event: add new Subscription type and related utilities
This commit introduces a new Subscription type, which is synonymous with ethereum.Subscription. It also adds a couple of utilities that make working with Subscriptions easier. The mot complex utility is Feed, a synchronisation device that implements broadcast subscriptions. Feed is slightly faster than TypeMux and will replace uses of TypeMux across the go-ethereum codebase in the future.
This commit is contained in:
Felix Lange
parent
9b62facdd4
commit
6d5e100d0d
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@ -14,7 +14,7 @@
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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 implements an event multiplexer.
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// Package event deals with subscriptions to real-time events.
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package event
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import (
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@ -149,16 +149,34 @@ func emptySubscriber(mux *TypeMux, types ...interface{}) {
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}()
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}
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func BenchmarkPost3(b *testing.B) {
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var mux = new(TypeMux)
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defer mux.Stop()
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emptySubscriber(mux, testEvent(0))
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emptySubscriber(mux, testEvent(0))
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emptySubscriber(mux, testEvent(0))
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func BenchmarkPost1000(b *testing.B) {
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var (
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mux = new(TypeMux)
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subscribed, done sync.WaitGroup
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nsubs = 1000
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)
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subscribed.Add(nsubs)
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done.Add(nsubs)
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for i := 0; i < nsubs; i++ {
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go func() {
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s := mux.Subscribe(testEvent(0))
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subscribed.Done()
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for range s.Chan() {
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}
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done.Done()
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}()
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}
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subscribed.Wait()
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// The actual benchmark.
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b.ResetTimer()
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for i := 0; i < b.N; i++ {
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mux.Post(testEvent(0))
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}
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b.StopTimer()
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mux.Stop()
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done.Wait()
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}
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func BenchmarkPostConcurrent(b *testing.B) {
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@ -0,0 +1,73 @@
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// Copyright 2017 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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"github.com/ethereum/go-ethereum/event"
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)
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func ExampleFeed_acknowledgedEvents() {
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// This example shows how the return value of Send can be used for request/reply
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// interaction between event consumers and producers.
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var feed event.Feed
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type ackedEvent struct {
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i int
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ack chan<- struct{}
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}
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// Consumers wait for events on the feed and acknowledge processing.
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done := make(chan struct{})
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defer close(done)
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for i := 0; i < 3; i++ {
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ch := make(chan ackedEvent, 100)
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sub := feed.Subscribe(ch)
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go func() {
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defer sub.Unsubscribe()
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for {
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select {
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case ev := <-ch:
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fmt.Println(ev.i) // "process" the event
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ev.ack <- struct{}{}
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case <-done:
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return
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}
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}
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}()
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}
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// The producer sends values of type ackedEvent with increasing values of i.
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// It waits for all consumers to acknowledge before sending the next event.
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for i := 0; i < 3; i++ {
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acksignal := make(chan struct{})
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n := feed.Send(ackedEvent{i, acksignal})
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for ack := 0; ack < n; ack++ {
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<-acksignal
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}
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}
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// Output:
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// 0
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// 0
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// 0
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// 1
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// 1
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// 1
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// 2
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// 2
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// 2
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}
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@ -0,0 +1,128 @@
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// Copyright 2017 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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@ -0,0 +1,56 @@
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// Copyright 2017 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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"github.com/ethereum/go-ethereum/event"
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)
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func ExampleNewSubscription() {
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// Create a subscription that sends 10 integers on ch.
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ch := make(chan int)
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sub := event.NewSubscription(func(quit <-chan struct{}) error {
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for i := 0; i < 10; i++ {
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select {
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case ch <- i:
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case <-quit:
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fmt.Println("unsubscribed")
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return nil
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}
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}
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return nil
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})
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// This is the consumer. It reads 5 integers, then aborts the subscription.
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// Note that Unsubscribe waits until the producer has shut down.
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for i := range ch {
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fmt.Println(i)
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if i == 4 {
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sub.Unsubscribe()
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break
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}
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}
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// Output:
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// 0
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// 1
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// 2
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// 3
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// 4
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// unsubscribed
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}
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@ -0,0 +1,240 @@
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// 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
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import (
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"errors"
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"reflect"
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"sync"
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)
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var errBadChannel = errors.New("event: Subscribe argument does not have sendable channel type")
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// Feed implements one-to-many subscriptions where the carrier of events is a channel.
