TDiscardableKeyValueCache | Unreal Engine 5.7 Documentation

Implements a thread-safe discardable Key/Value cache by using two maps - a primary and a backfill.

Find() checks the current map first then the backfill. Entries found in the backfill are moved into the primary map.

When Swap is called all items in the backfill are removed and the currentmap & backfill are swapped.

This results in most recently used items being retained and older/unused items being evicted. The more often Swap is called the shorter the lifespan for items


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

Syntax

template<class KeyType, class ValueType>  
class TDiscardableKeyValueCache

Constructors

Name	Remarks	Include Path	Unreal Specifiers
TDiscardableKeyValueCache()		Containers/DiscardableKeyValueCache.h

Structs

Name	Remarks
LockFlags	Flags used when calling Find()

Typedefs

Name	Type	Remarks	Include Path
TypedMap	TMap< KeyType, ValueType >		Containers/DiscardableKeyValueCache.h

Functions

Public

Name	Remarks	Include Path
bool Add ( const KeyType& Key, const ValueType& Value )	Add an entry to the current map.	Containers/DiscardableKeyValueCache.h
bool Add ( const KeyType& Key, const ValueType& Value, const uint32 LockFlags )	Add an entry to the current map.	Containers/DiscardableKeyValueCache.h
uint32 ApplyLock ( uint32 CurrentFlags, uint32 NewFlags )		Containers/DiscardableKeyValueCache.h
TypedMap & Backfill()	Reference to the current map	Containers/DiscardableKeyValueCache.h
TypedMap & Current()	Reference to the current map	Containers/DiscardableKeyValueCache.h
int32 Discard ()	Discard all items left in the backfill and swap the current & backfill pointers	Containers/DiscardableKeyValueCache.h
int32 Discard ( DeleteFunc Func )		Containers/DiscardableKeyValueCache.h
int32 Discard ( uint32 InCurrentLockFlags, uint32& OutNewLockFlags, DeleteFunc Func )	Discard all items in the backfill and swap the current & backfill pointers	Containers/DiscardableKeyValueCache.h
bool Find ( const KeyType& Key, ValueType& OutType )	Returns true and sets OutType to the value with the associated key if it exists.	Containers/DiscardableKeyValueCache.h
bool Find ( const KeyType& Key, ValueType& OutType, uint32 InCurrentLockFlags, uint32& OutLockFlags )	Externally-lock-aware Find function.	Containers/DiscardableKeyValueCache.h
int32 Num()	Returns the total number of items in the cache	Containers/DiscardableKeyValueCache.h
FRWLock & RWLock()	Access to the internal locking object	Containers/DiscardableKeyValueCache.h
void Unlock ( uint32 Flags )		Containers/DiscardableKeyValueCache.h

Protected

Name	Remarks	Include Path	Unreal Specifiers
bool InternalFindWhileLocked ( const KeyType& Key, ValueType& OutType, uint32 InCurrentLockFlags, uint32& OutFlags )	Checks for the entry in our current map, and if not found the backfill.	Containers/DiscardableKeyValueCache.h

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