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247 lines
5.7 KiB
247 lines
5.7 KiB
// Package events - Pub-Sub in go with event caching
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package events
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import (
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"fmt"
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"sync"
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"github.com/tendermint/tendermint/libs/service"
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)
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// ErrListenerWasRemoved is returned by AddEvent if the listener was removed.
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type ErrListenerWasRemoved struct {
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listenerID string
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}
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// Error implements the error interface.
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func (e ErrListenerWasRemoved) Error() string {
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return fmt.Sprintf("listener #%s was removed", e.listenerID)
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}
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// EventData is a generic event data can be typed and registered with
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// tendermint/go-amino via concrete implementation of this interface.
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type EventData interface{}
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// Eventable is the interface reactors and other modules must export to become
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// eventable.
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type Eventable interface {
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SetEventSwitch(evsw EventSwitch)
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}
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// Fireable is the interface that wraps the FireEvent method.
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//
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// FireEvent fires an event with the given name and data.
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type Fireable interface {
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FireEvent(event string, data EventData)
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}
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// EventSwitch is the interface for synchronous pubsub, where listeners
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// subscribe to certain events and, when an event is fired (see Fireable),
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// notified via a callback function.
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//
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// Listeners are added by calling AddListenerForEvent function.
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// They can be removed by calling either RemoveListenerForEvent or
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// RemoveListener (for all events).
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type EventSwitch interface {
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service.Service
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Fireable
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AddListenerForEvent(listenerID, event string, cb EventCallback) error
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RemoveListenerForEvent(event string, listenerID string)
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RemoveListener(listenerID string)
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}
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type eventSwitch struct {
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service.BaseService
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mtx sync.RWMutex
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eventCells map[string]*eventCell
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listeners map[string]*eventListener
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}
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func NewEventSwitch() EventSwitch {
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evsw := &eventSwitch{
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eventCells: make(map[string]*eventCell),
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listeners: make(map[string]*eventListener),
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}
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evsw.BaseService = *service.NewBaseService(nil, "EventSwitch", evsw)
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return evsw
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}
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func (evsw *eventSwitch) OnStart() error {
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return nil
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}
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func (evsw *eventSwitch) OnStop() {}
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func (evsw *eventSwitch) AddListenerForEvent(listenerID, event string, cb EventCallback) error {
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// Get/Create eventCell and listener.
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evsw.mtx.Lock()
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eventCell := evsw.eventCells[event]
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if eventCell == nil {
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eventCell = newEventCell()
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evsw.eventCells[event] = eventCell
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}
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listener := evsw.listeners[listenerID]
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if listener == nil {
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listener = newEventListener(listenerID)
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evsw.listeners[listenerID] = listener
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}
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evsw.mtx.Unlock()
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// Add event and listener.
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if err := listener.AddEvent(event); err != nil {
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return err
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}
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eventCell.AddListener(listenerID, cb)
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return nil
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}
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func (evsw *eventSwitch) RemoveListener(listenerID string) {
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// Get and remove listener.
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evsw.mtx.RLock()
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listener := evsw.listeners[listenerID]
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evsw.mtx.RUnlock()
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if listener == nil {
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return
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}
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evsw.mtx.Lock()
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delete(evsw.listeners, listenerID)
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evsw.mtx.Unlock()
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// Remove callback for each event.
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listener.SetRemoved()
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for _, event := range listener.GetEvents() {
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evsw.RemoveListenerForEvent(event, listenerID)
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}
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}
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func (evsw *eventSwitch) RemoveListenerForEvent(event string, listenerID string) {
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// Get eventCell
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evsw.mtx.Lock()
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eventCell := evsw.eventCells[event]
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evsw.mtx.Unlock()
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if eventCell == nil {
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return
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}
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// Remove listenerID from eventCell
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numListeners := eventCell.RemoveListener(listenerID)
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// Maybe garbage collect eventCell.
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if numListeners == 0 {
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// Lock again and double check.
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evsw.mtx.Lock() // OUTER LOCK
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eventCell.mtx.Lock() // INNER LOCK
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if len(eventCell.listeners) == 0 {
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delete(evsw.eventCells, event)
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}
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eventCell.mtx.Unlock() // INNER LOCK
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evsw.mtx.Unlock() // OUTER LOCK
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}
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}
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func (evsw *eventSwitch) FireEvent(event string, data EventData) {
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// Get the eventCell
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evsw.mtx.RLock()
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eventCell := evsw.eventCells[event]
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evsw.mtx.RUnlock()
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if eventCell == nil {
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return
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}
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// Fire event for all listeners in eventCell
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eventCell.FireEvent(data)
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}
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//-----------------------------------------------------------------------------
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// eventCell handles keeping track of listener callbacks for a given event.
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type eventCell struct {
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mtx sync.RWMutex
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listeners map[string]EventCallback
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}
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func newEventCell() *eventCell {
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return &eventCell{
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listeners: make(map[string]EventCallback),
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}
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}
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func (cell *eventCell) AddListener(listenerID string, cb EventCallback) {
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cell.mtx.Lock()
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cell.listeners[listenerID] = cb
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cell.mtx.Unlock()
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}
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func (cell *eventCell) RemoveListener(listenerID string) int {
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cell.mtx.Lock()
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delete(cell.listeners, listenerID)
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numListeners := len(cell.listeners)
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cell.mtx.Unlock()
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return numListeners
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}
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func (cell *eventCell) FireEvent(data EventData) {
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cell.mtx.RLock()
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eventCallbacks := make([]EventCallback, 0, len(cell.listeners))
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for _, cb := range cell.listeners {
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eventCallbacks = append(eventCallbacks, cb)
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}
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cell.mtx.RUnlock()
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for _, cb := range eventCallbacks {
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cb(data)
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}
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}
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//-----------------------------------------------------------------------------
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type EventCallback func(data EventData)
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type eventListener struct {
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id string
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mtx sync.RWMutex
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removed bool
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events []string
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}
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func newEventListener(id string) *eventListener {
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return &eventListener{
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id: id,
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removed: false,
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events: nil,
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}
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}
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func (evl *eventListener) AddEvent(event string) error {
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evl.mtx.Lock()
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if evl.removed {
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evl.mtx.Unlock()
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return ErrListenerWasRemoved{listenerID: evl.id}
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}
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evl.events = append(evl.events, event)
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evl.mtx.Unlock()
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return nil
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}
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func (evl *eventListener) GetEvents() []string {
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evl.mtx.RLock()
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events := make([]string, len(evl.events))
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copy(events, evl.events)
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evl.mtx.RUnlock()
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return events
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}
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func (evl *eventListener) SetRemoved() {
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evl.mtx.Lock()
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evl.removed = true
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evl.mtx.Unlock()
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}
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