jmemmgr.c

一个国人自己实现图像库的程序（有参考价值）

/*
 * jmemmgr.c
 *
 * Copyright (C) 1991-1997, 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 file contains the JPEG system-independent memory management
 * routines.  This code is usable across a wide variety of machines; most
 * of the system dependencies have been isolated in a separate file.
 * The major functions provided here are:
 *   * pool-based allocation and freeing of memory;
 *   * policy decisions about how to divide available memory among the
 *     virtual arrays;
 *   * control logic for swapping virtual arrays between main memory and
 *     backing storage.
 * The separate system-dependent file provides the actual backing-storage
 * access code, and it contains the policy decision about how much total
 * main memory to use.
 * This file is system-dependent in the sense that some of its functions
 * are unnecessary in some systems.  For example, if there is enough virtual
 * memory so that backing storage will never be used, much of the virtual
 * array control logic could be removed.  (Of course, if you have that much
 * memory then you shouldn't care about a little bit of unused code...)
 */

#define JPEG_INTERNALS
#define AM_MEMORY_MANAGER	/* we define jvirt_Xarray_control structs */
#include "jinclude.h"
#include "jpeglib.h"
#include "jmemsys.h"		/* import the system-dependent declarations */

#ifndef NO_GETENV
#ifndef HAVE_STDLIB_H		/* <stdlib.h> should declare getenv() */
extern char * getenv JPP((const char * name));
#endif
#endif


/*
 * Some important notes:
 *   The allocation routines provided here must never return NULL.
 *   They should exit to error_exit if unsuccessful.
 *
 *   It's not a good idea to try to merge the sarray and barray routines,
 *   even though they are textually almost the same, because samples are
 *   usually stored as bytes while coefficients are shorts or ints.  Thus,
 *   in machines where byte pointers have a different representation from
 *   word pointers, the resulting machine code could not be the same.
 */


/*
 * Many machines require storage alignment: longs must start on 4-byte
 * boundaries, doubles on 8-byte boundaries, etc.  On such machines, malloc()
 * always returns pointers that are multiples of the worst-case alignment
 * requirement, and we had better do so too.
 * There isn't any really portable way to determine the worst-case alignment
 * requirement.  This module assumes that the alignment requirement is
 * multiples of sizeof(ALIGN_TYPE).
 * By default, we define ALIGN_TYPE as double.  This is necessary on some
 * workstations (where doubles really do need 8-byte alignment) and will work
 * fine on nearly everything.  If your machine has lesser alignment needs,
 * you can save a few bytes by making ALIGN_TYPE smaller.
 * The only place I know of where this will NOT work is certain Macintosh
 * 680x0 compilers that define double as a 10-byte IEEE extended float.
 * Doing 10-byte alignment is counterproductive because longwords won't be
 * aligned well.  Put "#define ALIGN_TYPE long" in jconfig.h if you have
 * such a compiler.
 */

#ifndef ALIGN_TYPE		/* so can override from jconfig.h */
#define ALIGN_TYPE  double
#endif


/*
 * We allocate objects from "pools", where each pool is gotten with a single
 * request to jpeg_get_small() or jpeg_get_large().  There is no per-object
 * overhead within a pool, except for alignment padding.  Each pool has a
 * header with a link to the next pool of the same class.
 * Small and large pool headers are identical except that the latter's
 * link pointer must be FAR on 80x86 machines.
 * Notice that the "real" header fields are union'ed with a dummy ALIGN_TYPE
 * field.  This forces the compiler to make SIZEOF(small_pool_hdr) a multiple
 * of the alignment requirement of ALIGN_TYPE.
 */

typedef union small_pool_struct * small_pool_ptr;

typedef union small_pool_struct {
  struct {
    small_pool_ptr next;	/* next in list of pools */
    size_t bytes_used;		/* how many bytes already used within pool */
    size_t bytes_left;		/* bytes still available in this pool */
  } hdr;
  ALIGN_TYPE dummy;		/* included in union to ensure alignment */
} small_pool_hdr;

typedef union large_pool_struct FAR * large_pool_ptr;

typedef union large_pool_struct {
  struct {
    large_pool_ptr next;	/* next in list of pools */
    size_t bytes_used;		/* how many bytes already used within pool */
    size_t bytes_left;		/* bytes still available in this pool */
  } hdr;
  ALIGN_TYPE dummy;		/* included in union to ensure alignment */
} large_pool_hdr;


