Gaudi::Arena::Monotonic< Alignment, UpstreamAllocator > Class Template Reference

A fast memory arena that does not track deallocations. More...

#include </builds/gaudi/Gaudi/GaudiKernel/include/Gaudi/Arena/Monotonic.h>

Collaboration diagram for Gaudi::Arena::Monotonic< Alignment, UpstreamAllocator >:

Public Member Functions
	Monotonic (std::size_t next_block_size) noexcept
	Construct an arena whose first block have approximately the given size. More...
	~Monotonic () noexcept
	Monotonic (Monotonic &&)=delete
	Monotonic (Monotonic const &)=delete
Monotonic &	operator= (Monotonic &&)=delete
Monotonic &	operator= (Monotonic const &)=delete
template<std::size_t ReqAlign>
std::byte *	allocate (std::size_t n)
	Return an aligned point to n bytes of memory. More...
constexpr void	deallocate (std::byte *, std::size_t) noexcept
	Deallocations are not tracked, so this is a no-op! More...
void	reset () noexcept
	Signal that this arena may start re-using the memory resources. More...
std::size_t	capacity () const noexcept
	Query how much memory is owned by this arena, in bytes. More...
std::size_t	size () const noexcept
	Query how much memory was used from this arena, in bytes. More...
std::size_t	num_blocks () const noexcept
	Query how many blocks of memory this arena owns. More...
std::size_t	num_allocations () const noexcept
	Query how many allocations this arena has served. More...

Static Public Attributes
static constexpr std::size_t	alignment = Alignment

Private Attributes
std::size_t	m_next_block_size {}
	Size (in bytes) of the next block to be allocated. More...
std::size_t	m_allocations { 0 }
	Number of allocation requests served by this arena. More...
std::byte *	m_current { nullptr }
	Current position in the current block, or nullptr if there is no current block. More...
std::byte *	m_current_end { nullptr }
	One byte past the end of the current block, or nullptr if it doesn't exist. More...
boost::container::small_vector< gsl::span< std::byte >, 1 >	m_all_blocks
	All memory blocks owned by this arena. More...

Static Private Attributes
static constexpr std::size_t	growth_factor = 2
	Approximate factor by which each block is larger than its predecessor. More...

Detailed Description

template<std::size_t Alignment = alignof( std::max_align_t ), typename UpstreamAllocator = std::allocator<std::byte>>
class Gaudi::Arena::Monotonic< Alignment, UpstreamAllocator >

A fast memory arena that does not track deallocations.

This is a memory arena suitable for use with Gaudi::Allocators::Arena. It allocates memory from an upstream resource in blocks of geometrically increasing size and serves allocation requests from those blocks. Deallocations are not tracked, so the memory footprint of a Monotonic arena increases monotonically until either it is destroyed or its reset() method is called. All requests are served with alignment specified in the template parameter.

Todo:

Efficiently support stateful upstream allocators, probably by putting an instance of the upstream allocator in a boost::compressed_pair.

Use the given UpstreamAllocator to serve dynamic allocations required by boost::container::small_vector.

Definition at line 46 of file Monotonic.h.

Constructor & Destructor Documentation

Monotonic() [1/3]

template<std::size_t Alignment = alignof( std::max_align_t ), typename UpstreamAllocator = std::allocator<std::byte>>

Gaudi::Arena::Monotonic< Alignment, UpstreamAllocator >::Monotonic ( std::size_t  next_block_size )

inlinenoexcept

Construct an arena whose first block have approximately the given size.

This constructor does not trigger any allocation.

Definition at line 74 of file Monotonic.h.

        : m_next_block_size{ details::align_up<Alignment>( next_block_size ) } {}

~Monotonic()

template<std::size_t Alignment = alignof( std::max_align_t ), typename UpstreamAllocator = std::allocator<std::byte>>

Gaudi::Arena::Monotonic< Alignment, UpstreamAllocator >::~Monotonic ( )

inlinenoexcept

Definition at line 77 of file Monotonic.h.

