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/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
/* vim: set ts=8 sts=2 et sw=2 tw=80: */
/* This Source Code Form is subject to the terms of the Mozilla Public
* License, v. 2.0. If a copy of the MPL was not distributed with this
//
// Implement TimeStamp::Now() with POSIX clocks.
//
// The "tick" unit for POSIX clocks is simply a nanosecond, as this is
// the smallest unit of time representable by struct timespec. That
// doesn't mean that a nanosecond is the resolution of TimeDurations
// obtained with this API; see TimeDuration::Resolution;
//
#include <sys/syscall.h>
#include <time.h>
#include <unistd.h>
#include <string.h>
#if defined(__DragonFly__) || defined(__FreeBSD__) || defined(__NetBSD__) || \
defined(__OpenBSD__)
# include <sys/param.h>
# include <sys/sysctl.h>
#endif
#if defined(__DragonFly__) || defined(__FreeBSD__)
# include <sys/user.h>
#endif
#if defined(__NetBSD__)
# undef KERN_PROC
# define KERN_PROC KERN_PROC2
# define KINFO_PROC struct kinfo_proc2
#else
# define KINFO_PROC struct kinfo_proc
#endif
#if defined(__DragonFly__)
# define KP_START_SEC kp_start.tv_sec
# define KP_START_USEC kp_start.tv_usec
#elif defined(__FreeBSD__)
# define KP_START_SEC ki_start.tv_sec
# define KP_START_USEC ki_start.tv_usec
#else
# define KP_START_SEC p_ustart_sec
# define KP_START_USEC p_ustart_usec
#endif
#include "mozilla/Sprintf.h"
#include "mozilla/TimeStamp.h"
#if !defined(__wasi__)
# include <pthread.h>
#endif
// Estimate of the smallest duration of time we can measure.
static uint64_t sResolution;
static uint64_t sResolutionSigDigs;
#ifdef CLOCK_MONOTONIC_COARSE
static bool sSupportsMonotonicCoarseClock = false;
#endif
#if !defined(__wasi__)
static const uint16_t kNsPerUs = 1000;
#endif
static const uint64_t kNsPerMs = 1000000;
static const uint64_t kNsPerSec = 1000000000;
static const double kNsPerMsd = 1000000.0;
static const double kNsPerSecd = 1000000000.0;
static uint64_t TimespecToNs(const struct timespec& aTs) {
uint64_t baseNs = uint64_t(aTs.tv_sec) * kNsPerSec;
return baseNs + uint64_t(aTs.tv_nsec);
}
static uint64_t ClockTimeNs(const clockid_t aClockId = CLOCK_MONOTONIC) {
struct timespec ts;
#ifdef CLOCK_MONOTONIC_COARSE
MOZ_RELEASE_ASSERT(
aClockId == CLOCK_MONOTONIC ||
(sSupportsMonotonicCoarseClock && aClockId == CLOCK_MONOTONIC_COARSE));
#else
MOZ_RELEASE_ASSERT(aClockId == CLOCK_MONOTONIC);
#endif
// this can't fail: we know &ts is valid, and TimeStamp::Startup()
// checks that CLOCK_MONOTONIC / CLOCK_MONOTONIC_COARSE are
// supported (and aborts if the former is not).
clock_gettime(aClockId, &ts);
// tv_sec is defined to be relative to an arbitrary point in time,
// but it would be madness for that point in time to be earlier than
// the Epoch. So we can safely assume that even if time_t is 32
// bits, tv_sec won't overflow while the browser is open. Revisit
// this argument if we're still building with 32-bit time_t around
// the year 2037.
return TimespecToNs(ts);
}
static uint64_t ClockResolutionNs() {
// NB: why not rely on clock_getres()? Two reasons: (i) it might
// lie, and (ii) it might return an "ideal" resolution that while
// theoretically true, could never be measured in practice. Since
// clock_gettime() likely involves a system call on your platform,
// the "actual" timing resolution shouldn't be lower than syscall
// overhead.
uint64_t start = ClockTimeNs();
uint64_t end = ClockTimeNs();
uint64_t minres = (end - start);
// 10 total trials is arbitrary: what we're trying to avoid by
// looping is getting unlucky and being interrupted by a context
// switch or signal, or being bitten by paging/cache effects
for (int i = 0; i < 9; ++i) {
start = ClockTimeNs();
end = ClockTimeNs();
uint64_t candidate = (start - end);
if (candidate < minres) {
minres = candidate;
}
}
if (0 == minres) {
// measurable resolution is either incredibly low, ~1ns, or very
// high. fall back on clock_getres()
struct timespec ts;
if (0 == clock_getres(CLOCK_MONOTONIC, &ts)) {
minres = TimespecToNs(ts);
}
}
if (0 == minres) {
// clock_getres probably failed. fall back on NSPR's resolution
// assumption
minres = 1 * kNsPerMs;
}
return minres;
}
namespace mozilla {
double BaseTimeDurationPlatformUtils::ToSeconds(int64_t aTicks) {
return double(aTicks) / kNsPerSecd;
}
double BaseTimeDurationPlatformUtils::ToSecondsSigDigits(int64_t aTicks) {
// don't report a value < mResolution ...
