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#ifndef QPID_FRAMING_BLOB_H
#define QPID_FRAMING_BLOB_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.
*
*/
#include <boost/aligned_storage.hpp>
#include <boost/checked_delete.hpp>
#include <boost/utility/typed_in_place_factory.hpp>
#include <new>
#include <assert.h>
namespace boost {
/**
* Boost doesn't provide the 0 arg version since it assumes
* in_place_factory will be used when there is no default ctor.
*/
template <class T>
class typed_in_place_factory0 : public typed_in_place_factory_base {
public:
typedef T value_type ;
void apply ( void* address ) const { new (address) T(); }
};
template<class T>
typed_in_place_factory0<T> in_place() { return typed_in_place_factory0<T>(); }
} // namespace boost
namespace qpid {
namespace framing {
using boost::in_place;
template <class T>
void destroyT(void* ptr) { static_cast<T*>(ptr)->~T(); }
inline void nullDestroy(void*) {}
/**
* A "blob" is a chunk of memory which can contain a single object at
* a time arbitrary type, provided sizeof(T)<=blob.size(). Blob
* ensures proper construction and destruction of its contents,
* nothing else.
*
* In particular the user must ensure the blob is big enough for its
* contents and must know the type of object in the blob to cast get().
*
* Objects can be allocated directly in place using
* construct(in_place<T>(...)) or copied using operator=.
* Constructing a new object in the blob destroys the old one.
*/
template <size_t Size>
class Blob
{
boost::aligned_storage<Size> store;
void (*destroy)(void*);
template<class TypedInPlaceFactory>
void construct (const TypedInPlaceFactory& factory,
const boost::typed_in_place_factory_base* )
{
typedef typename TypedInPlaceFactory::value_type T;
assert(sizeof(T) <= Size);
clear(); // Destroy old object.
factory.apply(store.address());
destroy=&destroyT<T>;
}
public:
/** Construct an empty blob. */
Blob() : destroy(&nullDestroy) {}
/** @see construct() */
template<class Expr>
Blob( const Expr & expr ) : destroy(nullDestroy) { construct(expr,&expr); }
~Blob() { clear(); }
/** Construcct an object in the blob. Destroyes the previous object.
*@param expr an expresion of the form: in_place<T>(x,y,z)
* will construct an object using the constructor T(x,y,z)
*/
template<class Expr> void
construct(const Expr& expr) { construct(expr,&expr); }
/** Copy construct an instance of T into the Blob. */
template<class T>
Blob& operator=(const T& x) { construct(in_place<T>(x)); }
/** Get pointer to blob contents. Caller must know how to cast it. */
void* get() { return store.address(); }
/** Get const pointer to blob contents */
const void* get() const { return store.address(); }
/** Destroy the object in the blob making it empty. */
void clear() {
void (*saveDestroy)(void*) = destroy; // Exception safety
destroy = &nullDestroy;
saveDestroy(store.address());
}
/** True if there is no object allocated in the blob */
bool empty() { return destroy==nullDestroy; }
static size_t size() { return Size; }
};
}} // namespace qpid::framing
#endif /*!QPID_FRAMING_BLOB_H*/
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