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118 lines
3.3 KiB
Go
118 lines
3.3 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 Maskable
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types Mask
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filter func(entry Maskable) 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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// atomics, keep at top:
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types uint64
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numSubscribers int32
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maxSubscribers int32
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// not atomics:
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subs []*Sub
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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 Maskable) {
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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.types.Contains(Mask(item.Mask())) && (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(mask Mask, subCh chan Maskable, doneCh <-chan struct{}, filter func(entry Maskable) 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{ch: subCh, types: mask, filter: filter}
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ps.subs = append(ps.subs, sub)
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// We hold a lock, so we are safe to update
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combined := Mask(atomic.LoadUint64(&ps.types))
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combined.Merge(mask)
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atomic.StoreUint64(&ps.types, uint64(combined))
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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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var remainTypes Mask
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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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} else {
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remainTypes.Merge(s.types)
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}
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}
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atomic.StoreUint64(&ps.types, uint64(remainTypes))
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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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// If t is non-nil, the type is checked against the active subscribed types,
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// and 0 will be returned if nobody is subscribed for the type,
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// otherwise the *total* number of subscribers is returned.
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func (ps *PubSub) NumSubscribers(m Maskable) int32 {
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if m != nil {
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types := Mask(atomic.LoadUint64(&ps.types))
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if !types.Overlaps(Mask(m.Mask())) {
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return 0
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}
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}
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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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