int64_t valueSigDigs = sResolution * (aTicks / sResolution);
// and chop off insignificant digits
valueSigDigs = sResolutionSigDigs * (valueSigDigs / sResolutionSigDigs);
return double(valueSigDigs) / kNsPerSecd;
}
int64_t BaseTimeDurationPlatformUtils::TicksFromMilliseconds(
double aMilliseconds) {
double result = aMilliseconds * kNsPerMsd;
if (result > double(INT64_MAX)) {
return INT64_MAX;
}
if (result < INT64_MIN) {
return INT64_MIN;
}
return result;
}
int64_t BaseTimeDurationPlatformUtils::ResolutionInTicks() {
return static_cast<int64_t>(sResolution);
}
static bool gInitialized = false;
void TimeStamp::Startup() {
if (gInitialized) {
return;
}
struct timespec dummy;
if (clock_gettime(CLOCK_MONOTONIC, &dummy) != 0) {
MOZ_CRASH("CLOCK_MONOTONIC is absent!");
}
#ifdef CLOCK_MONOTONIC_COARSE
if (clock_gettime(CLOCK_MONOTONIC_COARSE, &dummy) == 0) {
sSupportsMonotonicCoarseClock = true;
}
#endif
sResolution = ClockResolutionNs();
// find the number of significant digits in sResolution, for the
// sake of ToSecondsSigDigits()
for (sResolutionSigDigs = 1; !(sResolutionSigDigs == sResolution ||
10 * sResolutionSigDigs > sResolution);
sResolutionSigDigs *= 10);
gInitialized = true;
}
void TimeStamp::Shutdown() {}
TimeStamp TimeStamp::Now(bool aHighResolution) {
#ifdef CLOCK_MONOTONIC_COARSE
if (!aHighResolution && sSupportsMonotonicCoarseClock) {
return TimeStamp(ClockTimeNs(CLOCK_MONOTONIC_COARSE));
}
#endif
return TimeStamp(ClockTimeNs(CLOCK_MONOTONIC));
}
#if defined(XP_LINUX) || defined(ANDROID)
// Calculates the amount of jiffies that have elapsed since boot and up to the
// starttime value of a specific process as found in its /proc/*/stat file.
// Returns 0 if an error occurred.
static uint64_t JiffiesSinceBoot(const char* aFile) {
char stat[512];
FILE* f = fopen(aFile, "r");
if (!f) {
return 0;
}
int n = fread(&stat, 1, sizeof(stat) - 1, f);
fclose(f);
if (n <= 0) {
return 0;
}
stat[n] = 0;
long long unsigned startTime = 0; // instead of uint64_t to keep GCC quiet
char* s = strrchr(stat, ')');
if (!s) {
return 0;
}
int rv = sscanf(s + 2,
"%*c %*d %*d %*d %*d %*d %*u %*u %*u %*u "
"%*u %*u %*u %*d %*d %*d %*d %*d %*d %llu",
&startTime);
if (rv != 1 || !startTime) {
return 0;
}
return startTime;
}
// Computes the interval that has elapsed between the thread creation and the
// process creation by comparing the starttime fields in the respective
// /proc/*/stat files. The resulting value will be a good approximation of the
// process uptime. This value will be stored at the address pointed by aTime;
// if an error occurred 0 will be stored instead.
static void* ComputeProcessUptimeThread(void* aTime) {
uint64_t* uptime = static_cast<uint64_t*>(aTime);
long hz = sysconf(_SC_CLK_TCK);
*uptime = 0;
if (!hz) {
return nullptr;
}
char threadStat[40];
SprintfLiteral(threadStat, "/proc/self/task/%d/stat",
(pid_t)syscall(__NR_gettid));
uint64_t threadJiffies = JiffiesSinceBoot(threadStat);
uint64_t selfJiffies = JiffiesSinceBoot("/proc/self/stat");
if (!threadJiffies || !selfJiffies) {
return nullptr;
}
*uptime = ((threadJiffies - selfJiffies) * kNsPerSec) / hz;
return nullptr;
}
// Computes and returns the process uptime in us on Linux & its derivatives.
// Returns 0 if an error was encountered.
uint64_t TimeStamp::ComputeProcessUptime() {
uint64_t uptime = 0;
pthread_t uptime_pthread;
if (pthread_create(&uptime_pthread, nullptr, ComputeProcessUptimeThread,
&uptime)) {
MOZ_CRASH("Failed to create process uptime thread.");
return 0;
}
pthread_join(uptime_pthread, NULL);
return uptime / kNsPerUs;
}
#elif defined(__DragonFly__) || defined(__FreeBSD__) || defined(__NetBSD__) || \
defined(__OpenBSD__)
// Computes and returns the process uptime in us on various BSD flavors.
// Returns 0 if an error was encountered.
uint64_t TimeStamp::ComputeProcessUptime() {
struct timespec ts;
int rv = clock_gettime(CLOCK_REALTIME, &ts);
if (rv == -1) {
return 0;
}
int mib[] = {
// clang-format off
CTL_KERN,
KERN_PROC,
KERN_PROC_PID,
getpid(),
# if defined(__NetBSD__) || defined(__OpenBSD__)
sizeof(KINFO_PROC),
1,
# endif
// clang-format on
};
u_int mibLen = sizeof(mib) / sizeof(mib[0]);
KINFO_PROC proc;
size_t bufferSize = sizeof(proc);
rv = sysctl(mib, mibLen, &proc, &bufferSize, nullptr, 0);
if (rv == -1) {
return 0;
}
uint64_t startTime = ((uint64_t)proc.KP_START_SEC * kNsPerSec) +
(proc.KP_START_USEC * kNsPerUs);
uint64_t now = ((uint64_t)ts.tv_sec * kNsPerSec) + ts.tv_nsec;
if (startTime > now) {
return 0;
}
return (now - startTime) / kNsPerUs;
}
#else
uint64_t TimeStamp::ComputeProcessUptime() { return 0; }
#endif
} // namespace mozilla