capnproto

timer.h (6075B)

---

 // Copyright (c) 2014 Google Inc. (contributed by Remy Blank <rblank@google.com>)
 // Copyright (c) 2013-2014 Sandstorm Development Group, Inc. and contributors
 // Licensed under the MIT License:
 //
 // Permission is hereby granted, free of charge, to any person obtaining a copy
 // of this software and associated documentation files (the "Software"), to deal
 // in the Software without restriction, including without limitation the rights
 // to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
 // copies of the Software, and to permit persons to whom the Software is
 // furnished to do so, subject to the following conditions:
 //
 // The above copyright notice and this permission notice shall be included in
 // all copies or substantial portions of the Software.
 //
 // THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 // IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 // FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
 // AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 // LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
 // OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
 // THE SOFTWARE.
 
 #pragma once
 
 #include "time.h"
 #include "async.h"
 
 KJ_BEGIN_HEADER
 
 namespace kj {
 
 class Timer: public MonotonicClock {
   // Interface to time and timer functionality.
   //
   // Each `Timer` may have a different origin, and some `Timer`s may in fact tick at a different
   // rate than real time (e.g. a `Timer` could represent CPU time consumed by a thread).  However,
   // all `Timer`s are monotonic: time will never appear to move backwards, even if the calendar
   // date as tracked by the system is manually modified.
   //
   // That said, the `Timer` returned by `kj::setupAsyncIo().provider->getTimer()` in particular is
   // guaranteed to be synchronized with the `MonotonicClock` returned by
   // `systemPreciseMonotonicClock()` (or, more precisely, is updated to match that clock whenever
   // the loop waits).
   //
   // Note that the value returned by `Timer::now()` only changes each time the
   // event loop waits for I/O from the system. While the event loop is actively
   // running, the time stays constant. This is intended to make behavior more
   // deterministic and reproducible. However, if you need up-to-the-cycle
   // accurate time, then `Timer::now()` is not appropriate. Instead, use
   // `systemPreciseMonotonicClock()` directly in this case.
 
 public:
   virtual TimePoint now() const = 0;
   // Returns the current value of a clock that moves steadily forward, independent of any
   // changes in the wall clock. The value is updated every time the event loop waits,
   // and is constant in-between waits.
 
   virtual Promise<void> atTime(TimePoint time) = 0;
   // Returns a promise that returns as soon as now() >= time.
 
   virtual Promise<void> afterDelay(Duration delay) = 0;
   // Equivalent to atTime(now() + delay).
 
   template <typename T>
   Promise<T> timeoutAt(TimePoint time, Promise<T>&& promise) KJ_WARN_UNUSED_RESULT;
   // Return a promise equivalent to `promise` but which throws an exception (and cancels the
   // original promise) if it hasn't completed by `time`. The thrown exception is of type
   // "OVERLOADED".
 
   template <typename T>
   Promise<T> timeoutAfter(Duration delay, Promise<T>&& promise) KJ_WARN_UNUSED_RESULT;
   // Return a promise equivalent to `promise` but which throws an exception (and cancels the
   // original promise) if it hasn't completed after `delay` from now. The thrown exception is of
   // type "OVERLOADED".
 
 private:
   static kj::Exception makeTimeoutException();
 };
 
 class TimerImpl final: public Timer {
   // Implementation of Timer that expects an external caller -- usually, the EventPort
   // implementation -- to tell it when time has advanced.
 
 public:
   TimerImpl(TimePoint startTime);
   ~TimerImpl() noexcept(false);
 
   Maybe<TimePoint> nextEvent();
   // Returns the time at which the next scheduled timer event will occur, or null if no timer
   // events are scheduled.
 
   Maybe<uint64_t> timeoutToNextEvent(TimePoint start, Duration unit, uint64_t max);
   // Convenience method which computes a timeout value to pass to an event-waiting system call to
   // cause it to time out when the next timer event occurs.
   //
   // `start` is the time at which the timeout starts counting. This is typically not the same as
   // now() since some time may have passed since the last time advanceTo() was called.
   //
   // `unit` is the time unit in which the timeout is measured. This is often MILLISECONDS. Note
   // that this method will fractional values *up*, to guarantee that the returned timeout waits
   // until just *after* the time the event is scheduled.
   //
   // The timeout will be clamped to `max`. Use this to avoid an overflow if e.g. the OS wants a
   // 32-bit value or a signed value.
   //
   // Returns nullptr if there are no future events.
 
   void advanceTo(TimePoint newTime);
   // Set the time to `time` and fire any at() events that have been passed.
 
   // implements Timer ----------------------------------------------------------
   TimePoint now() const override;
   Promise<void> atTime(TimePoint time) override;
   Promise<void> afterDelay(Duration delay) override;
 
 private:
   struct Impl;
   class TimerPromiseAdapter;
   TimePoint time;
   Own<Impl> impl;
 };
 
 // =======================================================================================
 // inline implementation details
 
 template <typename T>
 Promise<T> Timer::timeoutAt(TimePoint time, Promise<T>&& promise) {
   return promise.exclusiveJoin(atTime(time).then([]() -> kj::Promise<T> {
     return makeTimeoutException();
   }));
 }
 
 template <typename T>
 Promise<T> Timer::timeoutAfter(Duration delay, Promise<T>&& promise) {
   return promise.exclusiveJoin(afterDelay(delay).then([]() -> kj::Promise<T> {
     return makeTimeoutException();
   }));
 }
 
 inline TimePoint TimerImpl::now() const { return time; }
 
 }  // namespace kj
 
 KJ_END_HEADER