TCircularQueue< T > Class Template Reference

#include <CircularQueue.h>

Public Types
using	FElementType = T

Public Member Functions
	TCircularQueue (uint32 CapacityPlusOne)
uint32	Count () const
bool	Dequeue (FElementType &OutElement)
bool	Dequeue ()
void	Empty ()
bool	Enqueue (const FElementType &Element)
bool	Enqueue (FElementType &&Element)
UE_FORCEINLINE_HINT bool	IsEmpty () const
bool	IsFull () const
bool	Peek (FElementType &OutItem) const
const FElementType *	Peek () const

Detailed Description

template<typename T>
class TCircularQueue< T >

Implements a lock-free first-in first-out queue using a circular array.

This class is thread safe only in single-producer single-consumer scenarios.

The number of items that can be enqueued is one less than the queue's capacity, because one item will be used for detecting full and empty states.

There is some room for optimization via using fine grained memory fences, but the implications for all of our target platforms need further analysis, so we're using the simpler sequentially consistent model for now.

Parameters

T	The type of elements held in the queue.

Member Typedef Documentation

FElementType

template<typename T >

using TCircularQueue< T >::FElementType = T

Constructor & Destructor Documentation

TCircularQueue()

template<typename T >

TCircularQueue< T >::TCircularQueue ( uint32  CapacityPlusOne )

inlineexplicit

Constructor.

Parameters

CapacityPlusOne

The number of elements that the queue can hold (will be rounded up to the next power of 2).

Member Function Documentation

Count()

template<typename T >

uint32 TCircularQueue< T >::Count ( ) const

inline

Gets the number of elements in the queue.

Can be called from any thread. The result reflects the calling thread's current view. Since no locking is used, different threads may return different results.

Returns

Number of queued elements.

Dequeue() [1/2]

template<typename T >

bool TCircularQueue< T >::Dequeue ( )

inline

Removes an item from the front of the queue.

Returns

true if an element has been removed, false if the queue was empty.

Note

To be called only from consumer thread.

Dequeue() [2/2]

template<typename T >

bool TCircularQueue< T >::Dequeue ( FElementType &  OutElement )

inline

Removes an item from the front of the queue.

Parameters

OutElement

Will contain the element if the queue is not empty.

Returns

true if an element has been returned, false if the queue was empty.

Note

To be called only from consumer thread.

Empty()

template<typename T >

void TCircularQueue< T >::Empty ( )

inline

Empties the queue.

Note

To be called only from consumer thread.

See also

IsEmpty

Enqueue() [1/2]

template<typename T >

bool TCircularQueue< T >::Enqueue ( const FElementType &  Element )

inline

Adds an item to the end of the queue.

Parameters

Element

The element to add.

Returns

true if the item was added, false if the queue was full.

Note

To be called only from producer thread.

Enqueue() [2/2]

template<typename T >

bool TCircularQueue< T >::Enqueue ( FElementType &&  Element )

inline

Adds an item to the end of the queue.

Parameters

Element

The element to add.

Returns

true if the item was added, false if the queue was full.

Note

To be called only from producer thread.

IsEmpty()

template<typename T >

UE_FORCEINLINE_HINT bool TCircularQueue< T >::IsEmpty ( ) const

inline

Checks whether the queue is empty.

Can be called from any thread. The result reflects the calling thread's current view. Since no locking is used, different threads may return different results.

Returns

true if the queue is empty, false otherwise.

See also

Empty, IsFull

IsFull()

template<typename T >

bool TCircularQueue< T >::IsFull ( ) const

inline

Checks whether the queue is full.

Can be called from any thread. The result reflects the calling thread's current view. Since no locking is used, different threads may return different results.

Returns

true if the queue is full, false otherwise.

See also

IsEmpty

Peek() [1/2]

template<typename T >

const FElementType * TCircularQueue< T >::Peek ( ) const

inline

Returns the oldest item in the queue without removing it.

Returns

an FElementType pointer if an item has been returned, nullptr if the queue was empty.

Note

To be called only from consumer thread.

The return value is only valid until Dequeue, Empty, or the destructor has been called.

Peek() [2/2]

template<typename T >

bool TCircularQueue< T >::Peek ( FElementType &  OutItem ) const

inline

Returns the oldest item in the queue without removing it.

Parameters

OutItem

Will contain the item if the queue is not empty.

Returns

true if an item has been returned, false if the queue was empty.

Note

To be called only from consumer thread.

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

• Engine/Source/Runtime/Core/Public/Containers/CircularQueue.h