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List of Examples
gethostname from CLISPThis facility, also known as “Foreign Language Interface”, allows one to call a function implemented in C from inside CLISP and to do many related things, like inspect and modify foreign memory, define a “callback” (i.e., make a lisp function available to the C world), etc. To use this facility, one writes a foreign function description into an ordinary Lisp file, which is then compiled and loaded as usual; or just evaluates the appropriate form in the read-eval-print loop.
There are two basic ways to do define a foreign function:
Use dlopen and dlsym to get to the location of the
function code in a dynamic library.
To access this facility, pass the :LIBRARY option to FFI:DEF-CALL-OUT
and FFI:DEF-C-VAR.
Unfortunately, this functionality is not available on some
operating systems, and, also, it offers only a part of the foreign
functionality: cpp macros and inline functions
cannot be accessed this way. On the other hand, this functionality
is available in the read-eval-print loop and does not require a C compiler.
:LIBRARY argument, COMPILE-FILE produces a #P".c" file
(in addition to a #P".fas" and a #P".lib").
Then you compile (with a C compiler) and link it into CLISP
(statically, linking it into lisp.a, or
dynamically, loading it into a running CLISP using dlopen and dlsym).
This way you can use any functionality your foreign library exports,
whether using ordinary functions, inline functions,
or cpp macros (see Example 32.6, “Accessing cpp macros”).
All symbols relating to the foreign function interface are
exported from the package “FFI”.
To use them, (.USE-PACKAGE “FFI”)
Special “FFI” forms may appear anywhere in the Lisp file.
These are the special “FFI” forms. We have taken a pragmatic approach: the only foreign languages we support for now are C and ANSI C.
Unless specifically noted otherwise, type specification
parameters are not evaluated, so that they can be compiled by
FFI:PARSE-C-TYPE into the internal format at macroexpansion time.
High-level “FFI” forms; name is any Lisp
SYMBOL; c-name is a STRING
(FFI:DEF-C-TYPE name &OPTIONAL c-type)This form makes name a shortcut for c-type.
Note that c-type may already refer to name.
Forward declarations of types are not possible, however.
When c-type is omitted, the type is assumed to be an
integer, and its size and signedness are determined at link time,
e.g., (.FFI:DEF-C-TYPE size_t)
(FFI:DEF-C-VAR name
{option}*)This form defines a FFI:FOREIGN-VARIABLE.
name is the Lisp name, a regular Lisp SYMBOL.
Options for FFI:DEF-C-VAR
(:NAME c-name)STRING. If not specified, it is derived from the print name of
the Lisp name.(:TYPE c-type)(:READ-ONLY BOOLEAN)NIL,
it will be impossible to change the variable's value from within
Lisp (using SETQ or similar).(:ALLOC ALLOCATION):NONE or
:MALLOC-FREE and defaults to :NONE.
If it is :MALLOC-FREE, any values of type FFI:C-STRING, FFI:C-PTR,
FFI:C-PTR-NULL, FFI:C-ARRAY-PTR within the foreign value are assumed
to be pointers to malloc-allocated storage, and when SETQ
replaces an old value by a new one, the old storage is freed using
free and the new storage allocated using malloc.
If it is :NONE, SETQ assumes that the pointers point to good
storage (not NULL!) and overwrites the old values by the new ones.
This is dangerous (just think of overwriting a string with a longer
one or storing some data in a NULL pointer...) and deprecated.
(:LIBRARY name)FFI:DEFAULT-FOREIGN-LIBRARY.(:VERSION version):VERSION is supplied, :LIBRARY must also be supplied)
(:DOCUMENTATION string)VARIABLE documentation.
(FFI:DEF-C-CONST name
{option}*)This form defines a Lisp constant variable name whose value is
determined at build time using an internal FFI:FOREIGN-FUNCTION.
Options for FFI:DEF-C-CONST
(:NAME c-name)STRING. If not specified, it is derived from the print name
of the Lisp name.(:TYPE c-type)specifies the constant's foreign type, one of
| FFI:INT |
| FFI:C-STRING |
| FFI:C-POINTER |
(:GUARD
string)specifies the cpp check to wrap around c-name,
defaults to "defined(;
can be c-name)"NIL to omit the test. When the test fails, name is
unbound.
