Merge "init: use an eventfd instead of socketpair to wake the main loop" (44a6d9a5) · Commits · e / os / android_system_core

init/init.cpp

+18 −21

Original line number	Diff line number	Diff line
		@@ -22,6 +22,7 @@
		#include <signal.h>
		#include <stdlib.h>
		#include <string.h>
		#include <sys/eventfd.h>
		#include <sys/mount.h>
		#include <sys/signalfd.h>
		#include <sys/types.h>
		@@ -115,30 +116,26 @@ static std::queue<PendingControlMessage> pending_control_messages;
		// to fill that socket and deadlock the system. Now we use locks to handle the property changes
		// directly in the property thread, however we still must wake the epoll to inform init that there
		// is a change to process, so we use this FD. It is non-blocking, since we do not care how many
		// times WakeEpoll() is called, only that the epoll will wake.
		static int wake_epoll_fd = -1;
		// times WakeMainInitThread() is called, only that the epoll will wake.
		static int wake_main_thread_fd = -1;
		static void InstallInitNotifier(Epoll* epoll) {
		int sockets[2];
		if (socketpair(AF_UNIX, SOCK_STREAM \| SOCK_CLOEXEC \| SOCK_NONBLOCK, 0, sockets) != 0) {
		PLOG(FATAL) << "Failed to socketpair() between property_service and init";
		}
		int epoll_fd = sockets[0];
		wake_epoll_fd = sockets[1];

		auto drain_socket = [epoll_fd] {
		char buf[512];
		while (read(epoll_fd, buf, sizeof(buf)) > 0) {
		wake_main_thread_fd = eventfd(0, EFD_CLOEXEC);
		if (wake_main_thread_fd == -1) {
		PLOG(FATAL) << "Failed to create eventfd for waking init";
		}
		auto clear_eventfd = [] {
		uint64_t counter;
		TEMP_FAILURE_RETRY(read(wake_main_thread_fd, &counter, sizeof(counter)));
		};

		if (auto result = epoll->RegisterHandler(epoll_fd, drain_socket); !result.ok()) {
		if (auto result = epoll->RegisterHandler(wake_main_thread_fd, clear_eventfd); !result.ok()) {
		LOG(FATAL) << result.error();
		}
		}

		static void WakeEpoll() {
		constexpr char value[] = "1";
		TEMP_FAILURE_RETRY(write(wake_epoll_fd, value, sizeof(value)));
		static void WakeMainInitThread() {
		uint64_t counter = 1;
		TEMP_FAILURE_RETRY(write(wake_main_thread_fd, &counter, sizeof(counter)));
		}

		static class PropWaiterState {
		@@ -182,7 +179,7 @@ static class PropWaiterState {
		LOG(INFO) << "Wait for property '" << wait_prop_name_ << "=" << wait_prop_value_
		<< "' took " << *waiting_for_prop_;
		ResetWaitForPropLocked();
		WakeEpoll();
		WakeMainInitThread();
		}
		}
		}
		@@ -249,7 +246,7 @@ static class ShutdownState {
		}
		shutdown_command_ = command;
		do_shutdown_ = true;
		WakeEpoll();
		WakeMainInitThread();
		}

		std::optional<std::string> CheckShutdown() {
		@@ -333,7 +330,7 @@ void PropertyChanged(const std::string& name, const std::string& value) {

		if (property_triggers_enabled) {
		ActionManager::GetInstance().QueuePropertyChange(name, value);
		WakeEpoll();
		WakeMainInitThread();
		}

		prop_waiter_state.CheckAndResetWait(name, value);
		@@ -459,7 +456,7 @@ bool QueueControlMessage(const std::string& message, const std::string& name, pi
		return false;
		}
		pending_control_messages.push({message, name, pid, fd});
		WakeEpoll();
		WakeMainInitThread();
		return true;
		}

		@@ -485,7 +482,7 @@ static void HandleControlMessages() {
		}
		// If we still have items to process, make sure we wake back up to do so.
		if (!pending_control_messages.empty()) {
		WakeEpoll();
		WakeMainInitThread();
		}
		}