module for using POSIX mmap

 The Mmap module uses the POSIX mmap call to map in a file as a Perl variable.
 Memory access by mmap may be shared between threads or forked processes, and
 may be a disc file that has been mapped into memory. Sys::Mmap depends on
 your operating system supporting UNIX or POSIX.1b mmap, of course.
 .
 Note that PerlIO now defines a :mmap tag and presents mmap'd files as regular
 files, if that is your cup of joe.
 .
 Several processes may share one copy of the file or string, saving memory,
 and concurrently making changes to portions of the file or string. When not
 used with a file, it is an alternative to SysV shared memory. Unlike SysV
 shared memory, there are no arbitrary size limits on the shared memory area,
 and sparce memory usage is handled optimally on most modern UNIX
 implementations.