arangodb/arangod/Aql/AqlItemBlockManager.cpp

////////////////////////////////////////////////////////////////////////////////
/// 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 "AqlItemBlockManager.h"

#include "Aql/AqlItemBlock.h"
#include "Basics/VelocyPackHelper.h"

using namespace arangodb::aql;

using VelocyPackHelper = arangodb::basics::VelocyPackHelper;

/// @brief create the manager
AqlItemBlockManager::AqlItemBlockManager(ResourceMonitor* resourceMonitor) 
    : _resourceMonitor(resourceMonitor) {
  TRI_ASSERT(resourceMonitor != nullptr);
}

/// @brief destroy the manager
AqlItemBlockManager::~AqlItemBlockManager() = default;

/// @brief request a block with the specified size
SharedAqlItemBlockPtr AqlItemBlockManager::requestBlock(size_t nrItems, RegisterId nrRegs) {
  // LOG_TOPIC("47298", TRACE, arangodb::Logger::FIXME) << "requesting AqlItemBlock of "
  // << nrItems << " x " << nrRegs;
  size_t const targetSize = nrItems * nrRegs;

  AqlItemBlock* block = nullptr;
  size_t i = Bucket::getId(targetSize);

  int tries = 0;
  while (tries++ < 2) {
    TRI_ASSERT(i < numBuckets);
    if (!_buckets[i].empty()) {
      block = _buckets[i].pop();
      TRI_ASSERT(block != nullptr);
      TRI_ASSERT(block->numEntries() == 0);
      block->rescale(nrItems, nrRegs);
      // LOG_TOPIC("7157d", TRACE, arangodb::Logger::FIXME) << "returned cached
      // AqlItemBlock with dimensions " << block->size() << " x " <<
      // block->getNrRegs();
      break;
    }
    // try next (bigger) bucket
    if (++i >= numBuckets) {
      break;
    }
  }

  if (block == nullptr) {
    block = new AqlItemBlock(*this, nrItems, nrRegs);
    // LOG_TOPIC("eb998", TRACE, arangodb::Logger::FIXME) << "created AqlItemBlock with
    // dimensions " << block->size() << " x " << block->getNrRegs();
  }

  TRI_ASSERT(block != nullptr);
  TRI_ASSERT(block->size() == nrItems);
  TRI_ASSERT(block->getNrRegs() == nrRegs);
  TRI_ASSERT(block->numEntries() == targetSize);
  TRI_ASSERT(block->getRefCount() == 0);

  return SharedAqlItemBlockPtr{block};
}

/// @brief return a block to the manager
void AqlItemBlockManager::returnBlock(AqlItemBlock*& block) noexcept {
  TRI_ASSERT(block != nullptr);
  TRI_ASSERT(block->getRefCount() == 0);

  // LOG_TOPIC("93865", TRACE, arangodb::Logger::FIXME) << "returning AqlItemBlock of
  // dimensions " << block->size() << " x " << block->getNrRegs();

  size_t const targetSize = block->capacity();
  size_t const i = Bucket::getId(targetSize);
  TRI_ASSERT(i < numBuckets);

  // Destroying the block releases the AqlValues. Which in turn may hold DocVecs
  // and can thus return AqlItemBlocks to this very Manager. So the destroy must
  // not happen between the check whether `_buckets[i].full()` and
  // `_buckets[i].push(block)`, because the destroy() can add blocks to the
  // buckets!
  block->destroy();

  if (!_buckets[i].full()) {
    // recycle the block
    TRI_ASSERT(block->numEntries() == 0);
    // store block in bucket (this will not fail)
    _buckets[i].push(block);
  } else {
    // bucket is full. simply delete the block
    delete block;
  }
  block = nullptr;
}

SharedAqlItemBlockPtr AqlItemBlockManager::requestAndInitBlock(arangodb::velocypack::Slice slice) {
  auto const nrItemsSigned = VelocyPackHelper::getNumericValue<int64_t>(slice, "nrItems", 0);
  auto const nrRegs = VelocyPackHelper::getNumericValue<RegisterId>(slice, "nrRegs", 0);
  if (nrItemsSigned <= 0) {
    THROW_ARANGO_EXCEPTION_MESSAGE(TRI_ERROR_INTERNAL, "nrItems must be > 0");
  }
  auto const nrItems = static_cast<size_t>(nrItemsSigned);

  SharedAqlItemBlockPtr block = requestBlock(nrItems, nrRegs);
  block->initFromSlice(slice);

  TRI_ASSERT(block->size() == nrItems);
  TRI_ASSERT(block->getNrRegs() == nrRegs);

  return block;
}

AqlItemBlockManager::Bucket::Bucket() : numItems(0) {
  for (size_t i = 0; i < numBlocksPerBucket; ++i) {
    blocks[i] = nullptr;
  }
}

AqlItemBlockManager::Bucket::~Bucket() {
  while (!empty()) {
    delete pop();
  }
}