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Provide sequential memory using dynamically-allocated buffers. More...
Namespaces | |
| namespace | bdlma |
Functions | |
| void * | operator new (bsl::size_t size, BloombergLP::bdlma::SequentialPool &pool) |
| void | operator delete (void *address, BloombergLP::bdlma::SequentialPool &pool) |
| bdlma::SequentialPool | memory pool using dynamically-allocated buffers |
bdlma::SequentialPool, that dispenses heterogeneous memory blocks (of varying, user-specified sizes) from a dynamically-allocated internal buffer. If an allocation request exceeds the remaining free memory space in the internal buffer, the pool either replenishes its buffer with new memory to satisfy the request, or returns a separate memory block, depending on whether the request size exceeds an optionally-specified maximum buffer size. The release method releases all memory allocated through the pool, as does the destructor. The rewind method releases all memory allocated through the pool and returns to the underlying allocator only memory that was allocated outside of the typical internal buffer growth of the pool (i.e., large blocks). Note that individually allocated memory blocks cannot be separately deallocated. bdlma::SequentialPool is typically used when fast allocation and deallocation is needed, but the user does not know in advance the maximum amount of memory needed. initialSize parameter can be supplied at construction to specify the initial size of the internal buffer. If initialSize is not supplied, an implementation-defined value is used for the initial internal size of the buffer. initialSize is specified, an optional maxBufferSize parameter can be supplied at construction to specify the maximum buffer size for geometric growth. Once the internal buffer grows up to the maxBufferSize, further requests that exceed this size will be served by a separate memory block instead of the internal buffer. The behavior is undefined unless maxBufferSize >= initialSize. Note that reserveCapacity always ensures that the requested number of bytes is available (allocating a new internal buffer if necessary) regardless of whether the size of the request exceeds maxBufferSize. growthStrategy parameter can be supplied at construction to specify the growth rate of the dynamically-allocated buffers. The buffers can grow either geometrically or remain constant in size. If growthStrategy is not specified, geometric growth is used. See bsls_blockgrowth for more details. alignmentStrategy parameter can be supplied at construction to specify the memory alignment strategy. Allocated memory blocks can either follow maximum alignment, natural alignment, or 1-byte alignment. If alignmentStrategy is not specified, natural alignment is used. See bsls_alignment for more details. my_IntDoubleArray, that holds both int and double values. The class can be implemented using two parallel arrays: one storing the type information, and the other storing pointers to the int and double values. For efficient memory allocation, we can use a bdlma::SequentialPool for memory allocation: // my_intdoublearray.h class my_IntDoubleArray { // This class implements an efficient container for an array that // stores both 'int' and 'double' values. // DATA char *d_typeArray_p; // array indicating the type of corresponding // values stored in 'd_valueArray_p' void **d_valueArray_p; // array of pointers to the values stored int d_length; // number of values stored int d_capacity; // physical capacity of the type and value // arrays bdlma::SequentialPool d_pool; // sequential memory pool used to supply memory private: // PRIVATE MANIPULATORS void increaseSize(); // Increase the capacity of the internal arrays used to store // elements added to this array by at least one element. // Not implemented: my_IntDoubleArray(const my_IntDoubleArray&); public: // TYPES enum Type { k_MY_INT, k_MY_DOUBLE }; // CREATORS explicit my_IntDoubleArray(bslma::Allocator *basicAllocator = 0); // Create an 'int'-'double' array. Optionally specify a // 'basicAllocator' used to supply memory. If 'basicAllocator' is // 0, the currently installed default allocator is used. ~my_IntDoubleArray(); // Destroy this array and all elements held by it. // ... // MANIPULATORS void appendInt(int value); // Append the specified 'int' 'value' to this array. void appendDouble(double value); // Append the specified 'double' 'value' to this array. void removeAll(); // Remove all elements from this array. // ... };
