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/**
* Copyright (C) 2014 MongoDB, 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.
*/
#define MONGO_LOG_DEFAULT_COMPONENT ::mongo::logger::LogComponent::kDefault
#include "mongo/platform/basic.h"
#include "mongo/db/global_timestamp.h"
#include "mongo/db/service_context.h"
#include "mongo/platform/atomic_word.h"
#include "mongo/util/clock_source.h"
#include "mongo/util/log.h"
#include "mongo/util/time_support.h"
namespace mongo {
namespace {
// This is the value of the next timestamp to handed out.
AtomicUInt64 globalTimestamp(0);
} // namespace
void setGlobalTimestamp(const Timestamp& newTime) {
globalTimestamp.store(newTime.asULL() + 1);
}
Timestamp getLastSetTimestamp() {
return Timestamp(globalTimestamp.load() - 1);
}
Timestamp getNextGlobalTimestamp(unsigned count) {
const unsigned now = durationCount<Seconds>(
getGlobalServiceContext()->getFastClockSource()->now().toDurationSinceEpoch());
invariant(now != 0); // This is a sentinel value for null Timestamps.
invariant(count != 0);
// Optimistic approach: just increment the timestamp, assuming the seconds still match.
auto first = globalTimestamp.fetchAndAdd(count);
auto currentTimestamp = first + count; // What we just set it to.
unsigned globalSecs = Timestamp(currentTimestamp).getSecs();
// Fail if time is not moving forward for 2**31 calls to getNextGlobalTimestamp.
if (MONGO_unlikely(globalSecs > now) && Timestamp(currentTimestamp).getInc() >= 1U << 31) {
mongo::severe() << "clock skew detected, prev: " << globalSecs << " now: " << now;
fassertFailed(17449);
}
// If the seconds need to be updated, try to do it. This can happen at most once per second.
if (MONGO_unlikely(globalSecs < now)) {
// First fix the seconds portion.
while (globalSecs < now) {
const auto desired = Timestamp(now, 1).asULL();
auto actual = globalTimestamp.compareAndSwap(currentTimestamp, desired);
if (actual == currentTimestamp)
break; // We successfully set the secs, so we're done here.
// We raced with someone else. Try again, unless they fixed the secs field for us.
currentTimestamp = actual;
globalSecs = Timestamp(currentTimestamp).getSecs();
}
// Now reserve our timestamps with the new value of secs.
first = globalTimestamp.fetchAndAdd(count);
}
return Timestamp(first);
}
} // namespace mongo
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