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// Values sent to a Feed are delivered to all subscribed channels simultaneously.
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//
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// Feeds can only be used with a single type. The type is determined by the first Send or
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// Subscribe operation. Subsequent calls to these methods panic if the type does not
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// match.
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//
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// The zero value is ready to use.
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type Feed struct {
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sendLock chan struct{} // one-element buffer, empty when held
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removeSub chan interface{} // interrupts Send
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sendCases caseList // the active set of select cases used by Send
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// The inbox holds newly subscribed channels until they are added to sendCases.
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mu sync.Mutex
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inbox caseList
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etype reflect.Type
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closed bool
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}
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type feedTypeError struct {
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got, want reflect.Type
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op string
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}
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func (e feedTypeError) Error() string {
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return "event: wrong type in " + e.op + " got " + e.got.String() + ", want " + e.want.String()
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}
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func (f *Feed) init() {
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if f.sendLock != nil {
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return
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}
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f.removeSub = make(chan interface{})
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f.sendLock = make(chan struct{}, 1)
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f.sendLock <- struct{}{}
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f.sendCases = caseList{{Chan: reflect.ValueOf(f.removeSub), Dir: reflect.SelectRecv}}
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}
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// Subscribe adds a channel to the feed. Future sends will be delivered on the channel
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// until the subscription is canceled. All channels added must have the same element type.
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//
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// The channel should have ample buffer space to avoid blocking other subscribers.
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func (f *Feed) Subscribe(channel interface{}) Subscription {
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chanval := reflect.ValueOf(channel)
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chantyp := chanval.Type()
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if chantyp.Kind() != reflect.Chan || chantyp.ChanDir()&reflect.SendDir == 0 {
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panic(errBadChannel)
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}
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sub := &feedSub{feed: f, channel: chanval, err: make(chan error, 1)}
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f.mu.Lock()
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defer f.mu.Unlock()
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f.init()
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if !f.typecheck(chantyp.Elem()) {
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panic(feedTypeError{op: "Subscribe", got: chantyp, want: reflect.ChanOf(reflect.SendDir, f.etype)})
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}
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// Add the select case to the inbox.
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// The next Send will add it to f.sendCases.
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cas := reflect.SelectCase{Dir: reflect.SelectSend, Chan: chanval}
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f.inbox = append(f.inbox, cas)
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return sub
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}
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// note: callers must hold f.mu
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func (f *Feed) typecheck(typ reflect.Type) bool {
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if f.etype == nil {
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f.etype = typ
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return true
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}
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return f.etype == typ
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}
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func (f *Feed) remove(sub *feedSub) {
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// Delete from inbox first, which covers channels
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// that have not been added to f.sendCases yet.
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ch := sub.channel.Interface()
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f.mu.Lock()
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index := f.inbox.find(ch)
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if index != -1 {
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f.inbox = f.inbox.delete(index)
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f.mu.Unlock()
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return
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}
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f.mu.Unlock()
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select {
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case f.removeSub <- ch:
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// Send will remove the channel from f.sendCases.
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case <-f.sendLock:
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// No Send is in progress, delete the channel now that we have the send lock.
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f.sendCases = f.sendCases.delete(f.sendCases.find(ch))
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f.sendLock <- struct{}{}
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}
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}
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// Send delivers to all subscribed channels simultaneously.
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// It returns the number of subscribers that the value was sent to.
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func (f *Feed) Send(value interface{}) (nsent int) {
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f.mu.Lock()
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f.init()
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<-f.sendLock
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// Add new subscriptions from the inbox, then clear it.
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f.sendCases = append(f.sendCases, f.inbox...)
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for i := range f.inbox {
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f.inbox[i] = reflect.SelectCase{}
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}
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f.inbox = f.inbox[:0]
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f.mu.Unlock()
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// Set the sent value on all channels.
