On Tuesday, 4 July 2017 at 01:56:11 UTC, Moritz Maxeiner wrote:
On Monday, 3 July 2017 at 17:06:10 UTC, Ali Çehreli wrote:
On 07/02/2017 07:56 PM, Stefan Koch wrote:
On Monday, 3 July 2017 at 02:51:49 UTC, Filip Bystricky wrote:
Anyone?
The answer is no.
Partial deallocation in an arbitrary fashion is not advisable.
And there are no standard library mechanisms for it.
Would it be possible to write a custom
std.experimental.allocator that does this?
Since the `deallocate` function an Allocator has to implement
takes a `void[]` (-> known size), it's possible:
At deallocation the Allocator will have to check if the given
memory subblock lies within any of the previously allocated
memory blocks; if it does, it will have to "tear" the
to-be-deallocated memory subblock from within it, storing the
resulting prefix and suffix memory subblocks (both remain
allocated) and removing the original block. It will still have
to track those two subblocks as belonging together, though,
since it can only deallocate the original memory block back to
the parent allocator (another Allocator, or something else)
once both of these subblocks are no longer allocated. Obviously
this applies to further partial deallocations of subblocks
within subblocks.
I tend to agree with Stefan that this is likely not sensible,
but if in doubt, benchmark for the specific use case.
Thanks for the responses!
Moritz, that is a good suggestion. However, in many cases it is
unacceptable to have to prevent the whole block from being freed
(especially if the memory is managed by a compacting gc). I think
the feature would work better as an additional allocator
primitive, which should be easy to implement for most allocators
that support reallocate (e.g. bitmapped-block and free-list
allocators).
In the meantime I realized that since a child node can only be
freed after its parent is freed, I can allocate all 6 nodes in a
single allocation, but in reverse order, (putting the leaf at the
front and the root at the tail). That way, to free an ancestor,
we just realloc the corresponding leaf's memory.
