DO NOT DO THIS!!! SETLENGTH and SET_TRUELENGTH are NOT part of the API
and are for internal use only.
Tho proper way to do this is to copy the data you want into a smaller
vector and allow the larger one to be garbage collected.
[VECSXPs are like all other vectors in that they are contigously
allocated by malloc, and there is no mprtable way to return part
a memory region allocated by malloc back to malloc].
There is experimental INTERNAL support for growable vectors that is
managed with INTERNALLY with TRUELENGTH and a bit setting, but this is
NOT, at leat not yet, intended for use by packages. The ALTREP
framework that should be available in the next release might allow
something like this to be done, but care is needed to make sure R's
copying semantics are adhered to.
Best,
luke
On Tue, 21 Nov 2017, mbon...@posteo.de wrote:
Dear all,
I want to create a function shrinkVector(x) that takes x and truncates it
to the first element without copy.
With SETLENGTH and SET_TRUELENGTH, I can achieve that. You can find a
reproducible example below.
But the memory that was freed is not available for other objects
afterwards, except if x is a list (VECSXP). Any suggestions?
library(inline)
## define the shrinking function
shrinkVector <- cfunction(signature(x = "ANY"),
body = paste0("SETLENGTH(x, 1);",
"SET_TRUELENGTH(x, 1);",
"return(R_NilValue);"))
## create a large vector that only fits into memory once
x <- 1 : 2e9
## shrink it
shrinkVector(x)
## shrinking seems to have worked
print(length(x) == 1)
# [1] TRUE
print(object.size(x))
# 48 bytes
## but I can't reuse the memory for a large x2:
x2 <- 1 : 2e8
# Error: cannot allocate vector of size 762.9 Mb
## if I remove x, it works
rm(x)
gc()
x2 <- 1 : 2e8
Thank you very much for your help.
Kind regards,
Markus Bonsch
______________________________________________
R-devel@r-project.org mailing list
https://stat.ethz.ch/mailman/listinfo/r-devel
--
Luke Tierney
Ralph E. Wareham Professor of Mathematical Sciences
University of Iowa Phone: 319-335-3386
Department of Statistics and Fax: 319-335-3017
Actuarial Science
241 Schaeffer Hall email: luke-tier...@uiowa.edu
Iowa City, IA 52242 WWW: http://www.stat.uiowa.edu
______________________________________________
R-devel@r-project.org mailing list
https://stat.ethz.ch/mailman/listinfo/r-devel