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rvalue := reflect.ValueOf(value)
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if !f.typecheck(rvalue.Type()) {
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f.sendLock <- struct{}{}
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panic(feedTypeError{op: "Send", got: rvalue.Type(), want: f.etype})
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}
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for i := 1; i < len(f.sendCases); i++ {
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f.sendCases[i].Send = rvalue
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}
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// Send until all channels except removeSub have been chosen.
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cases := f.sendCases
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for {
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// Fast path: try sending without blocking before adding to the select set.
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// This should usually succeed if subscribers are fast enough and have free
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// buffer space.
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for i := 1; i < len(cases); i++ {
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if cases[i].Chan.TrySend(rvalue) {
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cases = cases.deactivate(i)
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nsent++
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}
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}
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if len(cases) == 1 {
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break
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}
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// Select on all the receivers, waiting for them to unblock.
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chosen, recv, _ := reflect.Select(cases)
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if chosen == 0 /* <-f.removeSub */ {
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index := f.sendCases.find(recv.Interface())
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f.sendCases = f.sendCases.delete(index)
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if index >= 0 && index < len(cases) {
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cases = f.sendCases[:len(cases)-1]
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}
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} else {
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cases = cases.deactivate(chosen)
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nsent++
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}
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}
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// Forget about the sent value and hand off the send lock.
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for i := 1; i < len(f.sendCases); i++ {
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f.sendCases[i].Send = reflect.Value{}
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}
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f.sendLock <- struct{}{}
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return nsent
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}
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type feedSub struct {
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feed *Feed
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channel reflect.Value
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errOnce sync.Once
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err chan error
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}
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|
||||
func (sub *feedSub) Unsubscribe() {
|
||||
sub.errOnce.Do(func() {
|
||||
