Function claim_more_memory

system/lib/emmalloc.c:457–544

}

static bool claim_more_memory(size_t numBytes) {
#ifdef EMMALLOC_VERBOSE
  MAIN_THREAD_ASYNC_EM_ASM(out('claim_more_memory(numBytes='+Number($0)+ ')'), numBytes);
#endif

#ifdef EMMALLOC_MEMVALIDATE
  validate_memory_regions();
#endif

  // Make sure we always send sbrk requests with the same alignment that sbrk()
  // allocates memory at. Otherwise we will not properly interpret returned memory
  // to form a seamlessly contiguous region with earlier root regions, which would
  // lead to inefficiently treating the sbrk()ed region to be a new disjoint root
  // region.
  numBytes = (size_t)ALIGN_UP(numBytes, MALLOC_ALIGNMENT);

  // Claim memory via sbrk
  assert((int64_t)numBytes >= 0);
  uint8_t *startPtr = (uint8_t*)_sbrk64((int64_t)numBytes);
  if ((intptr_t)startPtr == -1) {
#ifdef EMMALLOC_VERBOSE
    MAIN_THREAD_ASYNC_EM_ASM(err('claim_more_memory: sbrk failed!'));
#endif
    return false;
  }
#ifdef EMMALLOC_VERBOSE
  MAIN_THREAD_ASYNC_EM_ASM(out('claim_more_memory: claimed ' + ptrToString($0) + ' - ' + ptrToString($1) + ' (' + Number($2) + ' bytes) via sbrk()'), startPtr, startPtr + numBytes, numBytes);
#endif
  assert(HAS_ALIGNMENT(startPtr, alignof(size_t)));
  uint8_t *endPtr = startPtr + numBytes;

  // Create a sentinel region at the end of the new heap block
  Region *endSentinelRegion = (Region*)(endPtr - sizeof(Region));
  create_used_region(endSentinelRegion, sizeof(Region));
#ifdef EMMALLOC_VERBOSE
  MAIN_THREAD_ASYNC_EM_ASM(out('claim_more_memory: created a sentinel memory region at address ' + ptrToString($0)), endSentinelRegion);
#endif

  // If we are the sole user of sbrk(), it will feed us continuous/consecutive memory addresses - take advantage
  // of that if so: instead of creating two disjoint memory regions blocks, expand the previous one to a larger size.
  uint8_t *previousSbrkEndAddress = listOfAllRegions ? listOfAllRegions->endPtr : 0;
  if (startPtr == previousSbrkEndAddress) {
#ifdef EMMALLOC_VERBOSE
    MAIN_THREAD_ASYNC_EM_ASM(err('claim_more_memory: sbrk() returned a region contiguous to last root region, expanding the existing root region'));
#endif
    Region *prevEndSentinel = prev_region((Region*)startPtr);
    assert(debug_region_is_consistent(prevEndSentinel));
    assert(region_is_in_use(prevEndSentinel));
    Region *prevRegion = prev_region(prevEndSentinel);
    assert(debug_region_is_consistent(prevRegion));

    listOfAllRegions->endPtr = endPtr;

    // Two scenarios, either the last region of the previous block was in use, in which case we need to create
    // a new free region in the newly allocated space; or it was free, in which case we can extend that region
    // to cover a larger size.
    if (region_is_free(prevRegion)) {
      size_t newFreeRegionSize = (uint8_t*)endSentinelRegion - (uint8_t*)prevRegion;