Merge changes Ida4d8c5a,I2fd90778

* changes:
  Add a Rust ping/pong example
  Add timers for Rust event loops
diff --git a/aos/events/BUILD b/aos/events/BUILD
index eb77036..d78df3a 100644
--- a/aos/events/BUILD
+++ b/aos/events/BUILD
@@ -3,7 +3,7 @@
 load("//aos:flatbuffers.bzl", "cc_static_flatbuffer")
 load("//aos:config.bzl", "aos_config")
 load("//tools/build_rules:autocxx.bzl", "autocxx_library")
-load("@rules_rust//rust:defs.bzl", "rust_doc", "rust_doc_test", "rust_test")
+load("@rules_rust//rust:defs.bzl", "rust_binary", "rust_doc", "rust_doc_test", "rust_test")
 
 package(default_visibility = ["//visibility:public"])
 
@@ -184,7 +184,6 @@
 rust_doc(
     name = "event_loop_runtime_doc",
     crate = ":event_loop_runtime",
-    target_compatible_with = ["@platforms//cpu:x86_64"],
 )
 
 rust_doc_test(
@@ -265,6 +264,60 @@
     ],
 )
 
+rust_binary(
+    name = "ping_rs",
+    srcs = [
+        "ping.rs",
+    ],
+    data = [
+        ":pingpong_config",
+    ],
+    rustc_flags = ["-Crelocation-model=static"],
+    target_compatible_with = select({
+        "//conditions:default": ["//tools/platforms/rust:has_support"],
+        "//tools:has_msan": ["@platforms//:incompatible"],
+    }),
+    deps = [
+        ":event_loop_runtime",
+        ":ping_rust_fbs",
+        ":pong_rust_fbs",
+        ":shm_event_loop_rs",
+        "//aos:configuration_rs",
+        "//aos:configuration_rust_fbs",
+        "//aos:flatbuffers_rs",
+        "//aos:init_rs",
+        "@com_github_google_flatbuffers//rust",
+        "@crate_index//:futures",
+    ],
+)
+
+rust_binary(
+    name = "pong_rs",
+    srcs = [
+        "pong.rs",
+    ],
+    data = [
+        ":pingpong_config",
+    ],
+    rustc_flags = ["-Crelocation-model=static"],
+    target_compatible_with = select({
+        "//conditions:default": ["//tools/platforms/rust:has_support"],
+        "//tools:has_msan": ["@platforms//:incompatible"],
+    }),
+    deps = [
+        ":event_loop_runtime",
+        ":ping_rust_fbs",
+        ":pong_rust_fbs",
+        ":shm_event_loop_rs",
+        "//aos:configuration_rs",
+        "//aos:configuration_rust_fbs",
+        "//aos:flatbuffers_rs",
+        "//aos:init_rs",
+        "@com_github_google_flatbuffers//rust",
+        "@crate_index//:futures",
+    ],
+)
+
 aos_config(
     name = "aos_config",
     src = "aos.json",
diff --git a/aos/events/event_loop_runtime.cc b/aos/events/event_loop_runtime.cc
index 727d806..e3d73c1 100644
--- a/aos/events/event_loop_runtime.cc
+++ b/aos/events/event_loop_runtime.cc
@@ -8,4 +8,22 @@
 OnRunForRust::~OnRunForRust() { --runtime_->child_count_; }
 bool OnRunForRust::is_running() const { return runtime_->is_running(); }
 
+std::unique_ptr<TimerForRust> TimerForRust::Make(EventLoopRuntime *runtime) {
+  auto handler = std::unique_ptr<TimerForRust>(new TimerForRust());
+  TimerForRust *inner = handler.get();
+  handler->timer_ = runtime->event_loop()->AddTimer([inner, runtime] {
+    inner->expired_ = true;
+    runtime->DoPoll();
+  });
+  return handler;
+}
+
+bool TimerForRust::Poll() {
+  if (expired_) {
+    // Reset it for next poll.
+    expired_ = false;
+    return true;
+  }
+  return false;
+}
 }  // namespace aos
diff --git a/aos/events/event_loop_runtime.h b/aos/events/event_loop_runtime.h
index 325560f..7cc551f 100644
--- a/aos/events/event_loop_runtime.h
+++ b/aos/events/event_loop_runtime.h
@@ -6,6 +6,7 @@
 // particularly ergonomic for C++. See the Rust wrapper for detailed
 // documentation.
 
