handling sigterm in OSx - c++

Question

I have console C++ application built in XCode 6 and want to add SIGTERM handler to it. There are a lot of examples, but I can't get them to work.
#include <csignal>
namespace
{
volatile std::sig_atomic_t gDone = 0;
}
static void term_handler(int i)
{
gDone = 1;
}
int main(int argc, const char * argv[])
{
std::signal(SIGTERM, term_handler);
while (!gDone);
return 0;
}
The debugger stopped on the while statement, but the handler was not called. The same problem with this code
#include <signal.h>
volatile sig_atomic_t gDone = 0;
void term_handler(int i)
{
gDone = 1;
}
int main(int argc, char* argv[])
{
struct sigaction sa;
sigset_t newset;
sigemptyset(&newset);
sigaddset(&newset, SIGHUP);
sigprocmask(SIG_BLOCK, &newset, 0);
sa.sa_handler = term_handler;
sigaction(SIGTERM, &sa, 0);
while(!gDone);
return 0;
}
Is there a problem with the code? What is the right way to handle signals in OSX?

Answer 1

After you send the signal, and the debugger stops, you have to continue to get to your breakpoint inside the signal handler.
(lldb) break set -n term_handler
Breakpoint 1: where = a.out`term_handler(int) + 4 at sig.cc:11, address = 0x0000000100000f54
(lldb) run
Process 42532 launched: './a.out' (x86_64)
Process 42532 stopped
* thread #1: tid = 0x18dc39, 0x0000000100000f30 a.out`main(argc=15, argv=0x00007fff5fbffb58) + 32 at sig.cc:17, queue = 'com.apple.main-thread', stop reason = signal SIGTERM
frame #0: 0x0000000100000f30 a.out`main(argc=15, argv=0x00007fff5fbffb58) + 32 at sig.cc:17
14 int main(int argc, const char * argv[])
15 {
16 std::signal(SIGTERM, term_handler);
-> 17 while (!gDone);
18 std::puts("done!");
19 return 0;
20 }
(lldb) c
Process 42532 resuming
Process 42532 stopped
* thread #1: tid = 0x18dc39, 0x0000000100000f54 a.out`term_handler(i=15) + 4 at sig.cc:11, queue = 'com.apple.main-thread', stop reason = breakpoint 1.1
frame #0: 0x0000000100000f54 a.out`term_handler(i=15) + 4 at sig.cc:11
8
9 static void term_handler(int i)
10 {
-> 11 gDone = 1;
12 }
13
14 int main(int argc, const char * argv[])
(lldb) `

Answer 2

OK, I'm home now and working on my Mac. Again, your code (second sample specifically) has proven just fine. The confirmation was done in Terminal with gcc and "kill -TERM ". Source refers to SIGTERM, like normal, but kill refers (on OS X) to TERM. The XCode pause you are seeing is due to XCode, not your code. I tried it both ways, Terminal and XCode. I could not find a pref to inhibit that interruption, however.
Just to focus here ...You asked, Is there a problem with the code? Answer: No. You asked, What is the right way to handle signals in OSX? Answer: The way you're already doing it. New question: How do I get XCode (lldb) to not pause when signals occur? Answer: How to tell LLDB debugger not to handle SIGBUS?

Answer 3

Your code is fine. Kill with:
kill -SIGTERM 31573
because
kill -9 31573
where 31573 was my process ID, did not exit gracefully. I added a printf to your code to tell me it was exiting gracefully.