Function allocate_memory

system/lib/emmalloc.c:664–812

EM_JS_DEPS(_em_malloc_deps, "$ptrToString");

static void *allocate_memory(size_t alignment, size_t size) {
  ASSERT_MALLOC_IS_ACQUIRED();

#ifdef EMMALLOC_VERBOSE
  MAIN_THREAD_ASYNC_EM_ASM(out('allocate_memory(align=' + $0 + ', size=' + Number($1) + ' bytes)'), alignment, size);
#endif

#ifdef EMMALLOC_MEMVALIDATE
  validate_memory_regions();
#endif

  if (!IS_POWER_OF_2(alignment)) {
#ifdef EMMALLOC_VERBOSE
    MAIN_THREAD_ASYNC_EM_ASM(out('Allocation failed: alignment not power of 2!'));
#endif
    return 0;
  }

  if (size > MAX_ALLOC_SIZE) {
#ifdef EMMALLOC_VERBOSE
    MAIN_THREAD_ASYNC_EM_ASM(out('Allocation failed: attempted allocation size is too large: ' + Number($0) + 'bytes! (negative integer wraparound?)'), size);
#endif
    return 0;
  }

  alignment = validate_alloc_alignment(alignment);
  size = validate_alloc_size(size);

  // Attempt to allocate memory starting from smallest bucket that can contain the required amount of memory.
  // Under normal alignment conditions this should always be the first or second bucket we look at, but if
  // performing an allocation with complex alignment, we may need to look at multiple buckets.
  int bucketIndex = compute_free_list_bucket(size);
  BUCKET_BITMASK_T bucketMask = freeRegionBucketsUsed >> bucketIndex;

  // Loop through each bucket that has free regions in it, based on bits set in freeRegionBucketsUsed bitmap.
  while (bucketMask) {
    BUCKET_BITMASK_T indexAdd = __builtin_ctzll(bucketMask);
    bucketIndex += indexAdd;
    bucketMask >>= indexAdd;
    assert(bucketIndex >= 0);
    assert(bucketIndex <= NUM_FREE_BUCKETS-1);
    assert(freeRegionBucketsUsed & (((BUCKET_BITMASK_T)1) << bucketIndex));

    Region *freeRegion = freeRegionBuckets[bucketIndex].next;
    assert(freeRegion);
    if (freeRegion != &freeRegionBuckets[bucketIndex]) {
      void *ptr = attempt_allocate(freeRegion, alignment, size);
      if (ptr) {
        return ptr;
      }

      // We were not able to allocate from the first region found in this bucket, so penalize
      // the region by cycling it to the end of the doubly circular linked list. (constant time)
      // This provides a randomized guarantee that when performing allocations of size k to a
      // bucket of [k-something, k+something] range, we will not always attempt to satisfy the
      // allocation from the same available region at the front of the list, but we try each
      // region in turn.
      unlink_from_free_list(freeRegion);