SubscriptionsCache),
reap: true,
}
if es.reap {
go reap(es)
}
return es
}
func newSubscriptionsCache(subID string) *SubscriptionsCache {
return &SubscriptionsCache{
subID: subID,
mtx: &sync.Mutex{},
events: make([]interface{}, 0),
ts: time.Now(),
}
}
func (subsCache *SubscriptionsCache) poll() []interface{} {
subsCache.mtx.Lock()
defer subsCache.mtx.Unlock()
var evts []interface{}
if len(subsCache.events) > 0 {
evts = subsCache.events
subsCache.events = []interface{}{}
} else {
evts = []interface{}{}
}
subsCache.ts = time.Now()
return evts
}
// Remove old subscriptions not recently polled
func reap(es *Subscriptions) {
for {
time.Sleep(reaperPeriod)
for id, sub := range es.subs {
if time.Since(sub.ts) > reaperThreshold {
es.mtx.Lock()
delete(es.subs, id)
es.service.Unsubscribe(context.Background(), id)
es.mtx.Unlock()
}
}
}
}
// Add a subscription and return the generated id. Note event dispatcher
// has to call func which involves acquiring a mutex lock, so might be
// a delay - though a conflict is practically impossible, and if it does
// happen it's for an insignificant amount of time (the time it takes to
// carry out SubscriptionsCache.poll() ).
func (subs *Subscriptions) Add(eventId string) (string, error) {
subID, err := event.GenerateSubscriptionID()
if err != nil {
return "", err
}
subs.mtx.Lock()
defer subs.mtx.Unlock()
cache := newSubscriptionsCache(subID)
subs.subs[subID] = cache
err = subs.service.Subscribe(context.Background(), subID, eventId, func(resultEvent *ResultEvent) (stop bool) {
cache.mtx.Lock()
defer cache.mtx.Unlock()
cache.events = append(cache.events, resultEvent)
return
})
if err != nil {
return "", err
}
return subID, nil
}
func (subs *Subscriptions) Poll(subId string) ([]interface{}, error) {
subs.mtx.RLock()
defer subs.mtx.RUnlock()
sub, ok := subs.subs[subId]
if !ok {
return nil, fmt.Errorf("Subscription not active. ID: " + subId)
}
return sub.poll(), nil
}
func (subs *Subscriptions) Remove(subId string) error {
subs.mtx.Lock()
defer subs.mtx.Unlock()
_, ok := subs.subs[subId]
if !ok {
return fmt.Errorf("Subscription not active. ID: " + subId)
}
delete(subs.subs, subId)
return nil
}