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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.
*/
#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;
}
};
} // namespace mongo
#endif // DB_STATS_FINE_CLOCK_HEADER
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