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.

1 files changed, 226 insertions, 0 deletions

diff --git a/event/feed_test.go b/event/feed_test.go
new file mode 100644
index 000000000..4f897c162
--- /dev/null
+++ b/event/feed_test.go
@@ -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()
+}