src/google/protobuf/arenastring.h

// Protocol Buffers - Google's data interchange format
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#ifndef GOOGLE_PROTOBUF_ARENASTRING_H__
#define GOOGLE_PROTOBUF_ARENASTRING_H__

#include <string>

#include <google/protobuf/stubs/logging.h>
#include <google/protobuf/stubs/common.h>
#include <google/protobuf/stubs/fastmem.h>
#include <google/protobuf/arena.h>
#include <google/protobuf/generated_message_util.h>



// This is the implementation of arena string fields written for the open-source
// release. The ArenaStringPtr struct below is an internal implementation class
// and *should not be used* by user code. It is used to collect string
// operations together into one place and abstract away the underlying
// string-field pointer representation, so that (for example) an alternate
// implementation that knew more about ::std::string's internals could integrate more
// closely with the arena allocator.

namespace google {
namespace protobuf {
namespace internal {

struct LIBPROTOBUF_EXPORT ArenaStringPtr {
  inline void Set(const ::std::string* default_value,
                  const ::std::string& value, ::google::protobuf::Arena* arena) {
    if (ptr_ == default_value) {
      CreateInstance(arena, &value);
    } else {
      *ptr_ = value;
    }
  }

  // Basic accessors.
  inline const ::std::string& Get(const ::std::string* /* default_value */) const {
    return *ptr_;
  }

  inline ::std::string* Mutable(const ::std::string* default_value,
                           ::google::protobuf::Arena* arena) {
    if (ptr_ == default_value) {
      CreateInstance(arena, default_value);
    }
    return ptr_;
  }

  // Release returns a ::std::string* instance that is heap-allocated and is not
  // Own()'d by any arena. If the field was not set, it returns NULL. The caller
  // retains ownership. Clears this field back to NULL state. Used to implement
  // release_<field>() methods on generated classes.
  inline ::std::string* Release(const ::std::string* default_value,
                           ::google::protobuf::Arena* arena) {
    if (ptr_ == default_value) {
      return NULL;
    }
    ::std::string* released = NULL;
    if (arena != NULL) {
      // ptr_ is owned by the arena -- we need to return a copy.
      released = new ::std::string(*ptr_);
    } else {
      released = ptr_;
    }
    ptr_ = const_cast< ::std::string* >(default_value);
    return released;
  }

  // UnsafeArenaRelease returns a ::std::string*, but it may be arena-owned (i.e.
  // have its destructor already registered) if arena != NULL. If the field was
  // not set, this returns NULL. This method clears this field back to NULL
  // state. Used to implement unsafe_arena_release_<field>() methods on
  // generated classes.
  inline ::std::string* UnsafeArenaRelease(const ::std::string* default_value,
                                      ::google::protobuf::Arena* /* arena */) {
    if (ptr_ == default_value) {
      return NULL;
    }
    ::std::string* released = ptr_;
    ptr_ = const_cast< ::std::string* >(default_value);
    return released;
  }

  // Takes a string that is heap-allocated, and takes ownership. The string's
  // destructor is registered with the arena. Used to implement
  // set_allocated_<field> in generated classes.
  inline void SetAllocated(const ::std::string* default_value,
                           ::std::string* value, ::google::protobuf::Arena* arena) {
    if (arena == NULL && ptr_ != default_value) {
      Destroy(default_value, arena);
    }
    if (value != NULL) {
      ptr_ = value;
      if (arena != NULL) {
        arena->Own(value);
      }
    } else {
      ptr_ = const_cast< ::std::string* >(default_value);
    }
  }

  // Takes a string that has lifetime equal to the arena's lifetime. The arena
  // must be non-null. It is safe only to pass this method a value returned by
  // UnsafeArenaRelease() on another field of a message in the same arena. Used
  // to implement unsafe_arena_set_allocated_<field> in generated classes.
  inline void UnsafeArenaSetAllocated(const ::std::string* default_value,
                                      ::std::string* value, ::google::protobuf::Arena* /* arena */) {
    if (value != NULL) {
      ptr_ = value;
    } else {
      ptr_ = const_cast< ::std::string* >(default_value);
    }
  }

  // Swaps internal pointers. Arena-safety semantics: this is guarded by the
  // logic in Swap()/UnsafeArenaSwap() at the message level, so this method is
  // 'unsafe' if called directly.
  GOOGLE_ATTRIBUTE_ALWAYS_INLINE void Swap(ArenaStringPtr* other) {
    std::swap(ptr_, other->ptr_);
  }

  // Frees storage (if not on an arena) and sets field to default value.
  inline void Destroy(const ::std::string* default_value,
                      ::google::protobuf::Arena* arena) {
    if (arena == NULL && ptr_ != default_value) {
      delete ptr_;
    }
    ptr_ = const_cast< ::std::string* >(default_value);
  }