(:DOCUMENTATION string)VARIABLE documentation.
See also Example 32.6, “Accessing cpp macros”.
(FFI:DEF-CALL-OUT
name {option}*)This form defines a named call-out function (a foreign function called from Lisp: control flow temporarily leaves Lisp).
Options for FFI:DEF-CALL-OUT
(:NAME c-name)#'name
is redirected to call the C function c-name.
(:ARGUMENTS
{(argument c-type [PARAM-MODE [ALLOCATION]])}*)(:RETURN-TYPE c-type [ALLOCATION])(:LANGUAGE language)(:BUILT-IN BOOLEAN)FFI:*OUTPUT-C-FUNCTIONS*).
(:LIBRARY name)FFI:DEFAULT-FOREIGN-LIBRARY.(:VERSION version):VERSION is supplied, :LIBRARY must also be supplied).
(:GUARD guard)Specifies how to wrap the C code in the cpp
conditionals for portability and defaults to FFI:*FOREIGN-GUARD*:
NILTFFI:*FOREIGN-GUARD*.
Use as is, e.g., in
modules/bindings/glibc/linux.lisp:
(def-call-out canonicalize_file_name (:arguments (name c-string)) (:return-type c-string :malloc-free) (:guard "defined(__USE_GNU)"))
(:DOCUMENTATION string)FUNCTION documentation.
See also Section 32.3.7, “Foreign functions”.
(FFI:DEF-CALL-IN
function {option}*)This form defines a callback - a named call-in function (i.e., a Lisp function called from the foreign language: control flow temporary enters Lisp)
Options for FFI:DEF-CALL-IN
(:NAME c-name)c-name is redirected to call the Common Lisp function function, which
should be a function name.(:ARGUMENTS
{(argument c-type [PARAM-MODE [ALLOCATION]])}*)(:RETURN-TYPE c-type [ALLOCATION])(:LANGUAGE language)See also Section 32.3.7, “Foreign functions”.
(FFI:OPEN-FOREIGN-LIBRARY
name &KEY :REQUIRE)Open (load) a shared foreign library.
Some shared libraries depend on other shared libraries
and this dependency can be specified using
the :REQUIRE argument.
Unless the library has dependencies, this is only needed if
you want to test for presence of a library
without creating a foreign object referencing its contents.
When you create a FFI:FOREIGN-VARIABLE or a FFI:FOREIGN-FUNCTION
using FFI:DEF-C-VAR or FFI:DEF-CALL-OUT with a :LIBRARY argument,
the library name is opened automatically.
E.g., libgsl.so
requires libgslcblas.so:
(FFI:OPEN-FOREIGN-LIBRARY "libgsl.so")
*** - FFI:OPEN-FOREIGN-LIBRARY: Cannot open library "libgsl.so": "/usr/lib64/libgsl.so: undefined symbol: cblas_ctrmv"
so a common way is to pre-open the dependency:
(FFI:OPEN-FOREIGN-LIBRARY"libgslcblas.so") (FFI:DEF-CALL-OUTgsl_cheb_alloc (:LIBRARY"libgsl.so") (:language :stdc) (:arguments (n ffi:int)) (:return-type ffi:c-pointer)) ⇒GSL_CHEB_ALLOC
Alas, this would work in the current
image only: if you save the
image, GSL_CHEB_ALLOC will not work there
because CLISP will try to re-open libgsl.so and
fail as above. However, using the :REQUIRE argument
will tell CLISP to re-open both libraries in the right order:
$clisp > (FFI:OPEN-FOREIGN-LIBRARY"libgsl.so" :require '("libgslcblas.so")) > (FFI:DEF-CALL-OUTgsl_cheb_alloc (:library "libgsl.so") (:language :stdc) (:arguments (n ffi:int)) (:return-type ffi:c-pointer)) > (EXT:SAVEINITMEM"foo" :executable t) > (EXT:EXIT)$./foo > (gsl_cheb_alloc 10)#<FFI:FOREIGN-ADDRESS#x0000000017AC38A0>
(FFI:CLOSE-FOREIGN-LIBRARY
name)Close (unload) a shared foreign library (opened by
FFI:OPEN-FOREIGN-LIBRARY or the :LIBRARY argument to FFI:DEF-CALL-OUT
or FFI:DEF-C-VAR).
