> On March 11, 2015, 9:38 p.m., Ben Mahler wrote: > > src/master/http.cpp, line 471 > > <https://reviews.apache.org/r/31700/diff/2/?file=888170#file888170line471> > > > > Do you know if a move is helpful here or if the compiler is already > > optimizing this? > > > > ``` > > object.values["slaves"] = std::move(array); > > ``` > > > > Don't do it in this change, we need to measure and I'm just curious :) > > Alexander Rukletsov wrote: > I believe the compiler won't optimize this, since `array` is an lvalue > and may be used after this assignment. One thing how we can try to persuade > the compiler to move without writing `std::move()` is to wrap array > population in a function that returns an array, this will be a rvalue then > and c++11-capable compiler *should* choose the right overload, that takes a > rvalue ref: http://www.cplusplus.com/reference/map/map/insert/. > > But everything more complex than `.reserve()` should be benchmarked, on > all official supported compilers if possible. I'll play with this when I have > some free cycles.
>From writing my own JSON code, the std::move here is definitely necessary to >do this as quickly and cheaply as possible. Using std::move here I think is actually the right thing to do, rather than trying to convince the compiler via other means, it's explicitly saying to the reader "This variable you were using earlier, it is having it's contents ripped out of it". Putting it into a function and guaranteeing NRVO or RVO fire so that you get the "cheap" move insertion has a lot of things people can disturb only slightly and end up breaking it. - Cody ----------------------------------------------------------- This is an automatically generated e-mail. To reply, visit: https://reviews.apache.org/r/31700/#review76133 ----------------------------------------------------------- On March 11, 2015, 10:40 p.m., Alexander Rukletsov wrote: > > ----------------------------------------------------------- > This is an automatically generated e-mail. To reply, visit: > https://reviews.apache.org/r/31700/ > ----------------------------------------------------------- > > (Updated March 11, 2015, 10:40 p.m.) > > > Review request for mesos and Ben Mahler. > > > Bugs: MESOS-2353 > https://issues.apache.org/jira/browse/MESOS-2353 > > > Repository: mesos > > > Description > ------- > > See summary. > > > Diffs > ----- > > src/common/http.cpp 0b57fb01f7769031704e5341849bf95a0197ffd9 > src/master/http.cpp 0b56cb419b0e488eb4163739f57ee1837ca83d24 > > Diff: https://reviews.apache.org/r/31700/diff/ > > > Testing > ------- > > make check (OS X 10.9.5, Ubuntu 14.04) > > > Thanks, > > Alexander Rukletsov > >