/*
 * Here is the full definition of a memory manager object.
 */

typedef struct {
  struct jpeg_memory_mgr pub;	/* public fields */

  /* Each pool identifier (lifetime class) names a linked list of pools. */
  small_pool_ptr small_list[JPOOL_NUMPOOLS];
  large_pool_ptr large_list[JPOOL_NUMPOOLS];

  /* Since we only have one lifetime class of virtual arrays, only one
   * linked list is necessary (for each datatype).  Note that the virtual
   * array control blocks being linked together are actually stored somewhere
   * in the small-pool list.
   */
  jvirt_sarray_ptr virt_sarray_list;
  jvirt_barray_ptr virt_barray_list;

  /* This counts total space obtained from jpeg_get_small/large */
  long total_space_allocated;

  /* alloc_sarray and alloc_barray set this value for use by virtual
   * array routines.
   */
  JDIMENSION last_rowsperchunk;	/* from most recent alloc_sarray/barray */
} my_memory_mgr;

typedef my_memory_mgr * my_mem_ptr;


/*
 * The control blocks for virtual arrays.
 * Note that these blocks are allocated in the "small" pool area.
 * System-dependent info for the associated backing store (if any) is hidden
 * inside the backing_store_info struct.
 */

struct jvirt_sarray_control {
  JSAMPARRAY mem_buffer;	/* => the in-memory buffer */
  JDIMENSION rows_in_array;	/* total virtual array height */
  JDIMENSION samplesperrow;	/* width of array (and of memory buffer) */
  JDIMENSION maxaccess;		/* max rows accessed by access_virt_sarray */
  JDIMENSION rows_in_mem;	/* height of memory buffer */
  JDIMENSION rowsperchunk;	/* allocation chunk size in mem_buffer */
  JDIMENSION cur_start_row;	/* first logical row # in the buffer */
  JDIMENSION first_undef_row;	/* row # of first uninitialized row */
  boolean pre_zero;		/* pre-zero mode requested? */
  boolean dirty;		/* do current buffer contents need written? */
  boolean b_s_open;		/* is backing-store data valid? */
  jvirt_sarray_ptr next;	/* link to next virtual sarray control block */
  backing_store_info b_s_info;	/* System-dependent control info */
};

struct jvirt_barray_control {
  JBLOCKARRAY mem_buffer;	/* => the in-memory buffer */
  JDIMENSION rows_in_array;	/* total virtual array height */
  JDIMENSION blocksperrow;	/* width of array (and of memory buffer) */
  JDIMENSION maxaccess;		/* max rows accessed by access_virt_barray */
  JDIMENSION rows_in_mem;	/* height of memory buffer */
  JDIMENSION rowsperchunk;	/* allocation chunk size in mem_buffer */
  JDIMENSION cur_start_row;	/* first logical row # in the buffer */
  JDIMENSION first_undef_row;	/* row # of first uninitialized row */
  boolean pre_zero;		/* pre-zero mode requested? */
  boolean dirty;		/* do current buffer contents need written? */
  boolean b_s_open;		/* is backing-store data valid? */
  jvirt_barray_ptr next;	/* link to next virtual barray control block */
  backing_store_info b_s_info;	/* System-dependent control info */
};


#ifdef MEM_STATS		/* optional extra stuff for statistics */

LOCAL(void)
print_mem_stats (j_common_ptr cinfo, int pool_id)
{
  my_mem_ptr mem = (my_mem_ptr) cinfo->mem;
  small_pool_ptr shdr_ptr;
  large_pool_ptr lhdr_ptr;