If you want to modify your shared library, you need to close
it using FFI:CLOSE-FOREIGN-LIBRARY first. When you use a
FFI:FOREIGN-VARIABLE or a FFI:FOREIGN-FUNCTION which resides in the
library name, it will be re-opened automatically.
(FFI:DEFAULT-FOREIGN-LIBRARY
library-name)This macro sets the default :LIBRARY argument for
FFI:DEF-CALL-OUT and FFI:DEF-C-VAR. library-name should be NIL
(meaning use the C file produced by COMPILE-FILE), a
STRING, or, depending on the underlying dlsym
or dlvsym implementation,
:DEFAULT or :NEXT.
The default is set separately in each compilation unit, so, if you
are interfacing to a single library, you can set this variable in the
beginning of your lisp file and omit the :LIBRARY argument
throughout the file.
(FFI:DEF-C-STRUCT
name (symbol c-type)*)This form defines name to be both a
STRUCTURE-CLASS and a foreign C type with the given slots.
If this class representation overhead is not needed one should consider
writing ( instead.
FFI:DEF-C-TYPE name (FFI:C-STRUCT
{LIST | VECTOR} (symbol c-type)*))name is a SYMBOL (structure name) or a LIST whose FIRST
element is the structure name and the REST is options.
Two options are supported at this time:
Options for FFI:DEF-C-STRUCT
:TYPEDEFtypedef
elsewhere.:EXTERNAL(FFI:C-LINES "#include <filename.h>~%").
These options determine how the struct is written to the #P".c".
(FFI:DEF-C-ENUM
name {symbol | (symbol [value])}*)This form defines symbols
as constants, similarly to the C declaration enum {
symbol [= value], ... };
You can use ( and
FFI:ENUM-FROM-VALUE
name value)( to convert between the numeric and symbolic
representations (of course, the latter function boils down to
FFI:ENUM-TO-VALUE name
symbol)SYMBOL-VALUE plus a check that the symbol is indeed a constant
defined in the FFI:DEF-C-ENUM name).
(FFI:C-LINES format-string
{argument}*)This form outputs the string
(
to the C output file's top level.
This is usually used to include the relevant header files,
see FORMAT NIL format-string {argument}*):EXTERNAL
and FFI:*OUTPUT-C-FUNCTIONS*.
When format-string is not a STRING, is should be a SYMBOL,
and then the STRING (
is added to the appropriate C function:FORMAT NIL {argument}*)
:INIT-ALWAYS:INIT-ONCE:FINI(FFI:ELEMENT c-place index1
... indexn)c-place is of foreign type
(FFI:C-ARRAY c-type (dim1 ... dimn))
and 0 ≤ index1 < dim1, ..., 0 ≤ indexn < dimn,
this will be the place corresponding to (AREF c-place
index1 ... indexn) or
c-place[index1]...[indexn]c-type.
If c-place is of foreign type (FFI:C-ARRAY-MAX
c-type dim) and 0 ≤ index < dim,
this will be the place corresponding to (AREF c-place
index) or c-place[index]c-type.
(FFI:DEREF c-place)c-place is of foreign type
(FFI:C-PTR c-type),
(FFI:C-PTR-NULL c-type) or
(FFI:C-POINTER c-type),
this will be the place the pointer points to.
It is a place of type c-type.
For (FFI:C-PTR-NULL c-type),
the c-place may not be NULL.
(FFI:SLOT c-place
slot-name)c-place is of
foreign type (FFI:C-STRUCT class ...
(slot-name c-type) ...) or of
type (FFI:C-UNION
... (slot-name c-type) ...),
this will be of type c-type.(FFI:CAST
c-place c-type)c-place, but of type c-type.
(FFI:OFFSET
c-place offset c-type)c-place by an
offset counted in bytes, with type c-type.
