vm/alloc/HeapBitmap.c - platform/dalvik - Gitiles

 /*
  * Copyright (C) 2008 The Android Open Source Project
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
  * You may obtain a copy of the License at
  *
  *      http://www.apache.org/licenses/LICENSE-2.0
  *
  * Unless required by applicable law or agreed to in writing, software
  * distributed under the License is distributed on an "AS IS" BASIS,
  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
  * See the License for the specific language governing permissions and
  * limitations under the License.
  */

 #include "Dalvik.h"
 #include "HeapBitmap.h"
 #include "clz.h"
 #include <limits.h>     // for ULONG_MAX
 #include <sys/mman.h>   // for madvise(), mmap()
 #include <cutils/ashmem.h>

 #define HB_ASHMEM_NAME "dalvik-heap-bitmap"

 #ifndef PAGE_SIZE
 #define PAGE_SIZE 4096
 #endif
 #define ALIGN_UP_TO_PAGE_SIZE(p) \
     (((size_t)(p) + (PAGE_SIZE - 1)) & ~(PAGE_SIZE - 1))

 #define LIKELY(exp)     (__builtin_expect((exp) != 0, true))
 #define UNLIKELY(exp)   (__builtin_expect((exp) != 0, false))

 /*
  * Initialize a HeapBitmap so that it points to a bitmap large
  * enough to cover a heap at <base> of <maxSize> bytes, where
  * objects are guaranteed to be HB_OBJECT_ALIGNMENT-aligned.
  */
 bool
 dvmHeapBitmapInit(HeapBitmap *hb, const void *base, size_t maxSize,
         const char *name)
 {
     void *bits;
     size_t bitsLen;
     size_t allocLen;
     int fd;
     char nameBuf[ASHMEM_NAME_LEN] = HB_ASHMEM_NAME;

     assert(hb != NULL);

     bitsLen = HB_OFFSET_TO_INDEX(maxSize) * sizeof(*hb->bits);
     allocLen = ALIGN_UP_TO_PAGE_SIZE(bitsLen);   // required by ashmem

     if (name != NULL) {
         snprintf(nameBuf, sizeof(nameBuf), HB_ASHMEM_NAME "/%s", name);
     }
     fd = ashmem_create_region(nameBuf, allocLen);
     if (fd < 0) {
         LOGE("Could not create %zu-byte ashmem region \"%s\" to cover "
                 "%zu-byte heap (%d)\n",
                 allocLen, nameBuf, maxSize, fd);
         return false;
     }

     bits = mmap(NULL, bitsLen, PROT_READ | PROT_WRITE, MAP_PRIVATE, fd, 0);
     close(fd);
     if (bits == MAP_FAILED) {
         LOGE("Could not mmap %d-byte ashmem region \"%s\"\n",
                 bitsLen, nameBuf);
         return false;
     }

     memset(hb, 0, sizeof(*hb));
     hb->bits = bits;
     hb->bitsLen = bitsLen;
     hb->base = (uintptr_t)base;
     hb->max = hb->base - 1;

     return true;
 }

 /*
  * Initialize <hb> so that it covers the same extent as <templateBitmap>.
  */
 bool
 dvmHeapBitmapInitFromTemplate(HeapBitmap *hb, const HeapBitmap *templateBitmap,
         const char *name)
 {
     return dvmHeapBitmapInit(hb,
             (void *)templateBitmap->base, HB_MAX_OFFSET(templateBitmap), name);
 }

 /*
  * Initialize the bitmaps in <out> so that they cover the same extent as
  * the corresponding bitmaps in <templates>.
  */
 bool
 dvmHeapBitmapInitListFromTemplates(HeapBitmap out[], HeapBitmap templates[],
     size_t numBitmaps, const char *name)
 {
     size_t i;
     char fullName[PATH_MAX];

     fullName[sizeof(fullName)-1] = '\0';
     for (i = 0; i < numBitmaps; i++) {
         bool ok;

         /* If two ashmem regions have the same name, only one gets
          * the name when looking at the maps.
          */
         snprintf(fullName, sizeof(fullName)-1, "%s/%zd", name, i);

         ok = dvmHeapBitmapInitFromTemplate(&out[i], &templates[i], fullName);
         if (!ok) {
             dvmHeapBitmapDeleteList(out, i);
             return false;
         }
     }
     return true;
 }

