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// Copyright (c) 2023 Uber Technologies, Inc.
//
// 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.
package ztest
import (
"sort"
"sync"
"time"
)
// MockClock is a fake source of time.
// It implements standard time operations,
// but allows the user to control the passage of time.
//
// Use the [Add] method to progress time.
type MockClock struct {
mu sync.RWMutex
now time.Time
// The MockClock works by maintaining a list of waiters.
// Each waiter knows the time at which it should be resolved.
// When the clock advances, all waiters that are in range are resolved
// in chronological order.
waiters []waiter
}
// NewMockClock builds a new mock clock
// using the current actual time as the initial time.
func NewMockClock() *MockClock {
return &MockClock{
now: time.Now(),
}
}
// Now reports the current time.
func (c *MockClock) Now() time.Time {
c.mu.RLock()
defer c.mu.RUnlock()
return c.now
}
// NewTicker returns a time.Ticker that ticks at the specified frequency.
//
// As with [time.NewTicker],
// the ticker will drop ticks if the receiver is slow,
// and the channel is never closed.
//
// Calling Stop on the returned ticker is a no-op.
// The ticker only runs when the clock is advanced.
func (c *MockClock) NewTicker(d time.Duration) *time.Ticker {
ch := make(chan time.Time, 1)
var tick func(time.Time)
tick = func(now time.Time) {
next := now.Add(d)
c.runAt(next, func() {
defer tick(next)
select {
case ch <- next:
// ok
default:
// The receiver is slow.
// Drop the tick and continue.
}
})
}
tick(c.Now())
return &time.Ticker{C: ch}
}
// runAt schedules the given function to be run at the given time.
// The function runs without a lock held, so it may schedule more work.
func (c *MockClock) runAt(t time.Time, fn func()) {
c.mu.Lock()
defer c.mu.Unlock()
c.waiters = append(c.waiters, waiter{until: t, fn: fn})
}
type waiter struct {
until time.Time
fn func()
}
// Add progresses time by the given duration.
// Other operations waiting for the time to advance
// will be resolved if they are within range.
//
// Side effects of operations waiting for the time to advance
// will take effect on a best-effort basis.
// Avoid racing with operations that have side effects.
//
// Panics if the duration is negative.
func (c *MockClock) Add(d time.Duration) {
if d < 0 {
panic("cannot add negative duration")
}
c.mu.Lock()
defer c.mu.Unlock()
sort.Slice(c.waiters, func(i, j int) bool {
return c.waiters[i].until.Before(c.waiters[j].until)
})
newTime := c.now.Add(d)
// newTime won't be recorded until the end of this method.
// This ensures that any waiters that are resolved
// are resolved at the time they were expecting.
for len(c.waiters) > 0 {
w := c.waiters[0]
if w.until.After(newTime) {
break
}
c.waiters[0] = waiter{} // avoid memory leak
c.waiters = c.waiters[1:]
// The waiter is within range.
// Travel to the time of the waiter and resolve it.
c.now = w.until
// The waiter may schedule more work
// so we must release the lock.
c.mu.Unlock()
w.fn()
// Sleeping here is necessary to let the side effects of waiters
// take effect before we continue.
time.Sleep(1 * time.Millisecond)
c.mu.Lock()
}
c.now = newTime
}
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