src/heap.c

/*----------------------------------------------------------------------------
Copyright (c) 2018, Microsoft Research, Daan Leijen
This is free software; you can redistribute it and/or modify it under the
terms of the MIT license. A copy of the license can be found in the file
"LICENSE" at the root of this distribution.
-----------------------------------------------------------------------------*/

#include "mimalloc.h"
#include "mimalloc-internal.h"
#include "mimalloc-atomic.h"

#include <string.h>  // memset, memcpy


/* -----------------------------------------------------------
  Helpers
----------------------------------------------------------- */

// return `true` if ok, `false` to break
typedef bool (heap_page_visitor_fun)(mi_heap_t* heap, mi_page_queue_t* pq, mi_page_t* page, void* arg1, void* arg2);

// Visit all pages in a heap; returns `false` if break was called.
static bool mi_heap_visit_pages(mi_heap_t* heap, heap_page_visitor_fun* fn, void* arg1, void* arg2)
{
  if (heap==NULL || heap->page_count==0) return 0;

  // visit all pages
  #if MI_DEBUG>1
  size_t total = heap->page_count;
  #endif
  size_t count = 0;
  for (size_t i = 0; i <= MI_BIN_FULL; i++) {
    mi_page_queue_t* pq = &heap->pages[i];
    mi_page_t* page = pq->first;
    while(page != NULL) {
      mi_page_t* next = page->next; // save next in case the page gets removed from the queue
      mi_assert_internal(mi_page_heap(page) == heap);
      count++;
      if (!fn(heap, pq, page, arg1, arg2)) return false;
      page = next; // and continue
    }
  }
  mi_assert_internal(count == total);
  return true;
}


#if MI_DEBUG>=2
static bool mi_heap_page_is_valid(mi_heap_t* heap, mi_page_queue_t* pq, mi_page_t* page, void* arg1, void* arg2) {
  UNUSED(arg1);
  UNUSED(arg2);
  UNUSED(pq);
  mi_assert_internal(mi_page_heap(page) == heap);
  mi_segment_t* segment = _mi_page_segment(page);
  mi_assert_internal(segment->thread_id == heap->thread_id);
  mi_assert_expensive(_mi_page_is_valid(page));
  return true;
}
#endif
#if MI_DEBUG>=3
static bool mi_heap_is_valid(mi_heap_t* heap) {
  mi_assert_internal(heap!=NULL);
  mi_heap_visit_pages(heap, &mi_heap_page_is_valid, NULL, NULL);
  return true;
}
#endif




/* -----------------------------------------------------------
  "Collect" pages by migrating `local_free` and `thread_free`
  lists and freeing empty pages. This is done when a thread
  stops (and in that case abandons pages if there are still
  blocks alive)
----------------------------------------------------------- */

typedef enum mi_collect_e {
  MI_NORMAL,
  MI_FORCE,
  MI_ABANDON
} mi_collect_t;


static bool mi_heap_page_collect(mi_heap_t* heap, mi_page_queue_t* pq, mi_page_t* page, void* arg_collect, void* arg2 ) {
  UNUSED(arg2);
  UNUSED(heap);
  mi_assert_internal(mi_heap_page_is_valid(heap, pq, page, NULL, NULL));
  mi_collect_t collect = *((mi_collect_t*)arg_collect);
  _mi_page_free_collect(page, collect >= MI_FORCE);
  if (mi_page_all_free(page)) {
    // no more used blocks, free the page. 
    // note: this will free retired pages as well.
    _mi_page_free(page, pq, collect >= MI_FORCE);
  }
  else if (collect == MI_ABANDON) {
    // still used blocks but the thread is done; abandon the page
    _mi_page_abandon(page, pq);
  }
  return true; // don't break
}

static bool mi_heap_page_never_delayed_free(mi_heap_t* heap, mi_page_queue_t* pq, mi_page_t* page, void* arg1, void* arg2) {
  UNUSED(arg1);
  UNUSED(arg2);
  UNUSED(heap);
  UNUSED(pq);
  _mi_page_use_delayed_free(page, MI_NEVER_DELAYED_FREE, false);
  return true; // don't break
}

static void mi_heap_collect_ex(mi_heap_t* heap, mi_collect_t collect)
{
  if (!mi_heap_is_initialized(heap)) return;
  _mi_deferred_free(heap, collect >= MI_FORCE);