+#include <chrono>
 #include <memory>
 #include <optional>
 
@@ -139,6 +140,41 @@
   EventLoopRuntime *const runtime_;
 };
 
+class TimerForRust {
+ public:
+  static std::unique_ptr<TimerForRust> Make(EventLoopRuntime *runtime);
+
+  TimerForRust(const TimerForRust &) = delete;
+  TimerForRust(TimerForRust &&) = delete;
+
+  TimerForRust &operator=(const TimerForRust &) = delete;
+  TimerForRust &operator=(TimerForRust &&) = delete;
+
+  ~TimerForRust() { timer_->Disable(); }
+
+  void Schedule(int64_t base, int64_t repeat_offset) {
+    timer_->Schedule(
+        monotonic_clock::time_point(std::chrono::nanoseconds(base)),
+        std::chrono::nanoseconds(repeat_offset));
+  }
+
+  void Disable() { timer_->Disable(); }
+
+  bool IsDisabled() const { return timer_->IsDisabled(); }
+
+  void set_name(rust::Str name) { timer_->set_name(RustStrToStringView(name)); }
+  rust::Str name() const { return StringViewToRustStr(timer_->name()); }
+
+  // If true, the timer is expired.
+  bool Poll();
+
+ private:
+  TimerForRust() = default;
+
+  TimerHandler *timer_;
+  bool expired_ = false;
+};
+
 class EventLoopRuntime {
  public:
   EventLoopRuntime(EventLoop *event_loop) : event_loop_(event_loop) {}
@@ -199,8 +235,11 @@
 
   OnRunForRust MakeOnRun() { return OnRunForRust(this); }
 
+  std::unique_ptr<TimerForRust> AddTimer() { return TimerForRust::Make(this); }
+
  private:
   friend class OnRunForRust;
+  friend class TimerForRust;
 
   // Polls the top-level future once. This is what all the callbacks should do.
   void DoPoll() {
diff --git a/aos/events/event_loop_runtime.rs b/aos/events/event_loop_runtime.rs
index 76c1e2e..35a4225 100644
--- a/aos/events/event_loop_runtime.rs
+++ b/aos/events/event_loop_runtime.rs
@@ -47,6 +47,7 @@
     future::Future,
     marker::PhantomData,
     mem::ManuallyDrop,
+    ops::Add,
     panic::{catch_unwind, AssertUnwindSafe},
     pin::Pin,
     slice,
@@ -84,6 +85,7 @@
 generate!("aos::OnRunForRust")
 generate!("aos::EventLoopRuntime")
 generate!("aos::ExitHandle")
+generate!("aos::TimerForRust")
 
 subclass!("aos::ApplicationFuture", RustApplicationFuture)
 
