bslma_newdeleteallocator.h

Go to the documentation of this file.

/// @file bslma_newdeleteallocator.h
///
/// The content of this file has been pre-processed for Doxygen.
///
 
 
// bslma_newdeleteallocator.h                                         -*-C++-*-
#ifndef INCLUDED_BSLMA_NEWDELETEALLOCATOR
#define INCLUDED_BSLMA_NEWDELETEALLOCATOR
 
#include <bsls_ident.h>
BSLS_IDENT("$Id: $")
 
/// @defgroup bslma_newdeleteallocator bslma_newdeleteallocator
/// @brief  Provide singleton new/delete adaptor to `bslma::Allocator` protocol.
/// @addtogroup bsl
/// @{
/// @addtogroup bslma
/// @{
/// @addtogroup bslma_newdeleteallocator
/// @{
///
/// <h1> Outline </h1>
/// * <a href="#bslma_newdeleteallocator-purpose"> Purpose</a>
/// * <a href="#bslma_newdeleteallocator-classes"> Classes </a>
/// * <a href="#bslma_newdeleteallocator-description"> Description </a>
///   * <a href="#bslma_newdeleteallocator-thread-safety"> Thread Safety </a>
///   * <a href="#bslma_newdeleteallocator-usage"> Usage </a>
///
/// # Purpose {#bslma_newdeleteallocator-purpose}
/// Provide singleton new/delete adaptor to `bslma::Allocator` protocol.
///
/// # Classes {#bslma_newdeleteallocator-classes}
///
/// -  bslma::NewDeleteAllocator: support new/delete-style allocation/deallocation
///
/// @see  bslma_default, bslma_testallocator
///
/// # Description {#bslma_newdeleteallocator-description}
/// This component provides a concrete allocation mechanism,
/// `bslma::NewDeleteAllocator`, that implements the `bslma::Allocator` protocol
/// to provide direct access to the system-supplied (native) global
/// `operator new` and `operator delete` functions via that pure abstract
/// interface.
/// @code
///  ,-------------------------.
/// ( bslma::NewDeleteAllocator )
///  `-------------------------'
///              |         allocator
///              |         singleton
///              |         ctor/dtor
///              V
///      ,----------------.
///     ( bslma::Allocator )
///      `----------------'
///                      allocate
///                      deallocate
/// @endcode
/// The essential purpose of this component is to facilitate the default use of
/// global `new` and `delete` in all components that accept a user-supplied
/// allocator derived from `bslma::Allocator` (see @ref bslma_default ).  Hence, the
/// global `operator new` and `operator delete` functions are wrapped within
/// concrete methods of a derived `bslma::NewDeleteAllocator` class.  A `static`
/// (factory) method of `bslma::NewDeleteAllocator` can be used to obtain a
/// unique (singleton) `bslma::NewDeleteAllocator` object for the given process,
/// and whose lifetime is guaranteed to exceed any possibility of its use.  Note
/// that the standard also requires the global `operator new` to return
/// maximally-aligned memory, which is a stricter post condition than the
/// natural-alignment requirement imposed by the base-class contract, or than is
/// provided by many other concrete implementations.
///
/// ## Thread Safety {#bslma_newdeleteallocator-thread-safety}
///
///
/// This class is fully thread-safe, which means that all non-creator object
/// methods can be safely accessed concurrently (from multiple treads).  The
/// singleton `bslma::NewDeleteAllocator` can also be safely created/accessed
/// concurrently (from multiple threads) via either the `static` `singleton` or
/// `allocator` (factory) methods.  Moreover, the underlying (native)
/// implementation of `new` and `delete` are required by the C++ standard to
/// ensure that concurrent access to either the virtual `allocate` and/or
/// `deallocate` are also safe (i.e., will not not result in heap corruption).
/// Note that this allocator therefore has stronger thread-safety guarantees
/// than is required by the base-class contract or than is provided by many
/// other derived concrete allocators.
///
/// ## Usage {#bslma_newdeleteallocator-usage}
///
///
/// The most common and proper use of `bslma::NewDeleteAllocator` is both
/// *indirect* and *by* *default* (see @ref bslma_default ).  For example, consider
/// (along with its destructor) the default and copy constructors for, say, a
/// simple container, such as `my_ShortArray`, each of which take as its final
/// optional argument the address of a `bslma::Allocator` protocol:
/// @code
/// // my_shortarray.h:
/// // ...
/// namespace bslma { class Allocator; }
///
/// class my_ShortArray {
///     short            *d_array_p;     // dynamically-allocated array
///     int               d_capacity;    // physical capacity (in elements)
///     int               d_length;      // logical length (in elements)
///     bslma::Allocator *d_allocator_p; // memory allocator (not owned)
///
///   public:
///     /// Create an empty `my_shortArray`.  Optionally specify a
///     /// `basicAllocator` used to supply memory.  If `basicAllocator`
///     /// is 0, the currently installed default allocator is used.
///     my_ShortArray(bslma::Allocator *basicAllocator = 0);
///
///     /// Create a `bslma::ShortArray` having the same value as the
///     /// specified `other` array.  Optionally specify a `basicAllocator`
///     /// used to supply memory.  If `basicAllocator` is 0, the currently
///     /// installed default allocator is used.
///     my_ShortArray(const my_ShortArray&  other,
///                   bslma::Allocator     *basicAllocator = 0);
///
///     /// Destroy this object.
///     ~my_ShortArray();
///
///    // ...
/// };
///
/// // ...
/// @endcode
/// In order to satisfy this contract, we will need a globally accessible
/// utility (see @ref bslma_default ), which by default returns the singleton
/// `bslma::NewDeleteAllocator`, but which could be configured to return some
/// other allocator, say a *test* allocator (see @ref bslma_testallocator ):
/// @code
/// // my_default.h:
/// // ...
