In the C++11 standard, section 1.10/5 mentions, but does not formally define the terms acquire operation
, release operation
, and consume operation
. It then goes on in Section 29 to use these terms to describe the actions of certain memory orderings, atomic operations, and memory fences. For instance, 29.3/1 on "Order and Consistency" states:
memory_order_release, memory_order_acq_rel, and memory_order_seq_cst: a store operation performs a release operation [emphasis added] on the affected memory location.
This type of language is repeated throughout section 29, but it bothers me a bit that all meanings for the memory_order
enumerations are based on operation types that themselves do not seem to be formalized by the standard, yet must have some commonly agreed-to meaning for them to be effective as definitions.
Put a different way, if I said "A bar is a flipped foo", the concrete meaning of bar and foo are ambiguous since neither term is formally defined. Only their relative natures are defined.
Does the C++11 standard, or some other C++11 standards committee document formally define what exactly an acquire operation
, release operation
, etc. is, or are these simply commonly understood terms? If the latter, is there a good reference that is considered an industry standard for the meaning of these operations? I specifically ask because hardware memory consistency models are not created equal, and therefore I'm figuring there must be some commonly agreed-to reference that allows those implementing compilers, etc. to properly translate the semantics of these operations into native assembly commands.
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