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