2021-06-25 00:43:10 +00:00
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/*
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* Copyright 2021 The WebRTC Project Authors. All rights reserved.
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*
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* Use of this source code is governed by a BSD-style license
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* that can be found in the LICENSE file in the root of the source
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* tree. An additional intellectual property rights grant can be found
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* in the file PATENTS. All contributing project authors may
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* be found in the AUTHORS file in the root of the source tree.
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*/
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// If WEBRTC_EXCLUDE_SYSTEM_TIME is set, an implementation of
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// rtc::SystemTimeNanos() must be provided externally.
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#ifndef WEBRTC_EXCLUDE_SYSTEM_TIME
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#include <stdint.h>
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#include <limits>
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#if defined(WEBRTC_POSIX)
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#include <sys/time.h>
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#if defined(WEBRTC_MAC)
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#include <mach/mach_time.h>
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#endif
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#endif
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#if defined(WEBRTC_WIN)
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// clang-format off
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// clang formatting would put <windows.h> last,
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// which leads to compilation failure.
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#include <windows.h>
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#include <mmsystem.h>
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#include <sys/timeb.h>
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// clang-format on
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#endif
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#include "rtc_base/checks.h"
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#include "rtc_base/numerics/safe_conversions.h"
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#include "rtc_base/system_time.h"
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#include "rtc_base/time_utils.h"
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namespace rtc {
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int64_t SystemTimeNanos() {
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int64_t ticks;
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#if defined(WEBRTC_MAC)
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static mach_timebase_info_data_t timebase;
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if (timebase.denom == 0) {
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// Get the timebase if this is the first time we run.
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// Recommended by Apple's QA1398.
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if (mach_timebase_info(&timebase) != KERN_SUCCESS) {
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2022-03-11 16:49:54 +00:00
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RTC_DCHECK_NOTREACHED();
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2021-06-25 00:43:10 +00:00
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}
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}
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// Use timebase to convert absolute time tick units into nanoseconds.
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const auto mul = [](uint64_t a, uint32_t b) -> int64_t {
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RTC_DCHECK_NE(b, 0);
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RTC_DCHECK_LE(a, std::numeric_limits<int64_t>::max() / b)
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<< "The multiplication " << a << " * " << b << " overflows";
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return rtc::dchecked_cast<int64_t>(a * b);
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};
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ticks = mul(mach_absolute_time(), timebase.numer) / timebase.denom;
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#elif defined(WEBRTC_POSIX)
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struct timespec ts;
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// TODO(deadbeef): Do we need to handle the case when CLOCK_MONOTONIC is not
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// supported?
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clock_gettime(CLOCK_MONOTONIC, &ts);
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ticks = kNumNanosecsPerSec * static_cast<int64_t>(ts.tv_sec) +
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static_cast<int64_t>(ts.tv_nsec);
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#elif defined(WINUWP)
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ticks = WinUwpSystemTimeNanos();
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#elif defined(WEBRTC_WIN)
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static volatile LONG last_timegettime = 0;
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static volatile int64_t num_wrap_timegettime = 0;
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volatile LONG* last_timegettime_ptr = &last_timegettime;
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DWORD now = timeGetTime();
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// Atomically update the last gotten time
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DWORD old = InterlockedExchange(last_timegettime_ptr, now);
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if (now < old) {
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// If now is earlier than old, there may have been a race between threads.
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// 0x0fffffff ~3.1 days, the code will not take that long to execute
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// so it must have been a wrap around.
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if (old > 0xf0000000 && now < 0x0fffffff) {
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num_wrap_timegettime++;
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}
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}
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ticks = now + (num_wrap_timegettime << 32);
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// TODO(deadbeef): Calculate with nanosecond precision. Otherwise, we're
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// just wasting a multiply and divide when doing Time() on Windows.
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ticks = ticks * kNumNanosecsPerMillisec;
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#else
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#error Unsupported platform.
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#endif
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return ticks;
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}
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} // namespace rtc
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#endif // WEBRTC_EXCLUDE_SYSTEM_TIME
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