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: 2017-04-20T23:59:19Z
Lists: pgsql-hackers 
On 2017-04-20 19:53:02 -0400, Tom Lane wrote:
> I wrote:
> > Andres Freund <andres@anarazel.de> writes:
> >> On 2017-04-20 19:23:28 -0400, Tom Lane wrote:
> >>> or are the HANDLEs in a Windows WaitEventSet not inheritable
> >>> resources?
> 
> >> So that kind of sounds like it should be doable.
> 
> > Ah, good.  I'll add a comment about that and press on.
> 
> So ... what would you say to replacing epoll_create() with
> epoll_create1(EPOLL_CLOEXEC) ?  Then a WaitEventSet would not
> represent inheritable-across-exec resources on any platform,
> making it a lot easier to deal with the EXEC_BACKEND case.
> 
> AFAIK, both APIs are Linux-only, and epoll_create1() is not much
> newer than epoll_create(), so it seems like we'd not be giving up
> much portability if we insist on epoll_create1.

I'm generally quite in favor of using CLOEXEC as much as possible in our
tree.  I'm a bit concerned with epoll_create1's availability tho - the
glibc support for it was introduced in 2.9, whereas epoll_create is in
2.3.2.  On the other hand 2.9 was released 2008-11-13.   If we remain
concerned we could just fcntl(fd, F_SETFD, FD_CLOEXEC) instead - that
should only be like three lines more code or such, and should be
available for a lot longer.

- 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.