1 /*
2 * Copyright 2021 The WebRTC Project Authors. All rights reserved.
3 *
4 * Use of this source code is governed by a BSD-style license
5 * that can be found in the LICENSE file in the root of the source
6 * tree. An additional intellectual property rights grant can be found
7 * in the file PATENTS. All contributing project authors may
8 * be found in the AUTHORS file in the root of the source tree.
9 */
10
11 // If WEBRTC_EXCLUDE_SYSTEM_TIME is set, an implementation of
12 // rtc::SystemTimeNanos() must be provided externally.
13 #ifndef WEBRTC_EXCLUDE_SYSTEM_TIME
14
15 #include <stdint.h>
16
17 #include <limits>
18
19 #if defined(WEBRTC_POSIX)
20 #include <sys/time.h>
21 #if defined(WEBRTC_MAC)
22 #include <mach/mach_time.h>
23 #endif
24 #endif
25
26 #if defined(WEBRTC_WIN)
27 // clang-format off
28 // clang formatting would put <windows.h> last,
29 // which leads to compilation failure.
30 #include <windows.h>
31 #include <mmsystem.h>
32 #include <sys/timeb.h>
33 // clang-format on
34 #endif
35
36 #include "rtc_base/checks.h"
37 #include "rtc_base/numerics/safe_conversions.h"
38 #include "rtc_base/system_time.h"
39 #include "rtc_base/time_utils.h"
40
41 namespace rtc {
42
SystemTimeNanos()43 int64_t SystemTimeNanos() {
44 int64_t ticks;
45 #if defined(WEBRTC_MAC)
46 static mach_timebase_info_data_t timebase;
47 if (timebase.denom == 0) {
48 // Get the timebase if this is the first time we run.
49 // Recommended by Apple's QA1398.
50 if (mach_timebase_info(&timebase) != KERN_SUCCESS) {
51 RTC_DCHECK_NOTREACHED();
52 }
53 }
54 // Use timebase to convert absolute time tick units into nanoseconds.
55 const auto mul = [](uint64_t a, uint32_t b) -> int64_t {
56 RTC_DCHECK_NE(b, 0);
57 RTC_DCHECK_LE(a, std::numeric_limits<int64_t>::max() / b)
58 << "The multiplication " << a << " * " << b << " overflows";
59 return rtc::dchecked_cast<int64_t>(a * b);
60 };
61 ticks = mul(mach_absolute_time(), timebase.numer) / timebase.denom;
62 #elif defined(WEBRTC_POSIX)
63 struct timespec ts;
64 // TODO(deadbeef): Do we need to handle the case when CLOCK_MONOTONIC is not
65 // supported?
66 clock_gettime(CLOCK_MONOTONIC, &ts);
67 ticks = kNumNanosecsPerSec * static_cast<int64_t>(ts.tv_sec) +
68 static_cast<int64_t>(ts.tv_nsec);
69 #elif defined(WINUWP)
70 ticks = WinUwpSystemTimeNanos();
71 #elif defined(WEBRTC_WIN)
72 // TODO(webrtc:14601): Fix the volatile increment instead of suppressing the
73 // warning.
74 #pragma clang diagnostic push
75 #pragma clang diagnostic ignored "-Wdeprecated-volatile"
76 static volatile LONG last_timegettime = 0;
77 static volatile int64_t num_wrap_timegettime = 0;
78 volatile LONG* last_timegettime_ptr = &last_timegettime;
79 DWORD now = timeGetTime();
80 // Atomically update the last gotten time
81 DWORD old = InterlockedExchange(last_timegettime_ptr, now);
82 if (now < old) {
83 // If now is earlier than old, there may have been a race between threads.
84 // 0x0fffffff ~3.1 days, the code will not take that long to execute
85 // so it must have been a wrap around.
86 if (old > 0xf0000000 && now < 0x0fffffff) {
87 num_wrap_timegettime++;
88 }
89 }
90 ticks = now + (num_wrap_timegettime << 32);
91 // TODO(deadbeef): Calculate with nanosecond precision. Otherwise, we're
92 // just wasting a multiply and divide when doing Time() on Windows.
93 ticks = ticks * kNumNanosecsPerMillisec;
94 #pragma clang diagnostic pop
95 #else
96 #error Unsupported platform.
97 #endif
98 return ticks;
99 }
100
101 } // namespace rtc
102 #endif // WEBRTC_EXCLUDE_SYSTEM_TIME
103