orthanc 读取数据库过程

index_.LookupAttachment

bool StatelessDatabaseOperations::LookupAttachment(FileInfo& attachment,
                                                     int64_t& revision,
                                                     const std::string& instancePublicId,
                                                     FileContentType contentType)
  {
    class Operations : public ReadOnlyOperationsT5<bool&, FileInfo&, int64_t&, const std::string&, FileContentType>
    {
    public:
      virtual void ApplyTuple(ReadOnlyTransaction& transaction,
                              const Tuple& tuple) ORTHANC_OVERRIDE
      {
        int64_t internalId;
        ResourceType type;
        if (!transaction.LookupResource(internalId, type, tuple.get<3>()))
        {
          throw OrthancException(ErrorCode_UnknownResource);
        }
        else if (transaction.LookupAttachment(tuple.get<1>(), tuple.get<2>(), internalId, tuple.get<4>()))
        {
          assert(tuple.get<1>().GetContentType() == tuple.get<4>());
          tuple.get<0>() = true;
        }
        else
        {
          tuple.get<0>() = false;
        }
      }
    };

    bool found;
    Operations operations;
    operations.Apply(*this, found, attachment, revision, instancePublicId, contentType);
    return found;
  }

template <typename T1,
              typename T2,
              typename T3,
              typename T4,
              typename T5>
    class ReadOnlyOperationsT5 : public boost::noncopyable
    {
    public:
      typedef typename boost::tuple<T1, T2, T3, T4, T5>  Tuple;
      
      virtual ~ReadOnlyOperationsT5()
      {
      }

      virtual void ApplyTuple(StatelessDatabaseOperations::ReadOnlyTransaction& transaction,
                              const Tuple& tuple) = 0;

      void Apply(StatelessDatabaseOperations& index,
                 T1 t1,
                 T2 t2,
                 T3 t3,
                 T4 t4,
                 T5 t5)
      {
        const Tuple tuple(t1, t2, t3, t4, t5);
        TupleOperationsWrapper<ReadOnlyOperationsT5, Tuple> wrapper(*this, tuple);
        index.Apply(wrapper);
      }
    };

 /**
     * Some handy templates to reduce the verbosity in the definitions
     * of the internal classes.
     **/
    
    template <typename Operations,
              typename Tuple>
    class TupleOperationsWrapper : public StatelessDatabaseOperations::IReadOnlyOperations
    {
    protected:
      Operations&   operations_;
      const Tuple&  tuple_;
    
    public:
      TupleOperationsWrapper(Operations& operations,
                             const Tuple& tuple) :
        operations_(operations),
        tuple_(tuple)
      {
      }
    
      virtual void Apply(StatelessDatabaseOperations::ReadOnlyTransaction& transaction) ORTHANC_OVERRIDE
      {
        operations_.ApplyTuple(transaction, tuple_);
      }
    };

void StatelessDatabaseOperations::Apply(IReadOnlyOperations& operations)
{
ApplyInternal(&operations, NULL);
}

void StatelessDatabaseOperations::ApplyInternal(IReadOnlyOperations* readOperations,
                                                  IReadWriteOperations* writeOperations)
  {
    boost::shared_lock<boost::shared_mutex> lock(mutex_);  // To protect "factory_" and "maxRetries_"

    if ((readOperations == NULL && writeOperations == NULL) ||
        (readOperations != NULL && writeOperations != NULL))
    {
      throw OrthancException(ErrorCode_InternalError);
    }

    if (factory_.get() == NULL)
    {
      throw OrthancException(ErrorCode_BadSequenceOfCalls, "No transaction context was provided");     
    }
    
    unsigned int attempt = 0;

    for (;;)
    {
      try
      {
        if (readOperations != NULL)
        {
          /**
           * IMPORTANT: In Orthanc <= 1.9.1, there was no transaction
           * in this case. This was OK because of the presence of the
           * global mutex that was protecting the database.
           **/
          
          Transaction transaction(db_, *factory_, TransactionType_ReadOnly);  // TODO - Only if not "TransactionType_Implicit"
          {
            ReadOnlyTransaction t(transaction.GetDatabaseTransaction(), transaction.GetContext(), db_.HasLabelsSupport());
            readOperations->Apply(t);
          }
          transaction.Commit();
        }
        else
        {
          assert(writeOperations != NULL);
          
          Transaction transaction(db_, *factory_, TransactionType_ReadWrite);
          {
            ReadWriteTransaction t(transaction.GetDatabaseTransaction(), transaction.GetContext(), db_.HasLabelsSupport());
            writeOperations->Apply(t);
          }
          transaction.Commit();
        }
        
        return;  // Success
      }
      catch (OrthancException& e)
      {
        if (e.GetErrorCode() == ErrorCode_DatabaseCannotSerialize)
        {
          if (attempt >= maxRetries_)
          {
            throw;
          }
          else
          {
            attempt++;

            // The "rand()" adds some jitter to de-synchronize writers
            boost::this_thread::sleep(boost::posix_time::milliseconds(100 * attempt + 5 * (rand() % 10)));
          }          
        }
        else
        {
          throw;
        }
      }
    }
  }