1 files changed, 130 insertions, 0 deletions
diff --git a/pkg/tcpip/stdclock.go b/pkg/tcpip/stdclock.go
new file mode 100644
index 000000000..7ce43a68e
--- /dev/null
+++ b/pkg/tcpip/stdclock.go
@@ -0,0 +1,130 @@
+// Copyright 2018 The gVisor Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package tcpip
+
+import (
+	"fmt"
+	"time"
+
+	"gvisor.dev/gvisor/pkg/sync"
+)
+
+// stdClock implements Clock with the time package.
+//
+// +stateify savable
+type stdClock struct {
+	// baseTime holds the time when the clock was constructed.
+	//
+	// This value is used to calculate the monotonic time from the time package.
+	// As per https://golang.org/pkg/time/#hdr-Monotonic_Clocks,
+	//
+	//   Operating systems provide both a “wall clock,” which is subject to
+	//   changes for clock synchronization, and a “monotonic clock,” which is not.
+	//   The general rule is that the wall clock is for telling time and the
+	//   monotonic clock is for measuring time. Rather than split the API, in this
+	//   package the Time returned by time.Now contains both a wall clock reading
+	//   and a monotonic clock reading; later time-telling operations use the wall
+	//   clock reading, but later time-measuring operations, specifically
+	//   comparisons and subtractions, use the monotonic clock reading.
+	//
+	//   ...
+	//
+	//   If Times t and u both contain monotonic clock readings, the operations
+	//   t.After(u), t.Before(u), t.Equal(u), and t.Sub(u) are carried out using
+	//   the monotonic clock readings alone, ignoring the wall clock readings. If
+	//   either t or u contains no monotonic clock reading, these operations fall
+	//   back to using the wall clock readings.
+	//
+	// Given the above, we can safely conclude that time.Since(baseTime) will
+	// return monotonically increasing values if we use time.Now() to set baseTime
+	// at the time of clock construction.
+	//
+	// Note that time.Since(t) is shorthand for time.Now().Sub(t), as per
+	// https://golang.org/pkg/time/#Since.
+	baseTime time.Time `state:"nosave"`
+
+	// monotonicOffset is the offset applied to the calculated monotonic time.
+	//
+	// monotonicOffset is assigned maxMonotonic after restore so that the
+	// monotonic time will continue from where it "left off" before saving as part
+	// of S/R.
+	monotonicOffset int64 `state:"nosave"`
+
+	// monotonicMU protects maxMonotonic.
+	monotonicMU  sync.Mutex `state:"nosave"`
+	maxMonotonic int64
+}
+
+// NewStdClock returns an instance of a clock that uses the time package.
+func NewStdClock() Clock {
+	return &stdClock{
+		baseTime: time.Now(),
+	}
+}
+
+var _ Clock = (*stdClock)(nil)
+
+// NowNanoseconds implements Clock.NowNanoseconds.
+func (*stdClock) NowNanoseconds() int64 {
+	return time.Now().UnixNano()
+}
+
+// NowMonotonic implements Clock.NowMonotonic.
+func (s *stdClock) NowMonotonic() int64 {
+	sinceBase := time.Since(s.baseTime)
+	if sinceBase < 0 {
+		panic(fmt.Sprintf("got negative duration = %s since base time = %s", sinceBase, s.baseTime))
+	}
+
+	monotonicValue := sinceBase.Nanoseconds() + s.monotonicOffset
+
+	s.monotonicMU.Lock()
+	defer s.monotonicMU.Unlock()
+
+	// Monotonic time values must never decrease.
+	if monotonicValue > s.maxMonotonic {
+		s.maxMonotonic = monotonicValue
+	}
+
+	return s.maxMonotonic
+}
+
+// AfterFunc implements Clock.AfterFunc.
+func (*stdClock) AfterFunc(d time.Duration, f func()) Timer {
+	return &stdTimer{
+		t: time.AfterFunc(d, f),
+	}
+}
+
+type stdTimer struct {
+	t *time.Timer
+}
+
+var _ Timer = (*stdTimer)(nil)
+
+// Stop implements Timer.Stop.
+func (st *stdTimer) Stop() bool {
+	return st.t.Stop()
+}
+
+// Reset implements Timer.Reset.
+func (st *stdTimer) Reset(d time.Duration) {
+	st.t.Reset(d)
+}
+
+// NewStdTimer returns a Timer implemented with the time package.
+func NewStdTimer(t *time.Timer) Timer {
+	return &stdTimer{t: t}
+}