Class: Malloc

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

Constant Summary collapse

@@base =

empty list to get started

Header.new
@@freep =

start of free list

0.cast_to(:Header)

Class Method Summary collapse

Class Method Details

.free(ap) ⇒ Object

Free memory block



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# File 'lib/rlang/lib/malloc.rb', line 126

def self.free(ap)
  arg ap: :UI32
  result :none
  local bp: :Header, p: :Header

  # NULL is a special value used for
  # all Rlag object instances that doesn't 
  # have any instance variables and therefore
  # doesn't use any memory
  return if ap == 0

  bp = ap.cast_to(:Header) - 1 # point to block header
  p = @@freep
  while !(bp > p && bp < p.ptr)
    # freed block at start or end of arena 
    break if (p >= p.ptr && (bp > p || bp < p.ptr))
    p = p.ptr
  end

  if (bp + bp.size == p.ptr)
    # join to upper nbr
    bp.size += p.ptr.size
    bp.ptr = p.ptr.ptr
  else
    bp.ptr = p.ptr
  end

  if (p + p.size == bp)
    # join to lower nbr
    p.size += bp.size
    p.ptr = bp.ptr
  else
    p.ptr = bp
  end
  @@freep = p
end

.malloc(nbytes) ⇒ Object

malloc: allocate n bytes of memory and return pointer to data block



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# File 'lib/rlang/lib/malloc.rb', line 57

def self.malloc(nbytes)
  arg nbytes: :UI32
  local p: :Header, prevp: :Header, nunits: :UI32

  # allocate memory by chunk of units (the unit is
  # the size of a Header object here)
  # units = (nbytes+sizeof(Header)-1)/sizeof(Header) + 1;
  nunits = (nbytes + Header._size_ - 1) / Header._size_ + 1

  # No free list yet. Initialize it.
  if (prevp = @@freep) == 0 
    @@base.ptr = @@freep = prevp = @@base
    @@base.size = 0
  end

  # scan the free list for a big enough free block
  # (first in list is taken)
  p = prevp.ptr
  while true
    if (p.size >= nunits) # big enough
      if (p.size == nunits) 
        # exactly the requested size
        prevp.ptr = p.ptr
      else
        # bigger free block found
        # Allocate tail end
        p.size -= nunits
        p += p.size
        p.size = nunits
      end
      @@freep = prevp
      # TODO: we should actually cast to default WASM type
      return (p + 1).cast_to(:I32)
    end

    # wrapped around free list
    if p == @@freep
      if (p = self.morecore(nunits)) == 0
        return 0
      end
    end

    prevp = p; p = p.ptr
  end

  # Rlang specific: remember that while construct 
  # doesn't evaluate to a value so we must add an
  # explicit return here.
  # However we should **never** get there so return NULL
  return 0
end

.morecore(nu) ⇒ Object

morecore: ask system for more memory



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# File 'lib/rlang/lib/malloc.rb', line 110

def self.morecore(nu)
  arg nu: :UI32
  result :Header
  local up: :Header

  nu = $NALLOC if nu < $NALLOC
  cp = Unistd::sbrk(nu * Header._size_)
  return 0 if cp == -1 # no space at all

  up = cp.cast_to(:Header)
  up.size = nu
  self.free((up + 1).to_I32)
  return @@freep
end