/// namespace bslma { class Allocator; }
///
/// /// This class maintains a process-wide `bslma::Allocator` object
/// /// to be used when an allocator is needed, and not suppled explicitly.
/// /// By default, the currently installed default allocator is the unique
/// /// `bslma::NewDeleteAllocator` object returned by the `static` method,
/// /// `bslma::NewDeleteAllocator::singleton()`.  Note that the default
/// /// allocator will exist longer than any possibility of its use.
/// struct my_Default {
///
///     /// Return the address of the specified modifiable
///     /// `basicAllocator` or, if `basicAllocator` is 0, an instance of
///     /// the currently installed default `bslma::Allocator` object, which
///     /// will exist longer than any possibility of its use.  Note
///     /// that this function can safely be called concurrently (from
///     /// multiple threads).
///     static bslma::Allocator *allocator(bslma::Allocator *basicAllocator);
///
///     /// Replace the address of the currently installed allocator with
///     /// that of the specified modifiable `basicAllocator` (or if 0,
///     /// with the "factory" default, `bslma::NewDeleteAllocator`), and
///     /// return the address of the previous allocator.  The behavior is
///     /// undefined unless `basicAllocator` will exist longer than any
///     /// possibility of its use.  Note that this function is *not* *at*
///     /// *all* thread-safe, and should *never* be called when multiple
///     /// threads are active.
///     static bslma::Allocator *replace(bslma::Allocator *basicAllocator);
/// };
///
/// // my_default.cpp:
/// // ...
///
/// #include <my_default.h>
///
/// static bslma::Allocator *s_default_p = 0; // load-time initialized
///
/// bslma::Allocator *my_Default::allocator(bslma::Allocator *basicAllocator)
/// {
///     return bslma::NewDeleteAllocator::allocator(s_default_p);
/// }
///
/// bslma::Allocator *my_Default::replace(bslma::Allocator *basicAllocator)
/// {
///     bslma::Allocator *tmp =
///                          bslma::NewDeleteAllocator::allocator(s_default_p);
///     s_default_p = bslma::NewDeleteAllocator::allocator(basicAllocator);
///     return tmp;
/// }
/// @endcode
/// Notice that the only part of the `bslma::NewDeleteAllocator` class we used
/// directly was its static `allocator` method, which -- in addition to safely
/// constructing the singleton `bslma::NewDeleteAllocator` object on first
/// access -- also automatically replaces a 0 address value with that of
/// singleton `bslma::NewDeleteAllocator` object.  From now on, we will never
/// again need to invoke the @ref bslma_newdeleteallocator  component's interface
/// directly, but instead use it through `my_Default` (see `bslma::Default` for
/// what is actually used in practice).
///
/// Turning back to our `my_shortarray` example, let's now implement the two
/// constructors using the @ref bslma_newdeleteallocator  component indirectly via
/// the `my_default` component:
/// @code
/// // my_shortarray.cpp:
/// #include <my_shortarray.h>
/// #include <my_default.h>
/// #include <bsls_assert.h>
///
/// // ...
///
/// enum {
///     INITIAL_CAPACITY = 0, // recommended to avoid unnecessary allocations
///                           // possibly resulting in locking and extra thread
///                           // contention for the 'bslma::NewDeleteAllocator'
///
///     GROW_FACTOR = 2       // typical value for geometric growth
/// };
///
/// // ...
///
/// my_ShortArray::my_ShortArray(bslma::Allocator *basicAllocator)
/// : d_capacity(INITIAL_CAPACITY)
/// , d_length(0)
/// , d_allocator_p(my_Default::allocator(basicAllocator))
/// {
///     assert(d_allocator_p);
///     d_array_p = (short *)  // no thread contention if 'd_capacity' is 0
///                 d_allocator_p->allocate(d_capacity * sizeof *d_array_p);
///     assert(0 == d_array_p);
/// }
///
/// my_ShortArray::my_ShortArray(const my_ShortArray&   other,
///                              bslma::Allocator      *basicAllocator)
/// : d_capacity(other.d_capacity)
/// , d_length(other.d_length)
/// , d_allocator_p(my_Default::allocator(basicAllocator))
/// {
///     assert(d_allocator_p);
///     d_array_p = (short *)
///                 d_allocator_p->allocate(d_capacity * sizeof *d_array_p);
///     assert(!d_capacity == !d_array_p);
///     memcpy(d_array_p, other.d_array_p, d_length * sizeof *d_array_p);
/// }
///
/// my_ShortArray::~my_ShortArray()
/// {
///     d_allocator_p->deallocate(d_array_p); // no locking if 'd_array_p' is 0
/// }
///
/// // ...
/// @endcode
/// When the default constructor is called, the default capacity and length are
/// recorded in data members via the initialization list.  The static function
/// `allocator` (provided in `my_Default`) is used to assign the value of the
/// `basicAllocator` address passed in, or if that is 0, the address of the
/// currently installed default allocator, which by default is the singleton
/// object of type `bslma::NewDeleteAllocator`, defined in this component.  Note
/// that since `INITIAL_CAPACITY` is 0, a default constructed object that is
/// created using a `bslma::NewDeleteAllocator` will *not* invoke the
/// `operator new` function, which on some platforms may needlessly acquire a
/// lock, causing unnecessary overhead (the same potential overhead is avoided
/// for `operator delete` whenever a 0 `d_array_p` value is deallocated in the
/// destructor) and `d_allocator_p` refers to a `bslma::NewDeleteAllocator`.
/// Note also that, for the copy constructor, the currently installed default
/// allocator, and not the `other` array's allocator is used whenever
/// `basicAllocator` is 0 or not explicitly supplied.
///
/// Finally note that this entire component is *not* intended for direct use by
/// typical clients: See @ref bslma_default  for more information or proper usage.
/// @}
/** @} */
/** @} */
 
