Overview

template<typename Prefix, typename Suffix = void, typename ErrorHandler = internal::DefaultFrameErrorHandler>
class pw::allocator::FramingAllocator< Prefix, Suffix, ErrorHandler >

An allocator that can "frame" its allocation with a leading prefix type, a trailing suffix type, or both.

At least one of Prefix and Suffix must be a type other than void, since in that case there is no need for a frame.

In addition to the template parameter types, each allocation will include up to three additional size_t fields.

The offset of the suffix field from the data, i.e. from the allocated pointer. This field is omitted if the suffix type is void. When present, this field is located just before the usable memory.
The offset of the data from the start of the frame. This field is located just after the prefix, if the prefix type is not void, or at the start of the frame.
The offset of the frame from the start of the data. This has the same value as the frame offset, but can be located using only the data pointer. This field is located just before the suffix offset, if the suffix type is not void, or just before the usable memory.

The frame offset and data offset locations may match, i.e. the field just after the prefix is right before the suffix offset or usable memory. In this case, only one offset is stored as both the frame and data offset.

Thus assuming sizeof(size_t) == 4, requesting a 64-byte allocation with a 16-byte alignment from a FramingAllocator<uint32_t, uint16_t> might result in an allocation that looks like:

  Address   Type          Contents             Pointed at by:
+---------+-------------+--------------------+--------------------------+
| 0x...00 | Prefix      | user-defined       | frame                    |
|         | (uint32_t)  |                    | GetFrame(data)           |
|         |             |                    | GetPrefix(data)          |
+---------+-------------+--------------------+--------------------------+
| 0x...04 | size_t      | frame_offset =0x10 | GetFrameOffsetPtr(frame) |
+---------+-------------+--------------------+--------------------------+
| 0x...08 | size_t      | data_offset  =0x10 | GetDataOffsetPtr(data)   |
+---------+-------------+--------------------+--------------------------+
| 0x...0C | size_t      | suffix_offset=0x40 | GetSuffixOffsetPtr(data) |
+---------+-------------+--------------------+--------------------------+
| 0x...10 | std::byte[] | usable space       | data                     |
|         |             |                    | GetData(frame)           |
+---------+-------------+--------------------+--------------------------+
| 0x...50 | Suffix      | user-defined       | GetSuffix(data)          |
|         | (uint16_t)  |                    |                          |
+---------+-------------+--------------------+--------------------------+

Alternatively, if the selected memory for the same allocation happens to start at 0x...04, the prefix offsets will be combined:

  Address   Type          Contents             Pointed at by:
+---------+-------------+--------------------+--------------------------+
| 0x...04 | Prefix      | user-defined       | frame                    |
|         | (uint32_t)  |                    | GetFrame(data)           |
|         |             |                    | GetPrefix(data)          |
+---------+-------------+--------------------+--------------------------+
| 0x...08 | size_t      | frame_offset,      | GetFrameOffsetPtr(frame) |
|         |             | data_offset  =0x0C | GetDataOffsetPtr(data)   |
+---------+-------------+--------------------+--------------------------+
| 0x...0C | size_t      | suffix_offset=0x40 | GetSuffixOffsetPtr(data) |
+---------+-------------+--------------------+--------------------------+
| 0x...10 | std::byte[] | usable space       | data                     |
|         |             |                    | GetData(frame)           |
+---------+-------------+--------------------+--------------------------+
| 0x...50 | Suffix      | user-defined       | GetSuffix(data)          |
|         | (uint16_t)  |                    |                          |
+---------+-------------+--------------------+--------------------------+

Let's drop the suffix for simplicity. If we make a similar allocation from a FramingAllocator<uint32_t, void> that happens to start at 0x...0C, we get the worst case scenario for padding to maintain alignment:

  Address   Type          Contents             Pointed at by:
+---------+-------------+--------------------+--------------------------+
| 0x...0C | Prefix      | user-defined       | frame                    |
|         | (uint32_t)  |                    | GetFrame(data)           |
|         |             |                    | GetPrefix(data)          |
+---------+-------------+--------------------+--------------------------+
| 0x...10 | size_t      | frame_offset =0x14 | GetFrameOffsetPtr(frame) |
+---------+-------------+--------------------+--------------------------+
| 0x...14 | N/A         | 8 bytes of padding | N/A                      |
+---------+-------------+--------------------+--------------------------+
| 0x...1C | size_t      | data_offset  =0x14 | GetDataOffsetPtr(data)   |
+---------+-------------+--------------------+--------------------------+
| 0x...20 | std::byte[] | usable space       | data                     |
|         |             |                    | GetData(frame)           |
+---------+-------------+--------------------+--------------------------+

