syscall: signal SIGURG(I/O condition) on go1.14.1, but no SIGURG signal before go 1.14

[yangwenmai]

What version of Go are you using (go version)?

$ go version
1.14.1
1.13.8

Does this issue reproduce with the latest release?

Yes

What operating system and processor architecture are you using (go env)?

go env Output

$ go env
GO111MODULE=""

GOARCH="amd64"

GOBIN="/Users/maiyang/develop/goworkspace/bin"

GOCACHE="/Users/maiyang/Library/Caches/go-build"

GOENV="/Users/maiyang/Library/Application Support/go/env"

GOEXE=""

GOFLAGS=""

GOHOSTARCH="amd64"

GOHOSTOS="darwin"

GONOPROXY=""

GONOSUMDB=""

GOOS="darwin"

GOPATH="/Users/maiyang/develop/goworkspace"

GOPRIVATE=""

GOPROXY="https://proxy.golang.org,direct"

GOROOT="/Users/maiyang/develop/go1.13.8"

GOSUMDB="sum.golang.org"

GOTMPDIR=""

GOTOOLDIR="/Users/maiyang/develop/go1.13.8/pkg/tool/darwin_amd64"

GCCGO="gccgo"

AR="ar"

CC="clang"

CXX="clang++"

CGO_ENABLED="1"

GOMOD=""

CGO_CFLAGS="-g -O2"

CGO_CPPFLAGS=""

CGO_CXXFLAGS="-g -O2"

CGO_FFLAGS="-g -O2"

CGO_LDFLAGS="-g -O2"

PKG_CONFIG="pkg-config"

GOGCCFLAGS="-fPIC -m64 -pthread -fno-caret-diagnostics -Qunused-arguments -fmessage-length=0 -fdebug-prefix-map=/var/folders/hy/qzqhs53939lg6b93mr419lnh0000gn/T/go-build297497902=/tmp/go-build -gno-record-gcc-switches -fno-common"

What did you do?

package main

import (
	"fmt"
	"os"
    "runtime"
	"os/signal"
	"syscall"
)

func main() {
	s := make(chan os.Signal, 1)
	signal.Notify(s)
	go func() {
		for {
		}
	}()
	for {
		switch signal := <-s; signal {
		case os.Interrupt, os.Kill, syscall.SIGABRT, syscall.SIGTERM:
			fmt.Println("stopped")
			return
			case syscall.SIGURG:
			 fmt.Println("sigurg")
			runtime.Gosched()
		default:
			fmt.Printf("unhandled signal: %v\n", signal)
		}
	}
}

What did you expect to see?

Output:

sigurg
sigurg
sigurg
sigurg
sigurg
sigurg
...

What did you see instead?

On go1.14.1 is output:

sigurg
sigurg
sigurg
sigurg
sigurg
sigurg
...

But on go1.13.8 is empty output.

Maybe we should keep the same with the old version(empty output)?

[OneOfOne]

That's due to the new Non-cooperative goroutine preemption.

• os/signal: notify should filter out runtime-generated SIGURG #37942
• runtime: non-cooperative goroutine preemption #24543

[andybons]

Duplicate of #37942

[yangwenmai]

Thanks.