On Thu, May 01, 2014 at 08:44:46PM -0400, Tom Lane wrote: > Noah Misch <n...@leadboat.com> writes: > > On Thu, May 01, 2014 at 05:59:08PM -0400, Tom Lane wrote: > >> However ... after looking around I notice that fflush(NULL) is already > >> being used in parallel pg_dump and pg_upgrade; and at least in the latter > >> case I'm afraid to change that because it looks like there are probably > >> other stdio output files open in the process. > > > Do those programs, operating in those modes, read from stdin or some other > > long-lived, pipe-backed FILE*? > > Probably not.
Then the use of fflush(NULL) in those programs tells us nothing about the status of the aforementioned HP-UX bug. > However, if that's your criterion, I'd say that I'd much > rather assume that the postmaster doesn't have a pipe connected to stdin > than that it has no stdio outputs besides stdout/stderr. Either way, the beneficiary is theoretical; who can tell which one deserves priority? Let's do what we usually do in the absence of a clear improvement: keep the longstanding behavior. > >> BTW, while working on this I noticed that there are a boatload of places > >> where we use system() or popen() without a prior fflush. I suspect most > >> of them are safe, or we'd have heard more complaints --- but shouldn't > >> we clamp down on that? > > > You need the fflush() when forking and then using stdio in the child before > > any exec(). Have you caught wind of any system() or popen() implementation > > having that property? > > You're only considering one aspect of the problem. Yeah, you might not > get duplicated output unless system() prints something before exec(), > but we would also like to have causality: that is, whatever we sent to > stdout before calling system() should appear there before anything the > child process sends to stdout. Good point. I suppose a couple of fflush() calls have negligible cost next to a system() or popen(). Introduce pg_popen()/pg_system(), and adopt a rule that they are [almost] our only callers of raw popen()/system()? -- Noah Misch EnterpriseDB http://www.enterprisedb.com -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