/** @addtogroup bsl
 * @{
 */
/** @addtogroup bslma
 * @{
 */
/** @addtogroup bslma_newdeleteallocator
 * @{
 */
 
#include <bslscm_version.h>
 
#include <bslma_allocator.h>
 
#include <bsls_keyword.h>
 
 
 
namespace bslma {
 
                        // ========================
                        // class NewDeleteAllocator
                        // ========================
 
/// This class defines a concrete mechanism that adapts the system-supplied
/// (native) global `operator new` and `operator delete` to the `Allocator`
/// protocol.  The class method `singleton` returns a process-wide unique
/// object of this class whose lifetime is guaranteed to extend from the
/// first call to `singleton` until the program terminates.  A second class
/// method, `allocator`, allows for conveniently replacing a "null"
/// allocator with this singleton object.  Note that this entire class
/// should generally not be used directly by typical clients (see
/// @ref bslma_default  for more information).
///
/// See @ref bslma_newdeleteallocator 
class NewDeleteAllocator : public Allocator {
 
  private:
    // NOT IMPLEMENTED
    NewDeleteAllocator(const NewDeleteAllocator&);
    NewDeleteAllocator& operator=(const NewDeleteAllocator&);
 
  public:
    // CLASS METHODS
 
    /// Return a reference to a process-wide unique object of this class.
    /// The lifetime of this object is guaranteed to extend from the first
    /// call of this method until the program terminates.  Note that this
    /// method should generally not be used directly by typical clients (see
    /// @ref bslma_default  for more information).
    static NewDeleteAllocator& singleton();
 
