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#include <thread>
#include <chrono>
#include <iostream>
#include <unistd.h>
#include <signal.h>
#include <cstring>
#include <sys/signalfd.h>
#include <sys/epoll.h>
#include <cstddef>
#include <stdexcept>
const int MAX_EVENTS = 10;
bool readall(int fd, char* p, std::size_t len) {
while( len != 0 ) {
ssize_t n = read(fd, p, len);
if( n == -1 ) {
if( errno == EAGAIN || errno == EWOULDBLOCK ) {
return false;
} else {
throw std::runtime_error("read failed.");
}
}
len -= n;
p += n;
}
return true;
}
void read_signal(int sfd) {
struct signalfd_siginfo si;
while( true ) {
if( ! readall(sfd, (char*)&si, sizeof(si)) )
return;
switch(si.ssi_signo) {
case SIGHUP:
std::cout << "SIGHUP" << std::endl;
break;
case SIGQUIT:
std::cout << "SIGQUIT" << std::endl;
break;
case SIGTERM:
std::cout << "SIGTERM" << std::endl;
break;
case SIGCHLD:
std::cout << "SIGCHLD" << std::endl;
break;
default:
std::cout << "Unknown signal: " << si.ssi_signo << std::endl;
}
}
}
int wait_signal(int sfd) {
int efd = epoll_create(10);
if( efd == -1 ) {
std::cerr << "epoll_create failed." << std::endl;
close(efd);
return 1;
}
struct epoll_event ev;
ev.events = EPOLLIN|EPOLLET;
ev.data.fd = sfd;
if( epoll_ctl(efd, EPOLL_CTL_ADD, sfd, &ev) == -1 ) {
std::cerr << "epoll_ctl failed." << std::endl;
close(efd);
return 1;
}
std::cerr << "pid=" << getpid() << std::endl;
std::cerr << "waiting for signals..." << std::endl;
std::this_thread::sleep_for(std::chrono::seconds(10));
struct epoll_event events[MAX_EVENTS];
int n = epoll_wait(efd, events, MAX_EVENTS, -1);
if( n == -1 ) {
std::cerr << "epoll_wait failed." << std::endl;
close(efd);
return 1;
}
for( int i = 0; i < n; ++i ) {
if( events[i].data.fd != sfd ) {
std::cerr << "wtf!?" << std::endl;
close(efd);
return 1;
}
read_signal(sfd);
}
close(efd);
return 0;
}
int main(int argc, char** argv) {
if( argc == 1 ) return 0;
// block signals and setup signalfd
// Threads created by the main thread inherit the signal mask.
sigset_t sigs[1];
sigemptyset(sigs);
sigaddset(sigs, SIGQUIT);
sigaddset(sigs, SIGHUP);
sigaddset(sigs, SIGTERM);
sigaddset(sigs, SIGCHLD);
if( pthread_sigmask(SIG_BLOCK, sigs, NULL) != 0 ) {
std::cerr << "pthread_sigmask failed." << std::endl;
return 1;
}
int sfd = signalfd(-1, sigs, SFD_NONBLOCK);
if( sfd == -1 ) {
std::cerr << "signalfd failed." << std::endl;
return 1;
}
// ignore SIGPIPE
// As per man 7 signal, the signal disposition is a per-process attribute.
struct sigaction act;
std::memset(&act, 0, sizeof(act));
act.sa_handler = SIG_IGN;
if( sigaction(SIGPIPE, &act, NULL) == -1 ) {
std::cerr << "sigaction failed." << std::endl;
return 1;
}
int ret = wait_signal(sfd);
close(sfd);
return ret;
}
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