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// Copyright 2017 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 <http://www.gnu.org/licenses/>.
package event_test
import (
"fmt"
"sync"
"github.com/ethereum/go-ethereum/event"
)
// This example demonstrates how SubscriptionScope can be used to control the lifetime of
// subscriptions.
//
// Our example program consists of two servers, each of which performs a calculation when
// requested. The servers also allow subscribing to results of all computations.
type divServer struct{ results event.Feed }
type mulServer struct{ results event.Feed }
func (s *divServer) do(a, b int) int {
r := a / b
s.results.Send(r)
return r
}
func (s *mulServer) do(a, b int) int {
r := a * b
s.results.Send(r)
return r
}
// The servers are contained in an App. The app controls the servers and exposes them
// through its API.
type App struct {
divServer
mulServer
scope event.SubscriptionScope
}
func (s *App) Calc(op byte, a, b int) int {
switch op {
case '/':
return s.divServer.do(a, b)
case '*':
return s.mulServer.do(a, b)
default:
panic("invalid op")
}
}
// The app's SubscribeResults method starts sending calculation results to the given
// channel. Subscriptions created through this method are tied to the lifetime of the App
// because they are registered in the scope.
func (s *App) SubscribeResults(op byte, ch chan<- int) event.Subscription {
switch op {
case '/':
return s.scope.Track(s.divServer.results.Subscribe(ch))
case '*':
return s.scope.Track(s.mulServer.results.Subscribe(ch))
default:
panic("invalid op")
}
}
// Stop stops the App, closing all subscriptions created through SubscribeResults.
func (s *App) Stop() {
s.scope.Close()
}
func ExampleSubscriptionScope() {
// Create the app.
var (
app App
wg sync.WaitGroup
divs = make(chan int)
muls = make(chan int)
)
// Run a subscriber in the background.
divsub := app.SubscribeResults('/', divs)
mulsub := app.SubscribeResults('*', muls)
wg.Add(1)
go func() {
defer wg.Done()
defer fmt.Println("subscriber exited")
defer divsub.Unsubscribe()
defer mulsub.Unsubscribe()
for {
select {
case result := <-divs:
fmt.Println("division happened:", result)
case result := <-muls:
fmt.Println("multiplication happened:", result)
case <-divsub.Err():
return
case <-mulsub.Err():
return
}
}
}()
// Interact with the app.
app.Calc('/', 22, 11)
app.Calc('*', 3, 4)
// Stop the app. This shuts down the subscriptions, causing the subscriber to exit.
app.Stop()
wg.Wait()
// Output:
// division happened: 2
// multiplication happened: 12
// subscriber exited
}
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