IPC::SharedMem

Section: Perl Programmers Reference Guide (3perl)
Updated: 2019-04-20
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NAME

IPC::SharedMem - SysV Shared Memory IPC object class

SYNOPSIS

    use IPC::SysV qw(IPC_PRIVATE S_IRUSR S_IWUSR);
    use IPC::SharedMem;

    $shm = IPC::SharedMem->new(IPC_PRIVATE, 8, S_IRWXU);

    $shm->write(pack("S", 4711), 2, 2);

    $data = $shm->read(0, 2);

    $ds = $shm->stat;

    $shm->remove;

DESCRIPTION

A class providing an object based interface to SysV IPC shared memory.

METHODS

new ( KEY , SIZE , FLAGS )

Creates a new shared memory segment of "SIZE" bytes size associated with "KEY". A new segment is created if

•: "KEY" is equal to "IPC_PRIVATE"
•: "KEY" does not already have a shared memory segment associated with it, and "FLAGS & IPC_CREAT" is true.

: On creation of a new shared memory segment "FLAGS" is used to set the permissions. Be careful not to set any flags that the Sys V IPC implementation does not allow: in some systems setting execute bits makes the operations fail.

id

Returns the shared memory identifier.

read ( POS, SIZE )

Read "SIZE" bytes from the shared memory segment at "POS". Returns the string read, or "undef" if there was an error. The return value becomes tainted. See shmread.

write ( STRING, POS, SIZE )

Write "SIZE" bytes to the shared memory segment at "POS". Returns true if successful, or false if there is an error. See shmwrite.

remove

Remove the shared memory segment from the system or mark it as removed as long as any processes are still attached to it.

is_removed

Returns true if the shared memory segment has been removed or marked for removal.

stat

Returns an object of type "IPC::SharedMem::stat" which is a sub-class of "Class::Struct". It provides the following fields. For a description of these fields see you system documentation.

    uid
    gid
    cuid
    cgid
    mode
    segsz
    lpid
    cpid
    nattch
    atime
    dtime
    ctime

attach ( [FLAG] )

Permanently attach to the shared memory segment. When a "IPC::SharedMem" object is attached, it will use memread and memwrite instead of shmread and shmwrite for accessing the shared memory segment. Returns true if successful, or false on error. See shmat(2).

detach

Detach from the shared memory segment that previously has been attached to. Returns true if successful, or false on error. See shmdt(2).

addr

Returns the address of the shared memory that has been attached to in a format suitable for use with "pack('P')". Returns "undef" if the shared memory has not been attached.

AUTHORS

Marcus Holland-Moritz <mhx@cpan.org>

COPYRIGHT

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