arangodb/arangod/Utils/CollectionKeysRepository.cpp

////////////////////////////////////////////////////////////////////////////////
/// @brief list of collection keys present in database
///
/// @file
///
/// DISCLAIMER
///
/// Copyright 2014 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
/// @author Copyright 2014, ArangoDB GmbH, Cologne, Germany
/// @author Copyright 2012-2013, triAGENS GmbH, Cologne, Germany
////////////////////////////////////////////////////////////////////////////////

#include "Utils/CollectionKeysRepository.h"
#include "Basics/json.h"
#include "Basics/logging.h"
#include "Basics/MutexLocker.h"
#include "VocBase/server.h"
#include "VocBase/vocbase.h"

using namespace triagens::arango;

// -----------------------------------------------------------------------------
// --SECTION--                                          CollectionKeysRepository
// -----------------------------------------------------------------------------

size_t const CollectionKeysRepository::MaxCollectCount = 32;

// -----------------------------------------------------------------------------
// --SECTION--                                        constructors / destructors
// -----------------------------------------------------------------------------

////////////////////////////////////////////////////////////////////////////////
/// @brief create a collection keys repository
////////////////////////////////////////////////////////////////////////////////

CollectionKeysRepository::CollectionKeysRepository (TRI_vocbase_t* vocbase) 
  : _vocbase(vocbase),
    _lock(),
    _keys() {

  _keys.reserve(64);
}

////////////////////////////////////////////////////////////////////////////////
/// @brief destroy a collection keys repository
////////////////////////////////////////////////////////////////////////////////

CollectionKeysRepository::~CollectionKeysRepository () {
  try {
    garbageCollect(true);
  }
  catch (...) {
  }

  // wait until all used entries have vanished
  int tries = 0;

  while (true) {
    if (! containsUsed()) {
      break;
    }

    if (tries == 0) {
      LOG_INFO("waiting for used keys to become unused");
    }
    else if (tries == 120) {
      LOG_WARNING("giving up waiting for unused keys");
    }

    usleep(500000);
    ++tries;
  }

  {
    MUTEX_LOCKER(_lock);

    for (auto it : _keys) {
      delete it.second;
    }

    _keys.clear();
  }
}

// -----------------------------------------------------------------------------
// --SECTION--                                                    public methods
// -----------------------------------------------------------------------------

////////////////////////////////////////////////////////////////////////////////
/// @brief stores collection keys in the repository
////////////////////////////////////////////////////////////////////////////////

void CollectionKeysRepository::store (triagens::arango::CollectionKeys* keys) {
  MUTEX_LOCKER(_lock);
  _keys.emplace(keys->id(), keys);
}

////////////////////////////////////////////////////////////////////////////////
/// @brief remove collection keys by id
////////////////////////////////////////////////////////////////////////////////

bool CollectionKeysRepository::remove (CollectionKeysId id) {
  triagens::arango::CollectionKeys* collectionKeys = nullptr;
  
  {
    MUTEX_LOCKER(_lock);

    auto it = _keys.find(id);

    if (it == _keys.end()) {
      // not found
      return false;
    }

    collectionKeys = (*it).second;

    if (collectionKeys->isDeleted()) {
      // already deleted
      return false;
    }
   
    if (collectionKeys->isUsed()) {
      // keys are in use by someone else. now mark as deleted
      collectionKeys->deleted();
      return true;
    }

    // keys are not in use by someone else
    _keys.erase(it);
  }

  TRI_ASSERT(collectionKeys != nullptr);

  delete collectionKeys;
  return true;
}

////////////////////////////////////////////////////////////////////////////////
/// @brief find an existing keys entry by id
/// if found, the keys will be returned with the usage flag set to true. 
/// they must be returned later using release() 
////////////////////////////////////////////////////////////////////////////////

CollectionKeys* CollectionKeysRepository::find (CollectionKeysId id) {
  triagens::arango::CollectionKeys* collectionKeys = nullptr;

  {
    MUTEX_LOCKER(_lock);

    auto it = _keys.find(id);

    if (it == _keys.end()) {
      // not found
      return nullptr;
    }

    collectionKeys = (*it).second;

    if (collectionKeys->isDeleted()) { 
      // already deleted
      return nullptr;
    }

    collectionKeys->use();
  }

  return collectionKeys;
}

////////////////////////////////////////////////////////////////////////////////
/// @brief return collection keys
////////////////////////////////////////////////////////////////////////////////

void CollectionKeysRepository::release (CollectionKeys* collectionKeys) {
  {
    MUTEX_LOCKER(_lock);
  
    TRI_ASSERT(collectionKeys->isUsed());
    collectionKeys->release();

    if (! collectionKeys->isDeleted()) {
      return;
    }

    // remove from the list
    _keys.erase(collectionKeys->id());
  }

  // and free the keys
  delete collectionKeys;
}

////////////////////////////////////////////////////////////////////////////////
/// @brief whether or not the repository contains a used keys entry
////////////////////////////////////////////////////////////////////////////////

bool CollectionKeysRepository::containsUsed () {
  MUTEX_LOCKER(_lock);
    
  for (auto it : _keys) {
    if (it.second->isUsed()) {
      return true;
    }
  }

  return false;
}

////////////////////////////////////////////////////////////////////////////////
/// @brief run a garbage collection on the data
////////////////////////////////////////////////////////////////////////////////

bool CollectionKeysRepository::garbageCollect (bool force) {
  std::vector<triagens::arango::CollectionKeys*> found;
  found.reserve(MaxCollectCount);

  auto const now = TRI_microtime();

  {
    MUTEX_LOCKER(_lock);

    for (auto it = _keys.begin(); it != _keys.end(); /* no hoisting */) {
      auto collectionKeys = (*it).second;

      if (collectionKeys->isUsed()) {
        // must not destroy anything currently in use
        ++it;
        continue;
      } 
   
      if (force || collectionKeys->expires() < now) {
        collectionKeys->deleted();
      }  

      if (collectionKeys->isDeleted()) {
        try {
          found.emplace_back(collectionKeys);
          it = _keys.erase(it);
        }
        catch (...) {
          // stop iteration
          break;
        }

        if (! force &&
            found.size() >= MaxCollectCount) {
          break;
        }
      }
      else {
        ++it;
      }
    }
  }

  // remove keys outside the lock
  for (auto it : found) {
    delete it;
  }

  return (! found.empty());
}

// -----------------------------------------------------------------------------
// --SECTION--                                                       END-OF-FILE
// -----------------------------------------------------------------------------

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