Update parallel raytrace example to use futures

Use the atomics support now implemented!

Author: alexcrichton

examples/raytrace-parallel/src/lib.rs

@@ -1,3 +1,4 @@
+use futures::sync::oneshot;
 use futures::Future;
 use js_sys::{Promise, Uint8ClampedArray, WebAssembly};
 use rayon::prelude::*;
@@ -69,27 +70,28 @@ impl Scene {
         // threads so we don't lock up the main thread, so we ship off a thread
         // which actually does the whole rayon business. When our returned
         // future is resolved we can pull out the final version of the image.
-        let done = pool
-            .run_notify(move || {
-                thread_pool.install(|| {
-                    rgb_data
-                        .par_chunks_mut(4)
-                        .enumerate()
-                        .for_each(|(i, chunk)| {
-                            let i = i as u32;
-                            let x = i % width;
-                            let y = i / width;
-                            let ray = raytracer::Ray::create_prime(x, y, &scene);
-                            let result = raytracer::cast_ray(&scene, &ray, 0).to_rgba();
-                            chunk[0] = result.data[0];
-                            chunk[1] = result.data[1];
-                            chunk[2] = result.data[2];
-                            chunk[3] = result.data[3];
-                        });
-                });
+        let (tx, rx) = oneshot::channel();
+        pool.run(move || {
+            thread_pool.install(|| {
                 rgb_data
-            })?
-            .map(move |_data| image_data(base, len, width, height).into());
+                    .par_chunks_mut(4)
+                    .enumerate()
+                    .for_each(|(i, chunk)| {
+                        let i = i as u32;
+                        let x = i % width;
+                        let y = i / width;
+                        let ray = raytracer::Ray::create_prime(x, y, &scene);
+                        let result = raytracer::cast_ray(&scene, &ray, 0).to_rgba();
+                        chunk[0] = result.data[0];
+                        chunk[1] = result.data[1];
+                        chunk[2] = result.data[2];
+                        chunk[3] = result.data[3];
+                    });
+            });
+            drop(tx.send(rgb_data));
+        })?;
+        let done = rx.map(move |_data| image_data(base, len, width, height).into())
+            .map_err(|_| JsValue::undefined());
 
         Ok(RenderingScene {
             promise: wasm_bindgen_futures::future_to_promise(done),

examples/raytrace-parallel/src/pool.rs

@@ -1,13 +1,8 @@
 //! A small module that's intended to provide an example of creating a pool of
 //! web workers which can be used to execute `rayon`-style work.
 
-use futures::sync::oneshot;
-use futures::Future;
-use std::cell::{RefCell, UnsafeCell};
-use std::mem;
+use std::cell::RefCell;
 use std::rc::Rc;
-use std::sync::atomic::{AtomicBool, Ordering::SeqCst};
-use std::sync::Arc;
 use wasm_bindgen::prelude::*;
 use wasm_bindgen::JsCast;
 use web_sys::{DedicatedWorkerGlobalScope, MessageEvent};
@@ -141,12 +136,11 @@ impl WorkerPool {
     /// whatn it's done the worker is ready to execute more work. This method is
     /// used for all spawned workers to ensure that when the work is finished
     /// the worker is reclaimed back into this pool.
-    fn reclaim_on_message(&self, worker: Worker, on_finish: impl FnOnce() + 'static) {
+    fn reclaim_on_message(&self, worker: Worker) {
         let state = Rc::downgrade(&self.state);
         let worker2 = worker.clone();
         let reclaim_slot = Rc::new(RefCell::new(None));
         let slot2 = reclaim_slot.clone();
-        let mut on_finish = Some(on_finish);
         let reclaim = Closure::wrap(Box::new(move |event: Event| {
             if let Some(error) = event.dyn_ref::<ErrorEvent>() {
                 console_log!("error in worker: {}", error.message());
@@ -155,11 +149,9 @@ impl WorkerPool {
                 return;
             }
 
-            // If this is a completion event then we can execute our `on_finish`
-            // callback and we can also deallocate our own callback by clearing
-            // out `slot2` which contains our own closure.
+            // If this is a completion event then can deallocate our own
+            // callback by clearing out `slot2` which contains our own closure.
             if let Some(_msg) = event.dyn_ref::<MessageEvent>() {
-                on_finish.take().unwrap()();
                 if let Some(state) = state.upgrade() {
                     state.push(worker2.clone());
                 }
@@ -193,80 +185,9 @@ impl WorkerPool {
     /// a web worker, that error is returned.
     pub fn run(&self, f: impl FnOnce() + Send + 'static) -> Result<(), JsValue> {
         let worker = self.execute(f)?;
-        self.reclaim_on_message(worker, || {});
+        self.reclaim_on_message(worker);
         Ok(())
     }
-
-    /// Executes the closure `f` in a web worker, returning a future of the
-    /// value that `f` produces.
-    ///
-    /// This method is the same as `run` execept that it allows recovering the
-    /// return value of the closure `f` in a nonblocking fashion with the future
-    /// returned.
-    ///
-    /// # Errors
-    ///
-    /// If an error happens while spawning a web worker or sending a message to
-    /// a web worker, that error is returned.
-    pub fn run_notify<T>(
-        &self,
-        f: impl FnOnce() -> T + Send + 'static,
-    ) -> Result<impl Future<Item = T, Error = JsValue> + 'static, JsValue>
-    where
-        T: Send + 'static,
-    {
-        // FIXME(#1379) we should just use the `oneshot` directly as the future,
-        // but we have to use JS callbacks to ensure we don't have futures cross
-        // threads as that's currently not safe to do so.
-        let (tx, rx) = oneshot::channel();
-        let storage = Arc::new(AtomicValue::new(None));
-        let storage2 = storage.clone();
-        let worker = self.execute(move || {
-            assert!(storage2.replace(Some(f())).is_ok());
-        })?;
-        self.reclaim_on_message(worker, move || match storage.replace(None) {
-            Ok(Some(val)) => drop(tx.send(val)),
-            _ => unreachable!(),
-        });
-
-        Ok(rx.map_err(|_| JsValue::undefined()))
-    }
-}
-
-/// A small helper struct representing atomic access to an internal value `T`
-///
-/// This struct only supports one API, `replace`, which will either succeed and
-/// replace the internal value with another (returning the previous one), or it
-/// will fail returning the value passed in. Failure happens when two threads
-/// try to `replace` at the same time.
-///
-/// This is only really intended to help safely transfer information between
-/// threads, it doesn't provide any synchronization capabilities itself other
-/// than a guaranteed safe API.
-struct AtomicValue<T> {
-    modifying: AtomicBool,
-    slot: UnsafeCell<T>,
-}
-
-unsafe impl<T: Send> Send for AtomicValue<T> {}
-unsafe impl<T: Send> Sync for AtomicValue<T> {}
-
-impl<T> AtomicValue<T> {
-    fn new(val: T) -> AtomicValue<T> {
-        AtomicValue {
-            modifying: AtomicBool::new(false),
-            slot: UnsafeCell::new(val),
-        }
-    }
-
-    fn replace(&self, val: T) -> Result<T, T> {
-        if self.modifying.swap(true, SeqCst) {
-            return Err(val);
-        }
-        let ret = unsafe { mem::replace(&mut *self.slot.get(), val) };
-        self.modifying.store(false, SeqCst);
-        Ok(ret)
-    }
 }
 
 impl PoolState {