heap no overflow, simplify, fix bugs

src/lib/yang/list.lua

@@ -32,8 +32,7 @@ function Heap:new ()
  [0] = ffi.new(block_t)
  },
  _free = 0, _maxfree = Heap.block_size,
- _recycle = nil, _maxrecycle = nil,
- _overflow = nil, _maxoverflow = nil
+ _recycle = nil, _maxrecycle = nil
  }
  return setmetatable(heap, {__index=Heap})
 end
@@ -91,7 +90,9 @@ end
 function Heap:_find_recycle (recycle)
  local hole
  local block = self:_block(recycle)
- while not hole and block <= #self._blocks do
+ local free_block = self:_block(self._free)
+ -- NB: scan only blocks before current free block
+ while not hole and block < free_block do
  hole = self:_find_hole(recycle)
  block = block + 1
  recycle = lshift(block, _block_pow)
@@ -101,18 +102,8 @@ function Heap:_find_recycle (recycle)
  end
 end
 
-function Heap:_overflow_alloc (bytes)
- local o, new_overflow = self._overflow, self._overflow + bytes
- if new_overflow <= self._maxoverflow then
- self._overflow = new_overflow
- return o
- end
-end
-
 function Heap:_recycle_alloc (bytes)
- if bytes > Heap.line_size then
- return self:_overflow_alloc(bytes)
- end
+ assert(bytes <= Heap.line_size)
  local o, new_recycle = self._recycle, self._recycle + bytes
  if new_recycle <= self._maxrecycle then
  self._recycle = new_recycle
@@ -134,17 +125,19 @@ function Heap:_new_block ()
 end
 
 function Heap:_collect ()
- self._recycle, self._maxrecycle = self:_find_recycle(0)
- if self._recycle then
- self._overflow, self._maxoverflow = self:_new_block()
- end
  self._free, self._maxfree = self:_new_block()
+ self._recycle, self._maxrecycle = self:_find_recycle(0)
 end
 
 function Heap:allocate (bytes)
  assert(bytes <= Heap.block_size)
- local o = (self._recycle and self:_recycle_alloc(bytes))
- or self:_bump_alloc(bytes)
+ local o
+ if self._recycle and bytes <= Heap.line_size then
+ o = self:_recycle_alloc(bytes)
+ end
+ if not o then
+ o = self:_bump_alloc(bytes)
+ end
  if o then
  self:_ref(o, bytes, 1)
  -- Allocated space is zeroed. We are civilized, after all.
@@ -181,15 +174,15 @@ local function selftest_heap ()
  local o1 = h:allocate(Heap.block_size)
  local o1_b, o1_o = h:_block(o1)
  assert(o1_b == 1 and o1_o == 0)
- assert(#h._blocks == 2)
+ assert(#h._blocks == 1)
  assert(h._recycle == 0)
  assert(h._maxrecycle == Heap.line_size)
- assert(h._overflow == Heap.block_size*2)
- assert(h._maxoverflow == Heap.block_size*2)
  assert(h._free == Heap.block_size*2)
- assert(h._maxfree == Heap.block_size*3)
+ assert(h._maxfree == Heap.block_size*2)
  local o2 = h:allocate(Heap.line_size/2)
+ assert(h._recycle == Heap.line_size/2)
  local o3 = h:allocate(Heap.line_size)
+ assert(h._recycle == h._maxrecycle)
 end