1 files changed, 69 insertions, 0 deletions
diff --git a/src/state.rs b/src/state.rs
new file mode 100644
index 0000000..2fc6cf3
--- /dev/null
+++ b/src/state.rs
@@ -0,0 +1,69 @@
+/// Set if the task is scheduled for running.
+///
+/// A task is considered to be scheduled whenever its `Runnable` exists.
+///
+/// This flag can't be set when the task is completed. However, it can be set while the task is
+/// running, in which case it will be rescheduled as soon as polling finishes.
+pub(crate) const SCHEDULED: usize = 1 << 0;
+
+/// Set if the task is running.
+///
+/// A task is in running state while its future is being polled.
+///
+/// This flag can't be set when the task is completed. However, it can be in scheduled state while
+/// it is running, in which case it will be rescheduled as soon as polling finishes.
+pub(crate) const RUNNING: usize = 1 << 1;
+
+/// Set if the task has been completed.
+///
+/// This flag is set when polling returns `Poll::Ready`. The output of the future is then stored
+/// inside the task until it becomes closed. In fact, `Task` picks up the output by marking
+/// the task as closed.
+///
+/// This flag can't be set when the task is scheduled or running.
+pub(crate) const COMPLETED: usize = 1 << 2;
+
+/// Set if the task is closed.
+///
+/// If a task is closed, that means it's either canceled or its output has been consumed by the
+/// `Task`. A task becomes closed in the following cases:
+///
+/// 1. It gets canceled by `Runnable::drop()`, `Task::drop()`, or `Task::cancel()`.
+/// 2. Its output gets awaited by the `Task`.
+/// 3. It panics while polling the future.
+/// 4. It is completed and the `Task` gets dropped.
+pub(crate) const CLOSED: usize = 1 << 3;
+
+/// Set if the `Task` still exists.
+///
+/// The `Task` is a special case in that it is only tracked by this flag, while all other
+/// task references (`Runnable` and `Waker`s) are tracked by the reference count.
+pub(crate) const TASK: usize = 1 << 4;
+
+/// Set if the `Task` is awaiting the output.
+///
+/// This flag is set while there is a registered awaiter of type `Waker` inside the task. When the
+/// task gets closed or completed, we need to wake the awaiter. This flag can be used as a fast
+/// check that tells us if we need to wake anyone.
+pub(crate) const AWAITER: usize = 1 << 5;
+
+/// Set if an awaiter is being registered.
+///
+/// This flag is set when `Task` is polled and we are registering a new awaiter.
+pub(crate) const REGISTERING: usize = 1 << 6;
+
+/// Set if the awaiter is being notified.
+///
+/// This flag is set when notifying the awaiter. If an awaiter is concurrently registered and
+/// notified, whichever side came first will take over the reposibility of resolving the race.
+pub(crate) const NOTIFYING: usize = 1 << 7;
+
+/// A single reference.
+///
+/// The lower bits in the state contain various flags representing the task state, while the upper
+/// bits contain the reference count. The value of `REFERENCE` represents a single reference in the
+/// total reference count.
+///
+/// Note that the reference counter only tracks the `Runnable` and `Waker`s. The `Task` is
+/// tracked separately by the `TASK` flag.
+pub(crate) const REFERENCE: usize = 1 << 8;