This can be used to resize an array, e.g. of c-type
(FFI:C-ARRAY uint16 n)
via (FFI:OFFSET c-place 0 '(FFI:C-ARRAY uint16
k)).
(FFI:C-VAR-ADDRESS
c-place)c-place as a Lisp object of
type FFI:FOREIGN-ADDRESS. This is useful as an argument
to foreign functions expecting a parameter of C type FFI:C-POINTER.
(FFI:C-VAR-OBJECT
c-place)FFI:FOREIGN-VARIABLE object underlying the
c-place. This is also an acceptable argument type to a FFI:C-POINTER
declaration.(FFI:TYPEOF c-place)c-type corresponding to the c-place.
(FFI:SIZEOF c-type)(FFI:SIZEOF c-place)The first form returns the size and alignment of the
C type c-type, measured in bytes.
The second form returns the size and alignment of the
C type of c-place, measured in bytes.
(FFI:BITSIZEOF c-type)(FFI:BITSIZEOF c-place)The first form returns the size and alignment of the
C type c-type, measured in bits.
The second form returns the size and alignment of the
C type of c-place, measured in bits.
(FFI:FOREIGN-ADDRESS-UNSIGNED foreign-entity)(FFI:UNSIGNED-FOREIGN-ADDRESS number)FFI:FOREIGN-ADDRESS-UNSIGNED returns the INTEGER
address embodied in the Lisp object of type FFI:FOREIGN-ADDRESS,
FFI:FOREIGN-POINTER, FFI:FOREIGN-VARIABLE or FFI:FOREIGN-FUNCTION.
FFI:UNSIGNED-FOREIGN-ADDRESS returns a FFI:FOREIGN-ADDRESS
object pointing to the given INTEGER address.
(FFI:FOREIGN-ADDRESS foreign-entity)FFI:FOREIGN-ADDRESS is both a type name and a
selector/constructor function. It is the Lisp object type
corresponding to a FFI:C-POINTER external type declaration, e.g. a
call-out function with ( yields
a Lisp object of type :RETURN-TYPE FFI:C-POINTER)FFI:FOREIGN-ADDRESS.
The function extracts the object of type FFI:FOREIGN-ADDRESS
living within any FFI:FOREIGN-VARIABLE or FFI:FOREIGN-FUNCTION object.
If the foreign-entity already is a FFI:FOREIGN-ADDRESS, it returns it.
If it is a FFI:FOREIGN-POINTER (e.g. a base foreign library address),
it encapsulates it into a FFI:FOREIGN-ADDRESS object, as suitable
for use with a FFI:C-POINTER external type declaration.
It does not construct addresses out of NUMBERs,
FFI:UNSIGNED-FOREIGN-ADDRESS must be used for that purpose.
(FFI:FOREIGN-VARIABLE foreign-entity
c-type-internal &KEY name)FFI:FOREIGN-VARIABLE
from the given FFI:FOREIGN-ADDRESS or FFI:FOREIGN-VARIABLE and the
internal C type descriptor (as obtained from FFI:PARSE-C-TYPE).
name, a STRING, is mostly useful for documentation and
interactive debugging since it appears in the printed representation
of the FFI:FOREIGN-VARIABLE object, as in
#<FFI:FOREIGN-VARIABLE "foo"
#x0ADD4E55>.
In effect, this is similar to FFI:CAST (or rather
(FFI:OFFSET ... 0 ...) for places),
except that it works with FFI:FOREIGN-ADDRESS objects and allows
caching of the internal C types.(FFI:FOREIGN-FUNCTION
foreign-entity c-type-internal &KEY name)This constructor creates a FFI:FOREIGN-FUNCTION
from the given FFI:FOREIGN-ADDRESS or FFI:FOREIGN-FUNCTION and the
internal C type descriptor (as obtained from
(,
in which case it is important to specify the FFI:PARSE-C-TYPE '(FFI:C-FUNCTION ...)):LANGUAGE because the
expressions are likely to be evaluated at run time, outside the compilation unit).
The name, a STRING, is mostly useful for documentation and
interactive debugging since it appears in the printed representation
of the FFI:FOREIGN-FUNCTION object, e.g.,
#<.
