go-ethereum/common/mclock/simclock.go

// Copyright 2016 The go-ethereum Authors
// This file is part of the go-ethereum library.
//
// The go-ethereum library is free software: you can redistribute it and/or modify
// it under the terms of the GNU Lesser General Public License as published by
// the Free Software Foundation, either version 3 of the License, or
// (at your option) any later version.
//
// The go-ethereum library is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
// GNU Lesser General Public License for more details.
//
// You should have received a copy of the GNU Lesser General Public License
// along with the go-ethereum library. If not, see <http://www.gnu.org/licenses/>.

// package mclock is a wrapper for a monotonic clock source
package mclock

import (
	"runtime"
	"sync"
	"time"
)

type event struct {
	do func()
	at AbsTime
}

// SimulatedClock implements a virtual Clock for reproducible time-sensitive tests.
// It simulates a scheduler on a virtual timescale where actual processing takes zero time.
//
// Note: since there is no way in Go to know when all goroutines have reached a waiting
// state (which should theoretically happen in each virtual moment), the algorithm runs
// GoSched a fixed number of times after each step and limits time steps in order to
// minimize precision loss (see maxStep and goSchedCount).
type SimulatedClock struct {
	now       AbsTime
	scheduled []event
	stop      bool
	lock      sync.RWMutex
}

const (
	maxStep      = time.Microsecond * 10
	goSchedCount = 10
)

// NewSimulatedClock creates a new simulated clock
func NewSimulatedClock() *SimulatedClock {
	s := &SimulatedClock{scheduled: make([]event, 0, 100)}

	go func() {
		lastScheduled := 0
		for {
			for i := 0; i < goSchedCount; i++ {
				runtime.Gosched()
			}
			//time.Sleep(time.Microsecond * 10)
			s.lock.Lock()
			if s.stop {
				s.lock.Unlock()
				return
			}
			scheduled := len(s.scheduled)
			if scheduled > 0 && scheduled == lastScheduled {
				ev := s.scheduled[0]
				if ev.at <= s.now+AbsTime(maxStep) {
					s.scheduled = s.scheduled[1:]
					s.now = ev.at
					ev.do()
				} else {
					s.now += AbsTime(maxStep)
				}
			}
			lastScheduled = scheduled
			s.lock.Unlock()
		}
	}()

	return s
}

// Stop stops the clock (Sleeps and Afters will never return after this)
func (s *SimulatedClock) Stop() {
	s.lock.Lock()
	s.stop = true
	s.lock.Unlock()
}

// Now implements Clock
func (s *SimulatedClock) Now() AbsTime {
	s.lock.RLock()
	defer s.lock.RUnlock()

	return s.now
}

// Sleep implements Clock
func (s *SimulatedClock) Sleep(d time.Duration) {
	done := make(chan struct{})
	s.insert(d, func() {
		close(done)
	})
	<-done
}

// After implements Clock
func (s *SimulatedClock) After(d time.Duration) <-chan time.Time {
	after := make(chan time.Time, 1)
	s.insert(d, func() {
		after <- time.Unix(0, int64(s.now))
	})
	return after
}

func (s *SimulatedClock) insert(d time.Duration, do func()) {
	s.lock.Lock()
	defer s.lock.Unlock()

	at := s.now + AbsTime(d)
	l, h := 0, len(s.scheduled)
	ll := h
	for l != h {
		m := (l + h) / 2
		if at < s.scheduled[m].at {
			h = m
		} else {
			l = m + 1
		}
	}
	s.scheduled = append(s.scheduled, event{})
	copy(s.scheduled[l+1:], s.scheduled[l:ll])
	s.scheduled[l] = event{do: do, at: at}
}