 /*
  * Clean up any resources associated with the bitmap.
  */
 void
 dvmHeapBitmapDelete(HeapBitmap *hb)
 {
     assert(hb != NULL);

     if (hb->bits != NULL) {
         // Re-calculate the size we passed to mmap().
         size_t allocLen = ALIGN_UP_TO_PAGE_SIZE(hb->bitsLen);
         munmap((char *)hb->bits, allocLen);
     }
     memset(hb, 0, sizeof(*hb));
 }

 /*
  * Clean up any resources associated with the bitmaps.
  */
 void
 dvmHeapBitmapDeleteList(HeapBitmap hbs[], size_t numBitmaps)
 {
     size_t i;

     for (i = 0; i < numBitmaps; i++) {
         dvmHeapBitmapDelete(&hbs[i]);
     }
 }

 /*
  * Fill the bitmap with zeroes.  Returns the bitmap's memory to
  * the system as a side-effect.
  */
 void
 dvmHeapBitmapZero(HeapBitmap *hb)
 {
     assert(hb != NULL);

     if (hb->bits != NULL) {
         /* This returns the memory to the system.
          * Successive page faults will return zeroed memory.
          */
         madvise(hb->bits, hb->bitsLen, MADV_DONTNEED);
         hb->max = hb->base - 1;
     }
 }

 /*
  * Walk through the bitmaps in increasing address order, and find the
  * object pointers that correspond to places where the bitmaps differ.
  * Call <callback> zero or more times with lists of these object pointers.
  *
  * The <finger> argument to the callback indicates the next-highest
  * address that hasn't been visited yet; setting bits for objects whose
  * addresses are less than <finger> are not guaranteed to be seen by
  * the current XorWalk.  <finger> will be set to ULONG_MAX when the
  * end of the bitmap is reached.
  */
 bool
 dvmHeapBitmapXorWalk(const HeapBitmap *hb1, const HeapBitmap *hb2,
         bool (*callback)(size_t numPtrs, void **ptrs,
                          const void *finger, void *arg),
         void *callbackArg)
 {
     static const size_t kPointerBufSize = 128;
     void *pointerBuf[kPointerBufSize];
     void **pb = pointerBuf;
     size_t index;
     size_t i;

 #define FLUSH_POINTERBUF(finger_) \
     do { \
         if (!callback(pb - pointerBuf, (void **)pointerBuf, \
                 (void *)(finger_), callbackArg)) \
         { \
             LOGW("dvmHeapBitmapXorWalk: callback failed\n"); \
             return false; \
         } \
         pb = pointerBuf; \
     } while (false)

 #define DECODE_BITS(hb_, bits_, update_index_) \
     do { \
         if (UNLIKELY(bits_ != 0)) { \
             static const unsigned long kHighBit = \
                     (unsigned long)1 << (HB_BITS_PER_WORD - 1); \
             const uintptr_t ptrBase = HB_INDEX_TO_OFFSET(i) + hb_->base; \
 /*TODO: hold onto ptrBase so we can shrink max later if possible */ \
 /*TODO: see if this is likely or unlikely */ \
             while (bits_ != 0) { \
                 const int rshift = CLZ(bits_); \
                 bits_ &= ~(kHighBit >> rshift); \
                 *pb++ = (void *)(ptrBase + rshift * HB_OBJECT_ALIGNMENT); \
             } \
             /* Make sure that there are always enough slots available */ \
             /* for an entire word of 1s. */ \
             if (kPointerBufSize - (pb - pointerBuf) < HB_BITS_PER_WORD) { \
                 FLUSH_POINTERBUF(ptrBase + \
                         HB_BITS_PER_WORD * HB_OBJECT_ALIGNMENT); \
                 if (update_index_) { \
                     /* The callback may have caused hb_->max to grow. */ \
                     index = HB_OFFSET_TO_INDEX(hb_->max - hb_->base); \
                 } \
             } \
         } \
     } while (false)

