1 files changed, 99 insertions, 0 deletions
diff --git a/third_party/libwebrtc/rtc_base/system_time.cc b/third_party/libwebrtc/rtc_base/system_time.cc
new file mode 100644
index 0000000000..431b0c2440
--- /dev/null
+++ b/third_party/libwebrtc/rtc_base/system_time.cc
@@ -0,0 +1,99 @@
+/*
+ *  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.
+ */
+
+// If WEBRTC_EXCLUDE_SYSTEM_TIME is set, an implementation of
+// rtc::SystemTimeNanos() must be provided externally.
+#ifndef WEBRTC_EXCLUDE_SYSTEM_TIME
+
+#error Mozilla: Must not use the built-in libwebrtc clock
+
+#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_DCHECK_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 = WinUwpSystemTimeNanos();
+#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
+#endif  // WEBRTC_EXCLUDE_SYSTEM_TIME