Add, test, and use clock utilities

util/misc/clock_test.cc

Index: util/misc/clock_test.cc
diff --git a/util/misc/clock_test.cc b/util/misc/clock_test.cc
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+// Copyright 2014 The Crashpad Authors. All rights reserved.
+//
+// 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.
+
+#include "util/misc/clock.h"
+
+#include <stdint.h>
+
+#include <algorithm>
+
+#include "base/basictypes.h"
+#include "base/logging.h"
+#include "base/strings/stringprintf.h"
+#include "gtest/gtest.h"
+
+namespace {
+
+using namespace crashpad;
+
+TEST(Clock, ClockMonotonicNanoseconds) {
+  uint64_t start = ClockMonotonicNanoseconds();
+  EXPECT_GT(start, 0u);
+
+  uint64_t now = start;
+  for (size_t iteration = 0; iteration < 10; ++iteration) {
+    uint64_t last = now;
+    now = ClockMonotonicNanoseconds();
+
+    // Use EXPECT_GE instead of EXPECT_GT, because there are no guarantees about
+    // the clock’s resolution.
+    EXPECT_GE(now, last);
+  }
+
+  // SleepNanoseconds() should sleep for at least the value of the clock’s
+  // resolution, so the clock’s value should definitely increase after a sleep.
+  // EXPECT_GT can be used instead of EXPECT_GE after the sleep.
+  SleepNanoseconds(1);
+  now = ClockMonotonicNanoseconds();
+  EXPECT_GT(now, start);
+}
+
+void TestSleepNanoseconds(uint64_t nanoseconds) {
+  uint64_t start = ClockMonotonicNanoseconds();
+
+  SleepNanoseconds(nanoseconds);
+
+  uint64_t end = ClockMonotonicNanoseconds();
+  uint64_t diff = end - start;
+
+  // |nanoseconds| is the lower bound for the actual amount of time spent
+  // sleeping.
+  EXPECT_GE(diff, nanoseconds);
+
+  // It’s difficult to set an upper bound for the time spent sleeping. Allow
+  // sleeps twice as long as requested, or sleeps a millisecond longer than
+  // requested, whichever is larger. This is quite a lot of slop, but the
+  // alternative would be test flakiness.
+  uint64_t slop = std::max(static_cast<uint64_t>(1E6), nanoseconds);
+  EXPECT_LE(diff, nanoseconds + slop);
+}
+
+TEST(Clock, SleepNanoseconds) {
+  const uint64_t kTestData[] = {
+      0,
+      1,
+      static_cast<uint64_t>(1E3),  // 1 microsecond
+      static_cast<uint64_t>(1E4),  // 10 microseconds
+      static_cast<uint64_t>(1E5),  // 100 microseconds
+      static_cast<uint64_t>(1E6),  // 1 millisecond
+      static_cast<uint64_t>(1E7),  // 10 milliseconds
+      static_cast<uint64_t>(2E7),  // 20 milliseconds
+      static_cast<uint64_t>(5E7),  // 50 milliseconds
+  };
+
+  for (size_t index = 0; index < arraysize(kTestData); ++index) {
+    const uint64_t nanoseconds = kTestData[index];
+    SCOPED_TRACE(
+        base::StringPrintf("index %zu, nanoseconds %llu", index, nanoseconds));
+
+    TestSleepNanoseconds(nanoseconds);
+  }
+}
+
+}  // namespace