Extract SystemTimeNanos to its own file

Prepare for this function to be overridden when WebRTC is included
into other applications such as chromium. This will make it
possible to remove code that keeps track of the difference between
WebRTC and chromium time.

Bug: chromium:516700
Change-Id: I73133804f945cc439f9827ec68a8e67b96d8560f
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/204304
Reviewed-by: Mirko Bonadei <mbonadei@webrtc.org>
Reviewed-by: Ilya Nikolaevskiy <ilnik@webrtc.org>
Reviewed-by: Niels Moller <nisse@webrtc.org>
Commit-Queue: Johannes Kron <kron@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#33273}

rtc_base/BUILD.gn

@@ -400,6 +400,8 @@ rtc_source_set("safe_conversions") {
 rtc_library("timeutils") {
   visibility = [ "*" ]
   sources = [
+    "system_time.cc",
+    "system_time.h",
     "time_utils.cc",
     "time_utils.h",
   ]

rtc_base/system_time.cc

@@ -0,0 +1,92 @@
+/*
+ *  Copyright 2021 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 <stdint.h>
+
+#include <limits>
+
+#if defined(WEBRTC_POSIX)
+#include <sys/time.h>
+#if defined(WEBRTC_MAC)
+#include <mach/mach_time.h>
+#endif
+#endif
+
+#if defined(WEBRTC_WIN)
+// clang-format off
+// clang formatting would put <windows.h> last,
+// which leads to compilation failure.
+#include <windows.h>
+#include <mmsystem.h>
+#include <sys/timeb.h>
+// clang-format on
+#endif
+
+#include "rtc_base/checks.h"
+#include "rtc_base/numerics/safe_conversions.h"
+#include "rtc_base/system_time.h"
+#include "rtc_base/time_utils.h"
+
+namespace rtc {
+
+int64_t SystemTimeNanos() {
+  int64_t ticks;
+#if defined(WEBRTC_MAC)
+  static mach_timebase_info_data_t timebase;
+  if (timebase.denom == 0) {
+    // Get the timebase if this is the first time we run.
+    // Recommended by Apple's QA1398.
+    if (mach_timebase_info(&timebase) != KERN_SUCCESS) {
+      RTC_NOTREACHED();
+    }
+  }
+  // Use timebase to convert absolute time tick units into nanoseconds.
+  const auto mul = [](uint64_t a, uint32_t b) -> int64_t {
+    RTC_DCHECK_NE(b, 0);
+    RTC_DCHECK_LE(a, std::numeric_limits<int64_t>::max() / b)
+        << "The multiplication " << a << " * " << b << " overflows";
+    return rtc::dchecked_cast<int64_t>(a * b);
+  };
+  ticks = mul(mach_absolute_time(), timebase.numer) / timebase.denom;
+#elif defined(WEBRTC_POSIX)
+  struct timespec ts;
+  // TODO(deadbeef): Do we need to handle the case when CLOCK_MONOTONIC is not
+  // supported?
+  clock_gettime(CLOCK_MONOTONIC, &ts);
+  ticks = kNumNanosecsPerSec * static_cast<int64_t>(ts.tv_sec) +
+          static_cast<int64_t>(ts.tv_nsec);
+#elif defined(WINUWP)
+  ticks = TimeHelper::TicksNs();
+#elif defined(WEBRTC_WIN)
+  static volatile LONG last_timegettime = 0;
+  static volatile int64_t num_wrap_timegettime = 0;
+  volatile LONG* last_timegettime_ptr = &last_timegettime;
+  DWORD now = timeGetTime();
+  // Atomically update the last gotten time
+  DWORD old = InterlockedExchange(last_timegettime_ptr, now);
+  if (now < old) {
+    // If now is earlier than old, there may have been a race between threads.
+    // 0x0fffffff ~3.1 days, the code will not take that long to execute
+    // so it must have been a wrap around.
+    if (old > 0xf0000000 && now < 0x0fffffff) {
+      num_wrap_timegettime++;
+    }
+  }
+  ticks = now + (num_wrap_timegettime << 32);
+  // TODO(deadbeef): Calculate with nanosecond precision. Otherwise, we're
+  // just wasting a multiply and divide when doing Time() on Windows.
+  ticks = ticks * kNumNanosecsPerMillisec;
+#else
+#error Unsupported platform.
+#endif
+  return ticks;
+}
+
+}  // namespace rtc

rtc_base/system_time.h

@@ -0,0 +1,22 @@
+/*
+ *  Copyright 2021 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.
+ */
+
+#ifndef RTC_BASE_SYSTEM_TIME_H_
+#define RTC_BASE_SYSTEM_TIME_H_
+
+namespace rtc {
+
+// Returns the actual system time, even if a clock is set for testing.
+// Useful for timeouts while using a test clock, or for logging.
+int64_t SystemTimeNanos();
+
+}  // namespace rtc
+
+#endif  // RTC_BASE_SYSTEM_TIME_H_

rtc_base/time_utils.cc

@@ -12,23 +12,15 @@
 
 #if defined(WEBRTC_POSIX)
 #include <sys/time.h>
-#if defined(WEBRTC_MAC)
-#include <mach/mach_time.h>
-#endif
 #endif
 
