`signal` function on CentOS: unexpected behavior - c++

Question

I need to disable SIGPIPE on CentOS application, because this signal crashes my application when it works with unstable Internet connection.
I use following code in main function:
signal(SIGPIPE, SIG_IGN);
However, program still crashes with SIGPIPE. What is the reason? Have I to call this function on each thread, or it is enough to call in main function, and program will ignore SIGPIPE globally? And if it is not required to be called on each thread, why SIGPIPE still crashes program if it is supposed to ignore the signal?

Answer 1

Here it is a code sample that let you set up your own signal handler on linux, catch SIGPIPE and do something with that.
#include <signal.h>
#include <unistd.h>
#include <cerrno>
#include <system_error>
#include <iostream>
static sigset_t theMask;
static int count = 0;
static void
signalWrapper(
int theSignalNumber,
siginfo_t* theSignalDescription,
void* theUserContext)
{
// Do something here as reaction to you SIGPIPE
// This is better way to react on such things
std::cout << "Got signal " << theSignalNumber << std::endl;
// Reinstall handler
struct ::sigaction sa;
sa.sa_sigaction = &signalWrapper;
sa.sa_mask = theMask;
sa.sa_flags = SA_SIGINFO;
try
{
if (::sigaction(theSignalNumber, &sa, NULL) == -1)
throw std::error_code(errno, std::system_category());
}
catch (const std::error_code& ec)
{
std::cerr << ec << std::endl;
}
count++;
}
void
setupSignalHandlers()
{
struct ::sigaction sa;
// Prepare mask
sigemptyset(&theMask);
sigaddset(&theMask, SIGPIPE);
// Add some more if you need it to process
sa.sa_mask = theMask;
sa.sa_flags = SA_SIGINFO;
sa.sa_sigaction = &signalWrapper;
// Perform setup
try
{
if (::sigaction(SIGPIPE, &sa, NULL) == -1)
throw std::error_code(errno, std::system_category());
}
catch (const std::error_code& ec)
{
std::cerr << ec << std::endl;
}
}
int
main()
{
std::cout << "Set handler!" << std::endl;
setupSignalHandlers();
std::cout << "Emit 5 SIGPIPE signals" << std::endl;
while (count < 5)
{
kill(getpid(), SIGPIPE);
usleep(100);
}
return 0;
}
and output:
Set handler!
Emit 5 SIGPIPE signals
Got signal 13
Got signal 13
Got signal 13
Got signal 13
Got signal 13
I provide signal handler since it is more correct to process signal that breaks your application than ignore it. Perhaps you need to reestablish connection or do some other stuff.

Answer 2

According to the man page for Signal(2), "The Effects of signal() in a multithreaded process are unspecified." You might try making sure to call signal() in the main thread before creating any other threads, but it's not guaranteed to work.
In any case signal() is deprecated, so I would suggest switching to sigaction(). I use it in multithreaded applications all the time without any problems.