Java example source code file (jmemsys.h)

This example Java source code file (jmemsys.h) is included in the alvinalexander.com "Java Source Code Warehouse" project. The intent of this project is to help you "Learn Java by Example" ^TM.

Learn more about this Java project at its project page.

Java - Java tags/keywords

dos\-specific, emsh, extern, far, file, fsspec, jmethod, jpp, mac\-specific, max_alloc_chunk, need_short_external_names, use_mac_memmgr, use_msdos_memmgr, xmsh

The jmemsys.h Java example source code

/*
 * reserved comment block
 * DO NOT REMOVE OR ALTER!
 */
/*
 * jmemsys.h
 *
 * Copyright (C) 1992-1997, Thomas G. Lane.
 * This file is part of the Independent JPEG Group's software.
 * For conditions of distribution and use, see the accompanying README file.
 *
 * This include file defines the interface between the system-independent
 * and system-dependent portions of the JPEG memory manager.  No other
 * modules need include it.  (The system-independent portion is jmemmgr.c;
 * there are several different versions of the system-dependent portion.)
 *
 * This file works as-is for the system-dependent memory managers supplied
 * in the IJG distribution.  You may need to modify it if you write a
 * custom memory manager.  If system-dependent changes are needed in
 * this file, the best method is to #ifdef them based on a configuration
 * symbol supplied in jconfig.h, as we have done with USE_MSDOS_MEMMGR
 * and USE_MAC_MEMMGR.
 */


/* Short forms of external names for systems with brain-damaged linkers. */

#ifdef NEED_SHORT_EXTERNAL_NAMES
#define jpeg_get_small          jGetSmall
#define jpeg_free_small         jFreeSmall
#define jpeg_get_large          jGetLarge
#define jpeg_free_large         jFreeLarge
#define jpeg_mem_available      jMemAvail
#define jpeg_open_backing_store jOpenBackStore
#define jpeg_mem_init           jMemInit
#define jpeg_mem_term           jMemTerm
#endif /* NEED_SHORT_EXTERNAL_NAMES */


/*
 * These two functions are used to allocate and release small chunks of
 * memory.  (Typically the total amount requested through jpeg_get_small is
 * no more than 20K or so; this will be requested in chunks of a few K each.)
 * Behavior should be the same as for the standard library functions malloc
 * and free; in particular, jpeg_get_small must return NULL on failure.
 * On most systems, these ARE malloc and free.  jpeg_free_small is passed the
 * size of the object being freed, just in case it's needed.
 * On an 80x86 machine using small-data memory model, these manage near heap.
 */

EXTERN(void *) jpeg_get_small JPP((j_common_ptr cinfo, size_t sizeofobject));
EXTERN(void) jpeg_free_small JPP((j_common_ptr cinfo, void * object,
                                  size_t sizeofobject));

/*
 * These two functions are used to allocate and release large chunks of
 * memory (up to the total free space designated by jpeg_mem_available).
 * The interface is the same as above, except that on an 80x86 machine,
 * far pointers are used.  On most other machines these are identical to
 * the jpeg_get/free_small routines; but we keep them separate anyway,
 * in case a different allocation strategy is desirable for large chunks.
 */

EXTERN(void FAR *) jpeg_get_large JPP((j_common_ptr cinfo,
                                       size_t sizeofobject));
EXTERN(void) jpeg_free_large JPP((j_common_ptr cinfo, void FAR * object,
                                  size_t sizeofobject));

/*
 * The macro MAX_ALLOC_CHUNK designates the maximum number of bytes that may
 * be requested in a single call to jpeg_get_large (and jpeg_get_small for that
 * matter, but that case should never come into play).  This macro is needed
 * to model the 64Kb-segment-size limit of far addressing on 80x86 machines.
 * On those machines, we expect that jconfig.h will provide a proper value.
 * On machines with 32-bit flat address spaces, any large constant may be used.
 *
 * NB: jmemmgr.c expects that MAX_ALLOC_CHUNK will be representable as type
 * size_t and will be a multiple of sizeof(align_type).
 */

#ifndef MAX_ALLOC_CHUNK         /* may be overridden in jconfig.h */
#define MAX_ALLOC_CHUNK  1000000000L
#endif

