minio/internal/pubsub/pubsub.go

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// Copyright (c) 2015-2021 MinIO, Inc.
//
// This file is part of MinIO Object Storage stack
//
// This program is free software: you can redistribute it and/or modify
// it under the terms of the GNU Affero General Public License as published by
// the Free Software Foundation, either version 3 of the License, or
// (at your option) any later version.
//
// This program is distributed in the hope that it will be useful
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
// GNU Affero General Public License for more details.
//
// You should have received a copy of the GNU Affero General Public License
// along with this program. If not, see <http://www.gnu.org/licenses/>.
package pubsub
import (
"fmt"
"sync"
"sync/atomic"
)
// Sub - subscriber entity.
type Sub struct {
ch chan interface{}
filter func(entry interface{}) bool
}
// PubSub holds publishers and subscribers
type PubSub struct {
subs []*Sub
numSubscribers int32
maxSubscribers int32
sync.RWMutex
}
// Publish message to the subscribers.
// Note that publish is always nob-blocking send so that we don't block on slow receivers.
// Hence receivers should use buffered channel so as not to miss the published events.
func (ps *PubSub) Publish(item interface{}) {
ps.RLock()
defer ps.RUnlock()
for _, sub := range ps.subs {
if sub.filter == nil || sub.filter(item) {
select {
case sub.ch <- item:
default:
}
}
}
}
// Subscribe - Adds a subscriber to pubsub system
func (ps *PubSub) Subscribe(subCh chan interface{}, doneCh <-chan struct{}, filter func(entry interface{}) bool) error {
totalSubs := atomic.AddInt32(&ps.numSubscribers, 1)
if ps.maxSubscribers > 0 && totalSubs > ps.maxSubscribers {
atomic.AddInt32(&ps.numSubscribers, -1)
return fmt.Errorf("the limit of `%d` subscribers is reached", ps.maxSubscribers)
}
ps.Lock()
defer ps.Unlock()
sub := &Sub{subCh, filter}
ps.subs = append(ps.subs, sub)
go func() {
<-doneCh
ps.Lock()
defer ps.Unlock()
for i, s := range ps.subs {
if s == sub {
ps.subs = append(ps.subs[:i], ps.subs[i+1:]...)
}
}
atomic.AddInt32(&ps.numSubscribers, -1)
}()
return nil
}
// NumSubscribers returns the number of current subscribers
func (ps *PubSub) NumSubscribers() int32 {
return atomic.LoadInt32(&ps.numSubscribers)
}
// New inits a PubSub system with a limit of maximum
// subscribers unless zero is specified
func New(maxSubscribers int32) *PubSub {
return &PubSub{maxSubscribers: maxSubscribers}
}