     assert(hb1 != NULL);
     assert(hb1->bits != NULL);
     assert(hb2 != NULL);
     assert(hb2->bits != NULL);
     assert(callback != NULL);

     if (hb1->base != hb2->base) {
         LOGW("dvmHeapBitmapXorWalk: bitmaps cover different heaps "
                 "(0x%08x != 0x%08x)\n",
                 (uintptr_t)hb1->base, (uintptr_t)hb2->base);
         return false;
     }
     if (hb1->bitsLen != hb2->bitsLen) {
         LOGW("dvmHeapBitmapXorWalk: size of bitmaps differ (%zd != %zd)\n",
                 hb1->bitsLen, hb2->bitsLen);
         return false;
     }
     if (hb1->max < hb1->base && hb2->max < hb2->base) {
         /* Easy case; both are obviously empty.
          */
         return true;
     }

     /* First, walk along the section of the bitmaps that may be the same.
      */
     if (hb1->max >= hb1->base && hb2->max >= hb2->base) {
         unsigned long int *p1, *p2;
         uintptr_t offset;

         offset = ((hb1->max < hb2->max) ? hb1->max : hb2->max) - hb1->base;
 //TODO: keep track of which (and whether) one is longer for later
         index = HB_OFFSET_TO_INDEX(offset);

         p1 = hb1->bits;
         p2 = hb2->bits;
         for (i = 0; i <= index; i++) {
 //TODO: unroll this. pile up a few in locals?
             unsigned long int diff = *p1++ ^ *p2++;
             DECODE_BITS(hb1, diff, false);
 //BUG: if the callback was called, either max could have changed.
         }
         /* The next index to look at.
          */
         index++;
     } else {
         /* One of the bitmaps is empty.
          */
         index = 0;
     }

     /* If one bitmap's max is larger, walk through the rest of the
      * set bits.
      */
 const HeapBitmap *longHb;
 unsigned long int *p;
 //TODO: may be the same size, in which case this is wasted work
     longHb = (hb1->max > hb2->max) ? hb1 : hb2;
     i = index;
     index = HB_OFFSET_TO_INDEX(longHb->max - longHb->base);
     p = longHb->bits + i;
     for (/* i = i */; i <= index; i++) {
 //TODO: unroll this
         unsigned long bits = *p++;
         DECODE_BITS(longHb, bits, true);
     }

     if (pb > pointerBuf) {
         /* Set the finger to the end of the heap (rather than longHb->max)
          * so that the callback doesn't expect to be called again
          * if it happens to change the current max.
          */
         FLUSH_POINTERBUF(longHb->base + HB_MAX_OFFSET(longHb));
     }

     return true;

 #undef FLUSH_POINTERBUF
 #undef DECODE_BITS
 }

 /*
  * Fills outIndexList with indices so that for all i:
  *
  *   hb[outIndexList[i]].base < hb[outIndexList[i+1]].base
  */
 static void
 createSortedBitmapIndexList(const HeapBitmap hbs[], size_t numBitmaps,
         size_t outIndexList[])
 {
     int i, j;

     /* numBitmaps is usually 2 or 3, so use a simple sort */
     for (i = 0; i < (int) numBitmaps; i++) {
         outIndexList[i] = i;
         for (j = 0; j < i; j++) {
             if (hbs[j].base > hbs[i].base) {
                 int tmp = outIndexList[i];
                 outIndexList[i] = outIndexList[j];
                 outIndexList[j] = tmp;
             }
         }
     }
 }

 /*
  * Similar to dvmHeapBitmapXorWalk(), but compare multiple bitmaps.
  * Regardless of the order of the arrays, the bitmaps will be visited
  * in address order, so that finger will increase monotonically.
  */
 bool
 dvmHeapBitmapXorWalkLists(const HeapBitmap hbs1[], const HeapBitmap hbs2[],
         size_t numBitmaps,
         bool (*callback)(size_t numPtrs, void **ptrs,
                          const void *finger, void *arg),
         void *callbackArg)
 {
     size_t indexList[numBitmaps];
     size_t i;

     /* Sort the bitmaps by address.  Assume that the two lists contain
      * congruent bitmaps.
      */
     createSortedBitmapIndexList(hbs1, numBitmaps, indexList);

