how cgo handle user define signal ? need go pass the signal handle to c

[hui zhang]

I am trying to extend a old c program with go.    Add websocket ability to this c program.

first  build  go as a  .so  dynamic lib

then link the so lib in c program

I run the cgo ok in an example program.

But when integrate with old c program,  c program will send a signal 42 to itself periodly.

this cause so lib terminate

rogram received signal SIG42, Real-time event 42.
[Switching to Thread 0xa53c6b70 (LWP 14957)]
runtime.futex () at /usr/local/go/src/runtime/sys_linux_386.s:444
444 /usr/local/go/src/runtime/sys_linux_386.s: No such file or directory.
in /usr/local/go/src/runtime/sys_linux_386.s
Missing separate debuginfos, use: debuginfo-install WBXcms-3.7.0-494.i686
(gdb) bt
#0 runtime.futex () at /usr/local/go/src/runtime/sys_linux_386.s:444
#1 0xb7b04c2a in runtime.futexsleep (addr=0xb7fa47ac, val=0, ns=-1) at /usr/local/go/src/runtime/os_linux.go:46
#2 0xb7ae5437 in runtime.notesleep (n=0xb7fa47ac) at /usr/local/go/src/runtime/lock_futex.go:151
#3 0xb7b0c8f4 in runtime.stopm () at /usr/local/go/src/runtime/proc.go:1936
#4 0xb7b0d848 in runtime.findrunnable (gp=@0x74421300, inheritTime=@0x0) at /usr/local/go/src/runtime/proc.go:2399
#5 0xb7b0e507 in runtime.schedule () at /usr/local/go/src/runtime/proc.go:2525
#6 0xb7b0edac in runtime.goexit0 (gp=0x744000e0) at /usr/local/go/src/runtime/proc.go:2722
#7 0xb7b2f868 in runtime.mcall () at /usr/local/go/src/runtime/asm_386.s:345
#8 0xb7b2f7c0 in runtime.rt0_go () at /usr/local/go/src/runtime/asm_386.s:241
#9 0xb7b2f7c7 in runtime.rt0_go () at /usr/local/go/src/runtime/asm_386.s:246
#10 0x00

My question is

how go so lib ignore this signal 42,  and pass the signal handle to old c program.

Thanks

[hui zhang]

I found the case is like this

c code

IgnoreSignal(42);

while(1) {

GoSleep(10);//simulate some call in go runtime , the runtime call stack is in last mail

int signo = sigwaitinfo(&signal_set, &signal_info); //will use this signo to do something ....

// usleep(1000*1000);

printf("sleep 10s \n");

// raise(42);

}

go code

//export IgnoreSignal

func IgnoreSignal(sig int) {

    signal.Ignore(syscall.Signal(sig))

}

//export GoSleep

func GoSleep(x int) {

    time.Sleep(time.Duration(x) * time.Second)

}

go build an  so lib ,  c link this so

run app

send signal like below

sigqueue(pid, 42, val);

go will catch that signal ,  and  but ignore it and delete it

what I expect  is passing the signal to  sigwaitinfo

hui zhang <fastf...@gmail.com> 于2019年8月13日周二 上午9:58写道：

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[hui zhang]

in other words

we need a go runtime signal mask .

just google, no such api provided by go yet .

I want know why ?

any workaround?

[Ian Lance Taylor]

All the details of signal handling in Go can be seen at
https://golang.org/pkg/os/signal.

There is no Go API to set the signal mask because the os/signal
package is intended to handle that for you.

It's hard to combine C and Go code in the same program and have them
both do signal handling. If your C program sends itself a signal
periodically, then I recommend that you have your C code call
sigaction to override the Go signal handler. If the Go code needs to
know about the signal, have the C code call a Go function to do so.

Ian

[LordRusk]

It seems this does not work. Any code ran from a C signal handler must be

async-signal-safe, no go code is async-signal-safe, so it sigfaults when you

try this. https://github.com/golang/go/issues/45499

 I really wish there was a way to get around this, there is really no go api

for anything to do with signals beyond what can be implemented cross platform.

for instance, there's been an issue that's almost 8 years old about the siginfo_t

struct being inaccessible from go. https://github.com/golang/go/issues/9764

I don't think anything will come of this soon.

[Ian Lance Taylor]

On Mon, Feb 28, 2022 at 5:08 AM LordRusk <zombieki...@gmail.com> wrote:
>
> It seems this does not work. Any code ran from a C signal handler must be
> async-signal-safe, no go code is async-signal-safe, so it sigfaults when you
> try this. https://github.com/golang/go/issues/45499

You can't call Go code directly from the C signal handler, no. But
whatever mechanism you use to make C code aware that a signal occurred
can also be used to make Go code aware that a signal occurred.

> I really wish there was a way to get around this, there is really no go api
> for anything to do with signals beyond what can be implemented cross platform.
>
> for instance, there's been an issue that's almost 8 years old about the siginfo_t
> struct being inaccessible from go. https://github.com/golang/go/issues/9764
>
> I don't think anything will come of this soon.

Go is an open source project. That issue will be fixed if someone
develops a workable API.

Ian

> On Friday, August 16, 2019 at 9:46:06 PM UTC-7 Ian Lance Taylor wrote:
>>
>> On Tue, Aug 13, 2019 at 1:03 AM hui zhang <fastf...@gmail.com> wrote:
>> >
>> > in other words
>> > we need a go runtime signal mask .
>> > just google, no such api provided by go yet .
>> > I want know why ?
>> > any workaround?
>>
>> All the details of signal handling in Go can be seen at
>> https://golang.org/pkg/os/signal.
>>
>> There is no Go API to set the signal mask because the os/signal
>> package is intended to handle that for you.
>>
>> It's hard to combine C and Go code in the same program and have them
>> both do signal handling. If your C program sends itself a signal
>> periodically, then I recommend that you have your C code call
>> sigaction to override the Go signal handler. If the Go code needs to
>> know about the signal, have the C code call a Go function to do so.
>>
>> Ian
>

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[Robert Engels]

Should be pretty easy to have a Go routine blocked in a C call waiting - then have the signal handler add an event to a memory queue and wake the C thread. Then dispatch to a Go side handler.

> On Feb 28, 2022, at 1:49 PM, Ian Lance Taylor <ia...@golang.org> wrote:

> To view this discussion on the web visit https://groups.google.com/d/msgid/golang-nuts/CAOyqgcWEDeVVAmQ2S7NETAddgY3REkX1KJJt5u_OADUKCduTnw%40mail.gmail.com.