R: Obtain a Description of one or more Native (C/Fortran)...
getNativeSymbolInfo
R Documentation
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.
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.
package
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
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.