net: Dial is slow on localhost #23366
Description
See #23366 (comment) for more details!
What version of Go are you using (go version)?
go version go1.9.2 windows/amd64
Does this issue reproduce with the latest release?
yes
What operating system and processor architecture are you using (go env)?
set GOARCH=amd64
set GOBIN=
set GOEXE=.exe
set GOHOSTARCH=amd64
set GOHOSTOS=windows
set GOOS=windows
set GORACE=
set GOROOT=C:\Go
set GOTOOLDIR=C:\Go\pkg\tool\windows_amd64
set GCCGO=gccgo
set CC=gcc
set CXX=g++
set CGO_ENABLED=1
set CGO_CFLAGS=-g -O2
set CGO_CPPFLAGS=
set CGO_CXXFLAGS=-g -O2
set CGO_FFLAGS=-g -O2
set CGO_LDFLAGS=-g -O2
set PKG_CONFIG=pkg-config
What did you do?
now := time.Now()
net.Dial("tcp", "localhost:3000")
fmt.Println(time.Since(now))This code outputs around 1s.
When replacing localhost with 127.0.0.1 it takes around 2ms, sometimes also <1ms.
google.de:80 is around 60ms.
Is this expected to take so much longer with localhost? Took me several hours to find out that this was the root cause of multiple issues in my application.