https://tomcat.apache.org/: Interface code to the native connector 
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package org.apache.tomcat.jni;

import java.nio.ByteBuffer;


Shm

Author:Mladen Turk
/** Shm
 *
 * @author Mladen Turk
 */
public class Shm {

    
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.

Params:
  • 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.
Throws:
  • Error – An error occurred
Returns:The created shared memory structure.
/**
     * Create and make accessible a shared memory segment.
     * <br>
     * A note about Anonymous vs. Named shared memory segments:<br>
     *         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.
     * <br>
     * A note about allocation sizes:<br>
     *         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.
     * @param reqsize The desired size of the segment.
     * @param filename The file to use for shared memory on platforms that
     *        require it.
     * @param pool the pool from which to allocate the shared memory
     *        structure.
     * @return The created shared memory structure.
     * @throws Error An error occurred
     */
    public static native long create(long reqsize, String filename, long pool)
        throws Error;

    
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.

Params:
  • filename – The filename associated with shared-memory segment which
       needs to be removed
  • pool – The pool used for file operations
Returns:the operation status
/**
     * Remove shared memory segment associated with a filename.
     * <br>
     * This function is only supported on platforms which support
     * name-based shared memory segments, and will return APR_ENOTIMPL on
     * platforms without such support.
     * @param filename The filename associated with shared-memory segment which
     *        needs to be removed
     * @param pool The pool used for file operations
     * @return the operation status
     */
    public static native int remove(String filename, long pool);

    
Destroy a shared memory segment and associated memory.

Params:
  • m – The shared memory segment structure to destroy.
Returns:the operation status
/**
     * Destroy a shared memory segment and associated memory.
     * @param m The shared memory segment structure to destroy.
     * @return the operation status
     */
    public static native int destroy(long m);

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

Params:
  • 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.
Throws:
  • Error – An error occurred
Returns:The created shared memory structure.
/**
     * Attach to a shared memory segment that was created
     * by another process.
     * @param filename The file used to create the original segment.
     *        (This MUST match the original filename.)
     * @param pool the pool from which to allocate the shared memory
     *        structure for this process.
     * @return The created shared memory structure.
     * @throws Error An error occurred
     */
    public static native long attach(String filename, long pool)
        throws Error;

    
Detach from a shared memory segment without destroying it.

Params:
  • m – The shared memory structure representing the segment
       to detach from.
Returns:the operation status
/**
     * Detach from a shared memory segment without destroying it.
     * @param m The shared memory structure representing the segment
     *        to detach from.
     * @return the operation status
     */
    public static native int detach(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.

Params:
  • m – The shared memory segment from which to retrieve
       the base address.
Returns:address, aligned by APR_ALIGN_DEFAULT.
/**
     * 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.
     * @param m The shared memory segment from which to retrieve
     *        the base address.
     * @return address, aligned by APR_ALIGN_DEFAULT.
     */
    public static native long baseaddr(long m);

    
Retrieve the length of a shared memory segment in bytes.

Params:
  • m – The shared memory segment from which to retrieve
       the segment length.
Returns:the length of the segment
/**
     * Retrieve the length of a shared memory segment in bytes.
     * @param m The shared memory segment from which to retrieve
     *        the segment length.
     * @return the length of the segment
     */
    public static native long size(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.

Params:
  • m – The shared memory segment from which to retrieve
       the base address.
Returns:address, aligned by APR_ALIGN_DEFAULT.
/**
     * 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.
     * @param m The shared memory segment from which to retrieve
     *        the base address.
     * @return address, aligned by APR_ALIGN_DEFAULT.
     */
    public static native ByteBuffer buffer(long m);

}