Signal Attach Epoll

Sample for showing case about Linux Signal (SIGALRM) callback then epoll handle all signal together.

ENVIRONMENT

platform: Linux
language: C++11
ide : Clion

Process

int(*sigfillset)(sigset_t* set):

initializes set to full, including all signals.

int(*sigaction)(int sig,struct sigaction* act, struct sigaction* oldact):

examine and change a signal action. set sig to new act, get oldact if exists.

voidaddsig(int sig) {
structsigaction sa;
memset(&sa, '\0', sizeof(sa));
sa.sa_handler = sig_handler;
sigfillset(&sa.sa_mask);
assert(sigaction(sig, &sa, NULL) != -1);
}

addsig helps sig setup sig to action as sa, it response to new handler.

int(*socketpair)(int domain, int type, int protocol, int sv[2]):

create a pair of connected sockets. sv[0] for read, and sv[1] is for write.

voidsetup_epoll() {
epollfd_ = epoll_create(0);
assert(epollfd_ != -1);
int ret = socketpair(PF_UNIX, SOCK_STREAM, 0, m_pipefd_);
assert(ret != -1);
addfd(epollfd_, m_pipefd_[0]);
fd_setnonblock(m_pipefd_[1]);
}

setup_epoll first create epoll, then create socketpair that make m_pipefd_ array to connect each other. After that, add m_pipefd_[0] to epoll, finally set m_pipefd_[1] to nonblock.

voideventLoop() {
bool stop_server = false;
while (!stop_server) {
int number = epoll_wait(epollfd_, events_, MAX_EVENT_NUMBER);
if (number < 0 && errno != EINTR)
break;
for (int i = 0; i < number; i++) {
int sockfd = events_[i].data.fd;
if (events_[i].events & (EPOLLRDHUP | EPOLLHUP | EPOLLERR)) {
std::cout << "Error" << std::endl;
} elseif (sockfd == m_pipefd_[0]) {
puts("Receive signal!");
alarm(5);
}
} }
}

void(*eventLoop)(void) is a block loop, which retrieve notification from kernel in indefinite mode. When sockfd is equal to m_pipefd_[0], it is sure the signal came from the SIGALRM!

Ref

epoll_socket