Fixed cpu time unittest to be less flaky

webrtc/base/cpu_time_unittest.cc

 /*
  *  Copyright (c) 2017 The WebRTC project authors. All Rights Reserved.
  *
  *  Use of this source code is governed by a BSD-style license
  *  that can be found in the LICENSE file in the root of the source
  *  tree. An additional intellectual property rights grant can be found
  *  in the file PATENTS.  All contributing project authors may
  *  be found in the AUTHORS file in the root of the source tree.
  */
 
 #include <memory>
 #include <algorithm>
 #include "webrtc/base/cpu_time.h"
 #include "webrtc/base/platform_thread.h"
 #include "webrtc/base/timeutils.h"
 #include "webrtc/test/gtest.h"
 #include "webrtc/system_wrappers/include/cpu_info.h"
+#include "webrtc/system_wrappers/include/sleep.h"
 
 namespace {
 const int kAllowedErrorMillisecs = 30;
 const int kProcessingTimeMillisecs = 300;
+const int kWorkingThreads = 2;
 
-// Consumes approximately kProcessingTimeMillisecs of CPU time.
+// Consumes approximately kProcessingTimeMillisecs of CPU time in single thread.
 bool WorkingFunction(void* counter_pointer) {
   int64_t* counter = reinterpret_cast<int64_t*>(counter_pointer);
   *counter = 0;
-  int64_t stop_time = rtc::SystemTimeNanos() +
-                      kProcessingTimeMillisecs * rtc::kNumNanosecsPerMillisec;
-  while (rtc::SystemTimeNanos() < stop_time) {
+  int64_t stop_cpu_time =
+      rtc::GetThreadCpuTimeNanos() +
+      kProcessingTimeMillisecs * rtc::kNumNanosecsPerMillisec;
+  while (rtc::GetThreadCpuTimeNanos() < stop_cpu_time) {
     (*counter)++;
   }
   return false;
 }
 }  // namespace
 
 namespace rtc {
 
-TEST(GetProcessCpuTimeTest, SingleThread) {
-  int64_t start_time_nanos = GetProcessCpuTimeNanos();
-  int64_t counter;
-  WorkingFunction(reinterpret_cast<void*>(&counter));
-  EXPECT_GT(counter, 0);
-  int64_t duration_nanos = GetProcessCpuTimeNanos() - start_time_nanos;
-  //  Should be about kProcessingTimeMillisecs.
-  EXPECT_NEAR(duration_nanos,
-              kProcessingTimeMillisecs * kNumNanosecsPerMillisec,
-              kAllowedErrorMillisecs * kNumNanosecsPerMillisec);
-}
-
-TEST(GetProcessCpuTimeTest, TwoThreads) {
-  int64_t start_time_nanos = GetProcessCpuTimeNanos();
+TEST(CpuTimeTest, TwoThreads) {
+  int64_t process_start_time_nanos = GetProcessCpuTimeNanos();
+  int64_t thread_start_time_nanos = GetThreadCpuTimeNanos();
   int64_t counter1;
   int64_t counter2;
   PlatformThread thread1(WorkingFunction, reinterpret_cast<void*>(&counter1),
                          "Thread1");
   PlatformThread thread2(WorkingFunction, reinterpret_cast<void*>(&counter2),
                          "Thread2");
   thread1.Start();
   thread2.Start();
   thread1.Stop();
   thread2.Stop();
 
   EXPECT_GE(counter1, 0);
   EXPECT_GE(counter2, 0);
-  int64_t duration_nanos = GetProcessCpuTimeNanos() - start_time_nanos;
-  const uint32_t kWorkingThreads = 2;
-  uint32_t used_cores =
-      std::min(webrtc::CpuInfo::DetectNumberOfCores(), kWorkingThreads);
-  // Two working threads for kProcessingTimeMillisecs consume double CPU time
-  // if there are at least 2 cores.
-  EXPECT_NEAR(duration_nanos,
-              used_cores * kProcessingTimeMillisecs * kNumNanosecsPerMillisec,
-              used_cores * kAllowedErrorMillisecs * kNumNanosecsPerMillisec);
+  int64_t process_duration_nanos =
+      GetProcessCpuTimeNanos() - process_start_time_nanos;
+  int64_t thread_duration_nanos =
+      GetThreadCpuTimeNanos() - thread_start_time_nanos;
+  // This thread did almost nothing.
+  // Therefore GetThreadCpuTime is not a wall clock.
+  EXPECT_LE(thread_duration_nanos,
+            kAllowedErrorMillisecs * kNumNanosecsPerMillisec);
+  // Total process time is twice working threads' CPU time.
+  // Therefore process and thread times are correctly related.
+  EXPECT_NEAR(
+      process_duration_nanos,
+      kWorkingThreads * kProcessingTimeMillisecs * kNumNanosecsPerMillisec,
+      kWorkingThreads * kAllowedErrorMillisecs * kNumNanosecsPerMillisec);
 }
 
-TEST(GetThreadCpuTimeTest, SingleThread) {
-  int64_t start_times_nanos = GetThreadCpuTimeNanos();
-  int64_t counter;
-  WorkingFunction(reinterpret_cast<void*>(&counter));
-  EXPECT_GT(counter, 0);
-  int64_t duration_nanos = GetThreadCpuTimeNanos() - start_times_nanos;
-  EXPECT_NEAR(duration_nanos,
-              kProcessingTimeMillisecs * kNumNanosecsPerMillisec,
-              kAllowedErrorMillisecs * kNumNanosecsPerMillisec);
-}
-
-TEST(GetThreadCpuTimeTest, TwoThreads) {
-  int64_t start_time_nanos = GetThreadCpuTimeNanos();
-  int64_t counter1;
-  int64_t counter2;
-  PlatformThread thread1(WorkingFunction, reinterpret_cast<void*>(&counter1),
-                         "Thread1");
-  PlatformThread thread2(WorkingFunction, reinterpret_cast<void*>(&counter2),
-                         "Thread2");
-  thread1.Start();
-  thread2.Start();
-  thread1.Stop();
-  thread2.Stop();
-
-  EXPECT_GE(counter1, 0);
-  EXPECT_GE(counter2, 0);
-  int64_t duration_nanos = GetThreadCpuTimeNanos() - start_time_nanos;
-  // This thread didn't do any work.
-  EXPECT_NEAR(duration_nanos, 0,
-              kAllowedErrorMillisecs * kNumNanosecsPerMillisec);
+TEST(CpuTimeTest, Sleeping) {
+  int64_t process_start_time_nanos = GetProcessCpuTimeNanos();
+  webrtc::SleepMs(kProcessingTimeMillisecs);
+  int64_t process_duration_nanos =
+      GetProcessCpuTimeNanos() - process_start_time_nanos;
+  // Sleeping should not introduce any additional CPU time.
+  // Therefore GetProcessCpuTime is not a wall clock.
+  EXPECT_LE(process_duration_nanos,
+            kWorkingThreads * kAllowedErrorMillisecs * kNumNanosecsPerMillisec);
 }
 
 }  // namespace rtc