I accidentally swapped head/tail load in ck_hp_fifo (not in
ck_fifo, however). We must acquire head snapshot before tail snapshot.
An example execution history which could cause an incorrect update to occur
is below.
- tail <- fifo.tail / fifo.head != fifo.tail
- dequeue to empty (until final CAS which renders fifo.head = fifo.tail)
- head <- fifo.head / (head != tail)
- next <- fifo.head->next / next = NULL
- As head != tail, update to next pointer (where next is NULL).
However, if
- head <- fifo.head / (fifo.head != fifo.tail)
- dequeue to empty (until final CAS which renders fifo.head = fifo.tail)
- tail <- fifo.tail / fifo.head != fifo.tail
- next <- fifo.head->next / next = NULL
If we caught tail in final transition, the by the time we read next pointer,
head would have also changed forcing us to re-read. Thanks to Hendrik Donner
for reporting this.
Documentation and regressions tests have been updated to reflect this.
This functionality allows for individual hash tables use to different
allocation functions. Thanks to Wez Furlong for pointing out the necessary
documentation update for ck_ht.
Pointer packing is now disabled by default for x86_64 targets.
Jeffrey M. Birnbaum <jmbny.@...> told me that according to his
discussions with Intel engineers, Haswell will be bumping up
VMA bits to 56 bits from 48.
If you control the hardware that CK is deployed to and don't
envision a migration to 48-bits anytime soon, then you may
enable old behavior (resulting in significant memory savings
for some data structures, namely ck_ht) by passing the
--enable-pointer-packing flag to configure.
Migrate available block list to CK_LIST.
New blocks are only allocated when the available list is exhausted.
Remove bag->avail_tail.
Print out number of writer iterations for unit test.
Lengthen duration of unit test.
This changes comes at the cost of clear linearizability, which
is suitable for my use-case. Users can easily implement linereazability
through an additional level of indirection to the ck_bitmap object.
Samy Al Bahra
Abel Mathew
Samy Al Bahra
Joao Fernandes