Re: #define ExclusiveLock in /usr/include/postgresql/9.1/server/storage/lock.h

Hi pg_Hackers,

I would like to express my wonder to see the following line

#define ExclusiveLock 7 /* blocks ROW
SHARE/SELECT...FOR

(line number 543) in /usr/include/postgresql/9.1/server/storage/lock.h
file, because ExclusiveLock is a name of a class in libspatialindex library
(see* *libspatialindex.github.io).

Using postgres SPI and the spatial library becomes quite a challenge in a
larger project, since the order of the includes starts making a big
difference. Suddenly the c++ pre-processor starts generating codes like

class 7
{

}

I suppose changing the define to be all capital letters becomes a huge
problem, doesn't it ?

Cheers,
arturas

$ lsb_release -a
No LSB modules are available.
Distributor ID: Ubuntu
Description: Ubuntu 12.04.2 LTS
Release: 12.04
Codename: precise

$ psql -c 'select version()'

version
------------------------------------------------------------------------------------------------------------
PostgreSQL 9.1.9 on x86_64-unknown-linux-gnu, compiled by gcc
(Ubuntu/Linaro 4.6.3-1ubuntu5) 4.6.3, 64-bit
(1 row)

Arturas Mazeika <mazeika(at)gmail(dot)com> writes:
> I would like to express my wonder to see the following line

> #define ExclusiveLock 7 /* blocks ROW
> SHARE/SELECT...FOR

> (line number 543) in /usr/include/postgresql/9.1/server/storage/lock.h
> file, because ExclusiveLock is a name of a class in libspatialindex library
> (see* *libspatialindex.github.io).

That seems like an awfully strange name for a class ...

> I suppose changing the define to be all capital letters becomes a huge
> problem, doesn't it ?

ExclusiveLock has been defined, with that name, in the Postgres code for
close to 20 years, and there are many references to it both in the core
code and add-ons. Yes, changing it would be painful.

More generally, we can never promise not to conflict with any identifiers
defined in third-party code. I don't see any strong reason why we should
do something about this particular case.

I'd suggest arranging your code so that the stuff that deals with
libspatialindex can be in a file separate from code that needs to
know about Postgres internals. Then you could avoid #include'ing
the conflicting headers in the same source file.

regards, tom lane