                          {
      for ( auto block : m_all_blocks ) { UpstreamAllocator{}.deallocate( block.data(), block.size() ); }
    }

Monotonic() [2/3]

template<std::size_t Alignment = alignof( std::max_align_t ), typename UpstreamAllocator = std::allocator<std::byte>>

Gaudi::Arena::Monotonic< Alignment, UpstreamAllocator >::Monotonic ( Monotonic< Alignment, UpstreamAllocator > &&  )

delete

Monotonic() [3/3]

template<std::size_t Alignment = alignof( std::max_align_t ), typename UpstreamAllocator = std::allocator<std::byte>>

Gaudi::Arena::Monotonic< Alignment, UpstreamAllocator >::Monotonic ( Monotonic< Alignment, UpstreamAllocator > const &  )

delete

Member Function Documentation

allocate()

template<std::size_t Alignment = alignof( std::max_align_t ), typename UpstreamAllocator = std::allocator<std::byte>>

template<std::size_t ReqAlign>

std::byte* Gaudi::Arena::Monotonic< Alignment, UpstreamAllocator >::allocate ( std::size_t  n )

inline

Return an aligned point to n bytes of memory.

This may trigger allocation from the upstream resource.

Definition at line 92 of file Monotonic.h.

                                     {
      // If the requested alignment was larger we would need to round up
      // m_current -- instead of implementing that, just assert it's not
      // the case.
      static_assert( ReqAlign <= alignment, "Requested alignment too large for this Gaudi::Arena::Monotonic!" );
      // Figure out how many bytes we need to allocate
      std::size_t const aligned_n = details::align_up<Alignment>( n );
      // Check that we have a current block and this request fits inside it
      if ( !m_current || m_current + aligned_n > m_current_end ) {
        // Calculate our next block size
        auto next_block_size = std::max( m_next_block_size, aligned_n );
        // And update the estimate of what comes after that, following a geometric series
        m_next_block_size = details::align_up<Alignment>( growth_factor * next_block_size );
        // Allocate the new block and mark it as the current one
        m_current     = UpstreamAllocator{}.allocate( next_block_size );
        m_current_end = m_current + next_block_size;
        // Add it to the list of blocks that we'll eventually deallocate
        m_all_blocks.emplace_back( m_current, next_block_size );
      }
      m_allocations++;
      return std::exchange( m_current, m_current + aligned_n );
    }

capacity()

template<std::size_t Alignment = alignof( std::max_align_t ), typename UpstreamAllocator = std::allocator<std::byte>>

std::size_t Gaudi::Arena::Monotonic< Alignment, UpstreamAllocator >::capacity ( ) const

inlinenoexcept

Query how much memory is owned by this arena, in bytes.

Definition at line 145 of file Monotonic.h.

                                                      {
      return std::accumulate( m_all_blocks.begin(), m_all_blocks.end(), 0ul,
                              []( std::size_t sum, auto block ) { return sum + block.size(); } );
    }

deallocate()

template<std::size_t Alignment = alignof( std::max_align_t ), typename UpstreamAllocator = std::allocator<std::byte>>

constexpr void Gaudi::Arena::Monotonic< Alignment, UpstreamAllocator >::deallocate ( std::byte *  , std::size_t    )

inlineconstexprnoexcept

Deallocations are not tracked, so this is a no-op!

Definition at line 117 of file Monotonic.h.

{}

num_allocations()

template<std::size_t Alignment = alignof( std::max_align_t ), typename UpstreamAllocator = std::allocator<std::byte>>

std::size_t Gaudi::Arena::Monotonic< Alignment, UpstreamAllocator >::num_allocations ( ) const

inlinenoexcept

Query how many allocations this arena has served.

Definition at line 160 of file Monotonic.h.

{ return m_allocations; }

num_blocks()

template<std::size_t Alignment = alignof( std::max_align_t ), typename UpstreamAllocator = std::allocator<std::byte>>

std::size_t Gaudi::Arena::Monotonic< Alignment, UpstreamAllocator >::num_blocks ( ) const

inlinenoexcept

Query how many blocks of memory this arena owns.

Definition at line 156 of file Monotonic.h.

{ return m_all_blocks.size(); }

operator=() [1/2]

template<std::size_t Alignment = alignof( std::max_align_t ), typename UpstreamAllocator = std::allocator<std::byte>>

Monotonic& Gaudi::Arena::Monotonic< Alignment, UpstreamAllocator >::operator= ( Monotonic< Alignment, UpstreamAllocator > &&  )

delete

operator=() [2/2]

template<std::size_t Alignment = alignof( std::max_align_t ), typename UpstreamAllocator = std::allocator<std::byte>>

Monotonic& Gaudi::Arena::Monotonic< Alignment, UpstreamAllocator >::operator= ( Monotonic< Alignment, UpstreamAllocator > const &  )

delete

reset()

template<std::size_t Alignment = alignof( std::max_align_t ), typename UpstreamAllocator = std::allocator<std::byte>>

void Gaudi::Arena::Monotonic< Alignment, UpstreamAllocator >::reset ( )

inlinenoexcept

Signal that this arena may start re-using the memory resources.

• If the arena owns zero blocks, there is no change.
• If the arena owns one block, it will reset to serving future requests from the start of that block.
• If the arena owns more than one block, it will deallocate all but the first one and serve future requests from the start of the remaining block.

Definition at line 126 of file Monotonic.h.

                          {
      m_allocations = 0;
      if ( !m_all_blocks.empty() ) {
        // Only re-use the first block, deallocate any others
        if ( m_all_blocks.size() > 1 ) {
          for ( std::size_t i = 1; i < m_all_blocks.size(); ++i ) {
            UpstreamAllocator{}.deallocate( m_all_blocks[i].data(), m_all_blocks[i].size() );
          }
          m_all_blocks.resize( 1 );
        }
        auto reused_block = m_all_blocks.front();
        m_current         = reused_block.data();
        m_current_end     = m_current + reused_block.size();
        m_next_block_size = details::align_up<Alignment>( growth_factor * reused_block.size() );
      }
    }

size()

template<std::size_t Alignment = alignof( std::max_align_t ), typename UpstreamAllocator = std::allocator<std::byte>>

std::size_t Gaudi::Arena::Monotonic< Alignment, UpstreamAllocator >::size ( ) const

inlinenoexcept

Query how much memory was used from this arena, in bytes.

Definition at line 152 of file Monotonic.h.

{ return capacity() - ( m_current_end - m_current ); }

Member Data Documentation

alignment

template<std::size_t Alignment = alignof( std::max_align_t ), typename UpstreamAllocator = std::allocator<std::byte>>

constexpr std::size_t Gaudi::Arena::Monotonic< Alignment, UpstreamAllocator >::alignment = Alignment

staticconstexpr

Definition at line 69 of file Monotonic.h.

growth_factor

template<std::size_t Alignment = alignof( std::max_align_t ), typename UpstreamAllocator = std::allocator<std::byte>>

constexpr std::size_t Gaudi::Arena::Monotonic< Alignment, UpstreamAllocator >::growth_factor = 2

staticconstexprprivate

Approximate factor by which each block is larger than its predecessor.

Definition at line 66 of file Monotonic.h.

m_all_blocks

template<std::size_t Alignment = alignof( std::max_align_t ), typename UpstreamAllocator = std::allocator<std::byte>>

boost::container::small_vector<gsl::span<std::byte>, 1> Gaudi::Arena::Monotonic< Alignment, UpstreamAllocator >::m_all_blocks

private

All memory blocks owned by this arena.

Definition at line 63 of file Monotonic.h.

m_allocations

template<std::size_t Alignment = alignof( std::max_align_t ), typename UpstreamAllocator = std::allocator<std::byte>>

std::size_t Gaudi::Arena::Monotonic< Alignment, UpstreamAllocator >::m_allocations { 0 }

private

Number of allocation requests served by this arena.

Definition at line 54 of file Monotonic.h.

m_current

template<std::size_t Alignment = alignof( std::max_align_t ), typename UpstreamAllocator = std::allocator<std::byte>>

std::byte* Gaudi::Arena::Monotonic< Alignment, UpstreamAllocator >::m_current { nullptr }

private

Current position in the current block, or nullptr if there is no current block.

Definition at line 57 of file Monotonic.h.

m_current_end

template<std::size_t Alignment = alignof( std::max_align_t ), typename UpstreamAllocator = std::allocator<std::byte>>

std::byte* Gaudi::Arena::Monotonic< Alignment, UpstreamAllocator >::m_current_end { nullptr }

private

One byte past the end of the current block, or nullptr if it doesn't exist.

Definition at line 60 of file Monotonic.h.

m_next_block_size

template<std::size_t Alignment = alignof( std::max_align_t ), typename UpstreamAllocator = std::allocator<std::byte>>

std::size_t Gaudi::Arena::Monotonic< Alignment, UpstreamAllocator >::m_next_block_size {}

private

Size (in bytes) of the next block to be allocated.

Definition at line 51 of file Monotonic.h.

---

The documentation for this class was generated from the following file:

• GaudiKernel/include/Gaudi/Arena/Monotonic.h