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15.5. Handling Handler Instantiation

The first method call your storage engine needs to support is the call for a new handler instance.

Before the handlerton is defined in the storage engine source file, a function header for the instantiation function must be defined. Here is an example from the CSV engine:

static handler* tina_create_handler(TABLE *table);

As you can see, the function accepts a pointer to the table the handler is intended to manage, and returns a handler object.

After the function header is defined, the function is named with a function pointer in the create() handlerton element, identifying the function as being responsible for generating new handler instances.

Here is an example of the MyISAM storage engine's instantiation function:

static handler *myisam_create_handler(TABLE *table)
  {
    return new ha_myisam(table);
  }

This call then works in conjunction with the storage engine's constructor. Here is an example from the FEDERATED storage engine:

ha_federated::ha_federated(TABLE *table_arg)
  :handler(&federated_hton, table_arg),
  mysql(0), stored_result(0), scan_flag(0),
  ref_length(sizeof(MYSQL_ROW_OFFSET)), current_position(0)
  {}

And here's one more example from the EXAMPLE storage engine:

ha_example::ha_example(TABLE *table_arg)
  :handler(&example_hton, table_arg)
  {}  

The additional elements in the FEDERATED example are extra initializations for the handler. The minimum implementation required is the handler() initialization shown in the EXAMPLE version.


 
 
  Published under the terms of the GNU General Public License Design by Interspire