diff --git a/event/feedof.go b/event/feedof.go new file mode 100644 index 0000000000..598038a19e --- /dev/null +++ b/event/feedof.go @@ -0,0 +1,167 @@ +// Copyright 2022 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 . + +//go:build go1.18 +// +build go1.18 + +package event + +import ( + "reflect" + "sync" +) + +// FeedOf implements one-to-many subscriptions where the carrier of events is a channel. +// Values sent to a Feed are delivered to all subscribed channels simultaneously. +// +// The zero value is ready to use. +type FeedOf[T any] struct { + once sync.Once // ensures that init only runs once + sendLock chan struct{} // sendLock has a one-element buffer and is empty when held.It protects sendCases. + removeSub chan chan<- T // interrupts Send + sendCases caseList // the active set of select cases used by Send + + // The inbox holds newly subscribed channels until they are added to sendCases. + mu sync.Mutex + inbox caseList +} + +func (f *FeedOf[T]) init() { + f.removeSub = make(chan chan<- T) + f.sendLock = make(chan struct{}, 1) + f.sendLock <- struct{}{} + f.sendCases = caseList{{Chan: reflect.ValueOf(f.removeSub), Dir: reflect.SelectRecv}} +} + +// Subscribe adds a channel to the feed. Future sends will be delivered on the channel +// until the subscription is canceled. +// +// The channel should have ample buffer space to avoid blocking other subscribers. Slow +// subscribers are not dropped. +func (f *FeedOf[T]) Subscribe(channel chan<- T) Subscription { + f.once.Do(f.init) + + chanval := reflect.ValueOf(channel) + sub := &feedOfSub[T]{feed: f, channel: channel, err: make(chan error, 1)} + + // Add the select case to the inbox. + // The next Send will add it to f.sendCases. + f.mu.Lock() + defer f.mu.Unlock() + cas := reflect.SelectCase{Dir: reflect.SelectSend, Chan: chanval} + f.inbox = append(f.inbox, cas) + return sub +} + +func (f *FeedOf[T]) remove(sub *feedOfSub[T]) { + // Delete from inbox first, which covers channels + // that have not been added to f.sendCases yet. + f.mu.Lock() + index := f.inbox.find(sub.channel) + if index != -1 { + f.inbox = f.inbox.delete(index) + f.mu.Unlock() + return + } + f.mu.Unlock() + + select { + case f.removeSub <- sub.channel: + // Send will remove the channel from f.sendCases. + case <-f.sendLock: + // No Send is in progress, delete the channel now that we have the send lock. + f.sendCases = f.sendCases.delete(f.sendCases.find(sub.channel)) + f.sendLock <- struct{}{} + } +} + +// Send delivers to all subscribed channels simultaneously. +// It returns the number of subscribers that the value was sent to. +func (f *FeedOf[T]) Send(value T) (nsent int) { + rvalue := reflect.ValueOf(value) + + f.once.Do(f.init) + <-f.sendLock + + // Add new cases from the inbox after taking the send lock. + f.mu.Lock() + f.sendCases = append(f.sendCases, f.inbox...) + f.inbox = nil + f.mu.Unlock() + + // Set the sent value on all channels. + for i := firstSubSendCase; i < len(f.sendCases); i++ { + f.sendCases[i].Send = rvalue + } + + // Send until all channels except removeSub have been chosen. 'cases' tracks a prefix + // of sendCases. When a send succeeds, the corresponding case moves to the end of + // 'cases' and it shrinks by one element. + cases := f.sendCases + for { + // Fast path: try sending without blocking before adding to the select set. + // This should usually succeed if subscribers are fast enough and have free + // buffer space. + for i := firstSubSendCase; i < len(cases); i++ { + if cases[i].Chan.TrySend(rvalue) { + nsent++ + cases = cases.deactivate(i) + i-- + } + } + if len(cases) == firstSubSendCase { + break + } + // Select on all the receivers, waiting for them to unblock. + chosen, recv, _ := reflect.Select(cases) + if chosen == 0 /* <-f.removeSub */ { + index := f.sendCases.find(recv.Interface()) + f.sendCases = f.sendCases.delete(index) + if index >= 0 && index < len(cases) { + // Shrink 'cases' too because the removed case was still active. + cases = f.sendCases[:len(cases)-1] + } + } else { + cases = cases.deactivate(chosen) + nsent++ + } + } + + // Forget about the sent value and hand off the send lock. + for i := firstSubSendCase; i < len(f.sendCases); i++ { + f.sendCases[i].Send = reflect.Value{} + } + f.sendLock <- struct{}{} + return nsent +} + +type feedOfSub[T any] struct { + feed *FeedOf[T] + channel chan<- T + errOnce sync.Once + err chan error +} + +func (sub *feedOfSub[T]) Unsubscribe() { + sub.errOnce.Do(func() { + sub.feed.remove(sub) + close(sub.err) + }) +} + +func (sub *feedOfSub[T]) Err() <-chan error { + return sub.err +} diff --git a/event/feedof_test.go b/event/feedof_test.go new file mode 100644 index 0000000000..8478eeffb1 --- /dev/null +++ b/event/feedof_test.go @@ -0,0 +1,282 @@ +// 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 . + +//go:build go1.18 +// +build go1.18 + +package event + +import ( + "sync" + "testing" + "time" +) + +func TestFeedOf(t *testing.T) { + var feed FeedOf[int] + 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) + defer timeout.Stop() + 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 TestFeedOfSubscribeSameChannel(t *testing.T) { + var ( + feed FeedOf[int] + 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 TestFeedOfSubscribeBlockedPost(t *testing.T) { + var ( + feed FeedOf[int] + nsends = 2000 + ch1 = make(chan int) + ch2 = make(chan int) + wg sync.WaitGroup + ) + defer wg.Wait() + + feed.Subscribe(ch1) + wg.Add(nsends) + for i := 0; i < nsends; i++ { + go func() { + feed.Send(99) + wg.Done() + }() + } + + sub2 := feed.Subscribe(ch2) + defer sub2.Unsubscribe() + + // We're done when ch1 has received N times. + // The number of receives on ch2 depends on scheduling. + for i := 0; i < nsends; { + select { + case <-ch1: + i++ + case <-ch2: + } + } +} + +func TestFeedOfUnsubscribeBlockedPost(t *testing.T) { + var ( + feed FeedOf[int] + nsends = 200 + chans = make([]chan int, 2000) + subs = make([]Subscription, len(chans)) + bchan = make(chan int) + bsub = feed.Subscribe(bchan) + wg sync.WaitGroup + ) + for i := range chans { + chans[i] = make(chan int, nsends) + } + + // Queue up some Sends. None of these can make progress while bchan isn't read. + wg.Add(nsends) + for i := 0; i < nsends; i++ { + go func() { + feed.Send(99) + wg.Done() + }() + } + // Subscribe the other channels. + for i, ch := range chans { + subs[i] = feed.Subscribe(ch) + } + // Unsubscribe them again. + for _, sub := range subs { + sub.Unsubscribe() + } + // Unblock the Sends. + bsub.Unsubscribe() + wg.Wait() +} + +// Checks that unsubscribing a channel during Send works even if that +// channel has already been sent on. +func TestFeedOfUnsubscribeSentChan(t *testing.T) { + var ( + feed FeedOf[int] + ch1 = make(chan int) + ch2 = make(chan int) + sub1 = feed.Subscribe(ch1) + sub2 = feed.Subscribe(ch2) + wg sync.WaitGroup + ) + defer sub2.Unsubscribe() + + wg.Add(1) + go func() { + feed.Send(0) + wg.Done() + }() + + // Wait for the value on ch1. + <-ch1 + // Unsubscribe ch1, removing it from the send cases. + sub1.Unsubscribe() + + // Receive ch2, finishing Send. + <-ch2 + wg.Wait() + + // Send again. This should send to ch2 only, so the wait group will unblock + // as soon as a value is received on ch2. + wg.Add(1) + go func() { + feed.Send(0) + wg.Done() + }() + <-ch2 + wg.Wait() +} + +func TestFeedOfUnsubscribeFromInbox(t *testing.T) { + var ( + feed FeedOf[int] + 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 BenchmarkFeedOfSend1000(b *testing.B) { + var ( + done sync.WaitGroup + feed FeedOf[int] + 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() +}