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feat: Add waker() method to AndroidAppWaker
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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 <dev@notgull.net>
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notgull committed Nov 11, 2024
1 parent 0d29930 commit 4f7010d
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Showing 3 changed files with 45 additions and 0 deletions.
1 change: 1 addition & 0 deletions .gitignore
Original file line number Diff line number Diff line change
@@ -1 +1,2 @@
target
Cargo.lock
22 changes: 22 additions & 0 deletions android-activity/src/game_activity/mod.rs
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Expand Up @@ -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;
Expand Down Expand Up @@ -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 {
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22 changes: 22 additions & 0 deletions android-activity/src/native_activity/mod.rs
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Expand Up @@ -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;
Expand Down Expand Up @@ -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 {
Expand Down

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