db_env_set_func_region_map
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## db_env_set_func_region_map

    #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.

### Parameters

#### func_region_map

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.

#### func_region_unmap

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.

### See Also

Run-time configuration

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