1. class
  2. Drupal
  3. \
  4. Core
  5. \
  6. Cache
  7. \
  8. BackendChain

BackendChain

class BackendChain implements CacheBackendInterface, CacheTagsInvalidatorInterface (View source)

Defines a chained cache implementation for combining multiple cache backends.

Can be used to combine two or more backends together to behave as if they were a single backend.

For example a slower, persistent storage engine could be combined with a faster, volatile storage engine. When retrieving items from cache, they will be fetched from the volatile backend first, only falling back to the persistent backend if an item is not available. An item not present in the volatile backend but found in the persistent one will be propagated back up to ensure fast retrieval on the next request. On cache sets and deletes, both backends will be invoked to ensure consistency.

Properties

protected array $backends

Ordered list of CacheBackendInterface instances.

Methods

$this
appendBackend(CacheBackendInterface $backend)

Appends a cache backend to the cache chain.

$this
prependBackend(CacheBackendInterface $backend)

Prepends a cache backend to the cache chain.

object|false
get(string $cid, bool $allow_invalid = FALSE)

Returns data from the persistent cache.

array
getMultiple(array $cids, bool $allow_invalid = FALSE)

Returns data from the persistent cache when given an array of cache IDs.

set(string $cid, mixed $data, int $expire = Cache::PERMANENT, array $tags = [])

Stores data in the persistent cache.

setMultiple(array $items)

Store multiple items in the persistent cache.

delete(string $cid)

Deletes an item from the cache.

deleteMultiple(array $cids)

Deletes multiple items from the cache.

deleteAll()

Deletes all cache items in a bin.

invalidate(string $cid)

Marks a cache item as invalid.

invalidateMultiple(array $cids)

Marks cache items as invalid.

invalidateTags(array $tags)

Marks cache items with any of the specified tags as invalid.

invalidateAll()

Marks all cache items as invalid.

garbageCollection()

Performs garbage collection on a cache bin.

removeBin()

Remove a cache bin.

Details

at line 41
$this appendBackend(CacheBackendInterface $backend)

Appends a cache backend to the cache chain.

Parameters

CacheBackendInterface $backend

The cache backend to be appended to the cache chain.

Return Value

$this

The called object.

at line 56
$this prependBackend(CacheBackendInterface $backend)

Prepends a cache backend to the cache chain.

Parameters

CacheBackendInterface $backend

The backend to be prepended to the cache chain.

Return Value

$this

The called object.

at line 65
object|false get(string $cid, bool $allow_invalid = FALSE)

Returns data from the persistent cache.

Parameters

string $cid

The cache ID of the data to retrieve.
bool $allow_invalid

(optional) If TRUE, a cache item may be returned even if it is expired or has been invalidated. Such items may sometimes be preferred, if the alternative is recalculating the value stored in the cache, especially if another concurrent request is already recalculating the same value. The "valid" property of the returned object indicates whether the item is valid or not. Defaults to FALSE.

Return Value

object|false

The cache item or FALSE on failure.

at line 85
array getMultiple(array $cids, bool $allow_invalid = FALSE)

Returns data from the persistent cache when given an array of cache IDs.

Parameters

array $cids

An array of cache IDs for the data to retrieve. This is passed by reference, and will have the IDs successfully returned from cache removed.
bool $allow_invalid

(optional) If TRUE, cache items may be returned even if they have expired or been invalidated. Such items may sometimes be preferred, if the alternative is recalculating the value stored in the cache, especially if another concurrent thread is already recalculating the same value. The "valid" property of the returned objects indicates whether the items are valid or not. Defaults to FALSE.

Return Value

array

An array of cache item objects indexed by cache ID.

at line 116
set(string $cid, mixed $data, int $expire = Cache::PERMANENT, array $tags = [])

Stores data in the persistent cache.

Core cache implementations set the created time on cache item with microtime(TRUE) rather than REQUEST_TIME_FLOAT, because the created time of cache items should match when they are created, not when the request started. Apart from being more accurate, this increases the chance an item will legitimately be considered valid.

Parameters

string $cid

The cache ID of the data to store.
mixed $data

The data to store in the cache. Some storage engines only allow objects up to a maximum of 1MB in size to be stored by default. When caching large arrays or similar, take care to ensure $data does not exceed this size.
int $expire

One of the following values:

  • CacheBackendInterface::CACHE_PERMANENT: Indicates that the item should not be removed unless it is deleted explicitly.
  • A Unix timestamp: Indicates that the item will be considered invalid after this time, i.e. it will not be returned by get() unless $allow_invalid has been set to TRUE. When the item has expired, it may be permanently deleted by the garbage collector at any time.
array $tags

An array of tags to be stored with the cache item. These should normally identify objects used to build the cache item, which should trigger cache invalidation when updated. For example if a cached item represents a node, both the node ID and the author's user ID might be passed in as tags. For example ['node:123', 'node:456', 'user:789'].

at line 125
setMultiple(array $items)

Store multiple items in the persistent cache.

Parameters

array $items

An array of cache items, keyed by cid. In the form: @code $items = array( $cid => array( // Required, will be automatically serialized if not a string. 'data' => $data, // Optional, defaults to CacheBackendInterface::CACHE_PERMANENT. 'expire' => CacheBackendInterface::CACHE_PERMANENT, // (optional) The cache tags for this item, see CacheBackendInterface::set(). 'tags' => array(), ), ); @endcode

at line 134
delete(string $cid)

Deletes an item from the cache.

If the cache item is being deleted because it is no longer "fresh", you may consider using invalidate() instead. This allows callers to retrieve the invalid item by calling get() with $allow_invalid set to TRUE. In some cases an invalid item may be acceptable rather than having to rebuild the cache.

Parameters

string $cid

The cache ID to delete.

at line 143
deleteMultiple(array $cids)

Deletes multiple items from the cache.

If the cache items are being deleted because they are no longer "fresh", you may consider using invalidateMultiple() instead. This allows callers to retrieve the invalid items by calling get() with $allow_invalid set to TRUE. In some cases an invalid item may be acceptable rather than having to rebuild the cache.

Parameters

array $cids

An array of cache IDs to delete.

at line 152
deleteAll()

Deletes all cache items in a bin.

at line 161
invalidate(string $cid)

Marks a cache item as invalid.

Invalid items may be returned in later calls to get(), if the $allow_invalid argument is TRUE.

Parameters

string $cid

The cache ID to invalidate.

at line 170
invalidateMultiple(array $cids)

Marks cache items as invalid.

Invalid items may be returned in later calls to get(), if the $allow_invalid argument is TRUE.

Parameters

array $cids

An array of cache IDs to invalidate.

at line 179
invalidateTags(array $tags)

Marks cache items with any of the specified tags as invalid.

Parameters

array $tags

The list of tags for which to invalidate cache items.

at line 190
invalidateAll()

Marks all cache items as invalid.

Invalid items may be returned in later calls to get(), if the $allow_invalid argument is TRUE.

at line 199
garbageCollection()

Performs garbage collection on a cache bin.

The backend may choose to delete expired or invalidated items.

at line 208
removeBin()

Remove a cache bin.