Add context-aware "time" library wrapper.

go/src/infra/libs/clock/testclock/testclock.go

+// Copyright 2014 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+package testclock
+
+import (
+        "sync"
+        "time"
+
+        "infra/libs/clock"
+)
+
+// TestClock is a Clock interface with additional methods to help instrument it.
+type TestClock interface {
+        clock.Clock
+        Set(time.Time)
+        Add(time.Duration)
+        SetTimerCallback(TimerCallback)
+}
+
+// TimerCallback that can be invoked when a timer has been set. This is useful for
+// sychronizing state when testing.

[iannucci, 2015/06/03 17:37:20]

I think we're still trying to wrap 80 on comments everywhere.

[dnj, 2015/06/03 18:21:27]

I did a best-effort run. I wonder if this is enforceable via golint settings...

+type TimerCallback func(clock.Timer)
+
+type cancelFunc func()
+
+// testClock is a test-oriented implementation of the 'Clock' interface.
+//
+// This implementation's Clock responses are configurable by modifying its member
+// variables. Time-based events are explicitly triggered by sending on a Timer
+// instance's channel.
+type testClock struct {
+        sync.RWMutex
+
+        now       time.Time  // The current clock time.
+        timerCond *sync.Cond // Condition used to manage timer blocking.
+
+        timerCallback TimerCallback // Optional callback when a timer has been set.
+}
+
+var _ TestClock = (*testClock)(nil)
+
+// New returns a TestClock instance set at the specified time.
+func New(now time.Time) TestClock {
+        c := testClock{
+                now: now,
+        }
+        c.timerCond = sync.NewCond(&c)
+        return &c
+}
+
+func (c *testClock) Now() time.Time {
+        c.RLock()
+        defer c.RUnlock()
+
+        return c.now
+}
+
+func (c *testClock) Sleep(d time.Duration) {
+        <-c.After(d)
+}
+
+func (c *testClock) NewTimer() clock.Timer {
+        return newTimer(c)
+}
+
+func (c *testClock) After(d time.Duration) <-chan time.Time {
+        t := c.NewTimer()
+        t.Reset(d)
+        return t.GetC()
+}
+
+func (c *testClock) Set(t time.Time) {
+        c.Lock()
+        defer c.Unlock()
+
+        c.setTimeLocked(t)
+}
+
+func (c *testClock) Add(d time.Duration) {
+        c.Lock()
+        defer c.Unlock()
+
+        c.setTimeLocked(c.now.Add(d))
+}
+
+func (c *testClock) setTimeLocked(t time.Time) {
+        if t.Before(c.now) {
+                panic("Cannot go backwards in time. You're not Doc Brown.")
+        }
+        c.now = t
+
+        // Unblock any blocking timers that are waiting on our lock.
+        c.pokeTimers(true)
+}
+
+func (c *testClock) SetTimerCallback(callback TimerCallback) {
+        c.Lock()
+        defer c.Unlock()
+
+        c.timerCallback = callback
+}
+
+func (c *testClock) getTimerCallback() TimerCallback {
+        c.Lock()
+        defer c.Unlock()
+
+        return c.timerCallback
+}
+
+func (c *testClock) signalTimerSet(t clock.Timer) {
+        callback := c.getTimerCallback()
+        if callback != nil {
+                callback(t)
+        }
+}
+
+func (c *testClock) pokeTimers(locked bool) {
+        if !locked {
+                c.Lock()
+                defer c.Unlock()
+        }
+
+        c.timerCond.Broadcast()
+}
+
+func (c *testClock) whenTimePasses(threshold time.Time, callback func(time.Time)) cancelFunc {
+        stopC := make(chan struct{})
+        finishedC := make(chan struct{})
+
+        // Our control goroutine will monitor both time and stop signals. It will only terminate
+        // when stopC has been closed.
+        //
+        // The lock that we take our here is owned by the following goroutine.
+        c.Lock()
+        go func() {
+                defer func() {
+                        now := c.now
+                        c.Unlock()
+                        close(finishedC)
+                        callback(now)
+                }()
+
+                for {
+                        // Determine if we are past our signalling threshold. We can safely access our
+                        // clock's time member directly, since we hold its lock from the condition firing.
+                        if !c.now.Before(threshold) {
+                                return
+                        }
+
+                        // Wait for a signal from our clock's condition.
+                        c.timerCond.Wait()
+
+                        // Have we been stopped?
+                        select {
+                        case <-stopC:
+                                return
+
+                        default:
+                                // Nope.
+                        }
+                }
+        }()
+
+        return func() {
+                // Close our stop channel and block pending goroutine termination.
+                close(stopC)
+                c.pokeTimers(false)
+                <-finishedC
+        }
+}