Hi Gophers, I have a question about a more subtle part of the language, the memory model regarding atomic operations. The memory model doc on go.dev states: >If the effect of an atomic operation *A* is observed by atomic operation *B*, then *A* is synchronized before *B*.[...]
I.e. "observing side-effects" by another atomic operation establishes a synchronizes-before and therefore a happen-before relationship between the write and the observation of that side-effect. My question is basically: Do only atomic *Loads* count as auch an "observation" or does CompareAndSwap also count here? Is there a happens-before between a Store and a later CompareAndSwap (independent of whether the CAS returns false or true?). I asked myself this because the documentation also makes a comparison to C++ and Java: >The preceding definition has the same semantics as C++’s sequentially consistent atomics and Java’s volatile variables. However, there is a small difference between the C++ CAS (compare_exchange) and Go's. In C++, if the swap fails (because the value of the atomic is not the provided expected old value), it will change the old value (which it receives as a reference) to the new value of the atomic. This makes it clear that it counts as a read in any case. In Go (and other languages, e.g. Java), CompareAndSwap does not do this. Thus, one could get the idea that maybe CompareAndSwap doesn't count as a "read" as far as memory model and compiler reorderings and so on are concerned, because it does not read the current value of the atomic on a "program level", returning nothing to the "user", it only reads (compares to) it internally in its inner workings. My question is thus: Does atomic.CompareAndSwap count as a read in this context and is there a happens-before relationship between a previous store and a later compare-and-swap (both if the CAS fails or succeeds?) Thank you all for reading this wall of text. -Antonio -- You received this message because you are subscribed to the Google Groups "golang-nuts" group. To unsubscribe from this group and stop receiving emails from it, send an email to golang-nuts+unsubscr...@googlegroups.com. To view this discussion on the web visit https://groups.google.com/d/msgid/golang-nuts/633df394-27f1-4416-9602-3c09ade78fban%40googlegroups.com.
