How to sue signal to get backtrace of other thread?

Question

I am an iOS developer and trying to get backtrace of the main thread when in a child thread.

First of all, anything like performSelector or dispatch_async doesn't work because it will destroy the current backtrace of main thread.

I am not good at C/C++ programming so look into the symbols in memory seems impossible to me.

In my opinion, the key to solve this problem is to get code executed in a particular thread without calling a method. This article inspires me to use signal.

I know that pthread_kill can send a signal to a particular thread and then a handler can catch this signal. However I can't find and runnable demo about this. All demos I found use a handler to catch signal generated outside the process, e.g. press Ctrl + C.

I tried the code below but still got a signal SIGINT which means it is not caught by the handler.

#include <stdio.h>
#include <stdlib.h>
#include <signal.h>
#include <unistd.h>
#include <pthread.h>

void sig_handler(int signum) {
    printf("Received signal %d\n", signum);
}

int main() {
    signal(SIGINT, sig_handler);
    pthread_kill(pthread_self(), SIGINT);
    return 0;
}

I've also heard that use printf is not safe in a signal handler. So I wonder is it possible to use signal to get backtrace of other threads.