Reduce the strength of the C11 atomics from memory_order_seq_cst to the
actually required memory order constraints for each operation. In
addition to reflecting the already documented memory order constraints,
this should allow for better code generation.
This fixes deprecation warnings when building for macOS >= 10.12 systems.
Additionally, using stdatomic.h (or the more modern __atomic_ builtins)
is required when targeting CHERI-enabled architectures such as
CHERI-RISC-V or Arm's Morello since the compiler rejects __sync_* atomic
for pointer types (they only work with integers).
Reverts the part of 6def66164a that
removed the fc_atomic_ptr_cmpexch compatibility code for systems earlier
than Mac OS X 10.5.
Reverts the part of 447b9ccc7d that moved
the definition of fc_atomic_ptr_get into the Mac OS X > 10.4 block. That
code is still needed on 10.4 and is implemented using functions that are
available on 10.4.
Compare against MAC_OS_X_VERSION_MIN_REQUIRED using a number not a
constant because the constant is not available on earlier SDKs.
Before this change building with ThreadSanitizer and running
test/test-pthread generated a large number of threading issues. These
mostly stemmed from fc_atomic_ptr_get not doing an atomic load and using
"acquire load" instead of "load acquire". After making these changes it
was still necessary to use fc_atomic_ptr_get where it was needed.
This also documents the current memory barrier requirements for the
atomic primitives.
iPhone 2.1 was released a long time ago, and the macro for checking
the target iOS SDK version has changed. We can simplify everything and
do a very basic check.
Ben Wagner
Alex Richardson
Ryan Schmidt
Akira TAGOH
Nirbheek Chauhan
Behdad Esfahbod