     /* Walk each pair of bitmaps, lowest address first.
      */
     for (i = 0; i < numBitmaps; i++) {
         bool ok;

         ok = dvmHeapBitmapXorWalk(&hbs1[indexList[i]], &hbs2[indexList[i]],
                 callback, callbackArg);
         if (!ok) {
             return false;
         }
     }

     return true;
 }

 /*
  * Similar to dvmHeapBitmapXorWalk(), but visit the set bits
  * in a single bitmap.
  */
 bool
 dvmHeapBitmapWalk(const HeapBitmap *hb,
         bool (*callback)(size_t numPtrs, void **ptrs,
                          const void *finger, void *arg),
         void *callbackArg)
 {
     /* Create an empty bitmap with the same extent as <hb>.
      * Don't actually allocate any memory.
      */
     HeapBitmap emptyHb = *hb;
     emptyHb.max = emptyHb.base - 1; // empty
     emptyHb.bits = (void *)1;       // non-NULL but intentionally bad

     return dvmHeapBitmapXorWalk(hb, &emptyHb, callback, callbackArg);
 }

 /*
  * Similar to dvmHeapBitmapXorWalkList(), but visit the set bits
  * in a single list of bitmaps.  Regardless of the order of the array,
  * the bitmaps will be visited in address order, so that finger will
  * increase monotonically.
  */
 bool dvmHeapBitmapWalkList(const HeapBitmap hbs[], size_t numBitmaps,
         bool (*callback)(size_t numPtrs, void **ptrs,
                          const void *finger, void *arg),
         void *callbackArg)
 {
     size_t indexList[numBitmaps];
     size_t i;

     /* Sort the bitmaps by address.
      */
     createSortedBitmapIndexList(hbs, numBitmaps, indexList);

     /* Walk each bitmap, lowest address first.
      */
     for (i = 0; i < numBitmaps; i++) {
         bool ok;

         ok = dvmHeapBitmapWalk(&hbs[indexList[i]], callback, callbackArg);
         if (!ok) {
             return false;
         }
     }

     return true;
 }
	/*
	* Copyright (C) 2008 The Android Open Source Project
	*
	* Licensed under the Apache License, Version 2.0 (the "License");
	* you may not use this file except in compliance with the License.
	* You may obtain a copy of the License at
	*
	* http://www.apache.org/licenses/LICENSE-2.0
	*
	* Unless required by applicable law or agreed to in writing, software
	* distributed under the License is distributed on an "AS IS" BASIS,
	* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
	* See the License for the specific language governing permissions and
	* limitations under the License.
	*/

	#include "Dalvik.h"
	#include "HeapBitmap.h"
	#include "clz.h"
	#include <limits.h> // for ULONG_MAX
	#include <sys/mman.h> // for madvise(), mmap()
	#include <cutils/ashmem.h>

	#define HB_ASHMEM_NAME "dalvik-heap-bitmap"

	#ifndef PAGE_SIZE
	#define PAGE_SIZE 4096
	#endif
	#define ALIGN_UP_TO_PAGE_SIZE(p) \
	(((size_t)(p) + (PAGE_SIZE - 1)) & ~(PAGE_SIZE - 1))

	#define LIKELY(exp) (__builtin_expect((exp) != 0, true))
	#define UNLIKELY(exp) (__builtin_expect((exp) != 0, false))

	/*
	* Initialize a HeapBitmap so that it points to a bitmap large
	* enough to cover a heap at <base> of <maxSize> bytes, where
	* objects are guaranteed to be HB_OBJECT_ALIGNMENT-aligned.
	*/
	bool
	dvmHeapBitmapInit(HeapBitmap hb, const void base, size_t maxSize,
	const char *name)
	{
	void *bits;
	size_t bitsLen;
	size_t allocLen;
	int fd;
	char nameBuf[ASHMEM_NAME_LEN] = HB_ASHMEM_NAME;

	assert(hb != NULL);

	bitsLen = HB_OFFSET_TO_INDEX(maxSize) * sizeof(*hb->bits);
	allocLen = ALIGN_UP_TO_PAGE_SIZE(bitsLen); // required by ashmem

