go: one shot event

benchmark.txt

$ go test -bench=. -run=NONE
goos: linux
goarch: amd64
cpu: Intel(R) Core(TM) i7-7700HQ CPU @ 2.80GHz
BenchmarkOneShotEvent-8          3904360               306.8 ns/op             8 B/op          1 allocs/op
BenchmarkChannel-8               3139602               381.7 ns/op            96 B/op          1 allocs/op
BenchmarkWaitGroup-8             2958838               408.5 ns/op            16 B/op          1 allocs/op

event.go

package unsafesync

import (
	"sync/atomic"
	"unsafe"
)

//go:noescape
//go:linkname gopark runtime.gopark
func gopark(
	onSuspend func(unsafe.Pointer, unsafe.Pointer) bool,
	argument unsafe.Pointer,
	suspendReason uint8,
	suspendTraceEvent byte,
	traceSkip int,
)

//go:noescape
//go:linkname goready runtime.goready
func goready(
	frame unsafe.Pointer,
	traceSkip int,
)

type OneShotEvent struct {
	frame unsafe.Pointer
}

func (self *OneShotEvent) Wait() {
	gopark(doSuspendBlock, unsafe.Pointer(self), 0, 0, 1)
}

func doSuspendBlock(frame, event unsafe.Pointer) bool {
	self := (*OneShotEvent)(event)
	return atomic.CompareAndSwapPointer(&self.frame, nil, frame)
}

func (self *OneShotEvent) Set() {
	frame := atomic.SwapPointer(&self.frame, unsafe.Pointer(self))
	if frame != nil {
		goready(frame, 1)
	}
}

event_test.go

package unsafesync

import (
	"fmt"
	"sync"
	"testing"
	"time"
)

func TestOneShotEvent(t *testing.T) {
	var event OneShotEvent

	go func() {
		fmt.Println("Sleep")
		time.Sleep(1 * time.Second)
		fmt.Println("Wake")
		event.Set()
	}()

	fmt.Println("Wait")
	event.Wait()
	fmt.Println("Notified")
}

func BenchmarkOneShotEvent(b *testing.B) {
	b.ReportAllocs()
	b.ResetTimer()

	for i := 0; i < b.N; i++ {
		var event OneShotEvent
		go func() { event.Set() }()
		event.Wait()
	}
}

func BenchmarkChannel(b *testing.B) {
	b.ReportAllocs()
	b.ResetTimer()

	for i := 0; i < b.N; i++ {
		ch := make(chan struct{})
		go func() { close(ch) }()
		<-ch
	}
}

func BenchmarkWaitGroup(b *testing.B) {
	b.ReportAllocs()
	b.ResetTimer()

	for i := 0; i < b.N; i++ {
		var wg sync.WaitGroup
		wg.Add(1)
		go func() { wg.Done() }()
		wg.Wait()
	}
}