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// @file mongo/util/timer.cpp
/* Copyright 2009 10gen Inc.
*
* This program is free software: you can redistribute it and/or modify
* it under the terms of the GNU Affero General Public License, version 3,
* as published by the Free Software Foundation.
*
* 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
* GNU Affero General Public License for more details.
*
* You should have received a copy of the GNU Affero General Public License
* along with this program. If not, see <http://www.gnu.org/licenses/>.
*
* 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 GNU Affero General 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/timer.h"
#include "mongo/config.h"
#include <ctime>
#include <limits>
#if defined(MONGO_CONFIG_HAVE_HEADER_UNISTD_H)
#include <unistd.h>
#endif
#include "mongo/util/assert_util.h"
#include "mongo/util/time_support.h"
namespace mongo {
// Set default value to reflect "generic" timer implementation.
// Define Timer::_countsPerSecond before static initializer "atstartuputil" to ensure correct
// relative sequencing regardless of how _countsPerSecond is initialized (static or dynamic).
long long Timer::_countsPerSecond = Timer::microsPerSecond;
double Timer::_microsPerCount = 1.0f;
namespace {
// TODO: SERVER-5112, better startup-time initialization of C++ modules.
struct AtStartup {
AtStartup();
} atstartuputil;
// "Generic" implementation for Timer::now().
long long _timerNowGeneric() {
return curTimeMicros64();
}
// Function pointer to Timer::now() implementation.
// Overridden in AtStartup() with better implementation where available.
long long (*_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.
*/
long long timerNowWindows() {
LARGE_INTEGER i;
fassert(16161, QueryPerformanceCounter(&i));
return i.QuadPart;
}
AtStartup::AtStartup() {
LARGE_INTEGER x;
bool ok = QueryPerformanceFrequency(&x);
verify(ok);
Timer::setCountsPerSecond(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.
*/
long long 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 *= Timer::nanosPerSecond;
result += static_cast<long long>(the_time.tv_nsec);
return result;
}
AtStartup::AtStartup() {
// If the monotonic clock is not available at runtime (sysconf() returns 0 or -1),
// do not override the generic implementation or modify Timer::_countsPerSecond.
if (sysconf(_SC_MONOTONIC_CLOCK) <= 0) {
return;
}
Timer::setCountsPerSecond(Timer::nanosPerSecond);
_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() /
Timer::nanosPerSecond;
timespec the_time;
fassert(16162, !clock_gettime(CLOCK_MONOTONIC, &the_time));
fassert(16163, static_cast<long long>(the_time.tv_sec) < maxSecs);
}
#else
AtStartup::AtStartup() { }
#endif
} // namespace
long long Timer::now() const {
return _timerNow();
}
} // namespace mongo
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