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  3. TRingBuffer

TRingBuffer

RingBuffer - an array with a Front and Back pointer and with implicit wraparound to the beginning of the array when reaching the end of the array when iterating from Front to Back Useful for providing O(1) push/pop at the end of the array (for Queue or Stack) while still having high cache coherency during iteration.

API > API/Runtime > API/Runtime/Core

RingBuffer - an array with a Front and Back pointer and with implicit wraparound to the beginning of the array when reaching the end of the array when iterating from Front to Back Useful for providing O(1) push/pop at the end of the array (for Queue or Stack) while still having high cache coherency during iteration. Not thread-safe; caller must ensure there is no simultaneous access from multiple threads.

Implementation Details: Relies on unsigned arithmetics and ever-increasing Front and Back indices to avoid having to store an extra element or maintain explicit empty state. Capacity will always be rounded up to the next power of two, to provide rapid masking of the index.

   
Name TRingBuffer
Type class
Header File /Engine/Source/Runtime/Core/Public/Containers/RingBuffer.h
Include Path #include "Containers/RingBuffer.h"

Syntax

template<typename T, typename AllocatorT>  
class TRingBuffer

Constructors

Name Remarks Include Path Unreal Specifiers

TRingBuffer ( TRingBuffer&& Other
)

   Containers/RingBuffer.h  
Construct Empty Queue with capacity 0. Containers/RingBuffer.h  

TRingBuffer ( SizeType InitialCapacity
)

 Construct Empty Queue with the given initial requested capacity. Containers/RingBuffer.h  

TRingBuffer ( std::initializer_list< ElementType > InitList
)

 Construct a Queue with initial state (from front to back) equal to the given list. Containers/RingBuffer.h  

TRingBuffer ( const TRingBuffer& Other
)

   Containers/RingBuffer.h  

Destructors

Name Remarks Include Path Unreal Specifiers

~TRingBuffer()

   Containers/RingBuffer.h  

Typedefs

Name Type Remarks Include Path
Allocator AllocatorT The Allocator type being used Containers/RingBuffer.h
ElementAllocatorType std::conditional_t< Allocator::NeedsElementType, typename Allocator::template ForElementType< ElementType >, typename Allocator::ForAnyElementType >   Containers/RingBuffer.h
ElementType T Type of the Elements in the container. Containers/RingBuffer.h
IndexType std::make_signed_t< typename Allocator::SizeType > Type used to request values at a given index in the container. Containers/RingBuffer.h
SizeType std::make_unsigned_t< typename Allocator::SizeType > Type used to communicate size and capacity and counts Containers/RingBuffer.h
StorageModuloType std::make_unsigned_t< typename Allocator::SizeType > Type used for variables that are indexes into the underlying storage. Containers/RingBuffer.h
TConstIterator TRingBufferIterator< const TRingBuffer, const ElementType, typename Allocator::SizeType >   Containers/RingBuffer.h
TIterator TRingBufferIterator< TRingBuffer, ElementType, typename Allocator::SizeType > Iterator type used for ranged-for traversal. Containers/RingBuffer.h

Variables

Protected

Name Type Remarks Include Path Unreal Specifiers
AfterBack StorageModuloType Pointer to the first location after the back pointer of the RingBuffer; when the RingBuffer is non-empty, one element before this index is the back of the RingBuffer AfterBack is in StorageModulo space. Containers/RingBuffer.h  
AllocatorInstance ElementAllocatorType The underlying storage of the RingBuffer is in the c-style array provided by this AllocatorInstance.GetAllocation(). Containers/RingBuffer.h  
Front StorageModuloType Front pointer of the RingBuffer; it points to the first element in the iteration of the RingBuffer, unless the RingBuffer is empty, in which case it can point to any value in the underlying storage. Containers/RingBuffer.h  
IndexMask StorageModuloType A bitmask used to convert from StorageModulo space into an index into Storage. Containers/RingBuffer.h  

Functions

Public

Name Remarks Include Path Unreal Specifiers

IndexType Add ( const ElementType& Element
)

 Add a new element after the back pointer of the RingBuffer, resizing if necessary. Containers/RingBuffer.h  

