void sigchld_handler_init() {// Create a signalling mechanism for SIGCHLD.int s[2];if (socketpair(AF_UNIX, SOCK_STREAM | SOCK_NONBLOCK | SOCK_CLOEXEC, 0, s) == -1) {PLOG(FATAL) << "socketpair failed in sigchld_handler_init";}signal_write_fd = s[0];signal_read_fd = s[1];// Write to signal_write_fd if we catch SIGCHLD.struct sigaction act;memset(&act, 0, sizeof(act));act.sa_handler = SIGCHLD_handler;act.sa_flags = SA_NOCLDSTOP;sigaction(SIGCHLD, &act, 0);ReapAnyOutstandingChildren();register_epoll_handler(signal_read_fd, handle_signal);
}

void register_epoll_handler(int fd, void (*fn)()) {epoll_event ev;ev.events = EPOLLIN;ev.data.ptr = reinterpret_cast<void*>(fn);if (epoll_ctl(epoll_fd, EPOLL_CTL_ADD, fd, &ev) == -1) {PLOG(ERROR) << "epoll_ctl failed";}
}

        epoll_event ev;int nr = TEMP_FAILURE_RETRY(epoll_wait(epoll_fd, &ev, 1, epoll_timeout_ms));if (nr == -1) {PLOG(ERROR) << "epoll_wait failed";} else if (nr == 1) {((void (*)()) ev.data.ptr)();}

void Service::KillProcessGroup(int signal) {// If we've already seen a successful result from killProcessGroup*(), then we have removed// the cgroup already and calling these functions a second time will simply result in an error.// This is true regardless of which signal was sent.// These functions handle their own logging, so no additional logging is needed.if (!process_cgroup_empty_) {LOG(INFO) << "Sending signal " << signal << " to service '" << name_ << "' (pid " << pid_<< ") process group...";int r;if (signal == SIGTERM) {r = killProcessGroupOnce(uid_, pid_, signal);} else {r = killProcessGroup(uid_, pid_, signal);}if (r == 0) process_cgroup_empty_ = true;}
}

void Service::Reap(const siginfo_t& siginfo) {if (!(flags_ & SVC_ONESHOT) || (flags_ & SVC_RESTART)) {KillProcessGroup(SIGKILL);}// Remove any descriptor resources we may have created.std::for_each(descriptors_.begin(), descriptors_.end(),std::bind(&DescriptorInfo::Clean, std::placeholders::_1));for (const auto& f : reap_callbacks_) {f(siginfo);}if (flags_ & SVC_EXEC) UnSetExec();if (flags_ & SVC_TEMPORARY) return;pid_ = 0;flags_ &= (~SVC_RUNNING);start_order_ = 0;// Oneshot processes go into the disabled state on exit,// except when manually restarted.if ((flags_ & SVC_ONESHOT) && !(flags_ & SVC_RESTART)) {flags_ |= SVC_DISABLED;}// Disabled and reset processes do not get restarted automatically.if (flags_ & (SVC_DISABLED | SVC_RESET))  {NotifyStateChange("stopped");return;}// If we crash > 4 times in 4 minutes, reboot into recovery.boot_clock::time_point now = boot_clock::now();if ((flags_ & SVC_CRITICAL) && !(flags_ & SVC_RESTART)) {if (now < time_crashed_ + 4min) {if (++crash_count_ > 4) {LOG(FATAL) << "critical process '" << name_ << "' exited 4 times in 4 minutes";}} else {time_crashed_ = now;crash_count_ = 1;}}flags_ &= (~SVC_RESTART);
    flags_ |= SVC_RESTARTING;
// Execute all onrestart commands for this service.onrestart_.ExecuteAllCommands();NotifyStateChange("restarting");return;
}