ball_countingallocator

Detailed Description

Outline

• Purpose
• Classes
• Description
  • Byte Count
  • Usage
    • Example 1: Basic Usage

Purpose

Provide a concrete allocator that keeps count of allocated bytes.

Classes

• ball::CountingAllocator: maximally-aligning, instrumented allocator adaptor

See also

ball_fixedsizerecordbuffer

Description

This component provides a special-purpose instrumented allocator, ball::CountingAllocator, that implements the bslma::Allocator protocol and guarantees maximal alignment of allocated blocks, even when the allocator supplied at construction guarantees only natural alignment (or no alignment at all). ball::CountingAllocator maintains a user-resettable running sum of the total number of bytes allocated (called byte count, see below).

 ,-----------------------.
( ball::CountingAllocator )
 `-----------------------'
             |         ctor/dtor
             |         numBytesTotal
             |         resetNumBytesTotal
             V
     ,----------------.
    ( bslma::Allocator )
     `----------------'
                     allocate
                     deallocate

Byte Count

The byte count maintained by ball::CountingAllocator is set to 0 upon construction and after each call to resetNumBytesTotal. Each call of allocate(size) increases the byte count by the sum of the least multiple of bsls::AlignmentUtil::BSLS_MAX_ALIGNMENT that is greater than or equal to size and bsls::AlignmentUtil::BSLS_MAX_ALIGNMENT. Each call of deallocate decrements the byte count by the same amount by which the byte count was incremented on matching allocate call. The current value of the byte count is returned by the numBytesTotal accessor.

Usage

This section illustrates intended use of this component.

Example 1: Basic Usage

In the following example we demonstrate how the counting allocator can be used to know the amount of dynamic memory allocated by a vector<int> after pushing one integer. Let us assume that memory for the vector comes from a bslma::Allocator named allocator.

  // First create the counting allocator using 'allocator'.
  BloombergLP::ball::CountingAllocator countingAllocator(allocator);
 
  // Now create the vector using the counting allocator.
  bsl::vector<int> vec(&countingAllocator);
 
  vec.push_back(1);
  // The following will print the memory consumed by the
  // vector and the counting allocator.
  bsl::cout << "dynamic memory after first push back: "
            << countingAllocator.numBytesTotal() << bsl::endl;