Horton

Re: global barrier & atomics in signal handlers (Re: Atomic operations within spinlocks)

Tom Lane <tgl@sss.pgh.pa.us>

View thread View on postgr.es
From: Tom Lane <tgl@sss.pgh.pa.us>
To: Robert Haas <robertmhaas@gmail.com>
Cc: Andres Freund <andres@anarazel.de>, PostgreSQL Hackers <pgsql-hackers@lists.postgresql.org>
Date: 2020-06-17T21:29:08Z
Lists: pgsql-hackers 
Robert Haas <robertmhaas@gmail.com> writes:
> On Wed, Jun 17, 2020 at 3:45 PM Tom Lane <tgl@sss.pgh.pa.us> wrote:
>> The macros are kind of necessary unless you want to make s_lock.h
>> a bunch messier, because we use #ifdef tests on them.

> Where?

See the "Default Definitions", down near the end.

>> We could get rid of the double layer of macros, sure, but TBH that
>> sounds like change for the sake of change rather than a useful
>> improvement.

> Really? Multiple layers of macros seem like they pretty clearly make
> the source code harder to understand. There are plenty of places where
> such devices are necessary for one reason or another, but it doesn't
> seem like something we ought to keep around for no reason.

I wouldn't object to making the outer-layer macros in spin.h into static
inlines; as mentioned, that might have some debugging benefits.  But I
think messing with s_lock.h for marginal cosmetic reasons is a foolish
idea.  For one thing, there's no way whoever does it can verify all the
architecture-specific stanzas.  (I don't think we even have all of them
covered in the buildfarm.)

			regards, tom lane

Commits

  1. Convert SpinLock* macros to static inline functions.

  2. Clean up includes of s_lock.h.

  3. Fix deadlock danger when atomic ops are done under spinlock.

  4. Add basic spinlock tests to regression tests.

  5. spinlock emulation: Fix bug when more than INT_MAX spinlocks are initialized.

  6. Avoid potential spinlock in a signal handler as part of global barriers.

  7. Make pg_stat_wal_receiver consistent with the WAL receiver's shmem info

  8. Improve 64bit atomics support.