Todd Lipcon has posted comments on this change. ( http://gerrit.cloudera.org:8080/15105 )
Change subject: WIP: Asynchronous code generation ...................................................................... Patch Set 9: (1 comment) http://gerrit.cloudera.org:8080/#/c/15105/9/be/src/codegen/codegen-fn-ptr.h File be/src/codegen/codegen-fn-ptr.h: http://gerrit.cloudera.org:8080/#/c/15105/9/be/src/codegen/codegen-fn-ptr.h@41 PS9, Line 41: static constexpr std::memory_order mem_order_ = std::memory_order_acq_rel; just passing through: I think you have it correct here. Relaxed is insuffiicent because it would permit reordering of the writing of the code and the storing of the pointer. In other words, your compilation thread does things like: 1. allocate memory for function machine code 2. write code to allocated memory 3. publish pointer and without "release" semantics on the publishing of the pointer, there is no guarantee that #2 and #3 won't be reordered. In practice, this is really unlikely to happen, because there are probably some other locking operations in between #2 and #3 and because x86 is a TSO architecture, but worth doing it right regardless. Also worth noting that acq/rel semantics on x86 isn't expensive, they are just simple load/store operations. It only prevents compiler reordering. So, there is little to gain by using relaxed. -- To view, visit http://gerrit.cloudera.org:8080/15105 To unsubscribe, visit http://gerrit.cloudera.org:8080/settings Gerrit-Project: Impala-ASF Gerrit-Branch: master Gerrit-MessageType: comment Gerrit-Change-Id: Ia7cbfa7c6734dcf03641629429057d6a4194aa6b Gerrit-Change-Number: 15105 Gerrit-PatchSet: 9 Gerrit-Owner: Daniel Becker <daniel.bec...@cloudera.com> Gerrit-Reviewer: Bikramjeet Vig <bikramjeet....@cloudera.com> Gerrit-Reviewer: Csaba Ringhofer <csringho...@cloudera.com> Gerrit-Reviewer: Daniel Becker <daniel.bec...@cloudera.com> Gerrit-Reviewer: Impala Public Jenkins <impala-public-jenk...@cloudera.com> Gerrit-Reviewer: Tim Armstrong <tarmstr...@cloudera.com> Gerrit-Reviewer: Todd Lipcon <t...@apache.org> Gerrit-Reviewer: Zoltan Borok-Nagy <borokna...@cloudera.com> Gerrit-Comment-Date: Thu, 13 Feb 2020 21:18:56 +0000 Gerrit-HasComments: Yes