@@ -681,6 +683,115 @@
     pub fn is_running(&self) -> bool {
         self.0.is_running()
     }
+
+    /// Returns an unarmed timer.
+    pub fn add_timer(&mut self) -> Timer {
+        Timer(self.0.as_mut().AddTimer())
+    }
+
+    /// Returns a timer that goes off every `duration`-long ticks.
+    pub fn add_interval(&mut self, duration: Duration) -> Timer {
+        let mut timer = self.add_timer();
+        timer.setup(self.monotonic_now(), Some(duration));
+        timer
+    }
+}
+
+/// An event loop primitive that allows sleeping asynchronously.
+///
+/// # Examples
+///
+/// ```no_run
+/// # use aos_events_event_loop_runtime::EventLoopRuntime;
+/// # use std::time::Duration;
+/// # fn compile_check(runtime: &mut EventLoopRuntime<'_>) {
+/// # let mut timer = runtime.add_timer();
+/// // Goes as soon as awaited.
+/// timer.setup(runtime.monotonic_now(), None);
+/// // Goes off once in 2 seconds.
+/// timer.setup(runtime.monotonic_now() + Duration::from_secs(2), None);
+/// // Goes off as soon as awaited and every 2 seconds afterwards.
+/// timer.setup(runtime.monotonic_now(), Some(Duration::from_secs(1)));
+/// async {
+///   for i in 0..10 {
+///     timer.tick().await;
+///   }
+///   // Timer won't off anymore. Next `tick` will never return.
+///   timer.disable();
+///   timer.tick().await;
+/// };
+/// # }
+/// ```
+pub struct Timer(UniquePtr<ffi::aos::TimerForRust>);
+
+/// A "tick" for a [`Timer`].
+///
+/// This is the raw future generated by the [`Timer::tick`] function.
+pub struct TimerTick<'a>(&'a mut Timer);
+
+impl Timer {
+    /// Arms the timer.
+    ///
+    /// The timer should sleep until `base`, `base + repeat`, `base + repeat * 2`, ...
+    /// If `repeat` is `None`, then the timer only expires once at `base`.
+    pub fn setup(&mut self, base: MonotonicInstant, repeat: Option<Duration>) {
+        self.0.pin_mut().Schedule(
+            base.0,
+            repeat
+                .unwrap_or(Duration::from_nanos(0))
+                .as_nanos()
+                .try_into()
+                .expect("Out of range: Internal clock uses 64 bits"),
+        );
+    }
+
+    /// Disarms the timer.
+    ///
+    /// Can be re-enabled by calling `setup` again.
+    pub fn disable(&mut self) {
+        self.0.pin_mut().Disable();
+    }
+
+    /// Returns `true` if the timer is enabled.
+    pub fn is_enabled(&self) -> bool {
+        !self.0.IsDisabled()
+    }
+
+    /// Sets the name of the timer.
+    ///
+    /// This can be useful to get a descriptive name in the timing reports.
+    pub fn set_name(&mut self, name: &str) {
+        self.0.pin_mut().set_name(name);
+    }
+
+    /// Gets the name of the timer.
+    pub fn name(&self) -> &str {
+        self.0.name()
+    }
+
+    /// Returns a tick which can be `.await`ed.
+    ///
+    /// This tick will resolve on the next timer expired.
+    pub fn tick(&mut self) -> TimerTick {
+        TimerTick(self)
+    }
+
+    /// Polls the timer, returning `[Poll::Ready]` only once the timer expired.
+    fn poll(&mut self) -> Poll<()> {
+        if self.0.pin_mut().Poll() {
+            Poll::Ready(())
+        } else {
+            Poll::Pending
+        }
+    }
+}
+
+impl Future for TimerTick<'_> {
+    type Output = ();
+
+    fn poll(mut self: Pin<&mut Self>, _: &mut std::task::Context) -> Poll<()> {
+        self.0.poll()
+    }
 }
 
 /// Provides async blocking access to messages on a channel. This will return every message on the
@@ -1342,6 +1453,14 @@
     }
 }
 
