lib/cpp/src/thrift/TReflectionLocal.h

/*
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements. See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership. The ASF licenses this file
 * to you 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.
 */

#ifndef _THRIFT_TREFLECTIONLOCAL_H_
#define _THRIFT_TREFLECTIONLOCAL_H_ 1

#include <stdint.h>
#include <cstring>
#include <thrift/protocol/TProtocol.h>

/**
 * Local Reflection is a blanket term referring to the the structure
 * and generation of this particular representation of Thrift types.
 * (It is called local because it cannot be serialized by Thrift).
 *
 */

namespace apache {
namespace thrift {
namespace reflection {
namespace local {

using apache::thrift::protocol::TType;

// We include this many bytes of the structure's fingerprint when serializing
// a top-level structure.  Long enough to make collisions unlikely, short
// enough to not significantly affect the amount of memory used.
const int FP_PREFIX_LEN = 4;

struct FieldMeta {
  int16_t tag;
  bool is_optional;
};

struct TypeSpec {
  TType ttype;
  uint8_t fp_prefix[FP_PREFIX_LEN];

  // Use an anonymous union here so we can fit two TypeSpecs in one cache line.
  union {
    struct {
      // Use parallel arrays here for denser packing (of the arrays).
      FieldMeta* metas;
      TypeSpec** specs;
    } tstruct;
    struct {
      TypeSpec* subtype1;
      TypeSpec* subtype2;
    } tcontainer;
  };

  // Static initialization of unions isn't really possible,
  // so take the plunge and use constructors.
  // Hopefully they'll be evaluated at compile time.

  TypeSpec(TType ttype) : ttype(ttype) { std::memset(fp_prefix, 0, FP_PREFIX_LEN); }

  TypeSpec(TType ttype, const uint8_t* fingerprint, FieldMeta* metas, TypeSpec** specs)
    : ttype(ttype) {
    std::memcpy(fp_prefix, fingerprint, FP_PREFIX_LEN);
    tstruct.metas = metas;
    tstruct.specs = specs;
  }

  TypeSpec(TType ttype, TypeSpec* subtype1, TypeSpec* subtype2) : ttype(ttype) {
    std::memset(fp_prefix, 0, FP_PREFIX_LEN);
    tcontainer.subtype1 = subtype1;
    tcontainer.subtype2 = subtype2;
  }
};
}
}
}
} // apache::thrift::reflection::local

#endif // #ifndef _THRIFT_TREFLECTIONLOCAL_H_