sub.feed.remove(sub)
|
||||
close(sub.err)
|
||||
})
|
||||
}
|
||||
|
||||
func (sub *feedSub) Err() <-chan error {
|
||||
return sub.err
|
||||
}
|
||||
|
||||
type caseList []reflect.SelectCase
|
||||
|
||||
// find returns the index of a case containing the given channel.
|
||||
func (cs caseList) find(channel interface{}) int {
|
||||
for i, cas := range cs {
|
||||
if cas.Chan.Interface() == channel {
|
||||
return i
|
||||
}
|
||||
}
|
||||
return -1
|
||||
}
|
||||
|
||||
// delete removes the given case from cs.
|
||||
func (cs caseList) delete(index int) caseList {
|
||||
return append(cs[:index], cs[index+1:]...)
|
||||
}
|
||||
|
||||
// deactivate moves the case at index into the non-accessible portion of the cs slice.
|
||||
func (cs caseList) deactivate(index int) caseList {
|
||||
last := len(cs) - 1
|
||||
cs[index], cs[last] = cs[last], cs[index]
|
||||
return cs[:last]
|
||||
}
|
||||
|
||||
// func (cs caseList) String() string {
|
||||
// s := "["
|
||||
// for i, cas := range cs {
|
||||
// if i != 0 {
|
||||
// s += ", "
|
||||
// }
|
||||
// switch cas.Dir {
|
||||
// case reflect.SelectSend:
|
||||
// s += fmt.Sprintf("%v<-", cas.Chan.Interface())
|
||||
// case reflect.SelectRecv:
|
||||
// s += fmt.Sprintf("<-%v", cas.Chan.Interface())
|
||||
// }
|
||||
// }
|
||||
// return s + "]"
|
||||
// }
|
||||
|
|
@ -0,0 +1,226 @@
|
|||
// Copyright 2016 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
|
||||
|
||||
import (
|
||||
"fmt"
|
||||
"reflect"
|
||||
"sync"
|
||||
"testing"
|
||||
"time"
|
||||
)
|
||||
|
||||
func TestFeedPanics(t *testing.T) {
|
||||
{
|
||||
var f Feed
|
||||
f.Send(int(2))
|
||||
want := feedTypeError{op: "Send", got: reflect.TypeOf(uint64(0)), want: reflect.TypeOf(int(0))}
|
||||
if err := checkPanic(want, func() { f.Send(uint64(2)) }); err != nil {
|
||||
t.Error(err)
|
||||
}
|
||||
}
|
||||
{
|
||||
var f Feed
|
||||
ch := make(chan int)
|
||||
f.Subscribe(ch)
|
||||
want := feedTypeError{op: "Send", got: reflect.TypeOf(uint64(0)), want: reflect.TypeOf(int(0))}
|
||||
if err := checkPanic(want, func() { f.Send(uint64(2)) }); err != nil {
|
||||
t.Error(err)
|
||||
}
|
||||
}
|
||||
{
|
||||
var f Feed
|
||||
f.Send(int(2))
|
||||
want := feedTypeError{op: "Subscribe", got: reflect.TypeOf(make(chan uint64)), want: reflect.TypeOf(make(chan<- int))}
|
||||
if err := checkPanic(want, func() { f.Subscribe(make(chan uint64)) }); err != nil {
|
||||
t.Error(err)
|
||||
}
|
||||
}
|
||||
{
|
||||
var f Feed
|
||||
if err := checkPanic(errBadChannel, func() { f.Subscribe(make(<-chan int)) }); err != nil {
|
||||
t.Error(err)
|
||||
}
|
||||
}
|
||||
{
|
||||
var f Feed
|
||||
if err := checkPanic(errBadChannel, func() { f.Subscribe(int(0)) }); err != nil {
|
||||
t.Error(err)
|
||||
}
|
||||
}
|
||||
}
|
||||
|
||||
func checkPanic(want error, fn func()) (err error) {
|
||||
defer func() {
|
||||
panic := recover()
|
||||
if panic == nil {
|
||||
err = fmt.Errorf("didn't panic")
|
||||
} else if !reflect.DeepEqual(panic, want) {
|
||||
err = fmt.Errorf("panicked with wrong error: got %q, want %q", panic, want)
|
||||
}
|
||||
}()
|
||||
fn()
|
||||
return nil
|
||||
}
|
||||
|
||||
func TestFeed(t *testing.T) {
|
||||
var feed Feed
|
||||
var done, subscribed sync.WaitGroup
|
||||
subscriber := func(i int) {
|
||||
defer done.Done()
|
||||
|
||||
subchan := make(chan int)
|
||||
sub := feed.Subscribe(subchan)
|
||||
timeout := time.NewTimer(2 * time.Second)
|
||||
subscribed.Done()
|
||||
|
||||
select {
|
||||
case v := <-subchan:
|
||||
if v != 1 {
|
||||
t.Errorf("%d: received value %d, want 1", i, v)
|
||||
}
|
||||
case <-timeout.C:
|
||||
t.Errorf("%d: receive timeout", i)
|
||||
}
|
||||
|
||||
sub.Unsubscribe()
|
||||
select {
|
||||
case _, ok := <-sub.Err():
|
||||
if ok {
|
||||
t.Errorf("%d: error channel not closed after unsubscribe", i)
|
||||
}
|
||||
case <-timeout.C:
|
||||
t.Errorf("%d: unsubscribe timeout", i)
|
||||
}
|
||||
}
|
||||
|
||||