  // note: never reclaim on collect but leave it to threads that need storage to reclaim 
  if (
  #ifdef NDEBUG
      collect == MI_FORCE
  #else
      collect >= MI_FORCE
  #endif
    && _mi_is_main_thread() && mi_heap_is_backing(heap) && !heap->no_reclaim)
  {
    // the main thread is abandoned (end-of-program), try to reclaim all abandoned segments.
    // if all memory is freed by now, all segments should be freed.
    _mi_abandoned_reclaim_all(heap, &heap->tld->segments);
  }
  

  // if abandoning, mark all pages to no longer add to delayed_free
  if (collect == MI_ABANDON) {
    mi_heap_visit_pages(heap, &mi_heap_page_never_delayed_free, NULL, NULL);
  }

  // free thread delayed blocks.
  // (if abandoning, after this there are no more thread-delayed references into the pages.)
  _mi_heap_delayed_free(heap);

  // collect retired pages
  _mi_heap_collect_retired(heap, collect >= MI_FORCE);

  // collect all pages owned by this thread
  mi_heap_visit_pages(heap, &mi_heap_page_collect, &collect, NULL);
  mi_assert_internal( collect != MI_ABANDON || mi_atomic_read_ptr(mi_block_t,&heap->thread_delayed_free) == NULL );

  // collect segment caches
  if (collect >= MI_FORCE) {
    _mi_segment_thread_collect(&heap->tld->segments);
  }

  #ifndef NDEBUG
  // collect regions
  if (collect >= MI_FORCE && _mi_is_main_thread() && mi_heap_is_backing(heap)) {
    _mi_mem_collect(&heap->tld->os);
  }
  #endif
}

void _mi_heap_collect_abandon(mi_heap_t* heap) {
  mi_heap_collect_ex(heap, MI_ABANDON);
}

void mi_heap_collect(mi_heap_t* heap, bool force) mi_attr_noexcept {
  mi_heap_collect_ex(heap, (force ? MI_FORCE : MI_NORMAL));
}

void mi_collect(bool force) mi_attr_noexcept {
  mi_heap_collect(mi_get_default_heap(), force);
}


/* -----------------------------------------------------------
  Heap new
----------------------------------------------------------- */

mi_heap_t* mi_heap_get_default(void) {
  mi_thread_init();
  return mi_get_default_heap();
}

mi_heap_t* mi_heap_get_backing(void) {
  mi_heap_t* heap = mi_heap_get_default();
  mi_assert_internal(heap!=NULL);
  mi_heap_t* bheap = heap->tld->heap_backing;
  mi_assert_internal(bheap!=NULL);
  mi_assert_internal(bheap->thread_id == _mi_thread_id());
  return bheap;
}

mi_heap_t* mi_heap_new(void) {
  mi_heap_t* bheap = mi_heap_get_backing();
  mi_heap_t* heap = mi_heap_malloc_tp(bheap, mi_heap_t);  // todo: OS allocate in secure mode?
  if (heap==NULL) return NULL;
  memcpy(heap, &_mi_heap_empty, sizeof(mi_heap_t));
  heap->tld = bheap->tld;
  heap->thread_id = _mi_thread_id();
  _mi_random_split(&bheap->random, &heap->random);
  heap->cookie  = _mi_heap_random_next(heap) | 1;
  heap->keys[0] = _mi_heap_random_next(heap);
  heap->keys[1] = _mi_heap_random_next(heap);
  heap->extra_padding = bheap->extra_padding;
  heap->no_reclaim = true;  // don't reclaim abandoned pages or otherwise destroy is unsafe
  // push on the thread local heaps list
  heap->next = heap->tld->heaps;
  heap->tld->heaps = heap;
  return heap;
}

uintptr_t _mi_heap_random_next(mi_heap_t* heap) {
  return _mi_random_next(&heap->random);
}

void mi_heap_set_extra_padding(mi_heap_t* heap, size_t extra_padding) {
  if (extra_padding > 1*MiB) extra_padding = 1*MiB;
  heap->extra_padding = extra_padding;
}

