bslma_defaultallocatorguard.h

Go to the documentation of this file.

/// @file bslma_defaultallocatorguard.h
///
/// The content of this file has been pre-processed for Doxygen.
///
 
 
// bslma_defaultallocatorguard.h                                      -*-C++-*-
#ifndef INCLUDED_BSLMA_DEFAULTALLOCATORGUARD
#define INCLUDED_BSLMA_DEFAULTALLOCATORGUARD
 
#include <bsls_ident.h>
BSLS_IDENT("$Id: $")
 
/// @defgroup bslma_defaultallocatorguard bslma_defaultallocatorguard
/// @brief  Provide scoped guard to temporarily change the default allocator.
/// @addtogroup bsl
/// @{
/// @addtogroup bslma
/// @{
/// @addtogroup bslma_defaultallocatorguard
/// @{
///
/// <h1> Outline </h1>
/// * <a href="#bslma_defaultallocatorguard-purpose"> Purpose</a>
/// * <a href="#bslma_defaultallocatorguard-classes"> Classes </a>
/// * <a href="#bslma_defaultallocatorguard-description"> Description </a>
///   * <a href="#bslma_defaultallocatorguard-usage"> Usage </a>
///
/// # Purpose {#bslma_defaultallocatorguard-purpose}
/// Provide scoped guard to temporarily change the default allocator.
///
/// # Classes {#bslma_defaultallocatorguard-classes}
///
/// -  bslma::DefaultAllocatorGuard: default-allocator scoped guard
///
/// @see  bslma_allocator, bslma_default
///
/// # Description {#bslma_defaultallocatorguard-description}
/// This component provides an object,
/// `bslma::DefaultAllocatorGuard`, that serves as a "scoped guard" to enable
/// the temporary replacement of the process-wide default allocator.  This
/// functionality is intended for *testing* only, and in no event should this
/// component be used except in `main`.
///
/// The guard object takes as its constructor argument the address of an object
/// of a class derived from `bslma::Allocator`.  The default allocator at the
/// time of guard construction is held by the guard, and the
/// constructor-argument allocator is installed as the new process-wide default
/// allocator (via a call to `bslma::Default::setDefaultAllocatorRaw`).  Upon
/// destruction of the guard object, its held allocator is restored as the
/// process-wide default allocator (via another call to
/// `bslma::Default::setDefaultAllocatorRaw`).
///
/// ## Usage {#bslma_defaultallocatorguard-usage}
///
///
/// The @ref bslma_default  component ensures that, unless the owner of `main` or
/// some intervening code explicitly installs a default allocator, the
/// `bslma::NewDeleteAllocator::singleton()` will be the default allocator for
/// that process (i.e., calls to `bslma::Default::defaultAllocator()` will
/// return the new-delete allocator unless someone has set the default allocator
/// to a different allocator intentionally).  Consider for purposes of this
/// illustrative example the case where we, as owners of a test driver `main`,
/// can count on the `bslma::NewDeleteAllocator` singleton being the default.
///
/// Consider now that, for testing purposes, we want a simple counting allocator
/// that uses `new` and `delete`, and that also keeps count of the number of
/// memory blocks that have been allocated but never deallocated.  (Note that,
/// in testing real production code, `bslma::TestAllocator` serves this
/// purpose.)
/// @code
/// class my_CountingAllocator : public bslma::Allocator
/// {
///     int d_blocksOutstanding;
///   public:
///     my_CountingAllocator();
///     ~my_CountingAllocator();
///
///     virtual void *allocate(int size);
///     virtual void deallocate(void *address);
///
///     int blocksOutstanding() const { return d_blocksOutstanding; }
/// };
///
/// inline
/// my_CountingAllocator::my_CountingAllocator()
/// : d_blocksOutstanding(0)
/// {
/// }
///
/// inline
/// my_CountingAllocator::~my_CountingAllocator()
/// {
///     if (0 < d_blocksOutstanding) {
///         std::cout << "***ERROR: Memory Leak***" << std::endl
///                   << d_blocksOutstanding << " block(s) leaked.  "
///                   << "Program aborting." << std::endl;
///         assert(0);
///     }
/// }
///
/// inline
/// void *my_CountingAllocator::allocate(int size)
/// {
///     ++d_blocksOutstanding;
///     return operator new(size);
/// }
///
/// inline
/// void my_CountingAllocator::deallocate(void *address)
/// {
///     --d_blocksOutstanding;
///     operator delete(address);
/// }
/// @endcode
/// We may now write a test driver for some component that uses a
/// `bslma::Allocator` and the `bslma::Default` mechanism.  First, we confirm
/// that the `bslma::NewDeleteAllocator` singleton is indeed installed.
/// @code
///  //my_component.t.cpp
///
///  // ...
///
/// int main()
/// {
///     // ...
///     bslma::NewDeleteAllocator *na =
///                                    &bslma::NewDeleteAllocator::singleton();
///     assert(na == bslma::Default::defaultAllocator());
/// @endcode
/// Now, we can go into some inner scope and use a guard object to install a
/// test allocator as the default for any newly created objects.  When the inner
/// scope ends, the guard will be destroyed, automatically restoring the
/// original default allocator.
/// @code
/// {
///     my_CountingAllocator        testAllocator;
///     bslma::DefaultAllocatorGuard guard(&testAllocator);
///     assert(&testAllocator == bslma::Default::defaultAllocator());
///
///     // Create and test the object under test, which will use the
///     // test allocator *by* *default*.
///
///     // ...
/// }
/// assert(na == bslma::Default::defaultAllocator());
/// @endcode
/// If the test block above has a memory leak, the program will print an error
/// to `stdout` and abort.  Otherwise, the new-delete allocator will be
/// re-installed as the default allocator, and the program will proceed to the
/// next block of code.
/// @}
/** @} */
/** @} */
 