const n = 1000
|
||||
done.Add(n)
|
||||
subscribed.Add(n)
|
||||
for i := 0; i < n; i++ {
|
||||
go subscriber(i)
|
||||
}
|
||||
subscribed.Wait()
|
||||
if nsent := feed.Send(1); nsent != n {
|
||||
t.Errorf("first send delivered %d times, want %d", nsent, n)
|
||||
}
|
||||
if nsent := feed.Send(2); nsent != 0 {
|
||||
t.Errorf("second send delivered %d times, want 0", nsent)
|
||||
}
|
||||
done.Wait()
|
||||
}
|
||||
|
||||
func TestFeedSubscribeSameChannel(t *testing.T) {
|
||||
var (
|
||||
feed Feed
|
||||
done sync.WaitGroup
|
||||
ch = make(chan int)
|
||||
sub1 = feed.Subscribe(ch)
|
||||
sub2 = feed.Subscribe(ch)
|
||||
_ = feed.Subscribe(ch)
|
||||
)
|
||||
expectSends := func(value, n int) {
|
||||
if nsent := feed.Send(value); nsent != n {
|
||||
t.Errorf("send delivered %d times, want %d", nsent, n)
|
||||
}
|
||||
done.Done()
|
||||
}
|
||||
expectRecv := func(wantValue, n int) {
|
||||
for i := 0; i < n; i++ {
|
||||
if v := <-ch; v != wantValue {
|
||||
t.Errorf("received %d, want %d", v, wantValue)
|
||||
}
|
||||
}
|
||||
}
|
||||
|
||||
done.Add(1)
|
||||
go expectSends(1, 3)
|
||||
expectRecv(1, 3)
|
||||
done.Wait()
|
||||
|
||||
sub1.Unsubscribe()
|
||||
|
||||
done.Add(1)
|
||||
go expectSends(2, 2)
|
||||
expectRecv(2, 2)
|
||||
done.Wait()
|
||||
|
||||
sub2.Unsubscribe()
|
||||
|
||||
done.Add(1)
|
||||
go expectSends(3, 1)
|
||||
expectRecv(3, 1)
|
||||
done.Wait()
|
||||
}
|
||||
|
||||
func TestFeedUnsubscribeFromInbox(t *testing.T) {
|
||||
var (
|
||||
feed Feed
|
||||
ch1 = make(chan int)
|
||||
ch2 = make(chan int)
|
||||
sub1 = feed.Subscribe(ch1)
|
||||
sub2 = feed.Subscribe(ch1)
|
||||
sub3 = feed.Subscribe(ch2)
|
||||
)
|
||||
if len(feed.inbox) != 3 {
|
||||
t.Errorf("inbox length != 3 after subscribe")
|
||||
}
|
||||
if len(feed.sendCases) != 1 {
|
||||
t.Errorf("sendCases is non-empty after unsubscribe")
|
||||
}
|
||||
|
||||
sub1.Unsubscribe()
|
||||
sub2.Unsubscribe()
|
||||
sub3.Unsubscribe()
|
||||
if len(feed.inbox) != 0 {
|
||||
t.Errorf("inbox is non-empty after unsubscribe")
|
||||
}
|
||||
if len(feed.sendCases) != 1 {
|
||||
t.Errorf("sendCases is non-empty after unsubscribe")
|
||||
}
|
||||
}
|
||||
|
||||
func BenchmarkFeedSend1000(b *testing.B) {
|
||||
var (
|
||||
done sync.WaitGroup
|
||||
feed Feed
|
||||
nsubs = 1000
|
||||
)
|
||||
subscriber := func(ch <-chan int) {
|
||||
for i := 0; i < b.N; i++ {
|
||||
<-ch
|
||||
}
|
||||
done.Done()
|
||||
}
|
||||
done.Add(nsubs)
|
||||
for i := 0; i < nsubs; i++ {
|
||||
ch := make(chan int, 200)
|
||||
feed.Subscribe(ch)
|
||||
go subscriber(ch)
|
||||
}
|
||||
|
||||
// The actual benchmark.
|
||||
b.ResetTimer()
|
||||
for i := 0; i < b.N; i++ {
|
||||
if feed.Send(i) != nsubs {
|
||||
panic("wrong number of sends")
|
||||
}
|
||||
}
|
||||
|
||||
b.StopTimer()
|
||||
done.Wait()
|
||||
}
|
||||
|
|
@ -0,0 +1,275 @@
|
|||
// 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
|
||||
|
||||
import (
|
||||
"sync"
|
||||
"time"
|
||||
|
||||
"github.com/ethereum/go-ethereum/common/mclock"
|
||||
"golang.org/x/net/context"
|
||||
)
|
||||
|
||||
// Subscription represents a stream of events. The carrier of the events is typically a
|
||||
// channel, but isn't part of the interface.
|
||||
//
|
||||
// Subscriptions can fail while established. Failures are reported through an error
|
||||
// channel. It receives a value if there is an issue with the subscription (e.g. the
|
||||
// network connection delivering the events has been closed). Only one value will ever be
|
||||
// sent.
|
||||
//
|
||||
// The error channel is closed when the subscription ends successfully (i.e. when the
|
||||
// source of events is closed). It is also closed when Unsubscribe is called.
|
||||
//
|
||||
// The Unsubscribe method cancels the sending of events. You must call Unsubscribe in all
|
||||
// cases to ensure that resources related to the subscription are released. It can be
|
||||
// called any number of times.
