pkg/timeutil: init

pkg/timeutil/timeutil.go

@@ -0,0 +1,58 @@
+// Copyright 2018 clair 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 timeutil implements extra utilities dealing with time not found
+// in the standard library.
+package timeutil
+
+import (
+	"math"
+	"math/rand"
+	"time"
+
+	"github.com/coreos/clair/pkg/stopper"
+	log "github.com/sirupsen/logrus"
+)
+
+// ApproxSleep is a stoppable time.Sleep that adds a slight random variation to
+// the wakeup time in order to prevent thundering herds.
+func ApproxSleep(approxWakeup time.Time, st *stopper.Stopper) (stopped bool) {
+	waitUntil := approxWakeup.Add(time.Duration(rand.ExpFloat64()/0.5) * time.Second)
+	log.WithField("wakeup", waitUntil).Debug("updater sleeping")
+	if !waitUntil.Before(time.Now().UTC()) {
+		if !st.Sleep(waitUntil.Sub(time.Now())) {
+			return true
+		}
+	}
+	return false
+}
+
+// ExpBackoff doubles the backoff time, if the result is longer than the
+// parameter max, max will be returned.
+func ExpBackoff(prev, max time.Duration) time.Duration {
+	t := 2 * prev
+	if t > max {
+		t = max
+	}
+	if t == 0 {
+		return time.Second
+	}
+	return t
+}
+
+// FractionalDuration calculates the fraction of a Duration rounding half way
+// from zero.
+func FractionalDuration(fraction float64, d time.Duration) time.Duration {
+	return time.Duration(math.Round(float64(d) * fraction))
+}

pkg/timeutil/timeutil_test.go

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+// Copyright 2018 clair 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 timeutil
+
+import (
+	"testing"
+	"time"
+)
+
+func TestExpBackoff(t *testing.T) {
+	tests := []struct {
+		prev, max, want time.Duration
+	}{
+		{time.Duration(0), 1 * time.Minute, 1 * time.Second},
+		{1 * time.Second, 1 * time.Minute, 2 * time.Second},
+		{16 * time.Second, 1 * time.Minute, 32 * time.Second},
+		{32 * time.Second, 1 * time.Minute, 1 * time.Minute},
+		{1 * time.Minute, 1 * time.Minute, 1 * time.Minute},
+		{2 * time.Minute, 1 * time.Minute, 1 * time.Minute},
+	}
+
+	for i, tt := range tests {
+		got := ExpBackoff(tt.prev, tt.max)
+		if tt.want != got {
+			t.Errorf("case %d: want=%v got=%v", i, tt.want, got)
+		}
+	}
+}