Horton

Re: Unportable implementation of background worker start

Andres Freund <andres@anarazel.de>

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From: Andres Freund <andres@anarazel.de>
To: Tom Lane <tgl@sss.pgh.pa.us>
Cc: Alvaro Herrera <alvherre@2ndquadrant.com>, pgsql-hackers@postgresql.org
Date: 2017-04-19T23:52:41Z
Lists: pgsql-hackers 
On 2017-04-19 18:56:26 -0400, Tom Lane wrote:
> Alvaro Herrera <alvherre@2ndquadrant.com> writes:
> > Tom Lane wrote:
> >> Hm.  Do you have a more-portable alternative?
> 
> > I was thinking in a WaitEventSet from latch.c.
> 
> Yeah, some googling turns up the suggestion that a self-pipe is a portable
> way to get consistent semantics from select(); latch.c has already done
> that.  I suppose that using latch.c would be convenient in that we'd have
> to write little new code, but it's a tad annoying to add the overhead of a
> self-pipe on platforms where we don't need it (which seems to be most).

FWIW, I'd wished before that we used something a bit more modern than
select() if available... It's nice to be able to listen to a larger
number of sockets without repeated O(sockets) overhead.

BTW, we IIRC had discussed removing the select() backed latch
implementation in this release.  I'll try to dig up that discussion.

- Andres

Commits

  1. Cope with glibc too old to have epoll_create1().

  2. Make latch.c more paranoid about child-process cases.

  3. Allow multiple bgworkers to be launched per postmaster iteration.

  4. Revert "Use pselect(2) not select(2), if available, to wait in postmaster's loop."

  5. Use pselect(2) not select(2), if available, to wait in postmaster's loop.

  6. Run the postmaster's signal handlers without SA_RESTART.

  7. Fix postmaster's handling of fork failure for a bgworker process.

  8. Partially revert commit 536d47bd9d5fce8d91929bee3128fa1d08dbcc57.

  9. Avoid depending on non-POSIX behavior of fcntl(2).

  10. Remove long-obsolete catering for platforms without F_SETFD/FD_CLOEXEC.