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eventstream.go
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eventstream.go
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// Copyright Amazon.com Inc. or its affiliates. All Rights Reserved.
//
// Licensed under the Apache License, Version 2.0 (the "License"). You may
// not use this file except in compliance with the License. A copy of the
// License is located at
//
// http://aws.amazon.com/apache2.0/
//
// or in the "license" file accompanying this file. This file is distributed
// on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either
// express or implied. See the License for the specific language governing
// permissions and limitations under the License.
// Package handler deals with appropriately reacting to all ACS messages as well
// as maintaining the connection to ACS.
package eventstream
import (
"context"
"fmt"
"sync"
"github.com/cihub/seelog"
)
type eventHandler func(...interface{}) error
// EventStream waiting for events and notifying the listeners by invoking
// the handler that listeners registered
type EventStream struct {
name string
open bool
event chan interface{}
handlers map[string]eventHandler
ctx context.Context
handlersLock sync.RWMutex
statusLock sync.RWMutex
}
func NewEventStream(name string, ctx context.Context) *EventStream {
return &EventStream{
name: name,
event: make(chan interface{}, 1),
ctx: ctx,
open: false,
handlers: make(map[string]eventHandler),
}
}
// Subscribe adds the handler to be called into EventStream
func (eventStream *EventStream) Subscribe(name string, handler eventHandler) error {
eventStream.handlersLock.Lock()
defer eventStream.handlersLock.Unlock()
if _, ok := eventStream.handlers[name]; ok {
return fmt.Errorf("handler %s already exists", name)
}
eventStream.handlers[name] = handler
return nil
}
// broadcast calls all handler's handler function
func (eventStream *EventStream) broadcast(event interface{}) {
eventStream.handlersLock.RLock()
defer eventStream.handlersLock.RUnlock()
seelog.Debugf("Event stream %s received events, broadcasting to listeners...", eventStream.name)
for _, handlerFunc := range eventStream.handlers {
go handlerFunc(event)
}
}
// Unsubscribe deletes the handler from the EventStream
func (eventStream *EventStream) Unsubscribe(name string) {
eventStream.handlersLock.Lock()
defer eventStream.handlersLock.Unlock()
for handler := range eventStream.handlers {
if handler == name {
seelog.Debugf("Unsubscribing event handler %s from event stream %s", handler, eventStream.name)
delete(eventStream.handlers, handler)
return
}
}
}
// WriteToEventStream writes event to the event stream
func (eventStream *EventStream) WriteToEventStream(event interface{}) error {
eventStream.statusLock.RLock()
defer eventStream.statusLock.RUnlock()
if !eventStream.open {
return fmt.Errorf("Event stream is closed")
}
eventStream.event <- event
return nil
}
// Context returns the context of event stream
func (eventStream *EventStream) Context() context.Context {
return eventStream.ctx
}
// listen listens to the event channel
func (eventStream *EventStream) listen() {
seelog.Infof("Event stream %s start listening...", eventStream.name)
for {
select {
case event := <-eventStream.event:
eventStream.broadcast(event)
case <-eventStream.ctx.Done():
seelog.Infof("Event stream %s stopped listening...", eventStream.name)
eventStream.statusLock.Lock()
eventStream.open = false
close(eventStream.event)
eventStream.statusLock.Unlock()
return
}
}
}
// StartListening mark the event stream as open and start listening
func (eventStream *EventStream) StartListening() {
eventStream.statusLock.Lock()
defer eventStream.statusLock.Unlock()
eventStream.open = true
go eventStream.listen()
}