Introduce tokio-test crate (#1030)

tokio-test/src/task.rs

@@ -0,0 +1,133 @@
+//! Futures task based helpers
+//!
+//! # Example
+//!
+//! This example will use the `MockTask` to set the current task on
+//! poll.
+//!
+//! ```
+//! # #[macro_use] extern crate tokio_test;
+//! # extern crate futures;
+//! # use tokio_test::task::MockTask;
+//! # use futures::{sync::mpsc, Stream, Sink, Future, Async};
+//! let mut task = MockTask::new();
+//! let (tx, mut rx) = mpsc::channel(5);
+//!
+//! tx.send(()).wait();
+//!
+//! assert_ready_eq!(task.enter(|| rx.poll()), Some(()));
+//! ```
+
+use futures::executor::{spawn, Notify};
+use futures::{future, Async};
+
+use std::sync::atomic::{AtomicUsize, Ordering};
+use std::sync::{Arc, Condvar, Mutex};
+
+/// Mock task
+///
+/// A mock task is able to intercept and track notifications.
+#[derive(Debug)]
+pub struct MockTask {
+    notify: Arc<ThreadNotify>,
+}
+
+#[derive(Debug)]
+struct ThreadNotify {
+    state: AtomicUsize,
+    mutex: Mutex<()>,
+    condvar: Condvar,
+}
+
+const IDLE: usize = 0;
+const NOTIFY: usize = 1;
+const SLEEP: usize = 2;
+
+impl MockTask {
+    /// Create a new mock task
+    pub fn new() -> Self {
+        MockTask {
+            notify: Arc::new(ThreadNotify::new()),
+        }
+    }
+
+    /// Run a closure from the context of the task.
+    ///
+    /// Any notifications resulting from the execution of the closure are
+    /// tracked.
+    pub fn enter<F, R>(&mut self, f: F) -> R
+    where
+        F: FnOnce() -> R,
+    {
+        self.notify.clear();
+
+        let res = spawn(future::lazy(|| Ok::<_, ()>(f()))).poll_future_notify(&self.notify, 0);
+
+        match res.unwrap() {
+            Async::Ready(v) => v,
+            _ => unreachable!(),
+        }
+    }
+
+    /// Returns `true` if the inner future has received a readiness notification
+    /// since the last call to `enter`.
+    pub fn is_notified(&self) -> bool {
+        self.notify.is_notified()
+    }
+
+    /// Returns the number of references to the task notifier
+    ///
+    /// The task itself holds a reference. The return value will never be zero.
+    pub fn notifier_ref_count(&self) -> usize {
+        Arc::strong_count(&self.notify)
+    }
+}
+
+impl ThreadNotify {
+    fn new() -> Self {
+        ThreadNotify {
+            state: AtomicUsize::new(IDLE),
+            mutex: Mutex::new(()),
+            condvar: Condvar::new(),
+        }
+    }
+
+    /// Clears any previously received notify, avoiding potential spurrious
+    /// notifications. This should only be called immediately before running the
+    /// task.
+    fn clear(&self) {
+        self.state.store(IDLE, Ordering::SeqCst);
+    }
+
+    fn is_notified(&self) -> bool {
+        match self.state.load(Ordering::SeqCst) {
+            IDLE => false,
+            NOTIFY => true,
+            _ => unreachable!(),
+        }
+    }
+}
+
+impl Notify for ThreadNotify {
+    fn notify(&self, _unpark_id: usize) {
+        // First, try transitioning from IDLE -> NOTIFY, this does not require a
+        // lock.
+        match self.state.compare_and_swap(IDLE, NOTIFY, Ordering::SeqCst) {
+            IDLE | NOTIFY => return,
+            SLEEP => {}
+            _ => unreachable!(),
+        }
+
+        // The other half is sleeping, this requires a lock
+        let _m = self.mutex.lock().unwrap();
+
+        // Transition from SLEEP -> NOTIFY
+        match self.state.compare_and_swap(SLEEP, NOTIFY, Ordering::SeqCst) {
+            SLEEP => {}
+            _ => return,
+        }
+
+        // Wakeup the sleeper
+        self.condvar.notify_one();
+    }
+}