    /// Return the address of the specified modifiable `basicAllocator` or,
    /// if `basicAllocator` is 0, the process-wide unique (see `singleton`)
    /// object of this class.  Note that the behavior of this function is
    /// equivalent to the following expression:
    /// @code
    /// basicAllocator
    /// ? basicAllocator
    /// : &NewDeleteAllocator::singleton()
    /// @endcode
    /// Also note that if a `NewDeleteAllocator` object is supplied, it is
    /// owned by the class and must NOT be deleted.  Finally note that this
    /// method should generally not be called directly by typical clients
    /// (see @ref bslma_default  for more information).
    static Allocator *allocator(Allocator *basicAllocator);
 
    // CREATORS
 
    /// Create a ("stateless") new-delete-allocator object that wraps the
    /// global native `operator new` and `operator delete` functions in
    /// order to supply memory via the `Allocator` protocol.  Note that all
    /// objects of this class share the same underlying resource; hence,
    /// this constructor should generally not be invoked directly by
    /// clients; instead, consider using the `static` `singleton` or
    /// `allocator` (factory) methods, or -- better -- the appropriate ones
    /// in `Default` (see @ref bslma_default  for more information).
    NewDeleteAllocator();
 
    /// Destroy this allocator object.  Note that destroying this allocator
    /// has no effect on any outstanding allocated memory.
    ~NewDeleteAllocator() BSLS_KEYWORD_OVERRIDE;
 
    // MANIPULATORS
 
    /// Return a newly allocated block of memory of (at least) the specified
    /// positive `size` (in bytes).  If `size` is 0, a null pointer is
    /// returned with no other effect.  The alignment of the address
    /// returned is the maximum alignment for any fundamental, pointer, or
    /// enumerated type defined for this platform.  The behavior is
    /// undefined unless `0 <= size`.  Note that global `operator new` is
    /// *not* called when `size` is 0 (in order to avoid having to acquire a
    /// lock, and potential contention in multi-threaded programs).
    void *allocate(size_type size) BSLS_KEYWORD_OVERRIDE;
 
    /// Return the memory block at the specified `address` back to this
    /// allocator.  If `address` is 0, this function has no effect.  The
    /// behavior is undefined unless `address` was allocated using this
    /// allocator object and has not already been deallocated.  Note that
    /// global `operator delete` is *not* called when `address` is 0 (in
    /// order to avoid having to acquire a lock, and potential contention in
    /// multi-threaded programs).
    void deallocate(void *address) BSLS_KEYWORD_OVERRIDE;
};
 
// ============================================================================
//                          INLINE DEFINITIONS
// ============================================================================
 
                        // ------------------------
                        // class NewDeleteAllocator
                        // ------------------------
 
// CLASS METHODS
inline
Allocator *NewDeleteAllocator::allocator(Allocator *basicAllocator)
{
    return basicAllocator ? basicAllocator : &singleton();
}
 
// CREATORS
inline
NewDeleteAllocator::NewDeleteAllocator()
{
}
 
// MANIPULATORS
inline
void NewDeleteAllocator::deallocate(void *address)
{
    // While the C++ standard guarantees that calling delete(0) is safe
    // (3.7.3.2 paragraph 3), some libc implementations take out a lock to deal
    // with the free(0) case, so this check can improve efficiency of threaded
    // programs.
 
    if (address) {
        ::operator delete(address);
    }
}
 
}  // close package namespace
 
#ifndef BDE_OPENSOURCE_PUBLICATION  // BACKWARD_COMPATIBILITY
// ============================================================================
//                           BACKWARD COMPATIBILITY
// ============================================================================
 
/// This alias is defined for backward compatibility.
typedef bslma::NewDeleteAllocator bslma_NewDeleteAllocator;
#endif  // BDE_OPENSOURCE_PUBLICATION -- BACKWARD_COMPATIBILITY
 
 
 
#endif
 
// ----------------------------------------------------------------------------
// Copyright 2013 Bloomberg Finance L.P.
//
// Licensed 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.
// ----------------------------- END-OF-FILE ----------------------------------
 
/** @} */
/** @} */
/** @} */