	if (name != NULL) {
	snprintf(nameBuf, sizeof(nameBuf), HB_ASHMEM_NAME "/%s", name);
	}
	fd = ashmem_create_region(nameBuf, allocLen);
	if (fd < 0) {
	LOGE("Could not create %zu-byte ashmem region \"%s\" to cover "
	"%zu-byte heap (%d)\n",
	allocLen, nameBuf, maxSize, fd);
	return false;
	}

	bits = mmap(NULL, bitsLen, PROT_READ \| PROT_WRITE, MAP_PRIVATE, fd, 0);
	close(fd);
	if (bits == MAP_FAILED) {
	LOGE("Could not mmap %d-byte ashmem region \"%s\"\n",
	bitsLen, nameBuf);
	return false;
	}

	memset(hb, 0, sizeof(*hb));
	hb->bits = bits;
	hb->bitsLen = bitsLen;
	hb->base = (uintptr_t)base;
	hb->max = hb->base - 1;

	return true;
	}

	/*
	* Initialize <hb> so that it covers the same extent as <templateBitmap>.
	*/
	bool
	dvmHeapBitmapInitFromTemplate(HeapBitmap hb, const HeapBitmap templateBitmap,
	const char *name)
	{
	return dvmHeapBitmapInit(hb,
	(void *)templateBitmap->base, HB_MAX_OFFSET(templateBitmap), name);
	}

	/*
	* Initialize the bitmaps in <out> so that they cover the same extent as
	* the corresponding bitmaps in <templates>.
	*/
	bool
	dvmHeapBitmapInitListFromTemplates(HeapBitmap out[], HeapBitmap templates[],
	size_t numBitmaps, const char *name)
	{
	size_t i;
	char fullName[PATH_MAX];

	fullName[sizeof(fullName)-1] = '\0';
	for (i = 0; i < numBitmaps; i++) {
	bool ok;

	/* If two ashmem regions have the same name, only one gets
	* the name when looking at the maps.
	*/
	snprintf(fullName, sizeof(fullName)-1, "%s/%zd", name, i);

	ok = dvmHeapBitmapInitFromTemplate(&out[i], &templates[i], fullName);
	if (!ok) {
	dvmHeapBitmapDeleteList(out, i);
	return false;
	}
	}
	return true;
	}

	/*
	* Clean up any resources associated with the bitmap.
	*/
	void
	dvmHeapBitmapDelete(HeapBitmap *hb)
	{
	assert(hb != NULL);

	if (hb->bits != NULL) {
	// Re-calculate the size we passed to mmap().
	size_t allocLen = ALIGN_UP_TO_PAGE_SIZE(hb->bitsLen);
	munmap((char *)hb->bits, allocLen);
	}
	memset(hb, 0, sizeof(*hb));
	}

	/*
	* Clean up any resources associated with the bitmaps.
	*/
	void
	dvmHeapBitmapDeleteList(HeapBitmap hbs[], size_t numBitmaps)
	{
	size_t i;

	for (i = 0; i < numBitmaps; i++) {
	dvmHeapBitmapDelete(&hbs[i]);
	}
	}

	/*
	* Fill the bitmap with zeroes. Returns the bitmap's memory to
	* the system as a side-effect.
	*/
	void
	dvmHeapBitmapZero(HeapBitmap *hb)
	{
	assert(hb != NULL);

	if (hb->bits != NULL) {
	/* This returns the memory to the system.
	* Successive page faults will return zeroed memory.
	*/
	madvise(hb->bits, hb->bitsLen, MADV_DONTNEED);
	hb->max = hb->base - 1;
	}
	}

	/*
	* Walk through the bitmaps in increasing address order, and find the
	* object pointers that correspond to places where the bitmaps differ.
	* Call <callback> zero or more times with lists of these object pointers.
	*
	* The <finger> argument to the callback indicates the next-highest
	* address that hasn't been visited yet; setting bits for objects whose
	* addresses are less than <finger> are not guaranteed to be seen by
	* the current XorWalk. <finger> will be set to ULONG_MAX when the
	* end of the bitmap is reached.
	*/
	bool
	dvmHeapBitmapXorWalk(const HeapBitmap hb1, const HeapBitmap hb2,
	bool (callback)(size_t numPtrs, void *ptrs,
	const void finger, void arg),
	void *callbackArg)
	{
	static const size_t kPointerBufSize = 128;
	void *pointerBuf[kPointerBufSize];
	void **pb = pointerBuf;
	size_t index;
	size_t i;

