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arangodb/arangod/Transaction/CountCache.cpp

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C++

////////////////////////////////////////////////////////////////////////////////
/// DISCLAIMER
///
/// Copyright 2014-2016 ArangoDB GmbH, Cologne, Germany
/// Copyright 2004-2014 triAGENS GmbH, Cologne, Germany
///
/// Licensed under the Apache License, Version 2.0 (the "License");
/// you may not use this file except in compliance with the License.
/// You may obtain a copy of the License at
///
/// http://www.apache.org/licenses/LICENSE-2.0
///
/// Unless required by applicable law or agreed to in writing, software
/// distributed under the License is distributed on an "AS IS" BASIS,
/// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
/// See the License for the specific language governing permissions and
/// limitations under the License.
///
/// Copyright holder is ArangoDB GmbH, Cologne, Germany
///
/// @author Jan Steemann
////////////////////////////////////////////////////////////////////////////////
#include "CountCache.h"
#include "Basics/debugging.h"
#include "Basics/system-functions.h"
using namespace arangodb;
using namespace arangodb::transaction;
CountCache::CountCache() : count(CountCache::NotPopulated), timestamp(0.0) {}
int64_t CountCache::get() const {
return count.load(std::memory_order_relaxed);
}
int64_t CountCache::get(double ttl) const {
// (1) - this acquire-load synchronizes with the release-store (2)
double ts = timestamp.load(std::memory_order_acquire);
if (ts + Ttl > TRI_microtime()) {
// not yet expired
return get();
}
return CountCache::NotPopulated;
}
void CountCache::store(int64_t value) {
TRI_ASSERT(value >= 0);
count.store(value, std::memory_order_relaxed);
// (2) - this release-store synchronizes with the acquire-load (1)
timestamp.store(TRI_microtime(), std::memory_order_release);
}