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/**
* Copyright (C) 2018-present MongoDB, Inc.
*
* This program is free software: you can redistribute it and/or modify
* it under the terms of the Server Side Public License, version 1,
* as published by MongoDB, Inc.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* Server Side Public License for more details.
*
* You should have received a copy of the Server Side Public License
* along with this program. If not, see
* <http://www.mongodb.com/licensing/server-side-public-license>.
*
* As a special exception, the copyright holders give permission to link the
* code of portions of this program with the OpenSSL library under certain
* conditions as described in each individual source file and distribute
* linked combinations including the program with the OpenSSL library. You
* must comply with the Server Side Public License in all respects for
* all of the code used other than as permitted herein. If you modify file(s)
* with this exception, you may extend this exception to your version of the
* file(s), but you are not obligated to do so. If you do not wish to do so,
* delete this exception statement from your version. If you delete this
* exception statement from all source files in the program, then also delete
* it in the license file.
*/
#include "mongo/platform/basic.h"
#include "mongo/util/system_tick_source.h"
#include "mongo/config.h"
#include <ctime>
#include <limits>
#if defined(MONGO_CONFIG_HAVE_HEADER_UNISTD_H)
#include <unistd.h>
#endif
#include <memory>
#include "mongo/base/init.h"
#include "mongo/util/assert_util.h"
#include "mongo/util/tick_source.h"
#include "mongo/util/time_support.h"
namespace mongo {
namespace {
const int64_t kMillisPerSecond = 1000;
const int64_t kMicrosPerSecond = 1000 * kMillisPerSecond;
const int64_t kNanosPerSecond = 1000 * kMicrosPerSecond;
/**
* Internally, the timer counts platform-dependent ticks of some sort, and
* must then convert those ticks to microseconds and their ilk. This field
* stores the frequency of the platform-dependent counter.
*
* Define ticksPerSecond before init to ensure correct relative sequencing
* regardless of how it is initialized (static or dynamic).
*/
TickSource::Tick ticksPerSecond = kMicrosPerSecond;
// "Generic" implementation for _timerNow.
TickSource::Tick _timerNowGeneric() {
return curTimeMicros64();
}
// Function pointer to timer implementation.
// Overridden in initTickSource() with better implementation where available.
TickSource::Tick (*_timerNow)() = &_timerNowGeneric;
#if defined(_WIN32)
/**
* Windows-specific implementation of the
* Timer class. Windows selects the best available timer, in its estimation, for
* measuring time at high resolution. This may be the HPET of the TSC on x86 systems,
* but is promised to be synchronized across processors, barring BIOS errors.
*/
TickSource::Tick timerNowWindows() {
LARGE_INTEGER i;
fassert(16161, QueryPerformanceCounter(&i));
return i.QuadPart;
}
void initTickSource() {
LARGE_INTEGER x;
bool ok = QueryPerformanceFrequency(&x);
verify(ok);
ticksPerSecond = x.QuadPart;
_timerNow = &timerNowWindows;
}
#elif defined(MONGO_CONFIG_HAVE_POSIX_MONOTONIC_CLOCK)
/**
* Implementation for timer on systems that support the
* POSIX clock API and CLOCK_MONOTONIC clock.
*/
TickSource::Tick timerNowPosixMonotonicClock() {
timespec the_time;
long long result;
fassert(16160, !clock_gettime(CLOCK_MONOTONIC, &the_time));
// Safe for 292 years after the clock epoch, even if we switch to a signed time value.
// On Linux, the monotonic clock's epoch is the UNIX epoch.
result = static_cast<long long>(the_time.tv_sec);
result *= kNanosPerSecond;
result += static_cast<long long>(the_time.tv_nsec);
return result;
}
void initTickSource() {
// If the monotonic clock is not available at runtime (sysconf() returns 0 or -1),
// do not override the generic implementation or modify ticksPerSecond.
if (sysconf(_SC_MONOTONIC_CLOCK) <= 0) {
return;
}
ticksPerSecond = kNanosPerSecond;
_timerNow = &timerNowPosixMonotonicClock;
// Make sure that the current time relative to the (unspecified) epoch isn't already too
// big to represent as a 64-bit count of nanoseconds.
long long maxSecs = std::numeric_limits<long long>::max() / kNanosPerSecond;
timespec the_time;
fassert(16162, !clock_gettime(CLOCK_MONOTONIC, &the_time));
fassert(16163, static_cast<long long>(the_time.tv_sec) < maxSecs);
}
#else
void initTickSource() {}
#endif
} // unnamed namespace
MONGO_INITIALIZER(SystemTickSourceInit)(InitializerContext* context) {
initTickSource();
SystemTickSource::get();
}
TickSource::Tick SystemTickSource::getTicks() {
return _timerNow();
}
TickSource::Tick SystemTickSource::getTicksPerSecond() {
return ticksPerSecond;
}
SystemTickSource* SystemTickSource::get() {
static const auto globalSystemTickSource = std::make_unique<SystemTickSource>();
return globalSystemTickSource.get();
}
} // namespace mongo
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