	#define FLUSH_POINTERBUF(finger_) \
	do { \
	if (!callback(pb - pointerBuf, (void **)pointerBuf, \
	(void *)(finger_), callbackArg)) \
	{ \
	LOGW("dvmHeapBitmapXorWalk: callback failed\n"); \
	return false; \
	} \
	pb = pointerBuf; \
	} while (false)

	#define DECODE_BITS(hb_, bits_, update_index_) \
	do { \
	if (UNLIKELY(bits_ != 0)) { \
	static const unsigned long kHighBit = \
	(unsigned long)1 << (HB_BITS_PER_WORD - 1); \
	const uintptr_t ptrBase = HB_INDEX_TO_OFFSET(i) + hb_->base; \
	/TODO: hold onto ptrBase so we can shrink max later if possible / \
	/TODO: see if this is likely or unlikely / \
	while (bits_ != 0) { \
	const int rshift = CLZ(bits_); \
	bits_ &= ~(kHighBit >> rshift); \
	pb++ = (void )(ptrBase + rshift * HB_OBJECT_ALIGNMENT); \
	} \
	/* Make sure that there are always enough slots available */ \
	/* for an entire word of 1s. */ \
	if (kPointerBufSize - (pb - pointerBuf) < HB_BITS_PER_WORD) { \
	FLUSH_POINTERBUF(ptrBase + \
	HB_BITS_PER_WORD * HB_OBJECT_ALIGNMENT); \
	if (update_index_) { \
	/* The callback may have caused hb_->max to grow. */ \
	index = HB_OFFSET_TO_INDEX(hb_->max - hb_->base); \
	} \
	} \
	} \
	} while (false)

	assert(hb1 != NULL);
	assert(hb1->bits != NULL);
	assert(hb2 != NULL);
	assert(hb2->bits != NULL);
	assert(callback != NULL);

	if (hb1->base != hb2->base) {
	LOGW("dvmHeapBitmapXorWalk: bitmaps cover different heaps "
	"(0x%08x != 0x%08x)\n",
	(uintptr_t)hb1->base, (uintptr_t)hb2->base);
	return false;
	}
	if (hb1->bitsLen != hb2->bitsLen) {
	LOGW("dvmHeapBitmapXorWalk: size of bitmaps differ (%zd != %zd)\n",
	hb1->bitsLen, hb2->bitsLen);
	return false;
	}
	if (hb1->max < hb1->base && hb2->max < hb2->base) {
	/* Easy case; both are obviously empty.
	*/
	return true;
	}

	/* First, walk along the section of the bitmaps that may be the same.
	*/
	if (hb1->max >= hb1->base && hb2->max >= hb2->base) {
	unsigned long int p1, p2;
	uintptr_t offset;

	offset = ((hb1->max < hb2->max) ? hb1->max : hb2->max) - hb1->base;
	//TODO: keep track of which (and whether) one is longer for later
	index = HB_OFFSET_TO_INDEX(offset);

	p1 = hb1->bits;
	p2 = hb2->bits;
	for (i = 0; i <= index; i++) {
	//TODO: unroll this. pile up a few in locals?
	unsigned long int diff = p1++ ^ p2++;
	DECODE_BITS(hb1, diff, false);
	//BUG: if the callback was called, either max could have changed.
	}
	/* The next index to look at.
	*/
	index++;
	} else {
	/* One of the bitmaps is empty.
	*/
	index = 0;
	}