/** @addtogroup bsl
 * @{
 */
/** @addtogroup bslma
 * @{
 */
/** @addtogroup bslma_defaultallocatorguard
 * @{
 */
 
#include <bslscm_version.h>
 
 
 
 
namespace bslma {
 
class Allocator;
 
                        // ===========================
                        // class DefaultAllocatorGuard
                        // ===========================
 
/// Upon construction, an object of this class saves the current default
/// allocator and installs the user-specified allocator as the default
/// allocator.  On destruction, the original default allocator is restored.
/// Objects of this class are intended for testing purposes *only* and are
/// *not* guaranteed to be safe in production environments.
///
/// See @ref bslma_defaultallocatorguard 
class DefaultAllocatorGuard {
 
    Allocator *d_original_p;  // original (to be restored at destruction)
 
  private:
    // NOT IMPLEMENTED
    DefaultAllocatorGuard(const DefaultAllocatorGuard&);
    DefaultAllocatorGuard& operator=(const DefaultAllocatorGuard&);
 
  public:
    // CREATORS
 
    /// Create a scoped guard that installs the specified `temporary` allocator as the default allocator.  
    /// 
    /// \note Note that   the default allocator
    /// is automatically restored to the original allocator on destruction.
    explicit
    DefaultAllocatorGuard(Allocator *temporary);
 
    /// Restore the default allocator that was in place when this scoped
    /// guard was created and destroy this guard.
    ~DefaultAllocatorGuard();
};
 
}  // close package namespace
 
#ifndef BDE_OPENSOURCE_PUBLICATION  // BACKWARD_COMPATIBILITY
// ============================================================================
//                           BACKWARD COMPATIBILITY
// ============================================================================
 
/// This alias is defined for backward compatibility.
typedef bslma::DefaultAllocatorGuard bslma_DefaultAllocatorGuard;
#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 ----------------------------------
 
/** @} */
/** @} */
/** @} */