1 files changed, 266 insertions, 0 deletions
diff --git a/cli/util/sync/task_queue.rs b/cli/util/sync/task_queue.rs
new file mode 100644
index 000000000..6ef747e1a
--- /dev/null
+++ b/cli/util/sync/task_queue.rs
@@ -0,0 +1,266 @@
+// Copyright 2018-2024 the Deno authors. All rights reserved. MIT license.
+
+use std::collections::LinkedList;
+use std::sync::Arc;
+
+use deno_core::futures::task::AtomicWaker;
+use deno_core::futures::Future;
+use deno_core::parking_lot::Mutex;
+
+use super::AtomicFlag;
+
+#[derive(Debug, Default)]
+struct TaskQueueTaskItem {
+  is_ready: AtomicFlag,
+  is_future_dropped: AtomicFlag,
+  waker: AtomicWaker,
+}
+
+#[derive(Debug, Default)]
+struct TaskQueueTasks {
+  is_running: bool,
+  items: LinkedList<Arc<TaskQueueTaskItem>>,
+}
+
+/// A queue that executes tasks sequentially one after the other
+/// ensuring order and that no task runs at the same time as another.
+///
+/// Note that this differs from tokio's semaphore in that the order
+/// is acquired synchronously.
+#[derive(Debug, Default)]
+pub struct TaskQueue {
+  tasks: Mutex<TaskQueueTasks>,
+}
+
+impl TaskQueue {
+  /// Acquires a permit where the tasks are executed one at a time
+  /// and in the order that they were acquired.
+  pub fn acquire(&self) -> TaskQueuePermitAcquireFuture {
+    TaskQueuePermitAcquireFuture::new(self)
+  }
+
+  /// Alternate API that acquires a permit internally
+  /// for the duration of the future.
+  #[allow(unused)]
+  pub fn run<'a, R>(
+    &'a self,
+    future: impl Future<Output = R> + 'a,
+  ) -> impl Future<Output = R> + 'a {
+    let acquire_future = self.acquire();
+    async move {
+      let permit = acquire_future.await;
+      let result = future.await;
+      drop(permit); // explicit for clarity
+      result
+    }
+  }
+
+  fn raise_next(&self) {
+    let front_item = {
+      let mut tasks = self.tasks.lock();
+
+      // clear out any wakers for futures that were dropped
+      while let Some(front_waker) = tasks.items.front() {
+        if front_waker.is_future_dropped.is_raised() {
+          tasks.items.pop_front();
+        } else {
+          break;
+        }
+      }
+      let front_item = tasks.items.pop_front();
+      tasks.is_running = front_item.is_some();
+      front_item
+    };
+
+    // wake up the next waker
+    if let Some(front_item) = front_item {
+      front_item.is_ready.raise();
+      front_item.waker.wake();
+    }
+  }
+}
+
+/// A permit that when dropped will allow another task to proceed.
+pub struct TaskQueuePermit<'a>(&'a TaskQueue);
+
+impl<'a> Drop for TaskQueuePermit<'a> {
+  fn drop(&mut self) {
+    self.0.raise_next();
+  }
+}
+
+pub struct TaskQueuePermitAcquireFuture<'a> {
+  task_queue: Option<&'a TaskQueue>,
+  item: Arc<TaskQueueTaskItem>,
+}
+
+impl<'a> TaskQueuePermitAcquireFuture<'a> {
+  pub fn new(task_queue: &'a TaskQueue) -> Self {
+    // acquire the waker position synchronously
+    let mut tasks = task_queue.tasks.lock();
+    let item = if !tasks.is_running {
+      tasks.is_running = true;
+      let item = Arc::new(TaskQueueTaskItem::default());
+      item.is_ready.raise();
+      item
+    } else {
+      let item = Arc::new(TaskQueueTaskItem::default());
+      tasks.items.push_back(item.clone());
+      item
+    };
+    drop(tasks);
+    Self {
+      task_queue: Some(task_queue),
+      item,
+    }
+  }
+}
+
+impl<'a> Drop for TaskQueuePermitAcquireFuture<'a> {
+  fn drop(&mut self) {
+    if let Some(task_queue) = self.task_queue.take() {
+      if self.item.is_ready.is_raised() {
+        task_queue.raise_next();
+      } else {
+        self.item.is_future_dropped.raise();
+      }
+    }
+  }
+}
+