It is inherited from the given FFI:FOREIGN-FUNCTION "foo"
#x0052B060>FFI:FOREIGN-FUNCTION object when
available.
See also Section 32.3.7, “Foreign functions”.
(FFI:VALIDP foreign-entity)(SETF (FFI:VALIDP foreign-entity) value)This predicate returns NIL if the foreign-entity
(e.g. the Lisp equivalent of a FFI:C-POINTER) refers to a pointer
which is invalid (e.g., because it comes from a previous Lisp session).
It returns T if foreign-entity can be used within the current Lisp process
(thus it returns T for all non-foreign arguments).
You can invalidate a foreign object using
(.
You cannot resurrect a zombie, nor can you kill a non-foreign object.
SETF FFI:VALIDP)
(FFI:FOREIGN-POINTER foreign-entity)FFI:FOREIGN-POINTER returns the FFI:FOREIGN-POINTER
associated with the Lisp object of type FFI:FOREIGN-ADDRESS,
FFI:FOREIGN-POINTER, FFI:FOREIGN-VARIABLE or FFI:FOREIGN-FUNCTION.
(FFI:SET-FOREIGN-POINTER foreign-entity {foreign-entity |
:COPY})FFI:SET-FOREIGN-POINTER changes the
FFI:FOREIGN-POINTER associated with the Lisp object of type
FFI:FOREIGN-ADDRESS, FFI:FOREIGN-VARIABLE or FFI:FOREIGN-FUNCTION to
that of the other entity.
With :COPY, a fresh FFI:FOREIGN-POINTER is allocated.
The original foreign-entity still points to the same object and is returned.
This is particularly useful with (SETF FFI:VALIDP),
see Example 32.11, “Controlling validity of resources”.(FFI:WITH-FOREIGN-OBJECT (variable c-type
[initarg]) body)(FFI:WITH-C-VAR (variable c-type
[initarg]) body)These forms allocate space on the C execution
stack, bind respectively a FFI:FOREIGN-VARIABLE object or
a local SYMBOL-MACRO to variable and execute body.
When initarg is not supplied,
they allocate space only for ( bytes.
This space is filled with zeroes. E.g.,
using a FFI:SIZEOF c-type)c-type of FFI:C-STRING or even (FFI:C-PTR
(FFI:C-ARRAY uint8 32)) (!) both allocate space
for a single pointer, initialized to NULL.
When initarg is supplied, they
allocate space for an arbitrarily complex set of structures rooted in
c-type. Therefore, FFI:C-ARRAY-MAX, #()
and "" are your friends for creating a
pointer to the empty arrays:
(with-c-var (v '(c-ptr (c-array-max uint8 32)) #()) (setf (element (deref v) 0) 127) v)
c-type is evaluated, making creation of variable sized buffers easy:
(with-c-var (fv `(c-array uint8 ,(length my-vector)) my-vector) (print fv))
(FFI:FOREIGN-VALUE FFI:FOREIGN-VARIABLE)(SETF (FFI:FOREIGN-VALUE FFI:FOREIGN-VARIABLE) ...)This functions converts the reference to a C
data structure which the FFI:FOREIGN-VARIABLE describes, to Lisp. Such a
reference is typically obtained from FFI:ALLOCATE-SHALLOW,
FFI:ALLOCATE-DEEP, FFI:FOREIGN-ALLOCATE or via a (FFI:C-POINTER
C type description.
Alternatively, macros like c-type)FFI:WITH-C-PLACE or FFI:WITH-C-VAR and the
concept of foreign place hide many uses of this function.
The SETF form performs conversion from Lisp to C,
following to the FFI:FOREIGN-VARIABLE's type description.
