void *(*app_realloc)(void *, size_t),
void (*app_free)(void *));
Set the allocation functions used by the DB_ENV and DB
methods to allocate or free memory owned by the application.
There are a number of interfaces in Berkeley DB where memory is allocated by
the library and then given to the application. For example, the
DB_DBT_MALLOC flag, when specified in the DBT object,
will cause the DB methods to allocate and reallocate memory
which then becomes the responsibility of the calling application. (See
DBT for more information.) Other examples are the Berkeley DB
interfaces which return statistical information to the application:
DB->stat, DB_ENV->lock_stat, DB_ENV->log_archive,
DB_ENV->log_stat, DB_ENV->memp_stat, and DB_ENV->txn_stat. There is
one interface in the Berkeley DB where memory is allocated by the application
and then given to the library: DB->associate.
On systems in which there may be multiple library versions of the
standard allocation routines (notably Windows NT), transferring memory
between the library and the application will fail because the Berkeley DB
library allocates memory from a different heap than the application uses
to free it. To avoid this problem, the DB_ENV->set_alloc and
DB->set_alloc methods can be used to pass Berkeley DB references to the
application's allocation routines.
It is not an error to specify only one or two of the possible allocation
function arguments to these interfaces; however, in that case the
specified interfaces must be compatible with the standard library
interfaces, as they will be used together. The functions specified
must match the calling conventions of the ANSI C X3.159-1989 (ANSI C) library routines
of the same name.
Because databases opened within Berkeley DB environments use the allocation
interfaces specified to the environment, it is an error to attempt to
set those interfaces in a database created within an environment.
The DB->set_alloc interface may not be called after the DB->open
interface is called.
The DB->set_alloc method returns a non-zero error value on failure and 0 on success.
The DB->set_alloc method may fail and return a non-zero error for the following conditions:
- An invalid flag value or parameter was specified.
Called in a database environment.
Called after DB->open was called.
The DB->set_alloc method may fail and return a non-zero error for errors specified for other Berkeley DB and C library or system functions.
If a catastrophic error has occurred, the DB->set_alloc method may fail and
in which case all subsequent Berkeley DB calls will fail in the same way.
Databases and Related Methods
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