|
||||
type Subscription interface {
|
||||
Err() <-chan error // returns the error channel
|
||||
Unsubscribe() // cancels sending of events, closing the error channel
|
||||
}
|
||||
|
||||
// NewSubscription runs fn as a subscription in a new goroutine. The channel given to fn
|
||||
// is closed when Unsubscribe is called. If fn returns an error, it is sent on the
|
||||
// subscription's error channel.
|
||||
func NewSubscription(fn func(<-chan struct{}) error) Subscription {
|
||||
s := &funcSub{unsub: make(chan struct{}), err: make(chan error, 1)}
|
||||
go func() {
|
||||
defer close(s.err)
|
||||
err := fn(s.unsub)
|
||||
s.mu.Lock()
|
||||
defer s.mu.Unlock()
|
||||
if !s.unsubscribed {
|
||||
if err != nil {
|
||||
s.err <- err
|
||||
}
|
||||
s.unsubscribed = true
|
||||
}
|
||||
}()
|
||||
return s
|
||||
}
|
||||
|
||||
type funcSub struct {
|
||||
unsub chan struct{}
|
||||
err chan error
|
||||
mu sync.Mutex
|
||||
unsubscribed bool
|
||||
}
|
||||
|
||||
func (s *funcSub) Unsubscribe() {
|
||||
s.mu.Lock()
|
||||
if s.unsubscribed {
|
||||
s.mu.Unlock()
|
||||
return
|
||||
}
|
||||
s.unsubscribed = true
|
||||
close(s.unsub)
|
||||
s.mu.Unlock()
|
||||
// Wait for producer shutdown.
|
||||
<-s.err
|
||||
}
|
||||
|
||||
func (s *funcSub) Err() <-chan error {
|
||||
return s.err
|
||||
}
|
||||
|
||||
// Resubscribe calls fn repeatedly to keep a subscription established. When the
|
||||
// subscription is established, Resubscribe waits for it to fail and calls fn again. This
|
||||
// process repeats until Unsubscribe is called or the active subscription ends
|
||||
// successfully.
|
||||
//
|
||||
// Resubscribe applies backoff between calls to fn. The time between calls is adapted
|
||||
// based on the error rate, but will never exceed backoffMax.
|
||||
func Resubscribe(backoffMax time.Duration, fn ResubscribeFunc) Subscription {
|
||||
s := &resubscribeSub{
|
||||
waitTime: backoffMax / 10,
|
||||
backoffMax: backoffMax,
|
||||
fn: fn,
|
||||
err: make(chan error),
|
||||
unsub: make(chan struct{}),
|
||||
}
|
||||
go s.loop()
|
||||
return s
|
||||
}
|
||||
|
||||
// A ResubscribeFunc attempts to establish a subscription.
|
||||
type ResubscribeFunc func(context.Context) (Subscription, error)
|
||||
|
||||
type resubscribeSub struct {
|
||||
fn ResubscribeFunc
|
||||
err chan error
|
||||
unsub chan struct{}
|
||||
unsubOnce sync.Once
|
||||
lastTry mclock.AbsTime
|
||||
waitTime, backoffMax time.Duration
|
||||
}
|
||||
|
||||
func (s *resubscribeSub) Unsubscribe() {
|
||||
s.unsubOnce.Do(func() {
|
||||
s.unsub <- struct{}{}
|
||||
<-s.err
|
||||
})
|
||||
}
|
||||
|
||||
func (s *resubscribeSub) Err() <-chan error {
|
||||
return s.err
|
||||
}
|
||||
|
||||
func (s *resubscribeSub) loop() {
|
||||
defer close(s.err)
|
||||
var done bool
|
||||
for !done {
|
||||
sub := s.subscribe()
|
||||
if sub == nil {
|
||||
break
|
||||
}
|
||||
done = s.waitForError(sub)
|
||||
sub.Unsubscribe()
|
||||
}
|
||||
}
|
||||
|
||||
func (s *resubscribeSub) subscribe() Subscription {
|
||||
subscribed := make(chan error)
|
||||
var sub Subscription
|
||||
retry:
|
||||
for {
|
||||
s.lastTry = mclock.Now()
|
||||
ctx, cancel := context.WithCancel(context.Background())
|
||||
go func() {
|
||||
rsub, err := s.fn(ctx)
|
||||
sub = rsub
|
||||
subscribed <- err
|
||||
}()
|
||||
select {
|
||||
case err := <-subscribed:
|
||||
cancel()
|
||||
if err != nil {
|
||||
// Subscribing failed, wait before launching the next try.
