The "counter" Extension - A Continuing Example
PHP Manual

Constantes predefinidas

Estas constantes están definidas por esta extensión y estarán disponibles sólo cuando la extensión haya sido compilada con PHP, o bien sea cargada dinámicamente en ejecución.

COUNTER_FLAG_PERSIST (integer)
A counter with this flag will be created as a persistent resource.
COUNTER_FLAG_SAVE (integer)
A counter with this flag will be saved between invocations of PHP.
COUNTER_FLAG_NO_OVERWRITE (integer)
This flag causes counter_create() to avoid overwriting an existing named counter with a new one.
COUNTER_META_NAME (string)
Pass this constant to get the name of a counter resource or object.
COUNTER_META_IS_PERISTENT (string)
Pass this constant to determine whether a counter resource or object is persistent (has the COUNTER_FLAG_PERSIST flag).
COUNTER_RESET_NEVER (integer)
The counter will never be reset.
COUNTER_RESET_PER_LOAD (integer)
The counter will be reset on each invocation of PHP.
COUNTER_RESET_PER_REQUEST (integer)
The counter will be reset on each request.

The "counter" Extension - A Continuing Example
PHP Manual