Re: Atomic Operations

Markus Schiltknecht wrote:

Hi Markus,

> what are the assumptions PostgreSQL normally does about atomic 
> operations? I see sig_atomic_t is used in signal handlers. Additionally, 
> there is a match for a cmpxchg instruction in some solaris ports code, 
> but that's about what I found in the source.
> 
> Am I safe assuming that pointer assignments are atomic (on all platforms 
> PostgreSQL compiles on, that is)? (This is a 'practical advice' from the 
> GNU Libc Manual) How about other integers smaller or equal in size to 
> sizeof(sig_atomic_t)?
> 
> I'm asking to make sure I rely on the same guarantees in my code.

Currently we rely on TransactionId being atomic; see
GetNewTransactionId.  It's defined as uint32 somewhere, so I guess you
could rely on that.

-- 
Alvaro Herrera                                http://www.CommandPrompt.com/
PostgreSQL Replication, Consulting, Custom Development, 24x7 support