|
||||
if s.backoffWait() {
|
||||
return nil
|
||||
}
|
||||
continue retry
|
||||
}
|
||||
if sub == nil {
|
||||
panic("event: ResubscribeFunc returned nil subscription and no error")
|
||||
}
|
||||
return sub
|
||||
case <-s.unsub:
|
||||
cancel()
|
||||
return nil
|
||||
}
|
||||
}
|
||||
}
|
||||
|
||||
func (s *resubscribeSub) waitForError(sub Subscription) bool {
|
||||
defer sub.Unsubscribe()
|
||||
select {
|
||||
case err := <-sub.Err():
|
||||
return err == nil
|
||||
case <-s.unsub:
|
||||
return true
|
||||
}
|
||||
}
|
||||
|
||||
func (s *resubscribeSub) backoffWait() bool {
|
||||
if time.Duration(mclock.Now()-s.lastTry) > s.backoffMax {
|
||||
s.waitTime = s.backoffMax / 10
|
||||
} else {
|
||||
s.waitTime *= 2
|
||||
if s.waitTime > s.backoffMax {
|
||||
s.waitTime = s.backoffMax
|
||||
}
|
||||
}
|
||||
|
||||
t := time.NewTimer(s.waitTime)
|
||||
defer t.Stop()
|
||||
select {
|
||||
case <-t.C:
|
||||
return false
|
||||
case <-s.unsub:
|
||||
return true
|
||||
}
|
||||
}
|
||||
|
||||
// SubscriptionScope provides a facility to unsubscribe multiple subscriptions at once.
|
||||
//
|
||||
// For code that handle more than one subscription, a scope can be used to conveniently
|
||||
// unsubscribe all of them with a single call. The example demonstrates a typical use in a
|
||||
// larger program.
|
||||
//
|
||||
// The zero value is ready to use.
|
||||
type SubscriptionScope struct {
|
||||
mu sync.Mutex
|
||||
subs map[*scopeSub]struct{}
|
||||
closed bool
|
||||
}
|
||||
|
||||
type scopeSub struct {
|
||||
sc *SubscriptionScope
|
||||
s Subscription
|
||||
}
|
||||
|
||||
// Track starts tracking a subscription. If the scope is closed, Track returns nil. The
|
||||
// returned subscription is a wrapper. Unsubscribing the wrapper removes it from the
|
||||
// scope.
|
||||
func (sc *SubscriptionScope) Track(s Subscription) Subscription {
|
||||
sc.mu.Lock()
|
||||
defer sc.mu.Unlock()
|
||||
if sc.closed {
|
||||
return nil
|
||||
}
|
||||
if sc.subs == nil {
|
||||
sc.subs = make(map[*scopeSub]struct{})
|
||||
}
|
||||
ss := &scopeSub{sc, s}
|
||||
sc.subs[ss] = struct{}{}
|
||||
return ss
|
||||
}
|
||||
|
||||
// Close calls Unsubscribe on all tracked subscriptions and prevents further additions to
|
||||
// the tracked set. Calls to Track after Close return nil.
|
||||
func (sc *SubscriptionScope) Close() {
|
||||
sc.mu.Lock()
|
||||
defer sc.mu.Unlock()
|
||||
if sc.closed {
|
||||
return
|
||||
}
|
||||
sc.closed = true
|
||||
for s := range sc.subs {
|
||||
s.s.Unsubscribe()
|
||||
}
|
||||
sc.subs = nil
|
||||
}
|
||||
|
||||
// Count returns the number of tracked subscriptions.
|
||||
// It is meant to be used for debugging.
