Add thread loop infrastructure to NativeActivityThread (334bc554) · Commits · e / os / android_frameworks_base

libs/native_activity_thread/Android.bp

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		@@ -18,6 +18,19 @@ package {
		default_visibility: ["//system/zygote:__subpackages__"],
		}

		rust_bindgen {
		name: "liblooper_bindgen",
		crate_name: "looper_bindgen",
		wrapper_src: "src/bindings/looper.h",
		source_stem: "looper_bindings",
		header_libs: [
		"native_headers",
		],
		shared_libs: [
		"libandroid",
		],
		}

		rust_library {
		name: "libnative_activity_thread",
		crate_name: "native_activity_thread",
		@@ -26,7 +39,12 @@ rust_library {
		"src/lib.rs",
		],
		rustlibs: [
		"activitymanager_structured_aidl-rust",
		"libanyhow",
		"libbinder_rs",
		"liblogger",
		"liblibc",
		"liblog_rust",
		"liblooper_bindgen",
		],
		}

libs/native_activity_thread/src/bindings/looper.h

0 → 100644

+1 −0

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		#include <android/looper.h>

libs/native_activity_thread/src/lib.rs

+2 −0

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		@@ -17,6 +17,8 @@

		use log::{info, LevelFilter};

		mod task;

		/// Start NativeActivityThread to manage the process.
		pub fn run_native_activity_thread(start_seq: i64) -> ! {
		logger::init(

libs/native_activity_thread/src/task.rs

0 → 100644

+247 −0

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		//
		// Copyright (C) 2025 The Android Open-Source Project
		//
		// Licensed under the Apache License, Version 2.0 (the "License");
		// you may not use this file except in compliance with the License.
		// You may obtain a copy of the License at
		//
		// http://www.apache.org/licenses/LICENSE-2.0
		//
		// Unless required by applicable law or agreed to in writing, software
		// distributed under the License is distributed on an "AS IS" BASIS,
		// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
		// See the License for the specific language governing permissions and
		// limitations under the License.

		use anyhow::{anyhow, bail, Context, Result};
		use log::{error, info};
		use looper_bindgen::{
		ALooper, ALooper_addFd, ALooper_callbackFunc, ALooper_pollOnce, ALooper_prepare,
		ALooper_removeFd, ALOOPER_EVENT_INPUT, ALOOPER_POLL_CALLBACK, ALOOPER_POLL_ERROR,
		};
		use std::{
		ffi::{c_int, c_void},
		os::fd::{AsRawFd, FromRawFd, OwnedFd, RawFd},
		sync::mpsc::{self, channel, TryRecvError},
		thread,
		};

		const ALOOPER_CALLBACK_FUNC_RETURN_VALUE_CONTINUE: c_int = 1;

		macro_rules! retry_eintr {
		($libc_call:expr) => {
		loop {
		match $libc_call {
		-1 => {
		let e = std::io::Error::last_os_error();
		match e.raw_os_error() {
		Some(libc::EINTR) => continue,
		_ => break Err(e),
		}
		}
		result => {
		break Ok(result);
		}
		}
		}
		};
		}

		/// A struct used to send tasks to `Handler`.
		#[allow(dead_code)]
		pub struct Sender<T: Send> {
		tx: mpsc::Sender<T>,
		waker_fd: OwnedFd,
		}

		#[allow(dead_code)]
		impl<T: Send> Sender<T> {
		/// Send a task to the associated `Handler`.
		pub fn send(&self, task: T) -> Result<()> {
		self.tx.send(task).map_err(\|_\| anyhow!("Failed to send the task"))?;
		self.wake()
		}

		fn wake(&self) -> Result<()> {
		let res = retry_eintr!(
		// SAFETY: `self.waker_fd` is a valid eventfd.
		unsafe { libc::eventfd_write(self.waker_fd.as_raw_fd(), 1) }
		);
		if let Err(e) = res {
		bail!("Failed to write to the waker fd: {}", e);
		}
		Ok(())
		}
		}

		/// A trait defining expected behavior of callback functions for `Handler`.
		pub trait HandlerCallback<T: Send> {
		/// Handle a task.
		/// This function is called on the same thread that created the `Handler` owning the callback.
		/// If this function returns Err, the handler is deactivated and this function will never be
		/// called anymore even if there is a sent task.
		fn handle_task(&mut self, task: T) -> Result<()>;
		}

		struct HandlerInner<T: Send, C: HandlerCallback<T>> {
		callback: C,
		event_fd: OwnedFd,
		tx: mpsc::Sender<T>,
		rx: mpsc::Receiver<T>,
		}

		impl<T: Send, C: HandlerCallback<T>> HandlerInner<T, C> {
		fn handle_tasks(&mut self) -> Result<()> {
		loop {
		let req = self.rx.try_recv();
		match req {
		Ok(req) => self.callback.handle_task(req)?,
		Err(TryRecvError::Empty) => return Ok(()),
		Err(TryRecvError::Disconnected) => bail!("mpsc disconnected"),
		}
		}
		}
		}

		/// A struct representing a task handler.
		#[allow(dead_code)]
		pub struct Handler<T: Send, C: HandlerCallback<T>> {
		// This makes Handler !Send.
		looper: *mut ALooper,
		// Wrap members used for task handling with Box to ensure they are alive during the handler is
		// registered to the looper.
		inner: Box<HandlerInner<T, C>>,
		}