  /* Since this is only a debugging stub, we can cheat a little by using
   * fprintf directly rather than going through the trace message code.
   * This is helpful because message parm array can't handle longs.
   */
  fprintf(stderr, "Freeing pool %d, total space = %ld\n",
	  pool_id, mem->total_space_allocated);

  for (lhdr_ptr = mem->large_list[pool_id]; lhdr_ptr != NULL;
       lhdr_ptr = lhdr_ptr->hdr.next) {
    fprintf(stderr, "  Large chunk used %ld\n",
	    (long) lhdr_ptr->hdr.bytes_used);
  }

  for (shdr_ptr = mem->small_list[pool_id]; shdr_ptr != NULL;
       shdr_ptr = shdr_ptr->hdr.next) {
    fprintf(stderr, "  Small chunk used %ld free %ld\n",
	    (long) shdr_ptr->hdr.bytes_used,
	    (long) shdr_ptr->hdr.bytes_left);
  }
}

#endif /* MEM_STATS */


LOCAL(void)
out_of_memory (j_common_ptr cinfo, int which)
/* Report an out-of-memory error and stop execution */
/* If we compiled MEM_STATS support, report alloc requests before dying */
{
#ifdef MEM_STATS
  cinfo->err->trace_level = 2;	/* force self_destruct to report stats */
#endif
  ERREXIT1(cinfo, JERR_OUT_OF_MEMORY, which);
}


/*
 * Allocation of "small" objects.
 *
 * For these, we use pooled storage.  When a new pool must be created,
 * we try to get enough space for the current request plus a "slop" factor,
 * where the slop will be the amount of leftover space in the new pool.
 * The speed vs. space tradeoff is largely determined by the slop values.
 * A different slop value is provided for each pool class (lifetime),
 * and we also distinguish the first pool of a class from later ones.
 * NOTE: the values given work fairly well on both 16- and 32-bit-int
 * machines, but may be too small if longs are 64 bits or more.
 */

static const size_t first_pool_slop[JPOOL_NUMPOOLS] = 
{
	1600,			/* first PERMANENT pool */
	16000			/* first IMAGE pool */
};

static const size_t extra_pool_slop[JPOOL_NUMPOOLS] = 
{
	0,			/* additional PERMANENT pools */
	5000			/* additional IMAGE pools */
};

#define MIN_SLOP  50		/* greater than 0 to avoid futile looping */


METHODDEF(void *)
alloc_small (j_common_ptr cinfo, int pool_id, size_t sizeofobject)
/* Allocate a "small" object */
{
  my_mem_ptr mem = (my_mem_ptr) cinfo->mem;
  small_pool_ptr hdr_ptr, prev_hdr_ptr;
  char * data_ptr;
  size_t odd_bytes, min_request, slop;

  /* Check for unsatisfiable request (do now to ensure no overflow below) */
  if (sizeofobject > (size_t) (MAX_ALLOC_CHUNK-SIZEOF(small_pool_hdr)))
    out_of_memory(cinfo, 1);	/* request exceeds malloc's ability */

  /* Round up the requested size to a multiple of SIZEOF(ALIGN_TYPE) */
  odd_bytes = sizeofobject % SIZEOF(ALIGN_TYPE);
  if (odd_bytes > 0)
    sizeofobject += SIZEOF(ALIGN_TYPE) - odd_bytes;

  /* See if space is available in any existing pool */
  if (pool_id < 0 || pool_id >= JPOOL_NUMPOOLS)
    ERREXIT1(cinfo, JERR_BAD_POOL_ID, pool_id);	/* safety check */
  prev_hdr_ptr = NULL;
  hdr_ptr = mem->small_list[pool_id];
  while (hdr_ptr != NULL) {
    if (hdr_ptr->hdr.bytes_left >= sizeofobject)
      break;			/* found pool with enough space */
    prev_hdr_ptr = hdr_ptr;
    hdr_ptr = hdr_ptr->hdr.next;
  }