|
||||
func (sc *SubscriptionScope) Count() int {
|
||||
sc.mu.Lock()
|
||||
defer sc.mu.Unlock()
|
||||
return len(sc.subs)
|
||||
}
|
||||
|
||||
func (s *scopeSub) Unsubscribe() {
|
||||
s.s.Unsubscribe()
|
||||
s.sc.mu.Lock()
|
||||
defer s.sc.mu.Unlock()
|
||||
delete(s.sc.subs, s)
|
||||
}
|
||||
|
||||
func (s *scopeSub) Err() <-chan error {
|
||||
return s.s.Err()
|
||||
}
|
||||
|
|
@ -0,0 +1,121 @@
|
|||
// 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
|
||||
|
||||
import (
|
||||
"errors"
|
||||
"testing"
|
||||
"time"
|
||||
|
||||
"golang.org/x/net/context"
|
||||
)
|
||||
|
||||
var errInts = errors.New("error in subscribeInts")
|
||||
|
||||
func subscribeInts(max, fail int, c chan<- int) Subscription {
|
||||
return NewSubscription(func(quit <-chan struct{}) error {
|
||||
for i := 0; i < max; i++ {
|
||||
if i >= fail {
|
||||
return errInts
|
||||
}
|
||||
select {
|
||||
case c <- i:
|
||||
case <-quit:
|
||||
return nil
|
||||
}
|
||||
}
|
||||
return nil
|
||||
})
|
||||
}
|
||||
|
||||
func TestNewSubscriptionError(t *testing.T) {
|
||||
t.Parallel()
|
||||
|
||||
channel := make(chan int)
|
||||
sub := subscribeInts(10, 2, channel)
|
||||
loop:
|
||||
for want := 0; want < 10; want++ {
|
||||
select {
|
||||
case got := <-channel:
|
||||
if got != want {
|
||||
t.Fatalf("wrong int %d, want %d", got, want)
|
||||
}
|
||||
case err := <-sub.Err():
|
||||
if err != errInts {
|
||||
t.Fatalf("wrong error: got %q, want %q", err, errInts)
|
||||
}
|
||||
if want != 2 {
|
||||
t.Fatalf("got errInts at int %d, should be received at 2", want)
|
||||
}
|
||||
break loop
|
||||
}
|
||||
}
|
||||
sub.Unsubscribe()
|
||||
|
||||
err, ok := <-sub.Err()
|
||||
if err != nil {
|
||||
t.Fatal("got non-nil error after Unsubscribe")
|
||||
}
|
||||
if ok {
|
||||
t.Fatal("channel still open after Unsubscribe")
|
||||
}
|
||||
}
|
||||
|
||||
func TestResubscribe(t *testing.T) {
|
||||
t.Parallel()
|
||||
|
||||
var i int
|
||||
nfails := 6
|
||||
sub := Resubscribe(100*time.Millisecond, func(ctx context.Context) (Subscription, error) {
|
||||
// fmt.Printf("call #%d @ %v\n", i, time.Now())
|
||||
i++
|
||||
if i == 2 {
|
||||
// Delay the second failure a bit to reset the resubscribe interval.
|
||||
time.Sleep(200 * time.Millisecond)
|
||||
}
|
||||
if i < nfails {
|
||||
return nil, errors.New("oops")
|
||||
}
|
||||
sub := NewSubscription(func(unsubscribed <-chan struct{}) error { return nil })
|
||||
return sub, nil
|
||||
})
|
||||
|
||||
<-sub.Err()
|
||||
if i != nfails {
|
||||
t.Fatalf("resubscribe function called %d times, want %d times", i, nfails)
|
||||
}
|
||||
}
|
||||
|
||||
func TestResubscribeAbort(t *testing.T) {
|
||||
t.Parallel()
|
||||
|
||||
done := make(chan error)
|
||||
sub := Resubscribe(0, func(ctx context.Context) (Subscription, error) {
|
||||
select {
|
||||
case <-ctx.Done():
|
||||
done <- nil
|
||||
case <-time.After(2 * time.Second):
|
||||
done <- errors.New("context given to resubscribe function not canceled within 2s")
|
||||
}
|
||||
return nil, nil
|
||||
})
|
||||
|
||||
sub.Unsubscribe()
|
||||
if err := <-done; err != nil {
|
||||
t.Fatal(err)
|
||||
}
|
||||
}
|
||||
Loading…
Reference in New Issue