lib/cpp/src/TReflectionLocal.h

   1 // Copyright (c) 2006- Facebook
   2 // Distributed under the Thrift Software License
   3 //
   4 // See accompanying file LICENSE or visit the Thrift site at:
   5 // http://developers.facebook.com/thrift/
   6
   7 #ifndef _THRIFT_TREFLECTIONLOCAL_H_
   8 #define _THRIFT_TREFLECTIONLOCAL_H_ 1
   9
  10 #include <stdint.h>
  11 #include <cstring>
  12 #include <protocol/TProtocol.h>
  13
  14 /**
  15  * Local Reflection is a blanket term referring to the the structure
  16  * and generation of this particular representation of Thrift types.
  17  * (It is called local because it cannot be serialized by Thrift).
  18  *
  19  * @author David Reiss <dreiss@facebook.com>
  20  */
  21
  22 namespace facebook { namespace thrift { namespace reflection { namespace local {
  23
  24 using facebook::thrift::protocol::TType;
  25
  26 // We include this many bytes of the structure's fingerprint when serializing
  27 // a top-level structure.  Long enough to make collisions unlikely, short
  28 // enough to not significantly affect the amount of memory used.
  29 const int FP_PREFIX_LEN = 4;
  30
  31 struct FieldMeta {
  32   int16_t tag;
  33   bool is_optional;
  34 };
  35
  36 struct TypeSpec {
  37   TType ttype;
  38   uint8_t    fp_prefix[FP_PREFIX_LEN];
  39
  40   // Use an anonymous union here so we can fit two TypeSpecs in one cache line.
  41   union {
  42     struct {
  43       // Use parallel arrays here for denser packing (of the arrays).
  44       FieldMeta* metas;
  45       TypeSpec** specs;
  46     } tstruct;
  47     struct {
  48       TypeSpec *subtype1;
  49       TypeSpec *subtype2;
  50     } tcontainer;
  51   };
  52
  53   // Static initialization of unions isn't really possible,
  54   // so take the plunge and use constructors.
  55   // Hopefully they'll be evaluated at compile time.
  56
  57   TypeSpec(TType ttype) : ttype(ttype) {
  58     std::memset(fp_prefix, 0, FP_PREFIX_LEN);
  59   }
  60
  61   TypeSpec(TType ttype,
  62            const uint8_t* fingerprint,
  63            FieldMeta* metas,
  64            TypeSpec** specs) :
  65     ttype(ttype)
  66   {
  67     std::memcpy(fp_prefix, fingerprint, FP_PREFIX_LEN);
  68     tstruct.metas = metas;
  69     tstruct.specs = specs;
  70   }
  71
  72   TypeSpec(TType ttype, TypeSpec* subtype1, TypeSpec* subtype2) :
  73     ttype(ttype)
  74   {
  75     std::memset(fp_prefix, 0, FP_PREFIX_LEN);
  76     tcontainer.subtype1 = subtype1;
  77     tcontainer.subtype2 = subtype2;
  78   }
  79
  80 };
  81
  82 }}}} // facebook::thrift::reflection::local
  83
  84 #endif // #ifndef _THRIFT_TREFLECTIONLOCAL_H_