Finally, requesting a 64-byte allocation with a 16-byte alignment from a suffix-only FramingAllocator<void, uint16_t> might result in an allocation that looks like:

  Address   Type          Contents             Pointed at by:
+---------+-------------+--------------------+--------------------------+
| 0x...00 | size_t      | frame_offset =0x10 | frame                    |
|         |             |                    | GetFrame(data)           |
|         |             |                    | GetFrameOffsetPtr(frame) |
+---------+-------------+--------------------+--------------------------+
| 0x...04 | N/A         | 4 bytes of padding | N/A                      |
+---------+-------------+--------------------+--------------------------+
| 0x...08 | size_t      | data_offset  =0x10 | GetDataOffsetPtr(data)   |
+---------+-------------+--------------------+--------------------------+
| 0x...0C | size_t      | suffix_offset=0x40 | GetSuffixOffsetPtr(data) |
+---------+-------------+--------------------+--------------------------+
| 0x...10 | std::byte[] | usable space       | data                     |
|         |             |                    | GetData(frame)           |
+---------+-------------+--------------------+--------------------------+
| 0x...50 | Suffix      | user-defined       | GetSuffix(data)          |
|         | (uint16_t)  |                    |                          |
+---------+-------------+--------------------+--------------------------+

Note: As illustrated above, the choice of prefix and suffix types and overall alignment can significantly affect the amount of overhead required. When possible, keep alignment requirements low. Ideally, Suffix and the allocated data both have an alignment of alignof(size_t) or less.

Template Parameters

Prefix	A default constructible and trivially copyable type to place before each allocation, or `void`. `alignof(Prefix)` must be at most `alignof(size_t)`.
Suffix	A default constructible and trivially copyable type to place after each allocation, or `void`.
ErrorHandler	Used to report frame validation errors.

Inheritance diagram for pw::allocator::FramingAllocator< Prefix, Suffix, ErrorHandler >:

Protected Types
using	Base = internal::BaseFramingAllocator< ErrorHandler >

Protected Types inherited from pw::Deallocator
enum class	InfoType { kRequestedLayoutOf , kUsableLayoutOf , kAllocatedLayoutOf , kCapacity , kRecognizes }

Protected Member Functions
constexpr	FramingAllocator (pw::Allocator &allocator)

void *	DoAllocate (Layout layout) override

void	DoDeallocate (void *ptr) override

bool	DoResize (void *ptr, size_t new_size) override

bool	DoBeforeReallocate (void *ptr, Layout new_layout) override

void	DoAfterReallocateCopy (void ptr, Layout new_layout, void new_ptr) override

Result< Layout >	DoGetInfo (Deallocator::InfoType info_type, const void *ptr) const override


void *	GetFrame (void *data) const

const void *	GetFrame (const void *data) const


Prefix *	GetPrefix (void *data) const

const Prefix *	GetPrefix (const void *data) const


void *	GetData (void *frame) const

const void *	GetData (const void *data) const


Suffix *	GetSuffix (void *data) const

const Suffix *	GetSuffix (const void *data) const

Protected Member Functions inherited from pw::allocator::internal::BaseFramingAllocator< ErrorHandler >
constexpr	BaseFramingAllocator (Allocator &allocator)

ByteSpan	AllocateFrame (Layout prefix, Layout data, Layout suffix)

bool	ResizeFrame (void data, size_t new_size, Layout suffix, void tmp_suffix)

Result< Layout >	GetFrameInfo (InfoType info_type, const void *data, Layout suffix) const

Result< size_t >	GetFrameSize (const void *frame) const

Protected Member Functions inherited from pw::allocator::ForwardingAllocator
constexpr	ForwardingAllocator (const Capabilities &capabilities) noexcept

constexpr	ForwardingAllocator (pw::Allocator &allocator) noexcept

constexpr void	Init (pw::Allocator &allocator)

constexpr pw::Allocator &	allocator ()

constexpr const pw::Allocator &	allocator () const

void *	DoAllocate (Layout layout) override

void	DoDeallocate (void *ptr) override

bool	DoResize (void *ptr, size_t new_size) override

bool	DoBeforeReallocate (void *ptr, Layout new_layout) override

void	DoAfterReallocateCopy (void ptr, Layout new_layout, void new_ptr) override

void	DoAfterReallocateDone (Layout new_layout, void *new_ptr) override

size_t	DoGetAllocated () const override

std::optional< Fragmentation >	DoMeasureFragmentation () const override
	Returns fragmentation information for the allocator's memory region.

