This should normally be determined by a configure check, but until someone figures out how to do that on Windows, it's better that the code uses the new function by default.
This reverts commit 81069a9efc5a374dd39874a161f456f0fb3afba4. Buildfarm results suggest that some platforms have versions of pselect(2) that are not merely non-atomic, but flat out non-functional. Revert the use-pselect patch to confirm this diagnosis (and exclude the no-SA_RESTART patch as the source of trouble). If it's so, we should probably look into blacklisting specific platforms that have broken pselect. Discussion: https://postgr.es/m/9696.1493072081@sss.pgh.pa.us
Traditionally we've unblocked signals, called select(2), and then blocked signals again. The code expects that the select() will be cancelled with EINTR if an interrupt occurs; but there's a race condition, which is that an already-pending signal will be delivered as soon as we unblock, and then when we reach select() there will be nothing preventing it from waiting. This can result in a long delay before we perform any action that ServerLoop was supposed to have taken in response to the signal. As with the somewhat-similar symptoms fixed by commit 893902085, the main practical problem is slow launching of parallel workers. The window for trouble is usually pretty short, corresponding to one iteration of ServerLoop; but it's not negligible. To fix, use pselect(2) in place of select(2) where available, as that's designed to solve exactly this problem. Where not available, we continue to use the old way, and are no worse off than before. pselect(2) has been required by POSIX since about 2001, so most modern platforms should have it. A bigger portability issue is that some implementations are said to be non-atomic, ie pselect() isn't really any different from unblock/select/reblock. Still, we're no worse off than before on such a platform. There is talk of rewriting the postmaster to use a WaitEventSet and not do signal response work in signal handlers, at which point this could be reverted, since we'd be using a self-pipe to solve the race condition. But that's not happening before v11 at the earliest. Back-patch to 9.6. The problem exists much further back, but the worst symptom arises only in connection with parallel query, so it does not seem worth taking any portability risks in older branches. Discussion: https://postgr.es/m/9205.1492833041@sss.pgh.pa.us
poll.h is mandated by Single Unix Spec v2, the usual baseline for postgres on unix. None of the unixoid buildfarms animals has sys/poll.h but not poll.h. Therefore there's not much point to test for sys/poll.h's existence and include it optionally. Author: Andres Freund, per suggestion from Tom Lane Discussion: https://postgr.es/m/20505.1492723662@sss.pgh.pa.us
The test result that I had blindly stipulated didn't work out on the build farm, so disable the feature in Windows MSVC for now.
copyObject() is declared to return void *, which allows easily assigning the result independent of the input, but it loses all type checking. If the compiler supports typeof or something similar, cast the result to the input type. This creates a greater amount of type safety. In some cases, where the result is assigned to a generic type such as Node * or Expr *, new casts are now necessary, but in general casts are now unnecessary in the normal case and indicate that something unusual is happening. Reviewed-by: Mark Dilger <hornschnorter@gmail.com>
We'll need this for the upcoming patch to speed up expression evaluation. Might as well push it now to see if it behaves sanely in the buildfarm. Andres Freund Discussion: https://postgr.es/m/20170320062511.hp5qeurtxrwsvfxr@alap3.anarazel.de
We had some AC_CHECK_HEADER tests that were really wastes of cycles, because the code proceeded to #include those headers unconditionally anyway, in all or a large majority of cases. The lack of complaints shows that those headers are available on every platform of interest, so we might as well let configure run a bit faster by not probing those headers at all. I suspect that some of the tests I left alone are equally useless, but since all the existing #includes of the remaining headers are properly guarded, I didn't touch them.