IndexType Add ( ElementType&& Element
)

 Add a new element after the back pointer of the RingBuffer, resizing if necessary. Containers/RingBuffer.h  

ElementType & Add_GetRef ( const ElementType& Element
)

 Add a new element after the back pointer of the RingBuffer, resizing if necessary. Containers/RingBuffer.h  

ElementType & Add_GetRef ( ElementType&& Element
)

 Add a new element after the back pointer of the RingBuffer, resizing if necessary. Containers/RingBuffer.h  

IndexType AddFront ( const ElementType& Element
)

 Add a new element before the front pointer of the RingBuffer, resizing if necessary. Containers/RingBuffer.h  

IndexType AddFront ( ElementType&& Element
)

 Add a new element before the front pointer of the RingBuffer, resizing if necessary. Containers/RingBuffer.h  

ElementType & AddFront_GetRef ( ElementType&& Element
)

 Add a new element before the front pointer of the RingBuffer, resizing if necessary. Containers/RingBuffer.h  

ElementType & AddFront_GetRef ( const ElementType& Element
)

 Add a new element before the front pointer of the RingBuffer, resizing if necessary. Containers/RingBuffer.h  

IndexType AddFrontUninitialized ()

 Add a new element before the front pointer of the RingBuffer, resizing if necessary. Containers/RingBuffer.h  

ElementType & AddFrontUninitialized_GetRef ()

 Add a new element before the front pointer of the RingBuffer, resizing if necessary. Containers/RingBuffer.h  

IndexType AddUninitialized ()

 Add a new element after the back pointer of the RingBuffer, resizing if necessary. Containers/RingBuffer.h  

ElementType & AddUninitialized_GetRef ()

 Add a new element after the back pointer of the RingBuffer, resizing if necessary. Containers/RingBuffer.h  

TConstIterator begin ()

 Begin iterator for const ranged-for Containers/RingBuffer.h  

TIterator begin ()

 Begin iterator for ranged-for Containers/RingBuffer.h  
Shift all elements so that the front pointer's location in memory is less than the back pointer's. Containers/RingBuffer.h  

IndexType ConvertPointerToIndex ( const ElementType* Ptr
) const

 Given a pointer to an Element anywhere in memory, return the index of the element in the RingBuffer, or INDEX_NONE if it is not present. Containers/RingBuffer.h  

IndexType Emplace ( ArgsType&&... Args
)

 Add a new element after the back pointer of the RingBuffer, resizing if necessary. Containers/RingBuffer.h  

ElementType & Emplace_GetRef ( ArgsType&&... Args
)

 Add a new element after the back pointer of the RingBuffer, resizing if necessary. Containers/RingBuffer.h  

IndexType EmplaceFront ( ArgsType&&... Args
)

 Add a new element before the front pointer of the RingBuffer, resizing if necessary. Containers/RingBuffer.h  

ElementType & EmplaceFront_GetRef ( ArgsType&&... Args
)

 Add a new element before the front pointer of the RingBuffer, resizing if necessary. Containers/RingBuffer.h  

void Empty ( SizeType Capacity
)

 Empty the RingBuffer, destructing any elements and releasing the RingBuffer's storage. Containers/RingBuffer.h  

TConstIterator end ()

 End iterator for const ranged-for Containers/RingBuffer.h  

TIterator end ()

 End iterator for ranged-for Containers/RingBuffer.h  

ElementType & First ()

 Return a reference to the element at the front pointer of the RingBuffer. Containers/RingBuffer.h  

const ElementType & First ()

 Return a const reference to the element at the front pointer of the RingBuffer. Containers/RingBuffer.h  

SIZE_T GetAllocatedSize ()

 Helper function to return the amount of memory allocated by this container. Containers/RingBuffer.h  

const ElementType & GetAtIndexNoCheck ( IndexType Index
) const

 Unsafely return a const reference to the value at the given Index. Containers/RingBuffer.h  

ElementType & GetAtIndexNoCheck ( IndexType Index
)

 Unsafely return a writable reference to the value at the given Index. Containers/RingBuffer.h  

bool IsEmpty()