release method allows the removeAll method to quickly deallocate memory of all elements: // MANIPULATORS inline void my_IntDoubleArray::removeAll() { d_pool.release(); d_length = 0; }
// my_intdoublearray.cpp enum { k_INITIAL_SIZE = 1 }; // PRIVATE MANIPULATORS void my_IntDoubleArray::increaseSize() { // Implementation elided. // ... } // CREATORS my_IntDoubleArray::my_IntDoubleArray(bslma::Allocator *basicAllocator) : d_length(0) , d_capacity(k_INITIAL_SIZE) , d_pool(basicAllocator) { d_typeArray_p = static_cast<char *>( d_pool.allocate(d_capacity * sizeof *d_typeArray_p)); d_valueArray_p = static_cast<void **>( d_pool.allocate(d_capacity * sizeof *d_valueArray_p)); }
d_pool is destroyed: my_IntDoubleArray::~my_IntDoubleArray()
{
assert(0 <= d_length);
assert(0 <= d_capacity);
assert(d_length <= d_capacity);
}
// MANIPULATORS
void my_IntDoubleArray::appendInt(int value)
{
if (d_length >= d_capacity) {
increaseSize();
}
int *item = static_cast<int *>(d_pool.allocate(sizeof *item));
*item = value;
d_typeArray_p[d_length] = static_cast<char>(k_MY_INT);
d_valueArray_p[d_length] = item;
++d_length;
}
void my_IntDoubleArray::appendDouble(double value)
{
if (d_length >= d_capacity) {
increaseSize();
}
double *item = static_cast<double *>(d_pool.allocate(sizeof *item));
*item = value;
d_typeArray_p[d_length] = static_cast<char>(k_MY_DOUBLE);
d_valueArray_p[d_length] = item;
++d_length;
}
bslma::Allocator is used throughout the interfaces of BDE components. Suppose we would like to create a fast allocator, my_FastAllocator, that allocates memory from a buffer in a similar fashion to bdlma::SequentialPool. bdlma::SequentialPool can be used directly to implement such an allocator. bdlma_sequentialallocator for full documentation of a similar class. class my_SequentialAllocator : public bslma::Allocator { // This class implements the 'bslma::Allocator' protocol to provide a // fast allocator of heterogeneous blocks of memory (of varying, // user-specified sizes) from dynamically-allocated internal buffers. // DATA bdlma::SequentialPool d_pool; // memory manager for allocated memory // blocks public: // CREATORS explicit my_SequentialAllocator(bslma::Allocator *basicAllocator = 0); // Create an allocator for allocating memory blocks from // dynamically-allocated internal buffers. Optionally specify a // 'basicAllocator' used to supply memory. If 'basicAllocator' is // 0, the currently installed default allocator is used. ~my_SequentialAllocator(); // Destroy this allocator. All memory allocated from this // allocator is released. // MANIPULATORS virtual void *allocate(size_type size); // Return the address of a contiguous block of memory of the // specified 'size' (in bytes). virtual void deallocate(void *address); // This method has no effect on the memory block at the specified // 'address' as all memory allocated by this allocator is managed. // The behavior is undefined unless 'address' was allocated by this // allocator, and has not already been deallocated. }; // CREATORS inline my_SequentialAllocator::my_SequentialAllocator( bslma::Allocator *basicAllocator) : d_pool(basicAllocator) { } inline my_SequentialAllocator::~my_SequentialAllocator() { d_pool.release(); } // MANIPULATORS inline void *my_SequentialAllocator::allocate(size_type size) { return d_pool.allocate(size); } inline void my_SequentialAllocator::deallocate(void *) { }
| void* operator new | ( | bsl::size_t | size, | |
| BloombergLP::bdlma::SequentialPool & | pool | |||
| ) |
Return a block of memory of the specified size (in bytes) allocated from the specified pool. Note that an object may allocate additional memory internally, requiring the allocator to be passed in as a constructor argument:
my_Type *newMyType(bdlma::SequentialPool *pool, bslma::Allocator *basicAllocator) { return new (*pool) my_Type(..., basicAllocator); }
Also note that the analogous version of operator delete should not be called directly. Instead, this component provides a static template member function, deleteObject, parameterized by TYPE that performs the following:
void deleteMyType(bdlma::SequentialPool *pool, my_Type *t) { t->~my_Type(); }
| void operator delete | ( | void * | address, | |
| BloombergLP::bdlma::SequentialPool & | pool | |||
| ) |
Use the specified pool to deallocate the memory at the specified address. The behavior is undefined unless address was allocated using pool and has not already been deallocated. This operator is supplied solely to allow the compiler to arrange for it to be called in case of an exception.
1.7.1