+impl Add<Duration> for MonotonicInstant {
+    type Output = MonotonicInstant;
+
+    fn add(self, rhs: Duration) -> Self::Output {
+        Self(self.0 + i64::try_from(rhs.as_nanos()).unwrap())
+    }
+}
+
 impl fmt::Debug for MonotonicInstant {
     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
         self.duration_since_epoch().fmt(f)
diff --git a/aos/events/ping.rs b/aos/events/ping.rs
new file mode 100644
index 0000000..b9725b8
--- /dev/null
+++ b/aos/events/ping.rs
@@ -0,0 +1,87 @@
+use aos_configuration as config;
+use aos_events_event_loop_runtime::{EventLoopRuntime, Sender, Watcher};
+use aos_events_shm_event_loop::ShmEventLoop;
+use core::cell::Cell;
+use core::future::Future;
+use core::time::Duration;
+use futures::never::Never;
+use std::path::Path;
+
+use ping_rust_fbs::aos::examples as ping;
+use pong_rust_fbs::aos::examples as pong;
+
+fn main() {
+    aos_init::init();
+    let config = config::read_config_from(Path::new("pingpong_config.json")).unwrap();
+    let ping = PingTask::new();
+    ShmEventLoop::new(&config).run_with(|runtime| {
+        let task = ping.tasks(runtime);
+        runtime.spawn(task);
+    });
+}
+
+#[derive(Debug)]
+struct PingTask {
+    counter: Cell<i32>,
+}
+
+impl PingTask {
+    pub fn new() -> Self {
+        Self {
+            counter: Cell::new(0),
+        }
+    }
+
+    /// Returns a future with all the tasks for the ping process
+    pub fn tasks(&self, event_loop: &mut EventLoopRuntime) -> impl Future<Output = Never> + '_ {
+        let ping = self.ping(event_loop);
+        let handle_pong = self.handle_pong(event_loop);
+
+        async move {
+            futures::join!(ping, handle_pong);
+            unreachable!("Let's hope `never_type` gets stabilized soon :)");
+        }
+    }
+
+    fn ping(&self, event_loop: &mut EventLoopRuntime) -> impl Future<Output = Never> + '_ {
+        // The sender is used to send messages back to the pong channel.
+        let mut ping_sender: Sender<ping::Ping> = event_loop.make_sender("/test").unwrap();
+        let startup = event_loop.on_run();
+
+        let mut interval = event_loop.add_interval(Duration::from_secs(1));
+
+        async move {
+            // Wait for startup.
+            startup.await;
+            loop {
+                interval.tick().await;
+                self.counter.set(self.counter.get() + 1);
+                let mut builder = ping_sender.make_builder();
+                let mut ping = ping::PingBuilder::new(builder.fbb());
+                let iter = self.counter.get();
+                ping.add_value(iter);
+                let ping = ping.finish();
+                builder.send(ping).expect("Can't send ping");
+            }
+        }
+    }
+
+    fn handle_pong(&self, event_loop: &mut EventLoopRuntime) -> impl Future<Output = Never> + '_ {
+        // The watcher gives us incoming ping messages.
+        let mut pong_watcher: Watcher<pong::Pong> = event_loop.make_watcher("/test").unwrap();
+        let startup = event_loop.on_run();
+
+        async move {
+            // Wait for startup.
+            startup.await;
+            loop {
+                let pong = dbg!(pong_watcher.next().await);
+                assert_eq!(
+                    pong.message().unwrap().value(),
+                    self.counter.get(),
+                    "Missed a reply"
+                );
+            }
+        }
+    }
+}
diff --git a/aos/events/pong.rs b/aos/events/pong.rs
new file mode 100644
index 0000000..b817ac2
--- /dev/null
+++ b/aos/events/pong.rs
@@ -0,0 +1,42 @@
+use aos_configuration as config;
+use aos_events_event_loop_runtime::{EventLoopRuntime, Sender, Watcher};
+use aos_events_shm_event_loop::ShmEventLoop;
+use core::future::Future;
+use futures::never::Never;
+use std::path::Path;
+
+use ping_rust_fbs::aos::examples as ping;
+use pong_rust_fbs::aos::examples as pong;
+
+fn main() {
+    aos_init::init();
+    let config = config::read_config_from(Path::new("pingpong_config.json")).unwrap();
+    ShmEventLoop::new(&config).run_with(|runtime| {
+        let task = pong(runtime);
+        runtime.spawn(task);
+    });
+}
+
+/// Responds to ping messages with an equivalent pong.
+fn pong(event_loop: &mut EventLoopRuntime) -> impl Future<Output = Never> {
+    // The watcher gives us incoming ping messages.
+    let mut ping_watcher: Watcher<ping::Ping> = event_loop.make_watcher("/test").unwrap();
+
+    // The sender is used to send messages back to the pong channel.
+    let mut pong_sender: Sender<pong::Pong> = event_loop.make_sender("/test").unwrap();
+    // Wait for startup.
+    let startup = event_loop.on_run();
+
+    async move {
+        startup.await;
+        loop {
+            let ping = dbg!(ping_watcher.next().await);
+
+            let mut builder = pong_sender.make_builder();
+            let mut pong = pong::PongBuilder::new(builder.fbb());
+            pong.add_value(ping.message().unwrap().value());
+            let pong = pong.finish();
+            builder.send(pong).expect("Can't send pong reponse");
+        }
+    }
+}
diff --git a/aos/init.rs b/aos/init.rs
index 8a5f262..9ac62f1 100644
--- a/aos/init.rs
+++ b/aos/init.rs
@@ -16,6 +16,12 @@
 ///
 /// Panics if non-test initialization has already been performed.
 pub fn test_init() {
+    init();
+    // TODO(Brian): Do we want any of the other stuff that `:gtest_main` has?
+    // TODO(Brian): Call `aos::SetShmBase` like `:gtest_main` does.
+}
+
+pub fn init() {
     static ONCE: Once = Once::new();
     ONCE.call_once(|| {
         let argv0 = std::env::args().next().expect("must have argv[0]");
@@ -23,7 +29,4 @@
         // SAFETY: argv0 is a NUL-terminated string.
         unsafe { ffi::aos::InitFromRust(argv0.as_ptr()) };
     });
-
-    // TODO(Brian): Do we want any of the other stuff that `:gtest_main` has?
-    // TODO(Brian): Call `aos::SetShmBase` like `:gtest_main` does.
 }