getNativeSymbolInfo Obtain a Description of one or more Native (C/Fortran) Symbols

Description

This finds and returns a description of one or more dynamically loaded or ‘exported’ built-in native symbols. For each name, it returns information about the name of the symbol, the library in which it is located and, if available, the number of arguments it expects and by which interface it should be called (i.e .Call, .C, .Fortran, or .External). Additionally, it returns the address of the symbol and this can be passed to other C routines. Specifically, this provides a way to explicitly share symbols between different dynamically loaded package libraries. Also, it provides a way to query where symbols were resolved, and aids diagnosing strange behavior associated with dynamic resolution.

Usage

getNativeSymbolInfo(name, PACKAGE, unlist = TRUE,
                    withRegistrationInfo = FALSE)

Arguments

name	the name(s) of the native symbol(s).
PACKAGE	an optional argument that specifies to which DLL to restrict the search for this symbol. If this is "base", we search in the R executable itself.
unlist	a logical value which controls how the result is returned if the function is called with the name of a single symbol. If unlist is TRUE and the number of symbol names in name is one, then the NativeSymbolInfo object is returned. If it is FALSE, then a list of NativeSymbolInfo objects is returned. This is ignored if the number of symbols passed in name is more than one. To be compatible with earlier versions of this function, this defaults to TRUE.
withRegistrationInfo	a logical value indicating whether, if TRUE, to return information that was registered with R about the symbol and its parameter types if such information is available, or if FALSE to return just the address of the symbol.

Details

This uses the same mechanism for resolving symbols as is used in all the native interfaces (.Call, etc.). If the symbol has been explicitly registered by the DLL in which it is contained, information about the number of arguments and the interface by which it should be called will be returned. Otherwise, a generic native symbol object is returned.

Value

Generally, a list of NativeSymbolInfo elements whose elements can be indexed by the elements of name in the call. Each NativeSymbolInfo object is a list containing the following elements:

name	the name of the symbol, as given by the name argument.
address	if withRegistrationInfo is FALSE, this is the native memory address of the symbol which can be used to invoke the routine, and also to compare with other symbol addresses. This is an external pointer object and of class NativeSymbol. If withRegistrationInfo is TRUE and registration information is available for the symbol, then this is an object of class RegisteredNativeSymbol and is a reference to an internal data type that has access to the routine pointer and registration information. This too can be used in calls to .Call, .C, .Fortran and .External.
dll	a list containing 3 elements: name the short form of the library name which can be used as the value of the PACKAGE argument in the different native interface functions. path the fully qualified name of the DLL. dynamicLookup a logical value indicating whether dynamic resolution is used when looking for symbols in this library, or only registered routines can be located.

If the routine was explicitly registered by the dynamically loaded library, the list contains a fourth field

numParameters

the number of arguments that should be passed in a call to this routine.

Additionally, the list will have an additional class, being CRoutine, CallRoutine, FortranRoutine or ExternalRoutine corresponding to the R interface by which it should be invoked.

If any of the symbols is not found, an error is raised.

If name contains only one symbol name and unlist is TRUE, then the single NativeSymbolInfo is returned rather than the list containing that one element.

Note

The third element of the NativeSymbolInfo objects was renamed from package to dll in R version 3.6.0, for consistency with the names of the NativeSymbolInfo objects returned by getDLLRegisteredRoutines().

Note

One motivation for accessing this reflectance information is to be able to pass native routines to C routines as function pointers in C. This allows us to treat native routines and R functions in a similar manner, such as when passing an R function to C code that makes callbacks to that function at different points in its computation (e.g., nls). Additionally, we can resolve the symbol just once and avoid resolving it repeatedly or using the internal cache.

Author(s)

Duncan Temple Lang

References

For information about registering native routines, see “In Search of C/C++ & FORTRAN Routines”, R-News, volume 1, number 3, 2001, p20–23 (https://www.r-project.org/doc/Rnews/Rnews_2001-3.pdf).

See Also

getDLLRegisteredRoutines, is.loaded, .C, .Fortran, .External, .Call, dyn.load.