Re: Using the fd's underlying guile fports

[Ian Grant <I.A.N.Grant@damtp.cam.ac.uk>]

On 27 Jun 1999, Gary Houston wrote:

> | > Could you use a mutex? 
> | > 
> | > The revealed count indicates whether the port owns its descriptor.
> | > If the count is greater than 0 then the descriptor shouldn't be
> | > closed when the port is gc'd (currently implemented by not gc'ing the
> | > port, but that's not required now.)
> | > 
> | 
> | I don't think a mutex is any use. It's a problem within any single thread:
> | at any time where it is possible for the fd to be used directly, it
> | mustn't be used by the scheme port code. I want the fd to be legitimately
> | borrowed from the port and returned some time later.
> 
> I see, you have your own port type and want to keep the FILE * around
> in its data structure.

No. I want to borrow the fd from an already-open guile fport and give it
to some third-party code which will use it. I implement two procedures,
(pg:trace port) and (pg:untrace). After a scheme program calls pg:trace
and before it calls pg:untrace, I want any access to the port to generate
a scheme error. This requires a borrowed-the-fd count for each fport and
the checking of this value before any of the ptobfuns are called.

The reason for wanting this is to save re-implementation of all the fopen/ 
popen code.

Ian