[Libpqxx-general] cancellation of synchronous sql statements

[Jeroen T. Vermeulen]

On Wed, August 19, 2009 00:07, Madden, Don (DCOR) wrote:

> If you execute commands (asynchronously) in a "pipeline", there is a
> public method to "cancel()" an ongoing query.
>
>  If you execute the SQL commands in a blocking call, you could the
> cancel the ongoing command via a signal handler (e.g SIGALRM). lIbpq
> supports this via PQcancel(). "libpqxx" doesn't seem to have any
> equivalent public method. In the connection_base, the wrapper method,
> "cancel_query()" is private.  Likewise I couldn't find any public method
> to get a raw libpq connection, PGConn in libpqxx's connection_base
> classes?

This sounds like a useful feature.  I just made cancel_query public for
your use, and made the function try a bit harder to be graceful about
deactivated connections.  See revision [1574].  It should work safely from
signal handlers; using it from other threads is safe for libpq versions
8.0 and up, but not before.  (The thread-safety descriptions already knew
about this).

What this still needs is a good test.  I'd be most grateful if you could
come up with one that fits in the test suite in test/unit/ !


Jeroen