TQueue< T, Mode > Class Template Reference

#include <Queue.h>

Public Types
using	FElementType = T

Public Member Functions
	TQueue ()
	~TQueue ()
	UE_NONCOPYABLE (TQueue)
bool	Dequeue (FElementType &OutItem)
void	Empty ()
bool	Enqueue (const FElementType &Item)
bool	Enqueue (FElementType &&Item)
bool	IsEmpty () const
bool	Peek (FElementType &OutItem) const
FElementType *	Peek ()
UE_FORCEINLINE_HINT const FElementType *	Peek () const
bool	Pop ()

Detailed Description

template<typename T, EQueueMode Mode = EQueueMode::Spsc>
class TQueue< T, Mode >

Template for queues.

This template implements an unbounded non-intrusive queue using a lock-free linked list that stores copies of the queued items. The template can operate in three modes: Multiple-producers single-consumer (MPSC), Single-producer single-consumer (SPSC), and Single-threaded.

The queue is thread-safe in both MPSC and SPSC modes. The Dequeue() method ensures thread-safety by writing it in a way that does not depend on possible instruction reordering on the CPU. The Enqueue() method uses an atomic compare-and-swap in multiple-producers scenarios.

The queue is not thread-safe in single-threaded mode, as the name suggests.

Parameters

T	The type of items stored in the queue.
Mode	The queue mode (single-producer, single-consumer by default).

Member Typedef Documentation

FElementType

template<typename T , EQueueMode Mode = EQueueMode::Spsc>

using TQueue< T, Mode >::FElementType = T

Constructor & Destructor Documentation

TQueue()

template<typename T , EQueueMode Mode = EQueueMode::Spsc>

TQueue< T, Mode >::TQueue ( )

inline

Default constructor.

~TQueue()

template<typename T , EQueueMode Mode = EQueueMode::Spsc>

TQueue< T, Mode >::~TQueue ( )

inline

Destructor.

Member Function Documentation

Dequeue()

template<typename T , EQueueMode Mode = EQueueMode::Spsc>

bool TQueue< T, Mode >::Dequeue ( FElementType &  OutItem )

inline

Removes and returns the item from the tail of the queue.

Parameters

OutValue

Will hold the returned value.

Returns

true if a value was returned, false if the queue was empty.

Note

To be called only from consumer thread.

See also

Empty, Enqueue, IsEmpty, Peek, Pop

Empty()

template<typename T , EQueueMode Mode = EQueueMode::Spsc>

void TQueue< T, Mode >::Empty ( )

inline

Empty the queue, discarding all items.

Note

To be called only from consumer thread.

See also

Dequeue, IsEmpty, Peek, Pop

Enqueue() [1/2]

template<typename T , EQueueMode Mode = EQueueMode::Spsc>

bool TQueue< T, Mode >::Enqueue ( const FElementType &  Item )

inline

Adds an item to the head of the queue.

Parameters

Item	The item to add.

Returns

true if the item was added, false otherwise.

Note

To be called only from producer thread(s).

See also

Dequeue, Pop

Enqueue() [2/2]

template<typename T , EQueueMode Mode = EQueueMode::Spsc>

bool TQueue< T, Mode >::Enqueue ( FElementType &&  Item )

inline

Adds an item to the head of the queue.

Parameters

Item	The item to add.

Returns

true if the item was added, false otherwise.

Note

To be called only from producer thread(s).

See also

Dequeue, Pop

IsEmpty()

template<typename T , EQueueMode Mode = EQueueMode::Spsc>

bool TQueue< T, Mode >::IsEmpty ( ) const

inline

Checks whether the queue is empty.

Returns

true if the queue is empty, false otherwise.

Note

To be called only from consumer thread.

See also

Dequeue, Empty, Peek, Pop

Peek() [1/3]

template<typename T , EQueueMode Mode = EQueueMode::Spsc>

FElementType * TQueue< T, Mode >::Peek ( )

inline

Peek at the queue's tail item without removing it.

This version of Peek allows peeking at a queue of items that do not allow copying, such as TUniquePtr.

Returns

Pointer to the item, or nullptr if queue is empty

Peek() [2/3]

template<typename T , EQueueMode Mode = EQueueMode::Spsc>

UE_FORCEINLINE_HINT const FElementType * TQueue< T, Mode >::Peek ( ) const

inline

Peek() [3/3]

template<typename T , EQueueMode Mode = EQueueMode::Spsc>

bool TQueue< T, Mode >::Peek ( FElementType &  OutItem ) const

inline

Peeks at the queue's tail item without removing it.

Parameters

OutItem

Will hold the peeked at item.

Returns

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

Note

To be called only from consumer thread.

See also

Dequeue, Empty, IsEmpty, Pop

Pop()

template<typename T , EQueueMode Mode = EQueueMode::Spsc>

bool TQueue< T, Mode >::Pop ( )

inline

Removes the item from the tail of the queue.

Returns

true if a value was removed, false if the queue was empty.

Note

To be called only from consumer thread.

See also

Dequeue, Empty, Enqueue, IsEmpty, Peek

UE_NONCOPYABLE()

template<typename T , EQueueMode Mode = EQueueMode::Spsc>

TQueue< T, Mode >::UE_NONCOPYABLE

(

TQueue< T, Mode >

)

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

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