  /* Time to make a new pool? */
  if (hdr_ptr == NULL) {
    /* min_request is what we need now, slop is what will be leftover */
    min_request = sizeofobject + SIZEOF(small_pool_hdr);
    if (prev_hdr_ptr == NULL)	/* first pool in class? */
      slop = first_pool_slop[pool_id];
    else
      slop = extra_pool_slop[pool_id];
    /* Don't ask for more than MAX_ALLOC_CHUNK */
    if (slop > (size_t) (MAX_ALLOC_CHUNK-min_request))
      slop = (size_t) (MAX_ALLOC_CHUNK-min_request);
    /* Try to get space, if fail reduce slop and try again */
    for (;;) {
      hdr_ptr = (small_pool_ptr) jpeg_get_small(cinfo, min_request + slop);
      if (hdr_ptr != NULL)
	break;
      slop /= 2;
      if (slop < MIN_SLOP)	/* give up when it gets real small */
	out_of_memory(cinfo, 2); /* jpeg_get_small failed */
    }
    mem->total_space_allocated += min_request + slop;
    /* Success, initialize the new pool header and add to end of list */
    hdr_ptr->hdr.next = NULL;
    hdr_ptr->hdr.bytes_used = 0;
    hdr_ptr->hdr.bytes_left = sizeofobject + slop;
    if (prev_hdr_ptr == NULL)	/* first pool in class? */
      mem->small_list[pool_id] = hdr_ptr;
    else
      prev_hdr_ptr->hdr.next = hdr_ptr;
  }

  /* OK, allocate the object from the current pool */
  data_ptr = (char *) (hdr_ptr + 1); /* point to first data byte in pool */
  data_ptr += hdr_ptr->hdr.bytes_used; /* point to place for object */
  hdr_ptr->hdr.bytes_used += sizeofobject;
  hdr_ptr->hdr.bytes_left -= sizeofobject;

  return (void *) data_ptr;
}


/*
 * Allocation of "large" objects.
 *
 * The external semantics of these are the same as "small" objects,
 * except that FAR pointers are used on 80x86.  However the pool
 * management heuristics are quite different.  We assume that each
 * request is large enough that it may as well be passed directly to
 * jpeg_get_large; the pool management just links everything together
 * so that we can free it all on demand.
 * Note: the major use of "large" objects is in JSAMPARRAY and JBLOCKARRAY
 * structures.  The routines that create these structures (see below)
 * deliberately bunch rows together to ensure a large request size.
 */

METHODDEF(void FAR *)
alloc_large (j_common_ptr cinfo, int pool_id, size_t sizeofobject)
/* Allocate a "large" object */
{
  my_mem_ptr mem = (my_mem_ptr) cinfo->mem;
  large_pool_ptr hdr_ptr;
  size_t odd_bytes;

  /* Check for unsatisfiable request (do now to ensure no overflow below) */
  if (sizeofobject > (size_t) (MAX_ALLOC_CHUNK-SIZEOF(large_pool_hdr)))
    out_of_memory(cinfo, 3);	/* request exceeds malloc's ability */

  /* Round up the requested size to a multiple of SIZEOF(ALIGN_TYPE) */
  odd_bytes = sizeofobject % SIZEOF(ALIGN_TYPE);
  if (odd_bytes > 0)
    sizeofobject += SIZEOF(ALIGN_TYPE) - odd_bytes;

  /* Always make a new pool */
  if (pool_id < 0 || pool_id >= JPOOL_NUMPOOLS)
    ERREXIT1(cinfo, JERR_BAD_POOL_ID, pool_id);	/* safety check */

  hdr_ptr = (large_pool_ptr) jpeg_get_large(cinfo, sizeofobject +
					    SIZEOF(large_pool_hdr));
  if (hdr_ptr == NULL)
    out_of_memory(cinfo, 4);	/* jpeg_get_large failed */
  mem->total_space_allocated += sizeofobject + SIZEOF(large_pool_hdr);

  /* Success, initialize the new pool header and add to list */
  hdr_ptr->hdr.next = mem->large_list[pool_id];
  /* We maintain space counts in each pool header for statistical purposes,
   * even though they are not needed for allocation.
   */
  hdr_ptr->hdr.bytes_used = sizeofobject;