Horton

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

Robert Haas <robertmhaas@gmail.com>

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From: Robert Haas <robertmhaas@gmail.com>
To: Andres Freund <andres@anarazel.de>
Cc: PostgreSQL Hackers <pgsql-hackers@lists.postgresql.org>, Tom Lane <tgl@sss.pgh.pa.us>
Date: 2020-06-17T19:27:26Z
Lists: pgsql-hackers 
On Wed, Jun 17, 2020 at 2:33 PM Andres Freund <andres@anarazel.de> wrote:
> > It seems odd and confusing that we have  both
> > S_LOCK() and s_lock(), anyway. Differentiating functions based on case
> > is not great practice.
>
> It's a terrible idea, yes.  Since we don't actually have any non-default
> implementations of S_LOCK, perhaps we should just rip it out?

I think we should rip out the conditional nature of the definition and
fix the comments. I don't think I prefer getting rid of it completely.

But then again on the other hand, what's the point of this crap anyway:

#define SpinLockInit(lock)      S_INIT_LOCK(lock)
#define SpinLockAcquire(lock) S_LOCK(lock)
#define SpinLockRelease(lock) S_UNLOCK(lock)
#define SpinLockFree(lock)      S_LOCK_FREE(lock)

This seems like it's straight out of the department of pointless
abstraction layers. Maybe we should remove all of the S_WHATEVER()
stuff and just define SpinLockAcquire() where we currently define
S_LOCK(), SpinLockRelease() where we currently define S_UNLOCK(), etc.

And, as you say, make them static inline functions while we're at it.

-- 
Robert Haas
EnterpriseDB: http://www.enterprisedb.com
The Enterprise PostgreSQL Company

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.