(FFI:WITH-FOREIGN-STRING
(foreign-address char-count
byte-count string
&KEY encoding null-terminated-p
start end) &BODY body)This forms converts a Lisp string according to
the encoding, allocating space on the C execution stack.
encoding can be any EXT:ENCODING, e.g. CHARSET:UTF-16 or CHARSET:UTF-8,
whereas CUSTOM:*FOREIGN-ENCODING* must be an ASCII-compatible encoding.
body is then executed with the three variables foreign-address,
char-count and
byte-count respectively bound to an
untyped FFI:FOREIGN-ADDRESS (as known from the FFI:C-POINTER foreign
type specification) pointing to the stack location, the number of
CHARACTERs of the Lisp string that were considered and the
number of ( bytes that were allocated for it on the C
stack.UNSIGNED-BYTE 8)
When null-terminated-p is true,
which is the default, a variable number of zero bytes is appended,
depending on the encoding, e.g. 2 for CHARSET:UTF-16,
and accounted for in byte-count,
and char-count is incremented by one.
The FFI:FOREIGN-ADDRESS object bound to foreign-address is
invalidated upon the exit from the form.
A stupid example (a quite costly interface
to mblen):
(with-foreign-string (fv elems bytes string
:encoding charset:jis... :null-terminated-p nil
:end 5)
(declare (ignore fv elems))
(format t "This string would take ~D bytes." bytes))
(FFI:PARSE-C-TYPE c-type)(FFI:DEPARSE-C-TYPE c-type-internal)Convert between the external (LIST) and internal
(VECTOR) C type representations (used by DESCRIBE).
Although you can memoize a c-type-internal (see
Section 31.11.3, “Macro EXT:MEMOIZED” - but do not expect type redefinitions to
work across memoization!), you cannot serialize it (write to
disk) because deserialization loses object identity.
(FFI:ALLOCATE-SHALLOW
c-type &KEY :COUNT :READ-ONLY)(FFI:ALLOCATE-DEEP c-type contents
&KEY :COUNT :READ-ONLY)(FFI:FOREIGN-FREE foreign-entity &KEY :FULL)(FFI:FOREIGN-ALLOCATE c-type-internal
&KEY :INITIAL-CONTENTS :COUNT :READ-ONLY)Macro FFI:ALLOCATE-SHALLOW allocates
(
bytes on the C heap and zeroes them out
(like FFI:SIZEOF c-type)calloc).
When :COUNT is supplied, c-type is substituted with
(FFI:C-ARRAY ,
except when c-type count)c-type is CHARACTER, in which case
(FFI:C-ARRAY-MAX
is used instead.
When CHARACTER count):READ-ONLY is supplied, the Lisp side is prevented from modifying the
memory contents. This can be used as an indication that some foreign
side is going to fill this memory (e.g. via read).
Returns a FFI:FOREIGN-VARIABLE object of the actual c-type,
whose address part points to the newly allocated memory.
FFI:ALLOCATE-DEEP will call C malloc as many times
as necessary to build a structure on the C heap of the given
c-type, initialized from the given contents.
E.g., (
performs 2 allocations: one for a C pointer to a string,
another for the contents of that string. This would be useful in
conjunction with a char** C type
declaration. FFI:ALLOCATE-DEEP 'FFI:C-STRING "ABCDE")(
allocates room for a single pointer (probably 4 bytes).FFI:ALLOCATE-SHALLOW 'FFI:C-STRING)
( allocates and initializes room for the type FFI:ALLOCATE-DEEP 'CHARACTER "ABCDEF" :count
10)(FFI:C-ARRAY-MAX ,
corresponding to char* or, more specifically,
char[10] in C.CHARACTER 10)
Function FFI:FOREIGN-FREE deallocates memory at the address
held by the given foreign-entity. If :FULL is supplied
and the argument is of type FFI:FOREIGN-VARIABLE, recursively frees
the whole complex structure pointed to by this variable.
If given a FFI:FOREIGN-FUNCTION object that corresponds to a
CLISP callback, deallocates it. Callbacks are automatically
created each time you pass a Lisp function via the “FFI”.
Use ( to disable further
references to this address from Lisp. This is currently not done
automatically. If the given pointer is already invalid,
SETF FFI:VALIDP)FFI:FOREIGN-FREE (currently) SIGNALs an ERROR. This may change to
make it easier to integrate with EXT:FINALIZE.
Function FFI:FOREIGN-ALLOCATE is a lower-level interface as it
requires an internal C type descriptor as returned by
FFI:PARSE-C-TYPE.
