[Rd] serializing recordedplot object

[Simon Urbanek]

On Jan 10, 2012, at 1:06 AM, Jeroen Ooms wrote:

> The underlying problem turns out to be serialization of objects of
> class "NativeSymbolInfo". When these are serialized and unserialized,
> the memory address turns into a nullpointer, causing the fail. To fix
> it, one can simply create new nativeSymbolInfo objects. E.g:
> 
> # The old example:
> library(lattice);
> histogram(rnorm(100));
> x <- recordPlot();
> saveRDS(x, "myplot.rds");
> y <- readRDS("myplot.rds");
> 
> # y contains nullpointers making it fail.
> print(y);
> 
> # To fix:
> for(i in 1:length(y[[1]])) {
>  if( "NativeSymbolInfo" %in% class(y[[1]][[i]][[2]][[1]]) ){
>    y[[1]][[i]][[2]][[1]] <- getNativeSymbolInfo(y[[1]][[i]][[2]][[1]]$name);
>  }
> }
> print(y);
> 
> Now this works, but it is a bit ugly. Is there a more general method
> of serializing objects in a way that native objects are restored where
> possible?
> 

Unfortunately R doesn't provide a way for this. Without changes to unserialization (on the wishlist for a few years now, but not easy to design) the best you can do is to check the native symbols for NULL pointers on usage and then re-fetch - that's something that could be done reasonably easily, although it's still a hack ...



> 
> 
> 
> 
> 
> On Mon, Jan 9, 2012 at 12:47 AM, Jeroen Ooms <jeroen.ooms at stat.ucla.edu> wrote:
>> 
>> I use recordPlot() to save plots to disk that I render later to a
>> variety of formats. This works fine for base R plots and ggplot2
>> plots, and also used to work for lattice plots. However somewhere in
>> version 2.14 things stopped working for lattice plots. Here is an
>> example:
>> 
>> library(lattice);
>> histogram(rnorm(100));
>> x <- recordPlot();
>> saveRDS(x, "myplot.rds");
>> y <- readRDS("myplot.rds");
>> print(y);
>> Error: NULL value passed as symbol address
>> 
>> printing x works fine, but printing y either gives an error or prints
>> an empty page. The problem seems to be related to serializing the
>> recordedplot object, which contains a lot of memory pointers. Any tips
>> or workarounds?
>> 
>>> sessionInfo()
>> R version 2.14.1 (2011-12-22)
>> Platform: i686-pc-linux-gnu (32-bit)
>> 
>> locale:
>> [1] LC_CTYPE=en_US.UTF-8       LC_NUMERIC=C
>> [3] LC_TIME=en_US.UTF-8        LC_COLLATE=en_US.UTF-8
>> [5] LC_MONETARY=en_US.UTF-8    LC_MESSAGES=en_US.UTF-8
>> [7] LC_PAPER=C                 LC_NAME=C
>> [9] LC_ADDRESS=C               LC_TELEPHONE=C
>> [11] LC_MEASUREMENT=en_US.UTF-8 LC_IDENTIFICATION=C
>> 
>> attached base packages:
>> [1] stats     graphics  grDevices utils     datasets  methods   base
>> 
>> other attached packages:
>> [1] lattice_0.20-0
>> 
>> loaded via a namespace (and not attached):
>> [1] grid_2.14.1
> 
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