time: Eagerly bind delays to timer (#1800)

## Motivation

Similar to #1666, it is no longer necessary to lazily register delays with the
executions default timer. All delays are expected to be created from within a
runtime, and should panic if not done so.

## Solution

`tokio::time` now assumes there to be a `CURRENT_TIMER` set when creating a
delay; this can be assumed if called within a tokio runtime. If there is no
current timer, the application will panic with a "no current timer" message.

## Follow-up

Similar to #1666, `HandlePriv` can probably be removed, but this mainly prepares
for 0.2 API changes. Because it is not in the public API, this can be done in a
following change.

Signed-off-by: Kevin Leimkuhler <kleimkuhler@icloud.com>

2 files changed, 24 insertions, 20 deletions

diff --git a/tokio/src/time/tests/mod.rs b/tokio/src/time/tests/mod.rs
index 0aead136..6a9f25da 100644
--- a/tokio/src/time/tests/mod.rs
+++ b/tokio/src/time/tests/mod.rs
@@ -1,4 +1,24 @@
 mod mock_clock;
-
 mod test_delay;
 mod test_queue;
+
+use crate::time::{self, Instant};
+use std::time::Duration;
+
+fn assert_send<T: Send>() {}
+fn assert_sync<T: Sync>() {}
+
+#[test]
+fn registration_is_send_and_sync() {
+    use crate::time::driver::Registration;
+
+    assert_send::<Registration>();
+    assert_sync::<Registration>();
+}
+
+#[test]
+#[should_panic]
+fn delay_is_eager() {
+    let when = Instant::now() + Duration::from_millis(100);
+    let _ = time::delay_until(when);
+}
diff --git a/tokio/src/time/tests/test_delay.rs b/tokio/src/time/tests/test_delay.rs
index 8b52e0a3..43bfe379 100644
--- a/tokio/src/time/tests/test_delay.rs
+++ b/tokio/src/time/tests/test_delay.rs
@@ -181,29 +181,13 @@ fn delayed_delay_level_1() {
 }
 
 #[test]
+#[should_panic]
 fn creating_delay_outside_of_context() {
     let now = Instant::now();
 
     // This creates a delay outside of the context of a mock timer. This tests
-    // that it will still expire.
-    let mut fut = task::spawn(delay_until(now + ms(500)));
-
-    mock(|clock| {
-        // This registers the delay with the timer
-        assert_pending!(fut.poll());
-
-        // Wait some time... the timer is cascading
-        clock.turn_for(ms(1000));
-        assert_eq!(clock.advanced(), ms(448));
-
-        assert_pending!(fut.poll());
-
-        clock.turn_for(ms(1000));
-        assert_eq!(clock.advanced(), ms(500));
-
-        // The delay has elapsed
-        assert_ready!(fut.poll());
-    });
+    // that it will panic.
+    let _fut = task::spawn(delay_until(now + ms(500)));
 }
 
 #[test]