// zero out the page queues
static void mi_heap_reset_pages(mi_heap_t* heap) {
  mi_assert_internal(mi_heap_is_initialized(heap));
  // TODO: copy full empty heap instead?
  memset(&heap->pages_free_direct, 0, sizeof(heap->pages_free_direct));
#ifdef MI_MEDIUM_DIRECT
  memset(&heap->pages_free_medium, 0, sizeof(heap->pages_free_medium));
#endif
  memcpy(&heap->pages, &_mi_heap_empty.pages, sizeof(heap->pages));
  heap->thread_delayed_free = NULL;
  heap->page_count = 0;
}

// called from `mi_heap_destroy` and `mi_heap_delete` to free the internal heap resources.
static void mi_heap_free(mi_heap_t* heap) {
  mi_assert(heap != NULL);
  mi_assert_internal(mi_heap_is_initialized(heap));
  if (mi_heap_is_backing(heap)) return; // dont free the backing heap

  // reset default
  if (mi_heap_is_default(heap)) {
    _mi_heap_set_default_direct(heap->tld->heap_backing);
  }

  // remove ourselves from the thread local heaps list
  // linear search but we expect the number of heaps to be relatively small
  mi_heap_t* prev = NULL;
  mi_heap_t* curr = heap->tld->heaps; 
  while (curr != heap && curr != NULL) {
    prev = curr;
    curr = curr->next;
  }
  mi_assert_internal(curr == heap);
  if (curr == heap) {
    if (prev != NULL) { prev->next = heap->next; }
                 else { heap->tld->heaps = heap->next; }
  }
  mi_assert_internal(heap->tld->heaps != NULL);

  // and free the used memory
  mi_free(heap);
}


/* -----------------------------------------------------------
  Heap destroy
----------------------------------------------------------- */

static bool _mi_heap_page_destroy(mi_heap_t* heap, mi_page_queue_t* pq, mi_page_t* page, void* arg1, void* arg2) {
  UNUSED(arg1);
  UNUSED(arg2);
  UNUSED(heap);
  UNUSED(pq);

  // ensure no more thread_delayed_free will be added
  _mi_page_use_delayed_free(page, MI_NEVER_DELAYED_FREE, false);

  // stats
  const size_t bsize = mi_page_block_size(page);
  if (bsize > MI_LARGE_OBJ_SIZE_MAX) {
    if (bsize > MI_HUGE_OBJ_SIZE_MAX) {
      _mi_stat_decrease(&heap->tld->stats.giant, bsize);
    }
    else {
      _mi_stat_decrease(&heap->tld->stats.huge, bsize);
    }
  }
#if (MI_STAT>1)
  _mi_page_free_collect(page, false);  // update used count
  const size_t inuse = page->used;
  if (bsize <= MI_LARGE_OBJ_SIZE_MAX) {
    mi_heap_stat_decrease(heap, normal[_mi_bin(bsize)], inuse);
  }
  mi_heap_stat_decrease(heap, malloc, bsize * inuse);  // todo: off for aligned blocks...
#endif

  /// pretend it is all free now
  mi_assert_internal(mi_page_thread_free(page) == NULL);
  page->used = 0;

  // and free the page
  // mi_page_free(page,false);
  page->next = NULL;
  page->prev = NULL;
  _mi_segment_page_free(page,false /* no force? */, &heap->tld->segments);

  return true; // keep going
}

void _mi_heap_destroy_pages(mi_heap_t* heap) {
  mi_heap_visit_pages(heap, &_mi_heap_page_destroy, NULL, NULL);
  mi_heap_reset_pages(heap);
}

void mi_heap_destroy(mi_heap_t* heap) {
  mi_assert(heap != NULL);
  mi_assert(mi_heap_is_initialized(heap));
  mi_assert(heap->no_reclaim);
  mi_assert_expensive(mi_heap_is_valid(heap));
  if (!mi_heap_is_initialized(heap)) return;
  if (!heap->no_reclaim) {
    // don't free in case it may contain reclaimed pages
    mi_heap_delete(heap);
  }
  else {
    // free all pages
    _mi_heap_destroy_pages(heap);
    mi_heap_free(heap);
  }
}



/* -----------------------------------------------------------
  Safe Heap delete
----------------------------------------------------------- */

// Tranfer the pages from one heap to the other
static void mi_heap_absorb(mi_heap_t* heap, mi_heap_t* from) {
  mi_assert_internal(heap!=NULL);
  if (from==NULL || from->page_count == 0) return;

  // reduce the size of the delayed frees
  _mi_heap_delayed_free(from);
  
