README.md

In lsilvest/linktest: Test Linking to Another Package

linktest

Package to showcase linking against another R package's C/C++ code.

Motivation

Some packages give R access to an underlying C/C++ library (e.g. RcppCCTZ). Under certain conditions, it is possible to access this C/C++ library from another package. This is alluded to in this Stackoverflow answer by @nathan-russell. There is however a little bit more work to do to make this portable. In particular Windows and MacOS need a bit more help. In the Windows case, the library location needs to also indicate the archicture. In the MacOS case, we need to tweak the produced dynamic library to ensure it has the correct path to the library it references.

Here we present a solution based on the install.libs.R file.

The branch initial-approach presents a solution based on adding a new target to Makevars using a configure script.

Solution

In the case of MacOS we have to generate the following command:

install_name_tool -change RcppCCTZ.so /usr/local/lib/R/3.6/site-library/RcppCCTZ/libs/RcppCCTZ.so linktest.so

which changes where RcppCCTZ.so will be fetched from:

lsilvest:~/repos$ otool -L /usr/local/lib/R/3.5/site-library/linktest/libs/linktest.so
/usr/local/lib/R/3.5/site-library/linktest/libs/linktest.so:
    linktest.so (compatibility version 0.0.0, current version 0.0.0)
    /usr/local/opt/gcc/lib/gcc/8/libstdc++.6.dylib (compatibility version 7.0.0, current version 7.25.0)
    RcppCCTZ.so (compatibility version 0.0.0, current version 0.0.0)
    /usr/local/opt/r/lib/R/lib/libR.dylib (compatibility version 3.5.0, current version 3.5.1)
    /usr/local/opt/gettext/lib/libintl.8.dylib (compatibility version 10.0.0, current version 10.5.0)
    /System/Library/Frameworks/CoreFoundation.framework/Versions/A/CoreFoundation (compatibility version 150.0.0, current version 1349.93.0)
    /usr/lib/libSystem.B.dylib (compatibility version 1.0.0, current version 1238.60.2)
    /usr/local/lib/gcc/8/libgcc_s.1.dylib (compatibility version 1.0.0, current version 1.0.0)

to:

lsilvest:~/repos$ otool -L /usr/local/lib/R/3.5/site-library/linktest/libs/linktest.so
/usr/local/lib/R/3.5/site-library/linktest/libs/linktest.so:
    linktest.so (compatibility version 0.0.0, current version 0.0.0)
    /usr/local/opt/gcc/lib/gcc/8/libstdc++.6.dylib (compatibility version 7.0.0, current version 7.25.0)
    /usr/local/lib/R/3.5/site-library/RcppCCTZ/libs/RcppCCTZ.so (compatibility version 0.0.0, current version 0.0.0)
    /usr/local/opt/r/lib/R/lib/libR.dylib (compatibility version 3.5.0, current version 3.5.1)
    /usr/local/opt/gettext/lib/libintl.8.dylib (compatibility version 10.0.0, current version 10.5.0)
    /System/Library/Frameworks/CoreFoundation.framework/Versions/A/CoreFoundation (compatibility version 150.0.0, current version 1349.93.0)
    /usr/lib/libSystem.B.dylib (compatibility version 1.0.0, current version 1238.60.2)
    /usr/local/lib/gcc/8/libgcc_s.1.dylib (compatibility version 1.0.0, current version 1.0.0)

To do this, we use the following script in the install.libs.R file:

uname <- system("uname", TRUE)

if (uname == "Darwin") {
  RCPPCCTZ <- paste0('RcppCCTZ', SHLIB_EXT)
  FULL_PATH_RCPPCCTZ <- file.path(installed.packages()['RcppCCTZ','LibPath'][1], "RcppCCTZ", "libs", paste0("RcppCCTZ", SHLIB_EXT))

  INSTALL_NAME_TOOL_COMMAND <- paste("install_name_tool -change", RCPPCCTZ, FULL_PATH_RCPPCCTZ, paste0("linktest", SHLIB_EXT))
  print(INSTALL_NAME_TOOL_COMMAND)
  system(INSTALL_NAME_TOOL_COMMAND)
}

## below we also copy ".rds", otherwise we get a `NOTE` during `R CMD check`:
files <- Sys.glob(paste0("*[", SHLIB_EXT, " | .rds]"))
dest <- file.path(R_PACKAGE_DIR, paste0('libs', R_ARCH))
dir.create(dest, recursive = TRUE, showWarnings = FALSE)
file.copy(files, dest, overwrite = TRUE)

The install.libs.R file is run as part of package installation and is documented in Writing R Extensions.

lsilvest/linktest documentation built on Nov. 4, 2019, 4:45 p.m.