This commit adds a new set of compare-and-exchange functions. These
functions have a signature similar to the functions found in C11. The
old cmpset functions are now deprecated and defined in terms of the
new compare-and-exchange functions. All asm backends have been
updated.
Signed-off-by: Nathan Hjelm <hjelmn@lanl.gov>
This commit renames the atomic compare-and-swap functions to indicate
the return value. This is in preperation for adding support for a
compare-and-swap that returns the old value. At the same time the
return type has been changed to bool.
Signed-off-by: Nathan Hjelm <hjelmn@lanl.gov>
This change has the side effect of improving the performance of all
atomic data structures (in addition to making the code crrect under a
certain interpretation of the volatile usage).
This commit fixes#3450.
Signed-off-by: George Bosilca <bosilca@icl.utk.edu>
This commit adds implementations for opal_atomic_lifo_pop and
opal_atomic_lifo_push that make use of the load-linked and
store-conditional instruction. These instruction allow for a more
efficient implementation on supported platforms.
Signed-off-by: Nathan Hjelm <hjelmn@lanl.gov>
On x86_64 reading a 128-bit value requires multiple instructions.
Under some conditions if the counted pointer counter is read before
the item pointer the fifo can be left in an inconsistent state. This
commit forces the read of the counter to always be read first.
The fifo does not appear to suffer from the same race.
It is possible the compiler can reorder the read of the head item and
the head itself. This could lead to a situation where the item
returned was not really the head item.
- Rename opal_atomic_lifo_t to opal_lifo_t to reflect both atomic and
non-atomic usage. Added new routines (opal_lifo_*_st) for non-atomic
usage as well as routines conditioned off opal_using_threads(). The
atomic versions are always thread safe and the non-atomic are always
not thread safe.
- Add a new atomic lifo implementation that makes use of 128-bit
compare-and-swap. The new implementation should scale better with
larger numbers of threads.
- Add threading unit test for opal_lifo_t.
