Sometimes signal not received to signal handler - linux

Question

I'm sending say 100 signal (SIGINT) from terminal in while loop continuously, as i have register signal handler for this signal, so any signal comes either in auxiliary thread or main thread (as signal disposition is shared by all threads) should print "caught signal: ..." message as output every time i send the signal. but i observed out of 100, some random less no of times say 95, 84 times being this message printed. can some one please explain why all 100 signal is not being printed and how to print all 100 signal with below code.
#include <pthread.h>
#include <signal.h>
#include <stdio.h>
#include <unistd.h>
// Signal Handler for entire Process (shared by all threads)
void signalHandler(int param)
{
printf("Caught signal: %d ", param);
}
void *childFun(void *arg)
{
// Register signal Handler here
struct sigaction childpsa;
childpsa.sa_handler = signalHandler;
sigaction(SIGTERM, &childpsa, NULL);
sigaction(SIGHUP, &childpsa, NULL);
sigaction(SIGINT, &childpsa, NULL);
sigaction(SIGCONT, &childpsa, NULL);
sigaction(SIGTSTP, &childpsa, NULL);
while (1) {
// doSomething in while loop
}
}
int main(void)
{
// create a auxiliary thread here
pthread_t child_threadId;
int err = pthread_create(&child_threadId, NULL, &childFun, NULL);
while (1) {
// main program do something
}
return 1;
}

Answer 1

Most of Linux implementation doesn't support queueing of signal, so if a process receives same signal 'x' number of times, it will be called only once.
Also you shouldn't use function like printf inside signal handler(instead use some counters(an integer) that increments for every invocation )
Except
POSIX.1 allows the system to deliver the signal either once or more than once in case a blocked signal is generated more than once before the process unblocks the signal. If the system delivers the signal more than once, we say that the signals are queued. Most UNIX systems, however, do not queue signals unless they support the real-time extensions to POSIX.1. Instead, the UNIX kernel simply delivers the signal once. [p336]
https://notes.shichao.io/apue/ch10/#reliable-signal-terminology-and-semantics