// Copyright 2014 The go-ethereum Authors
// This file is part of the go-ethereum library.
//
// The go-ethereum library is free software: you can redistribute it and/or modify
// it under the terms of the GNU Lesser General Public License as published by
// the Free Software Foundation, either version 3 of the License, or
// (at your option) any later version.
//
// The go-ethereum library 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 Lesser General Public License for more details.
//
// You should have received a copy of the GNU Lesser General Public License
// along with the go-ethereum library. If not, see .
// Package event implements an event multiplexer.
package event
import (
"errors"
"fmt"
"reflect"
"sync"
"time"
)
// Event is a time-tagged notification pushed to subscribers.
type Event struct {
Time time.Time
Data interface{}
}
// Subscription is implemented by event subscriptions.
type Subscription interface {
// Chan returns a channel that carries events.
// Implementations should return the same channel
// for any subsequent calls to Chan.
Chan() <-chan *Event
// Unsubscribe stops delivery of events to a subscription.
// The event channel is closed.
// Unsubscribe can be called more than once.
Unsubscribe()
}
// A TypeMux dispatches events to registered receivers. Receivers can be
// registered to handle events of certain type. Any operation
// called after mux is stopped will return ErrMuxClosed.
//
// The zero value is ready to use.
type TypeMux struct {
mutex sync.RWMutex
subm map[reflect.Type][]*muxsub
stopped bool
}
// ErrMuxClosed is returned when Posting on a closed TypeMux.
var ErrMuxClosed = errors.New("event: mux closed")
// Subscribe creates a subscription for events of the given types. The
// subscription's channel is closed when it is unsubscribed
// or the mux is closed.
func (mux *TypeMux) Subscribe(types ...interface{}) Subscription {
sub := newsub(mux)
mux.mutex.Lock()
defer mux.mutex.Unlock()
if mux.stopped {
close(sub.postC)
} else {
if mux.subm == nil {
mux.subm = make(map[reflect.Type][]*muxsub)
}
for _, t := range types {
rtyp := reflect.TypeOf(t)
oldsubs := mux.subm[rtyp]
if find(oldsubs, sub) != -1 {
panic(fmt.Sprintf("event: duplicate type %s in Subscribe", rtyp))
}
subs := make([]*muxsub, len(oldsubs)+1)
copy(subs, oldsubs)
subs[len(oldsubs)] = sub
mux.subm[rtyp] = subs
}
}
return sub
}
// Post sends an event to all receivers registered for the given type.
// It returns ErrMuxClosed if the mux has been stopped.
func (mux *TypeMux) Post(ev interface{}) error {
event := &Event{
Time: time.Now(),
Data: ev,
}
rtyp := reflect.TypeOf(ev)
mux.mutex.RLock()
if mux.stopped {
mux.mutex.RUnlock()
return ErrMuxClosed
}
subs := mux.subm[rtyp]
mux.mutex.RUnlock()
for _, sub := range subs {
sub.deliver(event)
}
return nil
}
// Stop closes a mux. The mux can no longer be used.
// Future Post calls will fail with ErrMuxClosed.
// Stop blocks until all current deliveries have finished.
func (mux *TypeMux) Stop() {
mux.mutex.Lock()
for _, subs := range mux.subm {
for _, sub := range subs {
sub.closewait()
}
}
mux.subm = nil
mux.stopped = true
mux.mutex.Unlock()
}
func (mux *TypeMux) del(s *muxsub) {
mux.mutex.Lock()
for typ, subs := range mux.subm {
if pos := find(subs, s); pos >= 0 {
if len(subs) == 1 {
delete(mux.subm, typ)
} else {
mux.subm[typ] = posdelete(subs, pos)
}
}
}
s.mux.mutex.Unlock()
}
func find(slice []*muxsub, item *muxsub) int {
for i, v := range slice {
if v == item {
return i
}
}
return -1
}
func posdelete(slice []*muxsub, pos int) []*muxsub {
news := make([]*muxsub, len(slice)-1)
copy(news[:pos], slice[:pos])
copy(news[pos:], slice[pos+1:])
return news
}
type muxsub struct {
mux *TypeMux
created time.Time
closeMu sync.Mutex
closing chan struct{}
closed bool
// these two are the same channel. they are stored separately so
// postC can be set to nil without affecting the return value of
// Chan.
postMu sync.RWMutex
readC <-chan *Event
postC chan<- *Event
}
func newsub(mux *TypeMux) *muxsub {
c := make(chan *Event)
return &muxsub{
mux: mux,
created: time.Now(),
readC: c,
postC: c,
closing: make(chan struct{}),
}
}
func (s *muxsub) Chan() <-chan *Event {
return s.readC
}
func (s *muxsub) Unsubscribe() {
s.mux.del(s)
s.closewait()
}
func (s *muxsub) closewait() {
s.closeMu.Lock()
defer s.closeMu.Unlock()
if s.closed {
return
}
close(s.closing)
s.closed = true
s.postMu.Lock()
close(s.postC)
s.postC = nil
s.postMu.Unlock()
}
func (s *muxsub) deliver(event *Event) {
// Short circuit delivery if stale event
if s.created.After(event.Time) {
return
}
// Otherwise deliver the event
s.postMu.RLock()
defer s.postMu.RUnlock()
select {
case s.postC <- event:
case <-s.closing:
}
}
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