Move Task to its own module

components/script/task.rs

@@ -0,0 +1,70 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+//! Machinery for [tasks](https://html.spec.whatwg.org/multipage/#concept-task).
+
+use std::fmt;
+use std::intrinsics;
+use std::sync::Arc;
+use std::sync::atomic::{AtomicBool, Ordering};
+
+/// A task that can be run. The name method is for profiling purposes.
+pub trait Task {
+    #[allow(unsafe_code)]
+    fn name(&self) -> &'static str { unsafe { intrinsics::type_name::<Self>() } }
+    fn run(self: Box<Self>);
+}
+
+impl fmt::Debug for Task + Send {
+    fn fmt(&self, fmt: &mut fmt::Formatter) -> fmt::Result {
+        fmt.debug_tuple(self.name()).field(&format_args!("...")).finish()
+    }
+}
+
+/// Encapsulated state required to create cancellable tasks from non-script threads.
+pub struct TaskCanceller {
+    pub cancelled: Option<Arc<AtomicBool>>,
+}
+
+impl TaskCanceller {
+    /// Returns a wrapped `task` that will be cancelled if the `TaskCanceller`
+    /// says so.
+    pub fn wrap_task<T>(&self, task: Box<T>) -> Box<Task + Send>
+    where
+        T: Send + Task + 'static,
+    {
+        box CancellableTask {
+            cancelled: self.cancelled.clone(),
+            inner: task,
+        }
+    }
+}
+
+/// A task that can be cancelled by toggling a shared flag.
+pub struct CancellableTask<T: Send + Task> {
+    cancelled: Option<Arc<AtomicBool>>,
+    inner: Box<T>,
+}
+
+impl<T> CancellableTask<T>
+where
+    T: Send + Task,
+{
+    fn is_cancelled(&self) -> bool {
+        self.cancelled.as_ref().map_or(false, |cancelled| {
+            cancelled.load(Ordering::SeqCst)
+        })
+    }
+}
+
+impl<T> Task for CancellableTask<T>
+where
+    T: Send + Task,
+{
+    fn run(self: Box<Self>) {
+        if !self.is_cancelled() {
+            self.inner.run()
+        }
+    }
+}