 Returns true if the RingBuffer is empty. Containers/RingBuffer.h  

bool IsValidIndex ( IndexType Index
) const

 Tests if index is valid, i.e. greater than or equal to zero, and less than the number of elements in the array. Containers/RingBuffer.h  

ElementType & Last ()

 Return a reference to the element at the back pointer of the RingBuffer. Containers/RingBuffer.h  

const ElementType & Last ()

 Return a const reference to the element at the back pointer of the RingBuffer. Containers/RingBuffer.h  

IndexType Max()

 Current allocated Capacity, note this will always be a power of two, or the special case 0. Containers/RingBuffer.h  

void MoveAppendRange ( ElementType* OtherData,
SizeType OtherNum
)

 Append elements from a range onto the back pointer of the RingBuffer, resizing if necessary. Containers/RingBuffer.h  

IndexType Num()

 Gets the number of elements in the RingBuffer. Containers/RingBuffer.h  

void Pop ( SizeType PopCount
)

 Pop the given number of arguments (default: 1) from the back pointer of the RingBuffer. Containers/RingBuffer.h  

void PopFront ( SizeType PopCount
)

 Pop the given number of elements (default: 1) from the front pointer of the RingBuffer. Containers/RingBuffer.h  

void PopFrontNoCheck ( SizeType PopCount
)

 Unsafely pop the given number of arguments (default: 1) from the front pointer of the RingBuffer. Containers/RingBuffer.h  

ElementType PopFrontValue ()

 Pop one element from the front pointer of the RingBuffer and return the popped value. Containers/RingBuffer.h  

void PopNoCheck ( SizeType PopCount
)

 Pop the given number of elements (default: 1) from the back pointer of the RingBuffer. Containers/RingBuffer.h  

ElementType PopValue ()

 Pop one element from the back pointer of the RingBuffer and return the popped value. Containers/RingBuffer.h  

SizeType Remove ( const ElementType& Item
)

 Removes as many instances of Item as there are in the array, maintaining order but not indices. Containers/RingBuffer.h  

SizeType RemoveAll ( PredicateType Predicate
)

 Removes all items for which a given predicate applies, maintaining order but not indices. Containers/RingBuffer.h  

void RemoveAt ( IndexType Index
)

 Remove the value at the given index from the RingBuffer, and shift values ahead or behind it into its location to fill the hole. Containers/RingBuffer.h  

void Reserve ( SizeType RequiredCapacity
)

 Set the capacity to the maximum of the current capacity and the (next power of two greater than or equal to) the given capacity. Containers/RingBuffer.h  

void Reset()

 Empty the RingBuffer, destructing any elements in the RingBuffer but not releasing the RingBuffer's storage. Containers/RingBuffer.h  

void ShiftIndexToBack ( IndexType Index
)

 Move the value at the given index into the back pointer of the RingBuffer, and shift all elements behind of it up by one to make room for it. Containers/RingBuffer.h  

void ShiftIndexToFront ( IndexType Index
)

 Move the value at the given index into the front pointer of the RingBuffer, and shift all elements ahead of it down by one to make room for it. Containers/RingBuffer.h  

void Trim()

 Set the capacity to the minimum power of two (or 0) greater than or equal to the current number of elements in the RingBuffer. Containers/RingBuffer.h  

Static

Name Remarks Include Path Unreal Specifiers

static bool NeedsDestructElements()

   Containers/RingBuffer.h  

Operators

Name Remarks Include Path Unreal Specifiers

bool operator!= ( const TRingBuffer< ElementType, OtherAllocator >& Other
) const

   Containers/RingBuffer.h  

ElementType & operator[] ( IndexType Index
)

 Return a writable reference to the value at the given Index. Containers/RingBuffer.h  

const ElementType & operator[] ( IndexType Index
) const

 Return a const reference to the value at the given Index. Containers/RingBuffer.h  
  Containers/RingBuffer.h  

TRingBuffer & operator= ( const TRingBuffer& Other
)

   Containers/RingBuffer.h  

bool operator== ( const TRingBuffer< ElementType, OtherAllocator >& Other
) const

   Containers/RingBuffer.h  

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