 #if defined(WEBRTC_WIN)
-// clang-format off
-// clang formatting would put <windows.h> last,
-// which leads to compilation failure.
-#include <windows.h>
-#include <mmsystem.h>
 #include <sys/timeb.h>
-// clang-format on
 #endif
 
 #include "rtc_base/checks.h"
 #include "rtc_base/numerics/safe_conversions.h"
+#include "rtc_base/system_time.h"
 #include "rtc_base/time_utils.h"
 
 namespace rtc {
@@ -143,59 +135,6 @@ void SyncWithNtp(int64_t time_from_ntp_server_ms) {
 
 #endif  // defined(WINUWP)
 
-int64_t SystemTimeNanos() {
-  int64_t ticks;
-#if defined(WEBRTC_MAC)
-  static mach_timebase_info_data_t timebase;
-  if (timebase.denom == 0) {
-    // Get the timebase if this is the first time we run.
-    // Recommended by Apple's QA1398.
-    if (mach_timebase_info(&timebase) != KERN_SUCCESS) {
-      RTC_NOTREACHED();
-    }
-  }
-  // Use timebase to convert absolute time tick units into nanoseconds.
-  const auto mul = [](uint64_t a, uint32_t b) -> int64_t {
-    RTC_DCHECK_NE(b, 0);
-    RTC_DCHECK_LE(a, std::numeric_limits<int64_t>::max() / b)
-        << "The multiplication " << a << " * " << b << " overflows";
-    return rtc::dchecked_cast<int64_t>(a * b);
-  };
-  ticks = mul(mach_absolute_time(), timebase.numer) / timebase.denom;
-#elif defined(WEBRTC_POSIX)
-  struct timespec ts;
-  // TODO(deadbeef): Do we need to handle the case when CLOCK_MONOTONIC is not
-  // supported?
-  clock_gettime(CLOCK_MONOTONIC, &ts);
-  ticks = kNumNanosecsPerSec * static_cast<int64_t>(ts.tv_sec) +
-          static_cast<int64_t>(ts.tv_nsec);
-#elif defined(WINUWP)
-  ticks = TimeHelper::TicksNs();
-#elif defined(WEBRTC_WIN)
-  static volatile LONG last_timegettime = 0;
-  static volatile int64_t num_wrap_timegettime = 0;
-  volatile LONG* last_timegettime_ptr = &last_timegettime;
-  DWORD now = timeGetTime();
-  // Atomically update the last gotten time
-  DWORD old = InterlockedExchange(last_timegettime_ptr, now);
-  if (now < old) {
-    // If now is earlier than old, there may have been a race between threads.
-    // 0x0fffffff ~3.1 days, the code will not take that long to execute
-    // so it must have been a wrap around.
-    if (old > 0xf0000000 && now < 0x0fffffff) {
-      num_wrap_timegettime++;
-    }
-  }
-  ticks = now + (num_wrap_timegettime << 32);
-  // TODO(deadbeef): Calculate with nanosecond precision. Otherwise, we're
-  // just wasting a multiply and divide when doing Time() on Windows.
-  ticks = ticks * kNumNanosecsPerMillisec;
-#else
-#error Unsupported platform.
-#endif
-  return ticks;
-}
-
 int64_t SystemTimeMillis() {
   return static_cast<int64_t>(SystemTimeNanos() / kNumNanosecsPerMillisec);
 }

rtc_base/time_utils.h

@@ -16,6 +16,7 @@
 
 #include "rtc_base/checks.h"
 #include "rtc_base/system/rtc_export.h"
+#include "rtc_base/system_time.h"
 
 namespace rtc {
 
@@ -65,7 +66,6 @@ void SyncWithNtp(int64_t time_from_ntp_server_ms);
 
 // Returns the actual system time, even if a clock is set for testing.
 // Useful for timeouts while using a test clock, or for logging.
-int64_t SystemTimeNanos();
 int64_t SystemTimeMillis();
 
 // Returns the current time in milliseconds in 32 bits.

video/video_analyzer.cc

@@ -23,6 +23,7 @@
 #include "rtc_base/memory_usage.h"
 #include "rtc_base/task_queue_for_test.h"
 #include "rtc_base/task_utils/repeating_task.h"
+#include "rtc_base/time_utils.h"
 #include "system_wrappers/include/cpu_info.h"
 #include "test/call_test.h"
 #include "test/testsupport/file_utils.h"