POSIX::RT::SharedMem - Create/open or unlink POSIX shared memory objects in Perl


version 0.10


 use POSIX::RT::SharedMem qw/shared_open/;

 shared_open my $map, '/some_file', '+>', size => 1024, perms => oct(777);


This module maps POSIX shared memory into a variable that can be read just like any other variable, and it can be written to using standard Perl techniques such as regexps and substr, as long as they don't change the length of the variable.


shared_open $map, $name, $mode, ...

Map the shared memory object $name into $map. For portable use, a shared memory object should be identified by a name of the form '/somename'; that is, a string consisting of an initial slash, followed by one or more characters, none of which are slashes.

$mode determines the read/write mode. It works the same as in open and map_file.

Beyond that it can take three named arguments:

  • size

    This determines the size of the map. If the map is map has writing permissions and the file is smaller than the given size it will be lengthened. Defaults to the length of the file and fails if it is zero. It is mandatory when using mode > or +>.

  • perms

    This determines the permissions with which the file is created (if $mode is +>). Default is 0600.

  • offset

    This determines the offset in the file that is mapped. Default is 0.

  • flags

    Extra flags that are used when opening the shared memory object (e.g. O_EXCL).

It returns a filehandle that can be used to with stat, chmod, chown. For portability you should not assume you can read or write directly from it.

Remove the shared memory object $name from the namespace. Note that while the shared memory object can't be opened anymore after this, it doesn't remove the contents until all processes have closed it.


  • SysV::SharedMem

    This is a rather similar module that works with SysV shared memory. SysV has confusing ideas of how to identify a segment, as well as having various special case functions that are handled by standard filehandle calls in POSIX shared memory. This module should usually be preferred unless portability requires otherwise.

  • File::Map

    This is used to map the shared memory handle into a scalar. If your processes have a parent-child relationship, you may want to look at map_anonymous instead.


Leon Timmermans <>


This software is copyright (c) 2010 by Leon Timmermans.

This is free software; you can redistribute it and/or modify it under the same terms as the Perl 5 programming language system itself.