Result< Layout >	DoGetInfo (InfoType info_type, const void *ptr) const override

Protected Member Functions inherited from pw::Allocator
constexpr	Allocator () noexcept=default
	TODO(b/326509341): Remove when downstream consumers migrate.

constexpr	Allocator (const Capabilities &capabilities) noexcept

virtual void *	DoAllocate (Layout layout)=0

virtual bool	DoResize (void *ptr, size_t new_size)

virtual void *	DoReallocate (void *ptr, Layout new_layout)

virtual bool	DoBeforeReallocate (void *ptr, Layout new_layout)

virtual void	DoAfterReallocateCopy (void ptr, Layout new_layout, void new_ptr)

virtual void	DoAfterReallocateDone (Layout new_layout, void *new_ptr)

virtual size_t	DoGetAllocated () const

virtual std::optional< Fragmentation >	DoMeasureFragmentation () const
	Returns fragmentation information for the allocator's memory region.

Protected Member Functions inherited from pw::Deallocator
constexpr	Deallocator ()=default
	TODO(b/326509341): Remove when downstream consumers migrate.

constexpr	Deallocator (const Capabilities &capabilities)

Result< Layout >	GetInfo (InfoType info_type, const void *ptr) const

Result< Layout >	GetRequestedLayout (const void *ptr) const

Result< Layout >	GetUsableLayout (const void *ptr) const

Result< Layout >	GetAllocatedLayout (const void *ptr) const

bool	Recognizes (const void *ptr) const

virtual void	DoDeallocate (void *ptr)=0

virtual Result< Layout >	DoGetInfo (InfoType, const void *) const

Additional Inherited Members
Public Types inherited from pw::Allocator
using	Fragmentation = allocator::Fragmentation

Public Types inherited from pw::Deallocator
using	Capabilities = allocator::Capabilities

using	Capability = allocator::Capability

using	Layout = allocator::Layout

Public Member Functions inherited from pw::Allocator
void *	Allocate (Layout layout)

template<typename T , int &... kExplicitGuard, std::enable_if_t<!std::is_array_v< T >, int > = 0, typename... Args>
T *	New (Args &&... args)

template<typename T , int &... kExplicitGuard, typename ElementType = std::remove_extent_t<T>, std::enable_if_t< is_bounded_array_v< T >, int > = 0>
ElementType *	New ()

template<typename T , int &... kExplicitGuard, typename ElementType = std::remove_extent_t<T>, std::enable_if_t< is_unbounded_array_v< T >, int > = 0>
ElementType *	New (size_t count)

template<typename T , int &... kExplicitGuard, typename ElementType = std::remove_extent_t<T>, std::enable_if_t< is_unbounded_array_v< T >, int > = 0>
ElementType *	New (size_t count, size_t alignment)
	Constructs an `alignment`-byte aligned array of `count` objects.

template<typename T , int &... kExplicitGuard, std::enable_if_t<!std::is_array_v< T >, int > = 0, typename... Args>
UniquePtr< T >	MakeUnique (Args &&... args)

template<typename T , std::enable_if_t< is_unbounded_array_v< T >, int > = 0>
UniquePtr< T >	MakeUnique (size_t size)

template<typename T , std::enable_if_t< is_unbounded_array_v< T >, int > = 0>
UniquePtr< T >	MakeUnique (size_t size, size_t alignment)

template<typename T , std::enable_if_t< is_bounded_array_v< T >, int > = 0>
UniquePtr< T >	MakeUnique ()

template<typename T , int &... kExplicitGuard, std::enable_if_t<!std::is_array_v< T >, int > = 0, typename... Args>
SharedPtr< T >	MakeShared (Args &&... args)

template<typename T , std::enable_if_t< is_unbounded_array_v< T >, int > = 0>
SharedPtr< T >	MakeShared (size_t size)

template<typename T , std::enable_if_t< is_unbounded_array_v< T >, int > = 0>
SharedPtr< T >	MakeShared (size_t size, size_t alignment)

template<typename T , std::enable_if_t< is_bounded_array_v< T >, int > = 0>
SharedPtr< T >	MakeShared ()

bool	Resize (void *ptr, size_t new_size)

void *	Reallocate (void *ptr, Layout new_layout)

size_t	GetAllocated () const

std::optional< Fragmentation >	MeasureFragmentation () const
	Returns fragmentation information for the allocator's memory region.

