feat: Add waker() method to AndroidAppWaker

This commit adds a "waker()" method to AndroidAppWaker. It converts it
into an `std::task::Waker`, which is the type of waker used by
asynchronous tasks for scheduling. The goal is to allow AndroidAppWaker
to be easily used to set up an asynchronous context.

The implementation is very efficient, owing to the "static pointer"
style of coding already used. The "wake" function just calls
ALooper_wake, and cloning/dropping the waker is just a copy.

Signed-off-by: John Nunley <[email protected]>

.gitignore

@@ -1 +1,2 @@
 target
+Cargo.lock

android-activity/src/game_activity/mod.rs

@@ -8,6 +8,7 @@ use std::ptr;
 use std::ptr::NonNull;
 use std::sync::Weak;
 use std::sync::{Arc, Mutex, RwLock};
+use std::task::{RawWaker, RawWakerVTable, Waker};
 use std::time::Duration;
 
 use libc::c_void;
@@ -118,6 +119,27 @@ impl AndroidAppWaker {
             ALooper_wake(self.looper.as_ptr());
         }
     }
+
+    /// Creates a [`Waker`] that wakes up the [`AndroidApp`].
+    ///
+    /// This is useful for using this crate in `async` environments.
+    ///
+    /// [`Waker`]: std::task::Waker
+    pub fn waker(self) -> Waker {
+        const VTABLE: RawWakerVTable = RawWakerVTable::new(clone, wake, wake, drop);
+
+        unsafe fn clone(data: *const ()) -> RawWaker {
+            RawWaker::new(data, &VTABLE)
+        }
+
+        unsafe fn wake(data: *const ()) {
+            ndk_sys::ALooper_wake(data as *const _ as *mut _)
+        }
+
+        unsafe fn drop(_: *const ()) {}
+
+        unsafe { Waker::from_raw(RawWaker::new(self.looper.as_ptr() as *const (), &VTABLE)) }
+    }
 }
 
 impl AndroidApp {

android-activity/src/native_activity/mod.rs

@@ -6,6 +6,7 @@ use std::panic::AssertUnwindSafe;
 use std::ptr;
 use std::ptr::NonNull;
 use std::sync::{Arc, Mutex, RwLock, Weak};
+use std::task::{RawWaker, RawWakerVTable, Waker};
 use std::time::Duration;
 
 use libc::c_void;
@@ -83,6 +84,27 @@ impl AndroidAppWaker {
             ndk_sys::ALooper_wake(self.looper.as_ptr());
         }
     }
+
+    /// Creates a [`Waker`] that wakes up the [`AndroidApp`].
+    ///
+    /// This is useful for using this crate in `async` environments.
+    ///
+    /// [`Waker`]: std::task::Waker
+    pub fn waker(self) -> Waker {
+        const VTABLE: RawWakerVTable = RawWakerVTable::new(clone, wake, wake, drop);
+
+        unsafe fn clone(data: *const ()) -> RawWaker {
+            RawWaker::new(data, &VTABLE)
+        }
+
+        unsafe fn wake(data: *const ()) {
+            ndk_sys::ALooper_wake(data as *const _ as *mut _)
+        }
+
+        unsafe fn drop(_: *const ()) {}
+
+        unsafe { Waker::from_raw(RawWaker::new(self.looper.as_ptr() as *const (), &VTABLE)) }
+    }
 }
 
 impl AndroidApp {