129 lines
3.3 KiB
Go
129 lines
3.3 KiB
Go
// Copyright 2016 The go-ethereum Authors
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// This file is part of the go-ethereum library.
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//
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// The go-ethereum library is free software: you can redistribute it and/or modify
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// it under the terms of the GNU Lesser 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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// The go-ethereum library 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 Lesser General Public License for more details.
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//
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// You should have received a copy of the GNU Lesser General Public License
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// along with the go-ethereum library. If not, see <http://www.gnu.org/licenses/>.
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package event_test
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import (
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"fmt"
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"sync"
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"github.com/ethereum/go-ethereum/event"
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)
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// This example demonstrates how SubscriptionScope can be used to control the lifetime of
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// subscriptions.
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//
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// Our example program consists of two servers, each of which performs a calculation when
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// requested. The servers also allow subscribing to results of all computations.
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type divServer struct{ results event.Feed }
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type mulServer struct{ results event.Feed }
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func (s *divServer) do(a, b int) int {
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r := a / b
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s.results.Send(r)
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return r
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}
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func (s *mulServer) do(a, b int) int {
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r := a * b
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s.results.Send(r)
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return r
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}
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// The servers are contained in an App. The app controls the servers and exposes them
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// through its API.
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type App struct {
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divServer
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mulServer
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scope event.SubscriptionScope
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}
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func (s *App) Calc(op byte, a, b int) int {
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switch op {
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case '/':
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return s.divServer.do(a, b)
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case '*':
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return s.mulServer.do(a, b)
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default:
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panic("invalid op")
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}
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}
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// The app's SubscribeResults method starts sending calculation results to the given
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// channel. Subscriptions created through this method are tied to the lifetime of the App
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// because they are registered in the scope.
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func (s *App) SubscribeResults(op byte, ch chan<- int) event.Subscription {
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switch op {
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case '/':
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return s.scope.Track(s.divServer.results.Subscribe(ch))
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case '*':
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return s.scope.Track(s.mulServer.results.Subscribe(ch))
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default:
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panic("invalid op")
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}
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}
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// Stop stops the App, closing all subscriptions created through SubscribeResults.
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func (s *App) Stop() {
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s.scope.Close()
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}
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func ExampleSubscriptionScope() {
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// Create the app.
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var (
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app App
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wg sync.WaitGroup
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divs = make(chan int)
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muls = make(chan int)
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)
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// Run a subscriber in the background.
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divsub := app.SubscribeResults('/', divs)
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mulsub := app.SubscribeResults('*', muls)
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wg.Add(1)
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go func() {
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defer wg.Done()
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defer fmt.Println("subscriber exited")
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defer divsub.Unsubscribe()
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defer mulsub.Unsubscribe()
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for {
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select {
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case result := <-divs:
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fmt.Println("division happened:", result)
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case result := <-muls:
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fmt.Println("multiplication happened:", result)
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case <-divsub.Err():
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return
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case <-mulsub.Err():
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return
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}
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}
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}()
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// Interact with the app.
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app.Calc('/', 22, 11)
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app.Calc('*', 3, 4)
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// Stop the app. This shuts down the subscriptions, causing the subscriber to exit.
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app.Stop()
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wg.Wait()
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// Output:
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// division happened: 2
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// multiplication happened: 12
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// subscriber exited
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}
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