  // transfer all pages by appending the queues; this will set a new heap field 
  // so threads may do delayed frees in either heap for a while.
  // note: appending waits for each page to not be in the `MI_DELAYED_FREEING` state
  // so after this only the new heap will get delayed frees
  for (size_t i = 0; i <= MI_BIN_FULL; i++) {
    mi_page_queue_t* pq = &heap->pages[i];
    mi_page_queue_t* append = &from->pages[i];
    size_t pcount = _mi_page_queue_append(heap, pq, append);
    heap->page_count += pcount;
    from->page_count -= pcount;
  }
  mi_assert_internal(from->page_count == 0);

  // and do outstanding delayed frees in the `from` heap  
  // note: be careful here as the `heap` field in all those pages no longer point to `from`,
  // turns out to be ok as `_mi_heap_delayed_free` only visits the list and calls a 
  // the regular `_mi_free_delayed_block` which is safe.
  _mi_heap_delayed_free(from);  
  mi_assert_internal(from->thread_delayed_free == NULL);

  // and reset the `from` heap
  mi_heap_reset_pages(from);  
}

// Safe delete a heap without freeing any still allocated blocks in that heap.
void mi_heap_delete(mi_heap_t* heap)
{
  mi_assert(heap != NULL);
  mi_assert(mi_heap_is_initialized(heap));
  mi_assert_expensive(mi_heap_is_valid(heap));
  if (!mi_heap_is_initialized(heap)) return;

  if (!mi_heap_is_backing(heap)) {
    // tranfer still used pages to the backing heap
    mi_heap_absorb(heap->tld->heap_backing, heap);
  }
  else {
    // the backing heap abandons its pages
    _mi_heap_collect_abandon(heap);
  }
  mi_assert_internal(heap->page_count==0);
  mi_heap_free(heap);
}

mi_heap_t* mi_heap_set_default(mi_heap_t* heap) {
  mi_assert(mi_heap_is_initialized(heap));
  if (!mi_heap_is_initialized(heap)) return NULL;
  mi_assert_expensive(mi_heap_is_valid(heap));
  mi_heap_t* old = mi_get_default_heap();
  _mi_heap_set_default_direct(heap);
  return old;
}




/* -----------------------------------------------------------
  Analysis
----------------------------------------------------------- */

// static since it is not thread safe to access heaps from other threads.
static mi_heap_t* mi_heap_of_block(const void* p) {
  if (p == NULL) return NULL;
  mi_segment_t* segment = _mi_ptr_segment(p);
  bool valid = (_mi_ptr_cookie(segment) == segment->cookie);
  mi_assert_internal(valid);
  if (mi_unlikely(!valid)) return NULL;
  return mi_page_heap(_mi_segment_page_of(segment,p));
}

bool mi_heap_contains_block(mi_heap_t* heap, const void* p) {
  mi_assert(heap != NULL);
  if (!mi_heap_is_initialized(heap)) return false;
  return (heap == mi_heap_of_block(p));
}


static bool mi_heap_page_check_owned(mi_heap_t* heap, mi_page_queue_t* pq, mi_page_t* page, void* p, void* vfound) {
  UNUSED(heap);
  UNUSED(pq);
  bool* found = (bool*)vfound;
  mi_segment_t* segment = _mi_page_segment(page);
  void* start = _mi_page_start(segment, page, NULL);
  void* end   = (uint8_t*)start + (page->capacity * mi_page_block_size(page));
  *found = (p >= start && p < end);
  return (!*found); // continue if not found
}

bool mi_heap_check_owned(mi_heap_t* heap, const void* p) {
  mi_assert(heap != NULL);
  if (!mi_heap_is_initialized(heap)) return false;
  if (((uintptr_t)p & (MI_INTPTR_SIZE - 1)) != 0) return false;  // only aligned pointers
  bool found = false;
  mi_heap_visit_pages(heap, &mi_heap_page_check_owned, (void*)p, &found);
  return found;
}

bool mi_check_owned(const void* p) {
  return mi_heap_check_owned(mi_get_default_heap(), p);
}

/* -----------------------------------------------------------
  Visit all heap blocks and areas
  Todo: enable visiting abandoned pages, and
        enable visiting all blocks of all heaps across threads
----------------------------------------------------------- */