Public Member Functions inherited from pw::Deallocator
constexpr const Capabilities &	capabilities () const

constexpr bool	HasCapability (Capability capability) const
	Returns whether a given capability is enabled for this object.

void	Deallocate (void *ptr)

template<typename ElementType >
void	DeleteArray (ElementType *ptr, size_t count)

template<typename ElementType >
void	Destroy (ElementType *ptr, size_t count)

StatusWithSize	GetCapacity () const

bool	IsEqual (const Deallocator &other) const

template<typename T , int &... kExplicitGuard, std::enable_if_t<!std::is_array_v< T >, int > = 0>
void	Delete (T *ptr)

template<typename T , int &... kExplicitGuard, typename ElementType = std::remove_extent_t<T>, std::enable_if_t< is_bounded_array_v< T >, int > = 0>
void	Delete (ElementType *ptr)

template<typename T , int &... kExplicitGuard, typename ElementType = std::remove_extent_t<T>, std::enable_if_t< is_unbounded_array_v< T >, int > = 0>
void	Delete (ElementType *ptr, size_t count)

Static Protected Member Functions inherited from pw::allocator::internal::BaseFramingAllocator< ErrorHandler >
static constexpr size_t	Distance (const void start, const void end)
	Returns the distance between two pointers in bytes.

static void	UpdateOffsets (void frame, void data, void *suffix)

static void *	GetFrame (void *data, bool has_suffix, bool checked=true)

static const void *	GetFrame (const void *data, bool has_suffix, bool checked=true)

static void *	GetData (void *frame, Result< size_t > frame_size, Layout prefix)

static const void *	GetData (const void *frame, Result< size_t > frame_size, Layout prefix)

static void *	GetSuffix (void *data, size_t data_size, Layout suffix)

static const void *	GetSuffix (const void *data, size_t data_size, Layout suffix)

Static Protected Member Functions inherited from pw::Allocator
static bool	BeforeReallocate (Allocator &allocator, void *ptr, Layout new_layout)

static void	AfterReallocateCopy (Allocator &allocator, void ptr, Layout new_layout, void new_ptr)

static void	AfterReallocateDone (Allocator &allocator, Layout new_layout, void *new_ptr)

Static Protected Member Functions inherited from pw::Deallocator
static Result< Layout >	GetInfo (const Deallocator &deallocator, InfoType info_type, const void *ptr)

static Result< Layout >	GetRequestedLayout (const Deallocator &deallocator, const void *ptr)

static Result< Layout >	GetUsableLayout (const Deallocator &deallocator, const void *ptr)

static Result< Layout >	GetAllocatedLayout (const Deallocator &deallocator, const void *ptr)

static bool	Recognizes (const Deallocator &deallocator, const void *ptr)

Static Protected Attributes inherited from pw::Deallocator
template<typename T >
static constexpr bool	is_bounded_array_v = ::pw::is_bounded_array_v<T>

template<typename T >
static constexpr bool	is_unbounded_array_v = ::pw::is_unbounded_array_v<T>

Member Function Documentation

◆ DoAfterReallocateCopy()

template<typename Prefix , typename Suffix , typename ErrorHandler >

void pw::allocator::FramingAllocator< Prefix, Suffix, ErrorHandler >::DoAfterReallocateCopy	(	void *	ptr,
		Layout	new_layout,
		void *	new_ptr
	)

overrideprotectedvirtual

Called as part of the default implementation of DoReallocate once the data from ptr has been resized or copied to new_ptr.

By default, does nothing. Derived types may implement this method to add additional behavior. If they do, they must call DoAfterReallocateCopy on their base type before performing any other action.

ptr and new_ptr are guaranteed to be non-null, and new_layout.size() is guaranteed to be non-zero.

Reimplemented from pw::allocator::ForwardingAllocator.

Reimplemented in pw::allocator::internal::BasicGuardedAllocator< internal::DefaultGuardErrorHandler >.

◆ DoAllocate()

template<typename Prefix , typename Suffix , typename ErrorHandler >

void * pw::allocator::FramingAllocator< Prefix, Suffix, ErrorHandler >::DoAllocate ( Layout layout )

overrideprotectedvirtual

Allocates a block of memory with the specified size and alignment.

Returns nullptr if the allocation cannot be made, or the layout has a size of 0.

Parameters

[in] layout Describes the memory to be allocated.

Reimplemented from pw::allocator::ForwardingAllocator.

Reimplemented in pw::allocator::internal::BasicGuardedAllocator< internal::DefaultGuardErrorHandler >.

