feat: improve TCPDialer by sync.map instead of map+mutex

[tylitianrui]

No description provided.

[erikdubbelboer]

The downside of sync.Map is that it requires two allocations instead of one:
https://play.golang.org/p/RVUVvngcHFi
vs
https://play.golang.org/p/OW7hGm0J1JN

Also this mutex isn't very much in contention. So I don't think we should do this.

[tylitianrui]

The downside of sync.Map is that it requires two allocations instead of one:
https://play.golang.org/p/RVUVvngcHFi
vs
https://play.golang.org/p/OW7hGm0J1JN

Also this mutex isn't very much in contention. So I don't think we should do this.

yes, sync.map requires more memory allocation than map , because of its downside implement . tcpAddrEntry.tcpAddrsMap is a cache ( read more , write less ) of net.TCPAddr . so i think we should focus on cache-read more than cache-write

• read

syncMap read：

var syncMap sync.Map
func BenchmarkSyncMap(b *testing.B) {
	syncMap.Store("example.com:443", &tcpAddrEntry{})
	b.RunParallel(func(pb *testing.PB) {
		for pb.Next() {
			syncMap.Load("example.com:443")
		}
	})
}

benchmark

goos: darwin
goarch: amd64
pkg: github.com/valyala/fasthttp
BenchmarkSyncMap
BenchmarkSyncMap-8   	173760667	         7.35 ns/op	       0 B/op	       0 allocs/op
PASS
ok  	github.com/valyala/fasthttp	2.218s

Map read：

var (
	mu sync.Mutex
	m  = make(map[string]*tcpAddrEntry)
)

func BenchmarkMap(b *testing.B) {
	m["example.com:443"] = &tcpAddrEntry{}
	b.RunParallel(func(pb *testing.PB) {
		for pb.Next() {
			mu.Lock()
			_ = m["example.com:443"]
			mu.Unlock()
		}
	})
}

benchmark

goos: darwin
goarch: amd64
pkg: github.com/valyala/fasthttp
BenchmarkMap
BenchmarkMap-8   	17126959	        69.7 ns/op	       0 B/op	       0 allocs/op
PASS
ok  	github.com/valyala/fasthttp	1.525s

when fasthttp.Dial is call in concurrent gorountine, as it faces me in real work , Map + mutex is not a better choice . when not in concurrency ， Map + mutex is better.

[erikdubbelboer]

Since the extra allocation isn't in a hot path and it makes the cache slightly faster I'll merge it.

[erikdubbelboer]

Thanks!