// Separate struct to keep `mi_page_t` out of the public interface
typedef struct mi_heap_area_ex_s {
  mi_heap_area_t area;
  mi_page_t*     page;
} mi_heap_area_ex_t;

static bool mi_heap_area_visit_blocks(const mi_heap_area_ex_t* xarea, mi_block_visit_fun* visitor, void* arg) {
  mi_assert(xarea != NULL);
  if (xarea==NULL) return true;
  const mi_heap_area_t* area = &xarea->area;
  mi_page_t* page = xarea->page;
  mi_assert(page != NULL);
  if (page == NULL) return true;

  _mi_page_free_collect(page,true);
  mi_assert_internal(page->local_free == NULL);
  if (page->used == 0) return true;

  const size_t bsize = mi_page_block_size(page);
  size_t   psize;
  uint8_t* pstart = _mi_page_start(_mi_page_segment(page), page, &psize);

  if (page->capacity == 1) {
    // optimize page with one block
    mi_assert_internal(page->used == 1 && page->free == NULL);
    mi_block_info_t info;
    mi_block_t* block = (mi_block_t*)(pstart);
    _mi_page_block_info(page, block, &info);
    return visitor(mi_page_heap(page), area, &info, arg);
  }

  // create a bitmap of free blocks.
  #define MI_MAX_BLOCKS   (MI_SMALL_PAGE_SIZE / sizeof(void*))
  uintptr_t free_map[MI_MAX_BLOCKS / sizeof(uintptr_t)];
  memset(free_map, 0, sizeof(free_map));

  size_t free_count = 0;
  for (mi_block_t* block = page->free; block != NULL; block = mi_block_next(page,block)) {
    free_count++;
    mi_assert_internal((uint8_t*)block >= pstart && (uint8_t*)block < (pstart + psize));
    size_t offset = (uint8_t*)block - pstart;
    mi_assert_internal(offset % bsize == 0);
    size_t blockidx = offset / bsize;  // Todo: avoid division?
    mi_assert_internal( blockidx < MI_MAX_BLOCKS);
    size_t bitidx = (blockidx / sizeof(uintptr_t));
    size_t bit = blockidx - (bitidx * sizeof(uintptr_t));
    free_map[bitidx] |= ((uintptr_t)1 << bit);
  }
  mi_assert_internal(page->capacity == (free_count + page->used));

  // walk through all blocks skipping the free ones
  size_t used_count = 0;
  for (size_t i = 0; i < page->capacity; i++) {
    size_t bitidx = (i / sizeof(uintptr_t));
    size_t bit = i - (bitidx * sizeof(uintptr_t));
    uintptr_t m = free_map[bitidx];
    if (bit == 0 && m == UINTPTR_MAX) {
      i += (sizeof(uintptr_t) - 1); // skip a run of free blocks
    }
    else if ((m & ((uintptr_t)1 << bit)) == 0) {
      used_count++;
      mi_block_info_t info;
      mi_block_t*     block = (mi_block_t*)(pstart + (i * bsize));
      _mi_page_block_info(page, block, &info);
      if (!visitor(mi_page_heap(page), area, &info, arg)) return false;
    }
  }
  mi_assert_internal(page->used == used_count);
  return true;
}

typedef bool (mi_heap_area_visit_fun)(const mi_heap_t* heap, const mi_heap_area_ex_t* area, void* arg);


static bool mi_heap_visit_areas_page(mi_heap_t* heap, mi_page_queue_t* pq, mi_page_t* page, void* vfun, void* arg) {
  UNUSED(heap);
  UNUSED(pq);
  mi_heap_area_visit_fun* fun = (mi_heap_area_visit_fun*)vfun;
  mi_heap_area_ex_t xarea;
  const size_t bsize = mi_page_block_size(page);
  xarea.page = page;
  xarea.area.reserved = page->reserved * bsize;
  xarea.area.committed = page->capacity * bsize;
  xarea.area.blocks = _mi_page_start(_mi_page_segment(page), page, NULL);
  xarea.area.used = page->used * bsize;
  xarea.area.block_size = bsize;
  return fun(heap, &xarea, arg);
}

// Visit all heap pages as areas
static bool mi_heap_visit_areas(const mi_heap_t* heap, mi_heap_area_visit_fun* visitor, void* arg) {
  if (visitor == NULL) return false;
  return mi_heap_visit_pages((mi_heap_t*)heap, &mi_heap_visit_areas_page, (void*)(visitor), arg); // note: function pointer to void* :-{
}

