feat: Promise/Future for multi-consumer async acquiring result

[jizhuozhi]

The syncx.Promise provides a facility to store a value or an error that is later acquired asynchronously via a syncx.Future created by the syncx.Promise object. Note that the syncx.Promise object is meant to be used only once.

As same as std::promise and std::future in C++(https://en.cppreference.com/w/cpp/thread/promise)

[NX-Official]

Use sync.WaitGroup and atomic.CompareAndSwapInt32 maybe can make code cleaner and more efficient 🧐

type state struct {
	// ...
	wg   sync.WaitGroup
}

func newState() *state {
	s := &state{}
	s.wg.Add(1)
	return s
}

func (s *state) set(val interface{}, err error) {
	if atomic.CompareAndSwapInt32(&s.done, 0, 1) {
		s.val, s.err = val, err
		s.wg.Done()
	} else {
		panic("promise already satisfied")
	}
}

func (s *state) get() (interface{}, error) {
	s.wg.Wait()
	return s.val, s.err
}

func BenchmarkPromiseAndFuture(b *testing.B) {
	b.ReportAllocs()

	for i := 0; i < b.N; i++ {
		p := NewPromise()
		f := p.Future()

		go func() {
			p.Set(1, errFoo)
		}()

		_, _ = f.Get()
	}
}

current version

goos: linux
goarch: amd64
pkg: github.com/bytedance/gopkg/lang/syncx
cpu: AMD Ryzen 7 4700G with Radeon Graphics         
BenchmarkPromiseAndFuture
BenchmarkPromiseAndFuture-16    	 1915816	       633.9 ns/op	     168 B/op	       4 allocs/op
PASS

new version

goos: linux
goarch: amd64
pkg: github.com/bytedance/gopkg/lang/syncx
cpu: AMD Ryzen 7 4700G with Radeon Graphics         
BenchmarkPromiseAndFuture
BenchmarkPromiseAndFuture-16    	 2030475	       590.7 ns/op	     104 B/op	       3 allocs/op
PASS

[jizhuozhi]

Promise/Future has reimplemented using sema primitives, and its performance is now better than sync.WaitGroup.

goos: darwin
goarch: arm64
pkg: github.com/bytedance/gopkg/lang/syncx
Benchmark
Benchmark/Promise
Benchmark/Promise-12         	 2950075	       392.0 ns/op
Benchmark/WaitGroup
Benchmark/WaitGroup-12       	 2714890	       442.5 ns/op
Benchmark/Channel
Benchmark/Channel-12         	 2666980	       417.7 ns/op
PASS