/*
- * Copyright 2015 Facebook, Inc.
+ * Copyright 2016 Facebook, Inc.
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
#pragma once
#include <folly/futures/detail/Types.h>
+#include <folly/Unit.h>
namespace folly {
-template <class> struct Future;
+template <class> class Future;
/// A Timekeeper handles the details of keeping time and fulfilling delay
-/// promises. The returned Future<void> will either complete after the
+/// promises. The returned Future<Unit> will either complete after the
/// elapsed time, or in the event of some kind of exceptional error may hold
/// an exception. These Futures respond to cancellation. If you use a lot of
/// Delays and many of them ultimately are unneeded (as would be the case for
/// use them implicitly behind the scenes by passing a timeout to some Future
/// operation.
///
-/// Although we don't formally alias Delay = Future<void>,
+/// Although we don't formally alias Delay = Future<Unit>,
/// that's an appropriate term for it. People will probably also call these
/// Timeouts, and that's ok I guess, but that term is so overloaded I thought
/// it made sense to introduce a cleaner term.
///
/// Remember that Duration is a std::chrono duration (millisecond resolution
-/// at the time of writing).
+/// at the time of writing). When writing code that uses specific durations,
+/// prefer using the explicit std::chrono type, e.g. std::chrono::milliseconds
+/// over Duration. This makes the code more legible and means you won't be
+/// unpleasantly surprised if we redefine Duration to microseconds, or
+/// something.
+///
+/// timekeeper.after(std::chrono::duration_cast<Duration>(
+/// someNanoseconds))
class Timekeeper {
public:
virtual ~Timekeeper() = default;
/// This future probably completes on the timer thread. You should almost
/// certainly follow it with a via() call or the accuracy of other timers
/// will suffer.
- virtual Future<void> after(Duration) = 0;
+ virtual Future<Unit> after(Duration) = 0;
/// Returns a future that will complete at the requested time.
///
/// the system clock but rather execute that many milliseconds in the future
/// according to the steady clock.
template <class Clock>
- Future<void> at(std::chrono::time_point<Clock> when);
+ Future<Unit> at(std::chrono::time_point<Clock> when);
};
} // namespace folly
namespace folly {
template <class Clock>
-Future<void> Timekeeper::at(std::chrono::time_point<Clock> when) {
+Future<Unit> Timekeeper::at(std::chrono::time_point<Clock> when) {
auto now = Clock::now();
if (when <= now) {
return makeFuture();
}
- return after(when - now);
+ return after(std::chrono::duration_cast<Duration>(when - now));
}
} // namespace folly