/*
 * This routine computes the total space still available for allocation by
 * jpeg_get_large.  If more space than this is needed, backing store will be
 * used.  NOTE: any memory already allocated must not be counted.
 *
 * There is a minimum space requirement, corresponding to the minimum
 * feasible buffer sizes; jmemmgr.c will request that much space even if
 * jpeg_mem_available returns zero.  The maximum space needed, enough to hold
 * all working storage in memory, is also passed in case it is useful.
 * Finally, the total space already allocated is passed.  If no better
 * method is available, cinfo->mem->max_memory_to_use - already_allocated
 * is often a suitable calculation.
 *
 * It is OK for jpeg_mem_available to underestimate the space available
 * (that'll just lead to more backing-store access than is really necessary).
 * However, an overestimate will lead to failure.  Hence it's wise to subtract
 * a slop factor from the true available space.  5% should be enough.
 *
 * On machines with lots of virtual memory, any large constant may be returned.
 * Conversely, zero may be returned to always use the minimum amount of memory.
 */

EXTERN(size_t) jpeg_mem_available JPP((j_common_ptr cinfo,
                                     size_t min_bytes_needed,
                                     size_t max_bytes_needed,
                                     size_t already_allocated));


/*
 * This structure holds whatever state is needed to access a single
 * backing-store object.  The read/write/close method pointers are called
 * by jmemmgr.c to manipulate the backing-store object; all other fields
 * are private to the system-dependent backing store routines.
 */

#define TEMP_NAME_LENGTH   64   /* max length of a temporary file's name */


#ifdef USE_MSDOS_MEMMGR         /* DOS-specific junk */

typedef unsigned short XMSH;    /* type of extended-memory handles */
typedef unsigned short EMSH;    /* type of expanded-memory handles */

typedef union {
  short file_handle;            /* DOS file handle if it's a temp file */
  XMSH xms_handle;              /* handle if it's a chunk of XMS */
  EMSH ems_handle;              /* handle if it's a chunk of EMS */
} handle_union;

#endif /* USE_MSDOS_MEMMGR */

#ifdef USE_MAC_MEMMGR           /* Mac-specific junk */
#include <Files.h>
#endif /* USE_MAC_MEMMGR */


typedef struct backing_store_struct * backing_store_ptr;

typedef struct backing_store_struct {
  /* Methods for reading/writing/closing this backing-store object */
  JMETHOD(void, read_backing_store, (j_common_ptr cinfo,
                                     backing_store_ptr info,
                                     void FAR * buffer_address,
                                     long file_offset, long byte_count));
  JMETHOD(void, write_backing_store, (j_common_ptr cinfo,
                                      backing_store_ptr info,
                                      void FAR * buffer_address,
                                      long file_offset, long byte_count));
  JMETHOD(void, close_backing_store, (j_common_ptr cinfo,
                                      backing_store_ptr info));

  /* Private fields for system-dependent backing-store management */
#ifdef USE_MSDOS_MEMMGR
  /* For the MS-DOS manager (jmemdos.c), we need: */
  handle_union handle;          /* reference to backing-store storage object */
  char temp_name[TEMP_NAME_LENGTH]; /* name if it's a file */
#else
#ifdef USE_MAC_MEMMGR
  /* For the Mac manager (jmemmac.c), we need: */
  short temp_file;              /* file reference number to temp file */
  FSSpec tempSpec;              /* the FSSpec for the temp file */
  char temp_name[TEMP_NAME_LENGTH]; /* name if it's a file */
#else
  /* For a typical implementation with temp files, we need: */
  FILE * temp_file;             /* stdio reference to temp file */
  char temp_name[TEMP_NAME_LENGTH]; /* name of temp file */
#endif
#endif
} backing_store_info;


/*
 * Initial opening of a backing-store object.  This must fill in the
 * read/write/close pointers in the object.  The read/write routines
 * may take an error exit if the specified maximum file size is exceeded.
 * (If jpeg_mem_available always returns a large value, this routine can
 * just take an error exit.)
 */

EXTERN(void) jpeg_open_backing_store JPP((j_common_ptr cinfo,
                                          backing_store_ptr info,
                                          long total_bytes_needed));


/*
 * These routines take care of any system-dependent initialization and
 * cleanup required.  jpeg_mem_init will be called before anything is
 * allocated (and, therefore, nothing in cinfo is of use except the error
 * manager pointer).  It should return a suitable default value for
 * max_memory_to_use; this may subsequently be overridden by the surrounding
 * application.  (Note that max_memory_to_use is only important if
 * jpeg_mem_available chooses to consult it ... no one else will.)
 * jpeg_mem_term may assume that all requested memory has been freed and that
 * all opened backing-store objects have been closed.
 */

EXTERN(size_t) jpeg_mem_init JPP((j_common_ptr cinfo));
EXTERN(void) jpeg_mem_term JPP((j_common_ptr cinfo));