WIP: field reflection example

Signed-off-by: Boqun Feng <[email protected]>

Author: fbq

examples/field_type.rs

@@ -0,0 +1,132 @@
+use field_projection::{
+    compat::HasFields,
+    field_of,
+    marker::{Field, UnalignedField},
+};
+
+use core::ptr::null_mut;
+use std::sync::Arc;
+
+/// An intrusive struct to link all queued work together.
+pub struct Work {
+    state: usize,
+    func: Option<fn(*mut Work)>,
+    next: *mut Work,
+}
+
+pub trait WorkItem<F: Field> {
+    fn run(&self);
+}
+
+impl WorkItem<field_of!(Foo, work)> for Foo {
+    fn run(&self) {
+        println!("hello work");
+    }
+}
+
+impl WorkItem<field_of!(Foo, work2)> for Foo {
+    fn run(&self) {
+        println!("hello work2");
+    }
+}
+
+fn bridge<F: Field<Type = Work>>(ptr: *mut Work)
+where
+    F::Base: WorkItem<F> + Sized,
+{
+    let ptr = unsafe { ptr.byte_sub(F::OFFSET) }.cast::<F::Base>();
+
+    unsafe { &*ptr }.run();
+}
+
+impl Work {
+    /// TODO: this should return PinInit.
+    ///
+    /// # Safety
+    ///
+    /// Callers must guarantee the `Work` is the exact field described by `F`.
+    pub const unsafe fn new<F: Field<Type = Work>>() -> Self
+    where
+        F::Base: WorkItem<F> + Sized,
+    {
+        Self {
+            state: 0,
+            func: Some(bridge::<F>),
+            next: null_mut(),
+        }
+    }
+}
+
+#[derive(HasFields)]
+pub struct Foo {
+    a: i32,
+    b: i32,
+    work: Work,
+    work2: Work,
+}
+
+impl Foo {
+    pub fn new_arc(a: i32, b: i32) -> Arc<Self> {
+        Arc::new(Self {
+            a,
+            b,
+            // SAFETY: `work` is Foo::work.
+            work: unsafe { Work::new::<field_of!(Foo, work)>() },
+            // SAFETY: `work2` is Foo::work2.
+            work2: unsafe { Work::new::<field_of!(Foo, work2)>() },
+        })
+    }
+}
+
+pub trait WorkItemPointer<F: Field<Type = Work>>: Sized {
+    // Simulates RawWorkItem
+    fn into_work(self) -> *mut Work;
+
+    fn c_run(ptr: *mut Work);
+}
+
+impl<T, F: Field<Base = T, Type = Work>> WorkItemPointer<F> for Arc<T>
+where
+    T: WorkItem<F>,
+{
+    fn into_work(self) -> *mut Work {
+        let ptr = Arc::into_raw(self);
+        unsafe { ptr.byte_add(F::OFFSET).cast_mut().cast() }
+    }
+
+    fn c_run(ptr: *mut Work) {
+        let ptr = unsafe { ptr.byte_sub(F::OFFSET).cast::<T>() };
+
+        let arc = unsafe { Arc::from_raw(ptr) };
+
+        arc.run();
+    }
+}
+
+/// # Safety
+///
+/// `work` must point to a valid pointer of `Work`.
+unsafe fn c_run_work(work: *mut Work) {
+    if let Some(func) = unsafe { (*work).func } {
+        func(work)
+    }
+}
+
+pub fn queue_work<F: Field<Base = T, Type = Work>, T: WorkItem<F>, P: WorkItemPointer<F>>(p: P) {
+    // Simulate queue work and run
+    //
+    // TODO: simulate linking work and execute them all together.
+    let ptr = p.into_work();
+
+    // SAFETY: `ptr` is a valid pointer of `Work`.
+    unsafe { c_run_work(ptr) };
+}
+
+#[test]
+fn main() {
+    let foo = Foo::new_arc(12, 42);
+    let foo2 = Foo::new_arc(12, 42);
+
+    queue_work::<field_of!(Foo, work), _, _>(foo);
+    queue_work::<field_of!(Foo, work2), _, _>(foo2);
+}