On Nov 16, 2013, at 8:30 AM, Romain Francois <rom...@r-enthusiasts.com> wrote:
> Hello,
>
> Are there any recipe to handle serialization / deserialization of external
> pointers.
>
> I'm thinking about something similar in spirit to the way we handle
> finalization of external pointers.
>
See refhook in serialize/unserialize.
> Currently, if we create an external pointer, save the session, quit R, then
> load the session, we get a null pointer.
>
Saving the session is a different story than serialization, because it also
involves loading the right code in addition to the data and you cannot use
refhooks. I recall discussing this with Luke a few years ago, and the main
problem is that R has no way of knowing what is needed to call the particular
hooks, because the package is not even loaded, so it cannot install hooks.
AFAIR the net result was that the proper way to do it is to handle the NULL
pointer code when you first access the pointer to restore the object based on
additional info that you store in the object. E.g. , in rJava we store the Java
serialization of the object so it can be restored on first use of the new
session.
One piece that is still missing it the ability to set a hook to update the save
object on save() - since we don’t necessarily want to add the extra information
every time the object is created or the serialization may become stale over
time. That would still be very useful to add …
Cheers,
Simon
> One way I'm thinking of is to have an environment in the "protected" part of
> the xp, then have an active binding there, since apparently active bindings:
> - are "get" during serialization
> - lose their active ness when reloaded:
>
> $ R
> [...]
> > f <- local( {
> + x <- 1
> + function(v) {
> + if (missing(v))
> + cat("get\n")
> + else {
> + cat("set\n")
> + x <<- v
> + }
> + x
> + }
> + })
> > makeActiveBinding("fred", f, .GlobalEnv)
> > bindingIsActive("fred", .GlobalEnv)
> [1] TRUE
> >
> > q("yes")
> get
> get
>
>
> romain@naxos /tmp $ R
> [..]
> > fred
> [1] 1
> > bindingIsActive("fred", .GlobalEnv)
> [1] FALSE
>
> Is this possible ? Is there any other hook to handle serialization,
> unserialization of external pointers ?
>
> Romain
>
> --
> Romain Francois
> Professional R Enthusiast
> +33(0) 6 28 91 30 30
>
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