+impl<'a> Future for TaskQueuePermitAcquireFuture<'a> {
+  type Output = TaskQueuePermit<'a>;
+
+  fn poll(
+    mut self: std::pin::Pin<&mut Self>,
+    cx: &mut std::task::Context<'_>,
+  ) -> std::task::Poll<Self::Output> {
+    if self.item.is_ready.is_raised() {
+      std::task::Poll::Ready(TaskQueuePermit(self.task_queue.take().unwrap()))
+    } else {
+      self.item.waker.register(cx.waker());
+      std::task::Poll::Pending
+    }
+  }
+}
+
+#[cfg(test)]
+mod test {
+  use deno_core::futures;
+  use deno_core::parking_lot::Mutex;
+  use std::sync::Arc;
+
+  use super::*;
+
+  #[tokio::test]
+  async fn task_queue_runs_one_after_other() {
+    let task_queue = TaskQueue::default();
+    let mut tasks = Vec::new();
+    let data = Arc::new(Mutex::new(0));
+    for i in 0..100 {
+      let data = data.clone();
+      tasks.push(task_queue.run(async move {
+        deno_core::unsync::spawn_blocking(move || {
+          let mut data = data.lock();
+          assert_eq!(*data, i);
+          *data = i + 1;
+        })
+        .await
+        .unwrap();
+      }));
+    }
+    futures::future::join_all(tasks).await;
+  }
+
+  #[tokio::test]
+  async fn task_queue_run_in_sequence() {
+    let task_queue = TaskQueue::default();
+    let data = Arc::new(Mutex::new(0));
+
+    let first = task_queue.run(async {
+      *data.lock() = 1;
+    });
+    let second = task_queue.run(async {
+      assert_eq!(*data.lock(), 1);
+      *data.lock() = 2;
+    });
+    let _ = tokio::join!(first, second);
+
+    assert_eq!(*data.lock(), 2);
+  }
+
+  #[tokio::test]
+  async fn task_queue_future_dropped_before_poll() {
+    let task_queue = Arc::new(TaskQueue::default());
+
+    // acquire a future, but do not await it
+    let future = task_queue.acquire();
+
+    // this task tries to acquire another permit, but will be blocked by the first permit.
+    let enter_flag = Arc::new(AtomicFlag::default());
+    let delayed_task = deno_core::unsync::spawn({
+      let enter_flag = enter_flag.clone();
+      let task_queue = task_queue.clone();
+      async move {
+        enter_flag.raise();
+        task_queue.acquire().await;
+        true
+      }
+    });
+
+    // ensure the task gets a chance to be scheduled and blocked
+    tokio::task::yield_now().await;
+    assert!(enter_flag.is_raised());
+
+    // now, drop the first future
+    drop(future);
+
+    assert!(delayed_task.await.unwrap());
+  }
+
+  #[tokio::test]
+  async fn task_queue_many_future_dropped_before_poll() {
+    let task_queue = Arc::new(TaskQueue::default());
+
+    // acquire a future, but do not await it
+    let mut futures = Vec::new();
+    for _ in 0..=10_000 {
+      futures.push(task_queue.acquire());
+    }
+
+    // this task tries to acquire another permit, but will be blocked by the first permit.
+    let enter_flag = Arc::new(AtomicFlag::default());
+    let delayed_task = deno_core::unsync::spawn({
+      let task_queue = task_queue.clone();
+      let enter_flag = enter_flag.clone();
+      async move {
+        enter_flag.raise();
+        task_queue.acquire().await;
+        true
+      }
+    });
+
+    // ensure the task gets a chance to be scheduled and blocked
+    tokio::task::yield_now().await;
+    assert!(enter_flag.is_raised());
+
+    // now, drop the futures
+    drop(futures);
+
+    assert!(delayed_task.await.unwrap());
+  }
+
+  #[tokio::test]
+  async fn task_queue_middle_future_dropped_while_permit_acquired() {
+    let task_queue = TaskQueue::default();
+
+    let fut1 = task_queue.acquire();
+    let fut2 = task_queue.acquire();
+    let fut3 = task_queue.acquire();
+
+    // should not hang
+    drop(fut2);
+    drop(fut1.await);
+    drop(fut3.await);
+  }
+}