#include <db.h>
int
db_env_set_func_region_map(int (*func_region_map)(DB_ENV *dbenv,
char *path, size_t len, int *is_create, void **addr),
int (*func_region_unmap)(DB_ENV *dbenv, void *addr));
The Berkeley DB library optionally uses the ability to create shared memory regions (which may or may not be backed by physical files). The memory will be used as a shared memory region for synchronization between Berkeley DB threads/processes; while the returned memory may be of any kind (for example, anonymous memory), it must be able to support semaphores.
The db_env_set_func_region_map() function configures all operations
performed by a process and all of its threads of control, not
operations confined to a single database environment.
Although the db_env_set_func_region_map() function may be called at any
time during the life of the application, it should normally be called
before making calls to the db_env_create or
db_create methods.
The db_env_set_func_region_map()
function returns a non-zero error value on failure and 0 on success.
The func_region_map parameter is the function which creates shared memory regions. The function takes 5 parameters:
dbenv
The dbenv parameter is the enclosing database environment handle. This handle is provided to uniquely identify a shared memory region: the dbenv parameter and the path are a unique identifier pair for mapping any new region, and the dbenv parameter and the address are a unique identifier pair for unmapping any region.
path
The path parameter is the name of the region. Repeated requests for the shared regions of the same name, in the same database environment, should return a reference to the same memory.
len
The len parameter is the length, in bytes, needed for the region.
is_create
The memory referenced by the is_create parameter will be non-zero if flags to Berkeley DB allowed creation of the mapped region; the memory referenced by the is_create parameter must be set to non-zero if the region is created by the func_region_map function, and set to zero if the region is not created by the function. This returned information will determine if the region is subsequently initialized by Berkeley DB.
addr
The addr parameter is the memory location into which a pointer to the region or mapped file is returned.
The func_region_unmap parameter is the function which unmaps a shared memory region. The function takes 2 parameters:
dbenv
The dbenv parameter is the enclosing database environment handle.
addr
The addr parameter is the value returned by the func_region_map function when the region was mapped into memory.