	/* If one bitmap's max is larger, walk through the rest of the
	* set bits.
	*/
	const HeapBitmap *longHb;
	unsigned long int *p;
	//TODO: may be the same size, in which case this is wasted work
	longHb = (hb1->max > hb2->max) ? hb1 : hb2;
	i = index;
	index = HB_OFFSET_TO_INDEX(longHb->max - longHb->base);
	p = longHb->bits + i;
	for (/* i = i */; i <= index; i++) {
	//TODO: unroll this
	unsigned long bits = *p++;
	DECODE_BITS(longHb, bits, true);
	}

	if (pb > pointerBuf) {
	/* Set the finger to the end of the heap (rather than longHb->max)
	* so that the callback doesn't expect to be called again
	* if it happens to change the current max.
	*/
	FLUSH_POINTERBUF(longHb->base + HB_MAX_OFFSET(longHb));
	}

	return true;

	#undef FLUSH_POINTERBUF
	#undef DECODE_BITS
	}

	/*
	* Fills outIndexList with indices so that for all i:
	*
	* hb[outIndexList[i]].base < hb[outIndexList[i+1]].base
	*/
	static void
	createSortedBitmapIndexList(const HeapBitmap hbs[], size_t numBitmaps,
	size_t outIndexList[])
	{
	int i, j;

	/* numBitmaps is usually 2 or 3, so use a simple sort */
	for (i = 0; i < (int) numBitmaps; i++) {
	outIndexList[i] = i;
	for (j = 0; j < i; j++) {
	if (hbs[j].base > hbs[i].base) {
	int tmp = outIndexList[i];
	outIndexList[i] = outIndexList[j];
	outIndexList[j] = tmp;
	}
	}
	}
	}

	/*
	* Similar to dvmHeapBitmapXorWalk(), but compare multiple bitmaps.
	* Regardless of the order of the arrays, the bitmaps will be visited
	* in address order, so that finger will increase monotonically.
	*/
	bool
	dvmHeapBitmapXorWalkLists(const HeapBitmap hbs1[], const HeapBitmap hbs2[],
	size_t numBitmaps,
	bool (callback)(size_t numPtrs, void *ptrs,
	const void finger, void arg),
	void *callbackArg)
	{
	size_t indexList[numBitmaps];
	size_t i;

	/* Sort the bitmaps by address. Assume that the two lists contain
	* congruent bitmaps.
	*/
	createSortedBitmapIndexList(hbs1, numBitmaps, indexList);

	/* Walk each pair of bitmaps, lowest address first.
	*/
	for (i = 0; i < numBitmaps; i++) {
	bool ok;

	ok = dvmHeapBitmapXorWalk(&hbs1[indexList[i]], &hbs2[indexList[i]],
	callback, callbackArg);
	if (!ok) {
	return false;
	}
	}

	return true;
	}

	/*
	* Similar to dvmHeapBitmapXorWalk(), but visit the set bits
	* in a single bitmap.
	*/
	bool
	dvmHeapBitmapWalk(const HeapBitmap *hb,
	bool (callback)(size_t numPtrs, void *ptrs,
	const void finger, void arg),
	void *callbackArg)
	{
	/* Create an empty bitmap with the same extent as <hb>.
	* Don't actually allocate any memory.
	*/
	HeapBitmap emptyHb = *hb;
	emptyHb.max = emptyHb.base - 1; // empty
	emptyHb.bits = (void *)1; // non-NULL but intentionally bad

	return dvmHeapBitmapXorWalk(hb, &emptyHb, callback, callbackArg);
	}

	/*
	* Similar to dvmHeapBitmapXorWalkList(), but visit the set bits
	* in a single list of bitmaps. Regardless of the order of the array,
	* the bitmaps will be visited in address order, so that finger will
	* increase monotonically.
	*/
	bool dvmHeapBitmapWalkList(const HeapBitmap hbs[], size_t numBitmaps,
	bool (callback)(size_t numPtrs, void *ptrs,
	const void finger, void arg),
	void *callbackArg)
	{
	size_t indexList[numBitmaps];
	size_t i;

	/* Sort the bitmaps by address.
	*/
	createSortedBitmapIndexList(hbs, numBitmaps, indexList);

	/* Walk each bitmap, lowest address first.
	*/
	for (i = 0; i < numBitmaps; i++) {
	bool ok;

	ok = dvmHeapBitmapWalk(&hbs[indexList[i]], callback, callbackArg);
	if (!ok) {
	return false;
	}
	}

	return true;
	}