Incorrect signal processing while using dlib detector - c++

Question

I try block some signals in the main thread, and then create a dedicated thread to fetch those signals via sigwait. After that, in the main thread I try to use dlib frontal face detector. If I comment out face detector use, then my code works fine, but with detector the program terminates by any signal. My source code (dlib 19.19):
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <signal.h>
#include <thread>
#include <dlib/image_processing/frontal_face_detector.h>
int main(int argc, char *argv[])
{
sigset_t set;
sigemptyset(&set);
sigaddset(&set, SIGINT);
sigaddset(&set, SIGUSR1);
sigaddset(&set, SIGUSR2);
pthread_sigmask(SIG_BLOCK, &set, NULL);
auto t = std::thread([&set]() {
for (int sig = -1; sig != SIGINT; ) {
sigwait(&set, &sig);
printf("Signal handling thread got signal %d\n", sig);
}
});
//auto d = dlib::get_frontal_face_detector();
t.join();
}
Moreover, this code works fine:
void handler(int sig, siginfo_t *, void *)
{
printf("Signal %d\n", sig);
}
int main(int argc, char *argv[])
{
struct sigaction sa;
sigemptyset(&sa.sa_mask);
sa.sa_flags = 0;
sa.sa_sigaction = handler;
sigaction(SIGUSR1, &sa, NULL);
sigaction(SIGUSR2, &sa, NULL);
sigaction(SIGINT, &sa, NULL);
auto d = dlib::get_frontal_face_detector();
pause();
}