posix
Class SharedMem

java.lang.Object
  posix.IPC
      posix.SharedMem

public class SharedMem
extends IPC

A Posix shared memory segment. Shared physical memory is not supported, since this requires superuser privilege and is very hardware dependent.

Nested Class Summary

static class

SharedMem.shmid_ds

Nested classes/interfaces inherited from class posix.IPC

IPC.Perm

Field Summary

static long

SHMLBA The modulus for attaching shared memory by logical address.

Fields inherited from class posix.IPC

egid, euid, id, IPC_ALLOC, IPC_CI, IPC_CREAT, IPC_EXCL, IPC_NOCLEAR, IPC_NOWAIT, IPC_PHYS, IPC_PRIVATE, owner, pid

Constructor Summary

SharedMem(int key, int flag)
Attach an existing shared memory segment.

SharedMem(int key, int size, int flag)
Attach or create a shared memory segment.

SharedMem(String path, int type)

Method Summary

CPtr	attach() Attach the shared memory for read/write at any available logical address.
void	dispose()
SharedMem.shmid_ds	getStatus() Return the permissions for this IPC data structure.
void	remove() Remove this IPC data structure from the system.
void	setPerm(IPC.Perm st) Set the user, group, mode for this IPC data structure.

Methods inherited from class posix.IPC

finalize, ftok, getId, getPerm, isPidValid, setPerm

Methods inherited from class java.lang.Object

clone, equals, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Field Detail

SHMLBA

public static final long SHMLBA

The modulus for attaching shared memory by logical address. This is system dependent and therefore computed by the class initializer. While attaching shared memory to a specific address is somewhat system dependent, it can be handled by configuration or property settings.

Constructor Detail

SharedMem

public SharedMem(int key,
                 int flag)
          throws IPCException

Attach an existing shared memory segment.

Throws:

IPCException

SharedMem

public SharedMem(int key,
                 int size,
                 int flag)
          throws IPCException

Attach or create a shared memory segment.

Parameters:

key - IPC key or IPC_PRIVATE

size - size of shared memory

flag - options

Throws:

IPCException

SharedMem

public SharedMem(String path,
                 int type)
          throws IPCException

Throws:

IPCException

Method Detail

getStatus

public SharedMem.shmid_ds getStatus()
                             throws IPCException

Description copied from class: IPC

Return the permissions for this IPC data structure.

Specified by:

getStatus in class IPC

Throws:

IPCException

setPerm

public void setPerm(IPC.Perm st)
             throws IPCException

Set the user, group, mode for this IPC data structure.

Specified by:

setPerm in class IPC

Parameters:

st - a status obtained from IPC.getPerm() for this IPC and modified

Throws:

IPCException

attach

public CPtr attach()
            throws IPCException

Attach the shared memory for read/write at any available logical address. While posix supports attaching at a specific address (within system dependent contraints), I cannot see any utility for this in a Java program - so it is not supported for now. FIXME: support attaching readonly. Support detaching and reattaching at the same address to change readonly status.

Returns:

a CPtr to the attached memory segment

Throws:

IPCException

remove

public void remove()

Description copied from class: IPC

Remove this IPC data structure from the system.

Specified by:

remove in class IPC

dispose

public void dispose()

Overrides:

dispose in class IPC