Shm

System V shared-memory cache backend.

class Shm extends \Hazaar\Cache\Backend

Extends: Hazaar\Cache\Backend

Provides very low-latency in-process cache access using SysV shared memory segments and semaphores for synchronization.

This backend supports:

• object storage
• per-value expiry
• keepalive-based expiry extension
• array export
• key-level locking

Namespace mapping is maintained in a dedicated shared segment to resolve namespace-to-segment addresses consistently across processes.

Constants

GC_KEY

private const GC_KEY = '__garbage_collection__'

Properties

weight

Backend priority weight used during backend chain ordering.

protected int $weight

Type: int

config

Typed view of this backend's options.

private Shm\Options $config

Type: Hazaar\Cache\Backend\Shm\Options

sem

Semaphore guarding namespace/index and shared-memory operations.

private false|\SysvSemaphore $sem

Type: false|SysvSemaphore

shm

Attached shared-memory segment for this namespace.

private false|\SysvSharedMemory $shm

Type: false|SysvSharedMemory

keepalive

Whether reads should extend item expiry when timeout metadata exists.

private bool $keepalive

Type: bool

indexKey

Shared-memory variable key storing namespace index metadata.

private int $indexKey

Type: int

locks

private array $locks

Type: array

Methods

available

Check if the shared memory cache backend is available.

public available(): bool

Returns: bool

init

Initializes the shared memory cache backend for a given namespace.

public init(string $namespace): void

Returns: void

Parameters

Parameter	Type	Description
$namespace	string	the namespace for the cache backend

close

Closes the shared memory cache.

public close(): bool

Returns: bool

has

Check if a key exists in the shared memory cache.

public has(string $key, bool $checkEmpty): bool

Returns: bool

Parameters

Parameter	Type	Description
$key	string	the key to check
$checkEmpty	bool	whether to check if the data associated with the key is empty

get

Retrieves the value associated with the given key from the cache.

public get(string $key): mixed

Returns: mixed

Parameters

Parameter	Type	Description
$key	string	the key to retrieve the value for

set

Sets a value in the shared memory cache.

public set(string $key, mixed $value, int $timeout): bool

Returns: bool

Parameters

Parameter	Type	Description
$key	string	the key to store the value under
$value	mixed	the value to be stored
$timeout	int	The timeout for the value in seconds. Default is 0 (no timeout).

remove

Remove a value from the shared memory cache.

public remove(string $key): bool

Returns: bool

Parameters

Parameter	Type	Description
$key	string	the key of the value to remove

clear

Clears the shared memory cache.

public clear(): bool

Returns: bool

toArray

Converts the cache data to an array.

public toArray(): array

Returns: array

count

Returns the number of items in the cache.

public count(): int

Returns: int

lock

Locks a cache entry for exclusive access.

public lock(string $key): bool

Returns: bool

Parameters

Parameter	Type	Description
$key	string	the key of the cache entry

unlock

Unlock a lock for a given key.

public unlock(string $key): bool

Returns: bool

Parameters

Parameter	Type	Description
$key	string	the key of the lock to unlock

findFirstAvailableAddress

private findFirstAvailableAddress(array $index): int

Returns: int

Parameters

Parameter	Type	Description
$index	array

getIndex

Retrieves the index from the shared memory.

private getIndex(): array

Returns: array

getAddr

Retrieves the address of a key in the cache.

private getAddr(string $key, bool $create): false|int

Returns: false|int

Parameters

Parameter	Type	Description
$key	string	the key to retrieve the address for
$create	bool	whether to create the key if it doesn't exist

addIndex

Adds an index for the given key in the shared memory cache backend.

private addIndex(string $key): false|int

Returns: false|int

Parameters

Parameter	Type	Description
$key	string	the key to add an index for

removeIndex

Remove an entry from the cache index.

private removeIndex(array|string $key): bool

Returns: bool

Parameters

Parameter	Type	Description
$key	array	string

infoByAddr

Retrieves information stored in shared memory by address.

private infoByAddr(int $addr, bool $noKeepalive): array|bool

Returns: array|bool

Parameters

Parameter	Type	Description
$addr	int	the address of the shared memory variable
$noKeepalive	bool

infoByKey

Retrieves information about a cache entry by its key.

private infoByKey(string $key): array|bool

Returns: array|bool

Parameters

Parameter	Type	Description
$key	string	the key of the cache entry

---

Generated by Hazaar API Doc Generator on Fri, 04 Sep 2026 23:32:16 +0000