// Just to pass arguments
typedef struct mi_visit_blocks_args_s {
  bool  visit_blocks;
  mi_block_visit_fun* visitor;
  void* arg;
} mi_visit_blocks_args_t;

static bool mi_heap_area_visitor(const mi_heap_t* heap, const mi_heap_area_ex_t* xarea, void* arg) {
  mi_visit_blocks_args_t* args = (mi_visit_blocks_args_t*)arg;
  if (!args->visitor(heap, &xarea->area, NULL, args->arg)) return false;
  if (args->visit_blocks) {
    return mi_heap_area_visit_blocks(xarea, args->visitor, args->arg);
  }
  else {
    return true;
  }
}

// Visit all blocks in a heap
bool mi_heap_visit_blocks(const mi_heap_t* heap, bool visit_blocks, mi_block_visit_fun* visitor, void* arg) {
  mi_visit_blocks_args_t args = { visit_blocks, visitor, arg };
  return mi_heap_visit_areas(heap, &mi_heap_area_visitor, &args);
}

// -----------------------------------------------------------------------
// Print heap blocks in JSON format
// -----------------------------------------------------------------------

typedef struct mi_print_json_s {
  size_t area_count;
  size_t block_count;
  mi_output_fun* out;
  void* out_arg;
} mi_print_json_t;

static bool mi_heap_print_json_visit(const mi_heap_t* heap, const mi_heap_area_t* area, const mi_block_info_t* info, void* arg) {
  UNUSED(heap);
  mi_print_json_t* varg = (mi_print_json_t*)(arg);
  if (info==NULL) {
    _mi_fprintf(varg->out, varg->out_arg, varg->area_count==0 ? " {" : "  ]\n}\n,{");
    varg->area_count++;
    varg->block_count = 0;
    _mi_fprintf(varg->out, varg->out_arg, 
                  "\"page\": %zu, \"start\": 0x%p, \"block_size\": %zu, \"used_size\": %zu,\n  \"reserved\": %zu, \"committed\": %zu, \"blocks\": [\n", 
                  varg->area_count, area->blocks, area->block_size, area->used, area->reserved, area->committed);
  }
  else {
    _mi_fprintf(varg->out, varg->out_arg, 
                   "%s\"block\": 0x%p, \"valid\": %s, \"size\": %zu, \"usable_size\": %zu, \"allocated_size\": %zu,\n    ", 
                    (varg->block_count==0 ? "   {" : "  ,{"), info->block, info->valid ? "true" : "false", info->size, info->usable_size, info->allocated_size);
    varg->block_count++;
    int lineno;
    const char* fname;
    void* ret = mi_source_unpack(info->source, &fname, &lineno);
    if (fname!=NULL) _mi_fprintf(varg->out, varg->out_arg, "\"source\": \"%s:%i\" }\n", fname, lineno);
    else if (ret != NULL) _mi_fprintf(varg->out, varg->out_arg, "\"source\": \"0x%p\" }\n", ret);
    else _mi_fprintf(varg->out, varg->out_arg, "\"source\": \"\" }\n");
  }
  return true;
}

void mi_heap_print_json(mi_heap_t* heap, mi_output_fun* out, void* arg) {
  if (heap==NULL) heap = mi_heap_get_default();
  mi_print_json_t info = { 0, 0, out, arg };
  _mi_fprintf(info.out, info.out_arg, "{ \"heap\": 0x%p, \"thread_id\": 0x%zx, \"page_count\": %zu, \"block_padding\": %zu, \"pages\": [\n", heap, heap->thread_id, heap->page_count, mi_extra_padding(heap) );
  mi_heap_visit_blocks(heap, true, &mi_heap_print_json_visit, &info);
  _mi_fprintf(info.out, info.out_arg, info.area_count==0 ? "]\n" : "  ] }\n] }\n");
}

bool mi_heap_is_empty(mi_heap_t* heap) {
  if (heap==NULL) heap = mi_heap_get_default();
  mi_heap_collect(heap,false);
  return (heap->page_count == 0);
}

void mi_heap_check_leak(mi_heap_t* heap, mi_output_fun* out, void* arg) {
  if (!mi_heap_is_empty(heap)) {
    _mi_fprintf(out,arg,"mimalloc: potential memory leak detected; current heap blocks:\n");
    mi_heap_print_json(heap, out, arg);
  }
}