		#[allow(dead_code)]
		impl<T: Send, C: HandlerCallback<T>> Handler<T, C> {
		pub fn new_on_current_thread(callback: C) -> Result<Self> {
		// SAFETY: 0 is a valid argument.
		let looper = unsafe { ALooper_prepare(0) };
		assert!(!looper.is_null());

		// SAFETY: Passing valid arguments.
		let fd: RawFd = unsafe { libc::eventfd(0, libc::EFD_CLOEXEC \| libc::EFD_NONBLOCK) };
		if fd == -1 {
		bail!("Failed to create an eventfd");
		}
		// SAFETY: `fd` is a valid owned fd.
		let event_fd = unsafe { OwnedFd::from_raw_fd(fd) };

		let (tx, rx) = channel::<T>();
		let mut inner = Box::new(HandlerInner { callback, event_fd, tx, rx });
		let inner_ptr = &mut inner as mut HandlerInner<T, C> as *mut c_void;
		let handler = Self { looper, inner };

		// SAFETY: `inner_ptr` outlives the duration `poll_callback` is registered.
		unsafe {
		handler.add_fd(
		handler.inner.event_fd.as_raw_fd(),
		ALOOPER_POLL_CALLBACK,
		ALOOPER_EVENT_INPUT as c_int,
		Some(Self::poll_callback),
		inner_ptr,
		)
		}
		.context("Failed to add the waker fd")?;

		info!("A handler is activated on the thread {:?}", thread::current().id());

		Ok(handler)
		}

		pub fn get_sender(&self) -> Result<Sender<T>> {
		let tx = self.inner.tx.clone();
		let waker_fd = self.inner.event_fd.try_clone().context("Failed to clone the eventfd")?;
		Ok(Sender::<T> { tx, waker_fd })
		}

		/// # Safety
		///
		/// Users must ensure the safety requirements for the callback function to be registered are
		/// met while it's registered.
		unsafe fn add_fd(
		&self,
		fd: RawFd,
		ident: c_int,
		events: c_int,
		callback: ALooper_callbackFunc,
		data: *mut c_void,
		) -> Result<()> {
		// SAFETY: `self.looper` is a valid ALooper pointer.
		let ret = unsafe { ALooper_addFd(self.looper, fd, ident, events, callback, data) };
		if ret == -1 {
		bail!("ALooper_addFd failed");
		}
		Ok(())
		}

		fn remove_fd(&self, fd: RawFd) -> Result<()> {
		// SAFETY: `self.looper` is a valid ALooper pointer.
		let ret = unsafe { ALooper_removeFd(self.looper, fd) };
		match ret {
		1 => Ok(()),
		0 => bail!("The fd hasn't been added"),
		_ => bail!("ALooper_removeFd failed"),
		}
		}

		/// This function is supposed to be used as a callback function for `ALooper_addFd`.
		/// There's no easy way to tell the caller of `ALooper_pollOnce` that an error occurred, so
		/// this function will panic instead of silently unregistering itself from the looper in such
		/// cases.
		///
		/// # Safety
		///
		/// Users must ensure that the associated `data` is a valid pointer to an HandlerInner
		/// instance while this callback is registered.
		unsafe extern "C" fn poll_callback(fd: RawFd, _events: c_int, data: *mut c_void) -> c_int {
		let inner_ptr = data as *mut HandlerInner<T, C>;
		// SAFETY: `inner_ptr` is a valid HandlerInner pointer.
		let inner = unsafe { inner_ptr.as_mut() }.unwrap();
		assert_eq!(fd, inner.event_fd.as_raw_fd());

		let mut val = std::mem::MaybeUninit::<libc::eventfd_t>::uninit();
		let res = retry_eintr!(
		// SAFETY: `inner.event_fd` is a valid eventfd and `val` is properly allocated.
		unsafe { libc::eventfd_read(inner.event_fd.as_raw_fd(), val.as_mut_ptr()) }
		);
		if let Err(e) = res {
		panic!("Failed to read from the event fd: {}", e);
		}

		let res = inner.handle_tasks();
		if let Err(e) = res {
		panic!("Failed to handle a task: {}", e);
		}
		ALOOPER_CALLBACK_FUNC_RETURN_VALUE_CONTINUE
		}
		}

		impl<T: Send, C: HandlerCallback<T>> Drop for Handler<T, C> {
		fn drop(&mut self) {
		if self.remove_fd(self.inner.event_fd.as_raw_fd()).is_err() {
		error!("Failed to remove the event fd");
		}
		}
		}

		/// Run the server loop on this thread.
		pub fn run_thread_loop_once() -> Result<()> {
		// SAFETY: `ALooper_pollOnce` accepts the null pointer for `outFd`, `outEvents` and `outData`.
		let ret = unsafe {
		ALooper_pollOnce(-1, std::ptr::null_mut(), std::ptr::null_mut(), std::ptr::null_mut())
		};
		if ret == ALOOPER_POLL_ERROR {
		bail!("ALooper_pollOnce failed");
		}
		Ok(())
		}

		/// Run the server loop on this thread. This function will never return until an error occurs.
		#[allow(dead_code)]
		pub fn run_thread_loop() -> Result<()> {
		loop {
		run_thread_loop_once()?;
		}
		}