  // Clears content, but keeps allocated string if arena != NULL, to avoid the
  // overhead of heap operations. After this returns, the content (as seen by
  // the user) will always be the empty string. Assumes that |default_value|
  // is an empty string.
  inline void ClearToEmpty(const ::std::string* default_value,
                           ::google::protobuf::Arena* /* arena */) {
    if (ptr_ == default_value) {
      // Already set to default (which is empty) -- do nothing.
    } else {
      ptr_->clear();
    }
  }

  // Clears content, but keeps allocated string if arena != NULL, to avoid the
  // overhead of heap operations. After this returns, the content (as seen by
  // the user) will always be equal to |default_value|.
  inline void ClearToDefault(const ::std::string* default_value,
                             ::google::protobuf::Arena* /* arena */) {
    if (ptr_ == default_value) {
      // Already set to default -- do nothing.
    } else {
      // Have another allocated string -- rather than throwing this away and
      // resetting ptr_ to the canonical default string instance, we just reuse
      // this instance.
      *ptr_ = *default_value;
    }
  }

  // Called from generated code / reflection runtime only. Resets value to point
  // to a default string pointer, with the semantics that this ArenaStringPtr
  // does not own the pointed-to memory. Disregards initial value of ptr_ (so
  // this is the *ONLY* safe method to call after construction or when
  // reinitializing after becoming the active field in a oneof union).
  inline void UnsafeSetDefault(const ::std::string* default_value) {
    // Casting away 'const' is safe here: accessors ensure that ptr_ is only
    // returned as a const if it is equal to default_value.
    ptr_ = const_cast< ::std::string* >(default_value);
  }

  // The 'NoArena' variants of methods below assume arena == NULL and are
  // optimized to provide very little overhead relative to a raw string pointer
  // (while still being in-memory compatible with other code that assumes
  // ArenaStringPtr). Note the invariant that a class instance that has only
  // ever been mutated by NoArena methods must *only* be in the String state
  // (i.e., tag bits are not used), *NEVER* ArenaString. This allows all
  // tagged-pointer manipulations to be avoided.
  inline void SetNoArena(const ::std::string* default_value,
                         const ::std::string& value) {
    if (ptr_ == default_value) {
      CreateInstanceNoArena(&value);
    } else {
      *ptr_ = value;
    }
  }

  void AssignWithDefault(const ::std::string* default_value, ArenaStringPtr value);

  inline const ::std::string& GetNoArena(const ::std::string* /* default_value */) const {
    return *ptr_;
  }

  inline ::std::string* MutableNoArena(const ::std::string* default_value) {
    if (ptr_ == default_value) {
      CreateInstanceNoArena(default_value);
    }
    return ptr_;
  }

  inline ::std::string* ReleaseNoArena(const ::std::string* default_value) {
    if (ptr_ == default_value) {
      return NULL;
    } else {
      ::std::string* released = ptr_;
      ptr_ = const_cast< ::std::string* >(default_value);
      return released;
    }
  }

  inline void SetAllocatedNoArena(const ::std::string* default_value,
                                  ::std::string* value) {
    if (ptr_ != default_value) {
      delete ptr_;
    }
    if (value != NULL) {
      ptr_ = value;
    } else {
      ptr_ = const_cast< ::std::string* >(default_value);
    }
  }

  inline void DestroyNoArena(const ::std::string* default_value) {
    if (ptr_ != default_value) {
      delete ptr_;
    }
    ptr_ = NULL;
  }

  inline void ClearToEmptyNoArena(const ::std::string* default_value) {
    if (ptr_ == default_value) {
      // Nothing: already equal to default (which is the empty string).
    } else {
      ptr_->clear();
    }
  }

  inline void ClearToDefaultNoArena(const ::std::string* default_value) {
    if (ptr_ == default_value) {
      // Nothing: already set to default.
    } else {
      // Reuse existing allocated instance.
      *ptr_ = *default_value;
    }
  }

  // Internal accessor used only at parse time to provide direct access to the
  // raw pointer from the shared parse routine (in the non-arenas case). The
  // parse routine does the string allocation in order to save code size in the
  // generated parsing code.
  inline ::std::string** UnsafeRawStringPointer() {
    return &ptr_;
  }

 private:
  ::std::string* ptr_;

  GOOGLE_ATTRIBUTE_NOINLINE void CreateInstance(::google::protobuf::Arena* arena,
                                         const ::std::string* initial_value) {
    // Assumes ptr_ is not NULL.
    if (initial_value != NULL) {
      ptr_ = new ::std::string(*initial_value);
    } else {
      ptr_ = new ::std::string();
    }
    if (arena != NULL) {
      arena->Own(ptr_);
    }
  }
  GOOGLE_ATTRIBUTE_NOINLINE void CreateInstanceNoArena(const ::std::string* initial_value) {
    if (initial_value != NULL) {
      ptr_ = new ::std::string(*initial_value);
    } else {
      ptr_ = new ::std::string();
    }
  }
};

}  // namespace internal
}  // namespace protobuf



}  // namespace google
#endif  // GOOGLE_PROTOBUF_ARENASTRING_H__