Allow JobQueue to concurrently run jobs (#3036)

* Allow `JobQueue` to concurrently run jobs

* Remove bounds on `run_jobs_async`

boa_engine/src/context/mod.rs

@@ -409,6 +409,19 @@ impl<'host> Context<'host> {
         self.clear_kept_objects();
     }
 
+    /// Asynchronously runs all the jobs in the job queue.
+    ///
+    /// # Note
+    ///
+    /// Concurrent job execution cannot be guaranteed by the engine, since this depends on the
+    /// specific handling of each [`JobQueue`]. If you need to ensure that jobs are executed
+    /// concurrently, you can provide a custom implementor of `JobQueue` to the context.
+    #[allow(clippy::future_not_send)]
+    pub async fn run_jobs_async(&mut self) {
+        self.job_queue().run_jobs_async(self).await;
+        self.clear_kept_objects();
+    }
+
     /// Abstract operation [`ClearKeptObjects`][clear].
     ///
     /// Clears all objects maintained alive by calls to the [`AddToKeptObjects`][add] abstract
@@ -424,7 +437,7 @@ impl<'host> Context<'host> {
 
     /// Retrieves the current stack trace of the context.
     #[inline]
-    pub fn stack_trace(&mut self) -> impl Iterator<Item = &CallFrame> {
+    pub fn stack_trace(&self) -> impl Iterator<Item = &CallFrame> {
         self.vm.frames.iter().rev()
     }
 

boa_engine/src/job.rs

@@ -225,6 +225,26 @@ pub trait JobQueue {
     /// to do this will leave the inner `Promise` in the `pending` state, which won't call any `then`
     /// or `catch` handlers, even if `future` was already completed.
     fn enqueue_future_job(&self, future: FutureJob, context: &mut Context<'_>);
+
+    /// Asynchronously runs all jobs in the queue.
+    ///
+    /// Running a job could enqueue more jobs in the queue. The implementor of the trait
+    /// determines if the method should loop until there are no more queued jobs or if
+    /// it should only run one iteration of the queue.
+    ///
+    /// By default forwards to [`JobQueue::run_jobs`]. Implementors using async should override this
+    /// with a proper algorithm to run jobs asynchronously.
+    fn run_jobs_async<'a, 'ctx, 'host, 'fut>(
+        &'a self,
+        context: &'ctx mut Context<'host>,
+    ) -> Pin<Box<dyn Future<Output = ()> + 'fut>>
+    where
+        'a: 'fut,
+        'ctx: 'fut,
+        'host: 'fut,
+    {
+        Box::pin(async { self.run_jobs(context) })
+    }
 }
 
 /// A job queue that does nothing.