Class: Unistd

Inherits:
Object show all
Defined in:
lib/rlang/lib/unistd.rb

Class Method Summary collapse

Class Method Details

.sbrk(n) ⇒ Object 



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# File 'lib/rlang/lib/unistd.rb', line 32

def self.sbrk(n)
  # local variables used. All default type
  # wasm_mem_size:  current wasm memory size (in bytes)
  # heap_break:     current heap break
  #
  # new_heap_size:  new heap size (HEAP_SIZE + n)
  # new_heap_break: new heap break (HEAP + HEAP_SIZE + n)
  # more_pages:     how many more WASM pages are needed

  # return current break if n is 0
  heap_break = $HEAP + $HEAP_SIZE
  return heap_break if n == 0

  # check if new heap size is beyond authorized limit
  new_heap_size = $HEAP_SIZE + n
  return -1 if new_heap_size >= $HEAP_MAX_SIZE

  # We are good, so now check if we need more WASM 
  # memory pages (1 page = 64 KB)
  wasm_mem_size = Memory.size * 65536
  new_heap_break = heap_break + n

  # need to grow memory? if so by how many WASM pages ?
  if new_heap_break >= wasm_mem_size
    more_pages = (new_heap_break - wasm_mem_size) / 65536 + 1
  end

  # go grow WASM memory by so many pages. Return -1 if it fails
  return -1 if Memory.grow(more_pages) == -1

  # set new heap size
  $HEAP_SIZE = new_heap_size

  # heap_break is the address where the new free space starts
  return heap_break
end