org.apache.tomcat.jni
Class Shm

java.lang.Object
  org.apache.tomcat.jni.Shm

public class Shm
extends java.lang.Object

Shm

Author:

Mladen Turk

Shm

public Shm()

create

public static long create(long reqsize,
                          java.lang.String filename,
                          long pool)
                   throws Error

Create and make accessible a shared memory segment.
A note about Anonymous vs. Named shared memory segments:
Not all platforms support anonymous shared memory segments, but in some cases it is preferred 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.

Parameters:

reqsize - The desired size of the segment.

filename - The file to use for shared memory on platforms that require it.

pool - the pool from which to allocate the shared memory structure.

Returns:

The created shared memory structure.

Throws:

Error

remove

public static int remove(java.lang.String filename,
                         long pool)

Remove shared memory segment associated with a filename.
This function is only supported on platforms which support name-based shared memory segments, and will return APR_ENOTIMPL on platforms without such support.

Parameters:

filename - The filename associated with shared-memory segment which needs to be removed

pool - The pool used for file operations

destroy

public static int destroy(long m)

Destroy a shared memory segment and associated memory.

Parameters:

m - The shared memory segment structure to destroy.

attach

public static long attach(java.lang.String filename,
                          long pool)
                   throws Error

Attach to a shared memory segment that was created by another process.

Parameters:

filename - The file used to create the original segment. (This MUST match the original filename.)

pool - the pool from which to allocate the shared memory structure for this process.

Returns:

The created shared memory structure.

Throws:

Error

detach

public static int detach(long m)

Detach from a shared memory segment without destroying it.

Parameters:

m - The shared memory structure representing the segment to detach from.

baseaddr

public static long baseaddr(long m)

Retrieve the base address of the shared memory segment. NOTE: This address is only usable within the callers address space, since this API does not guarantee that other attaching processes will maintain the same address mapping.

Parameters:

m - The shared memory segment from which to retrieve the base address.

Returns:

address, aligned by APR_ALIGN_DEFAULT.

size

public static long size(long m)

Retrieve the length of a shared memory segment in bytes.

Parameters:

m - The shared memory segment from which to retrieve the segment length.

buffer

public static java.nio.ByteBuffer buffer(long m)

Retrieve new ByteBuffer base address of the shared memory segment. NOTE: This address is only usable within the callers address space, since this API does not guarantee that other attaching processes will maintain the same address mapping.

Parameters:

m - The shared memory segment from which to retrieve the base address.

Returns:

address, aligned by APR_ALIGN_DEFAULT.