• 2021.4
  • 09/27/2021
  • Public Content
Contents

concurrent_lru_cache

To enable this feature, define the
TBB_PREVIEW_CONCURRENT_LRU_CACHE
macro to 1.
A Class Template for Least Recently Used cache with concurrent operations.

Description

A
concurrent_lru_cache
container maps keys to values with the ability to limit the number of stored unused values. For each key, there is at most one item stored in the container.
The container permits multiple threads to concurrently retrieve items from it.
The container tracks which items are in use by returning a proxy
concurrent_lru_cache::handle
object that refers to an item instead of its value. Once there are no
handle
objects holding reference to an item, it is considered unused.
The container stores all the items that are currently in use plus a limited number of unused items. Excessive unused items are erased according to least recently used policy.
When no item is found for a given key, the container calls the user-specified
value_function_type
object to construct a value for the key, and stores that value. The
value_function_type
object must be thread-safe.

API

Header
#include "oneapi/tbb/concurrent_lru_cache.h"
Synopsis
namespace oneapi { namespace tbb { template <typename Key, typename Value, typename ValueFunctionType = Value (*)(Key)> class concurrent_lru_cache { public: using key_type = Key; using value_type = Value; using pointer = value_type*; using const_pointer = const value_type*; using reference = value_type&; using const_reference = const value_type&; using value_function_type = ValueFunctionType; class handle { public: handle(); handle( handle&& other ); ~handle(); handle& operator=( handle&& other ); operator bool() const; value_type& value(); }; // class handle concurrent_lru_cache( value_function_type f, std::size_t number_of_lru_history_items ); ~concurrent_lru_cache(); handle operator[]( key_type key ); }; // class concurrent_lru_cache } // namespace tbb } // namespace oneapi
Member Functions
concurrent_lru_cache
(value_function_type
f
, std::size_t
number_of_lru_history_items
);
Effects
: Constructs an empty cache that can keep up to
number_of_lru_history_items
unused values, with a function object
f
for constructing new values.
~concurrent_lru_cache
();
Effects
: Destroys the
concurrent_lru_cache
. Calls the destructors of the stored elements and deallocates the used storage.
The behavior is undefined in case of concurrent operations with
*this
.
handle
operator[]
(key_type
k
);
Effects
: Searches the container for an item that corresponds to the given key. If such an item is not found, the user-specified function object is called to construct a value that is inserted into the container.
Returns
: a
handle
object holding reference to the matching value.
Member Objects
handle
class
Member Functions
handle
();
Effects
: Constructs a
handle
object that does not refer to any value.
handle
(handle &&
other
);
Effects
: Transfers the reference to the value stored in
concurrent_lru_cache
from
other
to the newly constructed object. Upon completion,
other
no longer refers to any value.
~handle
();
Effects
: Releases the reference (if it exists) to a value stored in
concurrent_lru_cache
.
The behavior is undefined for concurrent operations with
*this
.
handle &
operator=
(handle &&
other
);
Effects
: Transfers the reference to a value stored in
concurrent_lru_cache
from
other
to
*this
. If existed, the previous reference held by
*this
is released. Upon completion
other
no longer refers to any value.
Returns
: a reference to
*this
.
operator bool
()
const
;
Returns
:
true
if
*this
holds reference to a value,
false
otherwise.
value_type &
value
();
Returns
: a reference to a
value_type
object stored in
concurrent_lru_cache
.
The behavior is undefined if
*this
does not refer to any value.

Product and Performance Information

1

Performance varies by use, configuration and other factors. Learn more at www.Intel.com/PerformanceIndex.