In an attempt to prevent gcc from emiting warnings, ck_pr_md_load_ptr and
ck_pr_md_store_ptr were made wrong in commit
5ae12a19d0.
load_ptr would return target instead of *target, and store would store the
value in target instead of in *target.
This is an attempt at fixing this, while still trying to avoid warnings.
These primitives are meant to be used in lock implementations
where control dependency ordering is sufficient to enforce
ordering of critical section. At the moment, this only affects
PPC. Currently, we rely on lwsync for entry into critical sections
which is insufficient. sync is rather heavy-weight, and assuming
we aren't falling victim into compiler re-ordering, isync should
be sufficient.
There is follow-up work to be done in ARM, as we may have cheaper
(but target-specialized) ISB-tricks for load-load ordering.
We use some macro trickery to enforce that ck_pr_store_* is actually
storing the correct type into the target variable, without any actual
side effects--by making the assignment into an rvalue and using a
comma expression, the compiler should optimize it away.
On the load side, we simply cast the result to the type of the target
variable for pointer loads.
There is an unsafe version of the store_ptr macro called
ck_pr_store_ptr_unsafe for those times when you are _really_ sure that
you know what you're doing.
This commit also updates some of the source files (ck_ht, ck_hs,
ck_rhs): ck_ht now uses the unsafe macro, as its conversion between
uintptr_t and void * is invalid under the new macros. ck_hs and ck_rhs
have had some casts added to preserve validity.
These operations serialize atomic-RMW operations with respect
to each other, loads and stores. In addition to this, the
load_depends implementations have been removed.
Olivier Houchard
Samy Al Bahra
Michael Haberler
Samy Al Bahra
John Wittrock
Marcin Juszkiewicz
Samy Al Bahra
William Irwin