runtime: non-cooperative goroutine preemption does not work when built using c-archive or c-shared

[wangfakang]

Non-cooperative goroutine preemption does not work when built using c-archive or c-shared, because of this PR not install signal go handler and cause signal preemption disabled.

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

$ 1.14

Does this issue reproduce with the latest release?

yeah.

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

go env Output

$ go env
GO111MODULE=""

GOARCH="amd64"

GOBIN=""

GOCACHE="/home/fakang.wfk/.cache/go-build"

GOENV="/home/fakang.wfk/.config/go/env"

GOEXE=""

GOFLAGS=""

GOHOSTARCH="amd64"

GOHOSTOS="linux"

GOINSECURE=""

GONOPROXY=""

GONOSUMDB=""

GOOS="linux"

What did you do?

test.c

#include <stdio.h>
#include <unistd.h>

#include"cgo.h"

int main(){
    sleep(1);
    printf("start cgo\n");
    test();
    printf("exit cgo\n");
    sleep(5);
    return 0;
}

cgo.go

package main

import (
        "runtime"
)

import "C"

func init() {
        runtime.GOMAXPROCS(1)
        go func() {
                println("init ok")
                for {
                }
        }()
}

//export test
func test() {
        println("I got scheduled!")
}

func main() {}

run:

go build -o cgo.so -buildmode=c-shared cgo.go
gcc -o main main.c cgo.so

What did you expect to see?

./main

init ok
start cgo
I got scheduled!
exit cgo

What did you see instead?

./main

init ok
start cgo

[gopherbot]

Change https://golang.org/cl/360861 mentions this issue: runtime: install sigPreempt signal handler for c-archive/c-shared

[wangfakang]

@ianlancetaylor The signal _SIGPROF may also need to be added because CPUProfile depends on it.

[ianlancetaylor]

Please always write plain text as plain text, never as an image. Plain text is much easier to read and it is possible to cut and paste it. Thanks.

If Go profiling is requested a signal handler will be installed for SIGPROF if necessary. We definitely don't want c-archive or c-shared Go code to override the SIGPROF handling of the main program; we only want to use the Go handling if the Go program specifically requests it.

[wangfakang]

Please always write plain text as plain text, never as an image. Plain text is much easier to read and it is possible to cut and paste it. Thanks.

If Go profiling is requested a signal handler will be installed for SIGPROF if necessary. We definitely don't want c-archive or c-shared Go code to override the SIGPROF handling of the main program; we only want to use the Go handling if the Go program specifically requests it.

@ianlancetaylor Um, sorry. Because I didn't have permission to comment directly on the go-review.googlesource.com platform, so do it.
I have a question that if we don't want c-archive or c-shared Go code to override the SIGPROF handling of the main program, but why is it necessary to check SIGPROF in runtime·cgoSigtramp?

go/src/runtime/sys_linux_amd64.s

Lines 436 to 440 in 6b3f4d3

	sigtrampnog:
	// Signal arrived on a non-Go thread. If this is SIGPROF, get a
	// stack trace.
	CMPL DI, $27 // 27 == SIGPROF
	JNZ sigtramp

[ianlancetaylor]

The cgoSigtramp function is used in all build modes, not just c-archive and c-shared. Also, to be clear, I am saying that for c-archive and c-shared we must not override the handling of SIGPROF by default. If the program itself calls Go functions like runtime/pprof.StartCPUProfile, then the Go standard library will go ahead and override the handling of SIGPROF. And in that case of course it's important that cgoSigtramp handle SIGPROF correctly.

Further discussion of these points should take place in a forum, not here on the issue tracker. See https://golang.org/wiki/Questions. Thanks.