◆ DoBeforeReallocate()

template<typename Prefix , typename Suffix , typename ErrorHandler >

bool pw::allocator::FramingAllocator< Prefix, Suffix, ErrorHandler >::DoBeforeReallocate	(	void *	ptr,
		Layout	new_layout
	)

overrideprotectedvirtual

Called at the start of the default implementation of DoReallocate.

By default, returns true. Derived types may implement this method to add additional behavior. If they do, they must return false or the value returned by DoBeforeReallocate. If false is returned, the reallocation fails and returns null.

ptr is guaranteed to be non-null, and new_layout.size() is guaranteed to be non-zero.

Reimplemented from pw::allocator::ForwardingAllocator.

Reimplemented in pw::allocator::internal::BasicGuardedAllocator< internal::DefaultGuardErrorHandler >.

◆ DoDeallocate()

template<typename Prefix , typename Suffix , typename ErrorHandler >

void pw::allocator::FramingAllocator< Prefix, Suffix, ErrorHandler >::DoDeallocate ( void * ptr )

overrideprotectedvirtual

Releases a previously-allocated block of memory.

The given pointer must have been previously provided by this memory resource; otherwise the behavior is undefined.

Parameters

[in] ptr Pointer to previously-allocated memory.

Reimplemented from pw::allocator::ForwardingAllocator.

Reimplemented in pw::allocator::internal::BasicGuardedAllocator< internal::DefaultGuardErrorHandler >.

◆ DoGetInfo()

template<typename Prefix , typename Suffix = void, typename ErrorHandler = internal::DefaultFrameErrorHandler>

Result< Layout > pw::allocator::FramingAllocator< Prefix, Suffix, ErrorHandler >::DoGetInfo	(	Deallocator::InfoType	info_type,
		const void *	ptr
	)		const

inlineoverrideprotectedvirtual

Returns deallocator-specific information about allocations.

Deallocators may support any number of InfoTypes. See that type for what each supported type returns. For unsupported types, this method returns UNIMPLEMENTED.

Reimplemented from pw::allocator::ForwardingAllocator.

◆ DoResize()

template<typename Prefix , typename Suffix , typename ErrorHandler >

bool pw::allocator::FramingAllocator< Prefix, Suffix, ErrorHandler >::DoResize	(	void *	ptr,
		size_t	new_size
	)

overrideprotectedvirtual

Modifies the size of an previously-allocated block of memory without copying any data.

Returns true if its size was changed without copying data to a new allocation; otherwise returns false.

In particular, it always returns true if the old_layout.size() equals new_size, and always returns false if the given pointer is null, the old_layout.size() is 0, or the new_size is 0.

Parameters

[in]	ptr	Pointer to previously-allocated memory.
[in]	new_size	Requested new size for the memory allocation.

Reimplemented from pw::allocator::ForwardingAllocator.

Reimplemented in pw::allocator::internal::BasicGuardedAllocator< internal::DefaultGuardErrorHandler >.

◆ GetData()

template<typename Prefix , typename Suffix , typename ErrorHandler >

void * pw::allocator::FramingAllocator< Prefix, Suffix, ErrorHandler >::GetData ( void * frame ) const

protected

Returns a data pointer from a frame pointer.

◆ GetFrame()

template<typename Prefix , typename Suffix , typename ErrorHandler >

void * pw::allocator::FramingAllocator< Prefix, Suffix, ErrorHandler >::GetFrame ( void * data ) const

protected

Returns the frame pointer from a data pointer, that is, return a pointer to memory holding the prefix, usable memory, and suffix from a pointer to the usable memory.

◆ GetPrefix()

template<typename Prefix , typename Suffix , typename ErrorHandler >

auto pw::allocator::FramingAllocator< Prefix, Suffix, ErrorHandler >::GetPrefix ( void * data ) const

protected

Returns a pointer to prefix.

It is an error to call this method if the prefix type is void.

◆ GetSuffix()

template<typename Prefix , typename Suffix , typename ErrorHandler >

auto pw::allocator::FramingAllocator< Prefix, Suffix, ErrorHandler >::GetSuffix ( void * data ) const

protected

Returns a pointer to the suffix.

It is an error to call this method if the suffix type is void.

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

pw_allocator/public/pw_allocator/framing_allocator.h

Overview

Protected Types

Protected Member Functions

Additional Inherited Members

Member Function Documentation

◆ DoAfterReallocateCopy()

◆ DoAllocate()

◆ DoBeforeReallocate()

◆ DoDeallocate()

◆ DoGetInfo()

◆ DoResize()

◆ GetData()

◆ GetFrame()

◆ GetPrefix()

◆ GetSuffix()