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pw::allocator::AlignableBlock< Derived > Class Template Reference
pw_allocator » Blocks » Block mix-ins

Overview

template<typename Derived>
class pw::allocator::AlignableBlock< Derived >

Mix-in for blocks that can be split on alignment boundaries.

Block mix-ins are stateless and trivially constructible. See BasicBlock for details on how mix-ins can be combined to implement blocks.

This mix-in requires its derived type also derive from AllocatableBlock.

Inheritance diagram for pw::allocator::AlignableBlock< Derived >:
pw::allocator::internal::AlignableBase

Protected Member Functions

constexpr StatusWithSize DoCanAlloc (Layout layout) const
 

Static Protected Member Functions

static constexpr BlockResult< Derived > DoAllocFirst (Derived *&&block, Layout layout)
 
static constexpr BlockResult< Derived > DoAllocLast (Derived *&&block, Layout layout)
 

Friends

template<typename >
class BlockWithLayout
 

Member Function Documentation

◆ DoAllocFirst()

template<typename Derived >
constexpr BlockResult< Derived > pw::allocator::AlignableBlock< Derived >::DoAllocFirst ( Derived *&&  block,
Layout  layout 
)
staticconstexprprotected

Splits an aligned block from the start of the block, and marks it as used.

If successful, block will be replaced by a block that has an inner size of at least inner_size, and whose starting address is aligned to an alignment boundary. If unsuccessful, block will be unmodified.

This method is static in order to consume the given block pointer. On success, a pointer to the new, smaller block is returned. In total, up to two additional blocks may be created: one to pad the returned block to an alignment boundary and one for the trailing space. On error, the original pointer is returned.

For larger alignments, the AllocLast method is generally preferable to this method, as this method may create an additional fragments both before and after the returned block in order to align the usable space.

Precondition
The block must not be in use.
Returns
  • OK: The split completed successfully. The BlockAllocType indicates how extra memory was distributed to other blocks.
  • FAILED_PRECONDITION: This block is in use and cannot be split.
  • RESOURCE_EXHAUSTED: The available space is insufficient to fulfill the request. This may be due to a large requested size, or insufficient remaining space to fulfill the requested alignment create a valid leading block, and/or create a valid trailing block.

◆ DoAllocLast()

template<typename Derived >
constexpr BlockResult< Derived > pw::allocator::AlignableBlock< Derived >::DoAllocLast ( Derived *&&  block,
Layout  layout 
)
staticconstexprprotected

Splits an aligned block from the end of the block, and marks it as used.

If successful, block will be replaced by a block that has an inner size of at least inner_size, and whose starting address is aligned to an alignment boundary. If unsuccessful, block will be unmodified.

This method is static in order to consume the given block pointer. On success, a pointer to the new, smaller block is returned. In total, up to two additional blocks may be created: one to pad the returned block to an alignment boundary and one for the trailing space. On error, the original pointer is returned.

Precondition
The block must not be in use.
Returns
  • OK: The split completed successfully. The BlockAllocType indicates how extra memory was distributed to other blocks.
  • FAILED_PRECONDITION: This block is in use and cannot be split.
  • RESOURCE_EXHAUSTED: The available space is insufficient to fulfill the request. This may be due to a large requested size, or insufficient remaining space to fulfill the requested alignment create a valid leading block, and/or create a valid trailing block.

◆ DoCanAlloc()

template<typename Derived >
constexpr StatusWithSize pw::allocator::AlignableBlock< Derived >::DoCanAlloc ( Layout  layout) const
constexprprotected

Checks if a block could be split from the block.

On error, this method will return the same status as AllocFirst or AllocLast without performing any modifications.

Precondition
The block must not be in use.
Returns
A Result containing the number of bytes to shift this block in order to align its usable space on success or one of the following error codes on failure:
  • FAILED_PRECONDITION: This block is in use and cannot be split.
  • RESOURCE_EXHAUSTED: The available space is insufficient to fulfill the request. This may be due to a large requested size, or insufficient remaining space to fulfill the requested alignment create a valid leading block, and/or create a valid trailing block.
The documentation for this class was generated from the following file: