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67 lines
2.1 KiB
C++
67 lines
2.1 KiB
C++
// fine_clock.h
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/**
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* Copyright (C) 2008 10gen Inc.
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*
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* This program is free software: you can redistribute it and/or modify
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* it under the terms of the GNU Affero General Public License, version 3,
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* as published by the Free Software Foundation.
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*
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* This program is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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* GNU Affero General Public License for more details.
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*
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* You should have received a copy of the GNU Affero General Public License
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* along with this program. If not, see <http://www.gnu.org/licenses/>.
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*/
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#ifndef DB_STATS_FINE_CLOCK_HEADER
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#define DB_STATS_FINE_CLOCK_HEADER
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#include <time.h> // struct timespec
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namespace mongo {
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/**
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* This is a nano-second precision clock. We're skipping the
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* harware TSC in favor of clock_gettime() which in some systems
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* does not involve a trip to the OS (VDSO).
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*
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* We're exporting a type WallTime that is and should remain
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* opaque. The business of getting accurate time is still ongoing
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* and we may change the internal representation of this class.
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* (http://lwn.net/Articles/388188/)
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*
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* Really, you shouldn't be using this class in hot code paths for
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* platforms you're not sure whether the overhead is low.
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*/
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class FineClock{
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public:
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typedef timespec WallTime;
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static WallTime now(){
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struct timespec ts;
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clock_gettime(CLOCK_MONOTONIC, &ts);
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return ts;
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}
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static uint64_t diffInNanos( WallTime end, WallTime start ){
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uint64_t diff;
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if ( end.tv_nsec < start.tv_nsec ){
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diff = 1000000000 * ( end.tv_sec - start.tv_sec - 1);
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diff += 1000000000 + end.tv_nsec - start.tv_nsec;
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} else {
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diff = 1000000000 * ( end.tv_sec - start.tv_sec );
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diff += end.tv_nsec - start.tv_nsec;
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}
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return diff;
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}
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};
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}
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#endif // DB_STATS_FINE_CLOCK_HEADER
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