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// fine_clock.h
/**
* Copyright (C) 2008 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/>.
*/
#ifndef DB_STATS_FINE_CLOCK_HEADER
#define DB_STATS_FINE_CLOCK_HEADER
#include <time.h> // struct timespec
namespace mongo {
/**
* This is a nano-second precision clock. We're skipping the
* harware TSC in favor of clock_gettime() which in some systems
* does not involve a trip to the OS (VDSO).
*
* We're exporting a type WallTime that is and should remain
* opaque. The business of getting accurate time is still ongoing
* and we may change the internal representation of this class.
* (http://lwn.net/Articles/388188/)
*
* Really, you shouldn't be using this class in hot code paths for
* platforms you're not sure whether the overhead is low.
*/
class FineClock {
public:
typedef timespec WallTime;
static WallTime now() {
struct timespec ts;
clock_gettime(CLOCK_MONOTONIC, &ts);
return ts;
}
static uint64_t diffInNanos( WallTime end, WallTime start ) {
uint64_t diff;
if ( end.tv_nsec < start.tv_nsec ) {
diff = 1000000000 * ( end.tv_sec - start.tv_sec - 1);
diff += 1000000000 + end.tv_nsec - start.tv_nsec;
}
else {
diff = 1000000000 * ( end.tv_sec - start.tv_sec );
diff += end.tv_nsec - start.tv_nsec;
}
return diff;
}
};
}
#endif // DB_STATS_FINE_CLOCK_HEADER
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