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Question

I'm using Go to launch a couple of scripts and when they have some problems they use the "alert" signal, I know Go can capture those signals but I need to know the PID that originated the Signal. in C to the signal handler is passed a structure to know the pid who originated the signal but in Go looks like is not the case

package main

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

func main() {

    c := make(chan os.Signal, 1)
    signal.Notify(c, os.Interrupt, os.Kill)

    s := <-c
    fmt.Println("Got signal:", s)
    fmt.Printf("%+v
",s)
}

the example below (extracted from the signal doc) send me the signal who originated the call but not any useful info (like the pid)

Answer 1

No, you can't do this in an officially supported manner. The Go runtime needs to own the signal handlers, and that extra information isn't exposed in any way.

You may still be able to do this from C by setting up a new signal handler, but I would be very cautious going about this (see issues like issue/7227). You're probably better off using another method for communication other than a signal.

Here's a partial example based on Ian's code from issue 7227:

package main

/*
#include <stdio.h>
#include <signal.h>
#include <string.h>

struct sigaction old_action;
void handler(int signum, siginfo_t *info, void *context) {
    printf("Sent by %d
", info->si_pid);
}

void test() {
    struct sigaction action;
    sigaction(SIGUSR1, NULL, &action);
    memset(&action, 0, sizeof action);
    sigfillset(&action.sa_mask);
    action.sa_sigaction = handler;
    action.sa_flags = SA_NOCLDSTOP | SA_SIGINFO | SA_ONSTACK;
    sigaction(SIGUSR1, &action, &old_action);
}
*/
import "C"

import (
    "os"
    "syscall"
    "time"
)

func main() {
    C.test()
    pid := os.Getpid()
    for {
        syscall.Kill(pid, syscall.SIGUSR1)
        time.Sleep(time.Second)
    }
}