Create and make accessable a shared memory segment.
A note about Anonymous vs. Named shared memory segments:
Not all plaforms support anonymous shared memory segments, but in
some cases it is prefered over other types of shared memory
implementations. Passing a NULL 'file' parameter to this function
will cause the subsystem to use anonymous shared memory segments.
If such a system is not available, APR_ENOTIMPL is returned.
A note about allocation sizes:
On some platforms it is necessary to store some metainformation
about the segment within the actual segment. In order to supply
the caller with the requested size it may be necessary for the
implementation to request a slightly greater segment length
from the subsystem. In all cases, the apr_shm_baseaddr_get()
function will return the first usable byte of memory.
reqsize The desired size of the segment.
filename The file to use for shared memory on platforms that
pool the pool from which to allocate the shared memory
- The created shared memory structure.