1 files changed, 44 insertions, 0 deletions
diff --git a/third_party/rust/tokio/src/runtime/blocking/task.rs b/third_party/rust/tokio/src/runtime/blocking/task.rs
new file mode 100644
index 0000000000..0b7803a6c0
--- /dev/null
+++ b/third_party/rust/tokio/src/runtime/blocking/task.rs
@@ -0,0 +1,44 @@
+use std::future::Future;
+use std::pin::Pin;
+use std::task::{Context, Poll};
+
+/// Converts a function to a future that completes on poll.
+pub(crate) struct BlockingTask<T> {
+    func: Option<T>,
+}
+
+impl<T> BlockingTask<T> {
+    /// Initializes a new blocking task from the given function.
+    pub(crate) fn new(func: T) -> BlockingTask<T> {
+        BlockingTask { func: Some(func) }
+    }
+}
+
+// The closure `F` is never pinned
+impl<T> Unpin for BlockingTask<T> {}
+
+impl<T, R> Future for BlockingTask<T>
+where
+    T: FnOnce() -> R + Send + 'static,
+    R: Send + 'static,
+{
+    type Output = R;
+
+    fn poll(mut self: Pin<&mut Self>, _cx: &mut Context<'_>) -> Poll<R> {
+        let me = &mut *self;
+        let func = me
+            .func
+            .take()
+            .expect("[internal exception] blocking task ran twice.");
+
+        // This is a little subtle:
+        // For convenience, we'd like _every_ call tokio ever makes to Task::poll() to be budgeted
+        // using coop. However, the way things are currently modeled, even running a blocking task
+        // currently goes through Task::poll(), and so is subject to budgeting. That isn't really
+        // what we want; a blocking task may itself want to run tasks (it might be a Worker!), so
+        // we want it to start without any budgeting.
+        crate::coop::stop();
+
+        Poll::Ready(func())
+    }
+}