Documentation of memory

( foonathan/memory)

memory Documentation

This is the documentation of foonathan/memory.

For a quick start, read the Tutorial or skim the examples at the Github page. The concepts of this library are defined are here.

Features

New allocator concepts:

  • a RawAllocator that is similar to an Allocator but easier to use and write
  • a BlockAllocator that is an allocator for huge memory blocks

Several implementations:

  • heap_/malloc_/new_allocator
  • virtual memory allocators
  • allocator using a static memory block located on the stack
  • memory stack
  • different memory pools
  • a portable, improved alloca() in the form of temporary_allocator

Adapters, wrappers and storage classes:

  • incredible powerful allocator_traits allowing Allocators as RawAllocators
  • std_allocator to make a RawAllocator an Allocator again
  • adapters for the memory resource TS
  • allocator_deleter classes for smart pointers
  • (optionally type-erased) allocator_reference and other storage classes
  • memory tracking wrapper

In addition:

  • container node size debuggers that obtain information about the node size of an STL container at compile-time to specify node sizes for pools
  • debugging options for leak checking, double-free checks or buffer overflows
  • customizable error handling routines that can work with exceptions disabled
  • everything except the STL adapters works on a freestanding environment

Basic example

#include <algorithm>
#include <iostream>
#include <iterator>
#include <foonathan/memory/container.hpp> // vector, list, list_node_size,...
#include <foonathan/memory/memory_pool.hpp> // memory_pool
#include <foonathan/memory/smart_ptr.hpp> // allocate_unique
#include <foonathan/memory/static_allocator.hpp> // static_allocator_storage, static_block_allocator
#include <foonathan/memory/temporary_allocator.hpp> // temporary_allocator
// alias namespace foonathan::memory as memory for easier access
template <typename BiIter>
void merge_sort(BiIter begin, BiIter end);
int main()
{
using namespace memory::literals;
// a memory pool RawAllocator
// allocates a memory block - initially 4KiB - and splits it into chunks of list_node_size<int>::value big
// list_node_size<int>::value is the size of each node of a std::list
memory::memory_pool<> pool(memory::list_node_size<int>::value, 4_KiB);
// just an alias for std::list<int, memory::std_allocator<int, memory::memory_pool<>>
// a std::list using a memory_pool
// std_allocator stores a reference to a RawAllocator and provides the Allocator interface
list.push_back(3);
list.push_back(2);
list.push_back(1);
for (auto e : list)
std::cout << e << ' ';
std::cout << '\n';
merge_sort(list.begin(), list.end());
for (auto e : list)
std::cout << e << ' ';
std::cout << '\n';
// allocate a std::unique_ptr using the pool
// memory::allocate_shared is also available
auto ptr = memory::allocate_unique<int>(pool, *list.begin());
std::cout << *ptr << '\n';
// static storage of size 4KiB
// a memory pool again but this time with a BlockAllocator
// this controls the internal allocations of the pool itself
// we need to specify the first template parameter giving the type of the pool as well
// (node_pool is the default)
// we use a static_block_allocator that uses the static storage above
// all allocations will use a memory block on the stack
using static_pool_t = memory::memory_pool<memory::node_pool, memory::static_block_allocator>;
static_pool_t static_pool(memory::unordered_set_node_size<int>::value, 4_KiB, storage);
// again, just an alias for std::unordered_set<int, std::hash<int>, std::equal_to<int>, memory::std_allocator<int, static_pool_t>
// see why I wrote these? :D
// now we have a hash set that lives on the stack!
set(13, std::hash<int>{}, std::equal_to<int>{},
static_pool); // GCC 4.7 is missing the allocator-only ctor, breaks travis :(
set.insert(3);
set.insert(2);
set.insert(3); // running out of stack memory is properly handled, of course
for (auto e : set)
std::cout << e << ' ';
std::cout << '\n';
}
// naive implementation of merge_sort using temporary memory allocator
template <typename BiIter>
void merge_sort(BiIter begin, BiIter end)
{
using value_type = typename std::iterator_traits<BiIter>::value_type;
auto distance = std::distance(begin, end);
if (distance <= 1)
return;
auto mid = begin;
std::advance(mid, distance / 2);
// an allocator for temporary memory
// is similar to alloca() but uses its own stack
// this stack is thread_local and created the first time it's needed
// as soon as the allocator object goes out of scope everything allocated through it will be freed
// alias for std::vector<value_type, memory::std_allocator<value_type, memory::temporary_allocator>>
// a std::vector using a temporary_allocator
second(mid, end, alloc);
merge_sort(first.begin(), first.end());
merge_sort(second.begin(), second.end());
std::merge(first.begin(), first.end(), second.begin(), second.end(), begin);
}

See example/ for more.

Installation

This library can be used as [CMake] subdirectory. It is tested on GCC 4.7-4.9, Clang 3.4-3.5 and Visual Studio 2013. Newer versions should work too.

  1. Fetch it, e.g. using [git submodules] git submodule add https://github.com/foonathan/memory ext/memory and git submodule update --init --recursive.
  2. Call add_subdirectory(ext/memory) or whatever your local path is to make it available in CMake.
  3. Simply call target_link_libraries(your_target PUBLIC foonathan_memory) to link this library and setups the include search path.
  4. You need to activate C++11 at your target, if not already done, you can use [foonathan/compatibility] already available through add_subdirectory() and call comp_target_features(your_target PUBLIC CPP11).

Note: If during CMake you see an error message that compatibility is not on the newest version, run git submodule update --recursive --remote to force the compatiblity submodule of memory to update to the latest version.

You can also install the library:

  1. Run cmake -DCMAKE_BUILD_TYPE="buildtype" -DFOONATHAN_MEMORY_BUILD_EXAMPLES=OFF -DFOONATHAN_MEMORY_BUILD_TESTS=OFF . inside the library sources.
  2. Run cmake --build . -- install to install the library under ${CMAKE_INSTALL_PREFIX}.
  3. Repeat 1 and 2 for each build type/configuration you want to have (like Debug, RelWithDebInfo and Release or custom names).

The use an installed library:

  1. Call find_package(foonathan_memory major.minor REQUIRED) to find the library.
  2. Call target_link_libraries(your_target PUBLIC foonathan_memory) and activate C++11 to link to the library.

See http://foonathan.github.io/doc/memory/md_doc_installation.html for a detailed guide.

About this documentation

This documentation is written in a similar way as the C++ standard itself, although not that formal.

Concepts are documented using the names of the template parameters, for example the following class:

template <class Tracker, class RawAllocator>
class tracked_allocator;

It takes two template parameters, the first must model the Tracker concept, the second the RawAllocator concept.

Unless explicitly stated otherwise, it is not allowed to call a function that modifies state from two different threads. Functions that modify state are non-const member functions, functions taking a non-const reference to objects or functions where it is explictly documented that they change some hidden state.

If a function is documented as noexcept, it does not throw anything. Otherwise it has a Throws: clause specifying what it throws, or if it is a forwarding function, the information can be found there (see below).

If a class is described as RawAllocator it automatically has certain semantically information which are not explictly mentioned. This is especially true for the member functions of an allocator_traits specialization.

If a function is described as returning the value of another function or forwarding to it, it implicitly has the requirements and effects from the called function and can also throw the same things.