From d638d2078b342e93ab3e64709321a3178298d576 Mon Sep 17 00:00:00 2001
From: Zsolt Felfoldi <zsfelfoldi@gmail.com>
Date: Wed, 30 May 2018 14:45:15 +0200
Subject: [PATCH] common/mclock: add SimulatedClock

---
 common/mclock/mclock.go   |  26 ++++++++
 common/mclock/simclock.go | 130 ++++++++++++++++++++++++++++++++++++++
 2 files changed, 156 insertions(+)
 create mode 100644 common/mclock/simclock.go

diff --git a/common/mclock/mclock.go b/common/mclock/mclock.go
index 02608d17b0..76d1e5cdb7 100644
--- a/common/mclock/mclock.go
+++ b/common/mclock/mclock.go
@@ -30,3 +30,29 @@ type AbsTime time.Duration
 func Now() AbsTime {
 	return AbsTime(monotime.Now())
 }
+
+// Clock interface makes it possible to replace the monotonic system clock with
+// a simulated clock
+type Clock interface {
+	Now() AbsTime
+	Sleep(time.Duration)
+	After(time.Duration) <-chan time.Time
+}
+
+// MonotonicClock implements Clock using the system clock
+type MonotonicClock struct{}
+
+// Now implements Clock
+func (MonotonicClock) Now() AbsTime {
+	return AbsTime(monotime.Now())
+}
+
+// Sleep implements Clock
+func (MonotonicClock) Sleep(d time.Duration) {
+	time.Sleep(d)
+}
+
+// After implements Clock
+func (MonotonicClock) After(d time.Duration) <-chan time.Time {
+	return time.After(d)
+}
diff --git a/common/mclock/simclock.go b/common/mclock/simclock.go
new file mode 100644
index 0000000000..11cff0dc4a
--- /dev/null
+++ b/common/mclock/simclock.go
@@ -0,0 +1,130 @@
+// 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
+}
+
+// NewSimulatedClock creates a new simulated clock
+func NewSimulatedClock(maxStep time.Duration, goSchedCount int) *SimulatedClock {
+	s := &SimulatedClock{scheduled: make([]event, 0, 100)}
+
+	go func() {
+		lastScheduled := 0
+		for {
+			for i := 0; i < goSchedCount; i++ {
+				runtime.Gosched()
+			}
+			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}
+}