On 05/11/2015 08:06 PM, Timon Gehr wrote:
On 05/11/2015 05:28 PM, Andrei Alexandrescu wrote:
On 5/10/15 5:08 AM, Timon Gehr wrote:
On 05/10/2015 01:48 PM, Timon Gehr wrote:
"bool expand(ref void[] b, size_t delta);
Post: !result || b.length == old(b).length + delta Expands b by
delta bytes. If delta == 0, succeeds without changing b. If b is null,
the call evaluates b = allocate(delta) and returns b !is null.
Otherwise, *b must be a buffer previously allocated with the same
allocator*. If expansion was successful, expand changes b's length to
b.length + delta and returns true. Upon failure, the call effects no
change upon the allocator object, leaves b unchanged, and returns
false."
Actually, reading that snippet of the documentation, I notice more
problems in the implementation of expand/the documentation of the
rounding function.
If the rounding function returns a non-zero result for a zero argument,
expand can return invalid memory (starting from address 0) if given an
empty block 'b'.
Thanks again for the great review.
No problem!
Just updated quantizer.d, I think I've addressed all points:
https://github.com/andralex/phobos/blob/allocator/std/experimental/allocator/quantizer.d
Unfortunately,
- If the rounding function is not piecewise constant with one fixed
point per piece, it can happen that 'allocated >= needed' but 'allocated
< goodAllocSize(needed)'. Then, the allocated size will be inconsistent
with goodAllocSize. (This is why I recommended to require the rounding
function to have this property, which is stronger than monotonicity.)
- If b.ptr is null, then line 113 is bad in case goodAllocSize(0) > 0.
Oh, and
- The assertion in line 141 may fail. (expand can return false.)
(Rant: Go on, conflate assert and assume in -release and then, when a
sufficiently smart optimizer runs, suddenly expand will always return
true and user code that checks for success of expand will be removed.
Awesome.)
- 'expand' ought to call 'allocate' when passed an empty buffer in case
the parent does not define 'expand', no?
