1 files changed, 148 insertions, 0 deletions
diff --git a/runtime/ops/utils.rs b/runtime/ops/utils.rs
index d950ae9ab..f1414e8bc 100644
--- a/runtime/ops/utils.rs
+++ b/runtime/ops/utils.rs
@@ -1,6 +1,14 @@
 // Copyright 2018-2022 the Deno authors. All rights reserved. MIT license.
+
 use deno_core::error::custom_error;
 use deno_core::error::AnyError;
+use deno_core::futures::task::AtomicWaker;
+use deno_core::futures::Future;
+use deno_core::parking_lot::Mutex;
+use std::collections::LinkedList;
+use std::sync::atomic::AtomicBool;
+use std::sync::atomic::Ordering;
+use std::sync::Arc;
 
 /// A utility function to map OsStrings to Strings
 pub fn into_string(s: std::ffi::OsString) -> Result<String, AnyError> {
@@ -9,3 +17,143 @@ pub fn into_string(s: std::ffi::OsString) -> Result<String, AnyError> {
     custom_error("InvalidData", message)
   })
 }
+
+#[derive(Default)]
+struct TaskQueueTaskWaker {
+  is_ready: AtomicBool,
+  waker: AtomicWaker,
+}
+
+#[derive(Default)]
+struct TaskQueueTasks {
+  is_running: bool,
+  wakers: LinkedList<Arc<TaskQueueTaskWaker>>,
+}
+
+/// 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 tokio's semaphore doesn't seem to maintain order
+/// and so we can't use that in the code that uses this or use
+/// that here.
+#[derive(Clone, Default)]
+pub struct TaskQueue {
+  tasks: Arc<Mutex<TaskQueueTasks>>,
+}
+
+impl TaskQueue {
+  /// Alternate API that acquires a permit internally
+  /// for the duration of the future.
+  #[cfg(test)]
+  pub async fn queue<R>(&self, future: impl Future<Output = R>) -> R {
+    let _permit = self.acquire().await;
+    future.await
+  }
+
+  /// Acquires a permit where the tasks are executed one at a time
+  /// and in the order that they were acquired.
+  pub async fn acquire(&self) -> TaskQueuePermit {
+    let acquire = TaskQueuePermitAcquire::new(self.tasks.clone());
+    acquire.await;
+    TaskQueuePermit {
+      tasks: self.tasks.clone(),
+    }
+  }
+}
+
+/// A permit that when dropped will allow another task to proceed.
+pub struct TaskQueuePermit {
+  tasks: Arc<Mutex<TaskQueueTasks>>,
+}
+
+impl Drop for TaskQueuePermit {
+  fn drop(&mut self) {
+    let next_item = {
+      let mut tasks = self.tasks.lock();
+      let next_item = tasks.wakers.pop_front();
+      tasks.is_running = next_item.is_some();
+      next_item
+    };
+    if let Some(next_item) = next_item {
+      next_item.is_ready.store(true, Ordering::SeqCst);
+      next_item.waker.wake();
+    }
+  }
+}
+
+struct TaskQueuePermitAcquire {
+  tasks: Arc<Mutex<TaskQueueTasks>>,
+  initialized: AtomicBool,
+  waker: Arc<TaskQueueTaskWaker>,
+}
+
+impl TaskQueuePermitAcquire {
+  pub fn new(tasks: Arc<Mutex<TaskQueueTasks>>) -> Self {
+    Self {
+      tasks,
+      initialized: Default::default(),
+      waker: Default::default(),
+    }
+  }
+}
+
+impl Future for TaskQueuePermitAcquire {
+  type Output = ();
+
+  fn poll(
+    self: std::pin::Pin<&mut Self>,
+    cx: &mut std::task::Context<'_>,
+  ) -> std::task::Poll<Self::Output> {
+    // update with the latest waker
+    self.waker.waker.register(cx.waker());
+
+    // ensure this is initialized
+    if !self.initialized.swap(true, Ordering::SeqCst) {
+      let mut tasks = self.tasks.lock();
+      if !tasks.is_running {
+        tasks.is_running = true;
+        return std::task::Poll::Ready(());
+      }
+      tasks.wakers.push_back(self.waker.clone());
+      return std::task::Poll::Pending;
+    }
+
+    // check if we're ready to run
+    if self.waker.is_ready.load(Ordering::SeqCst) {
+      std::task::Poll::Ready(())
+    } else {
+      std::task::Poll::Pending
+    }
+  }
+}
+
+#[cfg(test)]
+mod tests {
+  use deno_core::futures;
+  use deno_core::parking_lot::Mutex;
+  use std::sync::Arc;
+
+  use super::TaskQueue;
+
+  #[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.queue(async move {
+        tokio::task::spawn_blocking(move || {
+          let mut data = data.lock();
+          if *data != i {
+            panic!("Value was not equal.");
+          }
+          *data = i + 1;
+        })
+        .await
+        .unwrap();
+      }));
+    }
+    futures::future::join_all(tasks).await;
+  }
+}