(FFI:WITH-C-PLACE (variable foreign-entity)
body)Create a place out of the given FFI:FOREIGN-VARIABLE
object so operations on places (e.g. FFI:CAST, FFI:DEREF, FFI:SLOT etc.) can
be used within body. FFI:WITH-C-VAR appears as a composition of
FFI:WITH-FOREIGN-OBJECT and FFI:WITH-C-PLACE.
Such a place can be used to access memory referenced by a foreign-entity
object:
(setq foo (allocate-deep '(c-array uint8 3) rgb)) (with-c-place (place foo) (element place 0))
FFI:*OUTPUT-C-FUNCTIONS*FFI:*OUTPUT-C-VARIABLES*FFI:DEF-CALL-OUT) and
foreign variables (defined with FFI:DEF-C-VAR) into the output #P".c"
(when the Lisp file is compiled with COMPILE-FILE)
unless these variables are NIL.
They are NIL by default, so the extern
declarations are not written; you are encouraged to use
FFI:C-LINES to include the appropriate C headers.
Set these variables to non-NIL if the headers are not available or
not usable.FFI:*FOREIGN-GUARD*When this variable is non-NIL at compile time,
CLISP will guard the C statements in the output file with
cpp conditionals to take advantage of GNU autoconf feature detection.
E.g.,
(EVAL-WHEN(compile) (setq *foreign-guard* t)) (FFI:DEF-CALL-OUTsome-function (:name "function_name") ...)
will produce
# if defined(HAVE_FUNCTION_NAME) register_foreign_function((void*)&function_name,"function_name",1024); # endif
and will compile and link on any system.
This is mostly useful for product delivery when you want your module to build on any system even if some features will not be available.
FFI:*FOREIGN-GUARD* is initialized to NIL for backwards compatibility.
FFI:FOREIGN-POINTER-INFOdladdr and it returns the 4 fields
of Dl_info as multiple values.Low-level “FFI” forms
(FFI:MEMORY-AS foreign-address c-type-internal &OPTIONAL
offset)(SETF (FFI:MEMORY-AS foreign-address c-type-internal &OPTIONAL
offset) value)This accessor is useful when operating with untyped
foreign pointers (FFI:FOREIGN-ADDRESS) as opposed to typed ones
(represented by FFI:FOREIGN-VARIABLE). It allows to type and
dereference the given pointer without the need to create an object of
type FFI:FOREIGN-VARIABLE.
Alternatively, one could use (
(also FFI:FOREIGN-VALUE
(FFI:FOREIGN-VARIABLE foreign-entity c-type-internal))SETFable).
Note that c-type-internal is the internal
representation of a foreign type, thus FFI:PARSE-C-TYPE is required
with literal names or types, e.g. ( or FFI:MEMORY-AS foreign-address
(FFI:PARSE-C-TYPE '(FFI:C-ARRAY uint8 3)))(.SETF
(FFI:MEMORY-AS foreign-address (FFI:PARSE-C-TYPE 'uint32)) 0)
Foreign C types are used in the “FFI”. They are not regular Common Lisp types or CLOS classes.
A c-type is either a predefined C type or the name of a
type defined by FFI:DEF-C-TYPE.
the predefined C types (c-type)
simple-c-typethe simple C types
| Lisp name | Lisp equivalent | C equivalent | ILU equivalent | Comment |
|---|---|---|---|---|
NIL | NIL | void | as a result type only | |
BOOLEAN | BOOLEAN | int | BOOLEAN | |
CHARACTER | CHARACTER | char | SHORT CHARACTER | |
| char | INTEGER | signed char | ||
| uchar | INTEGER | unsigned char | ||
| short | INTEGER | short | ||
| ushort | INTEGER | unsigned short | ||
| int | INTEGER | int | ||
| uint | INTEGER | unsigned int | ||
| long | INTEGER | long | ||
| ulong | INTEGER | unsigned long | ||
| uint8 | ( | uint8 | BYTE | |
| sint8 | ( | sint8 | ||
| uint16 | ( | uint16 | SHORT CARDINAL | |
| sint16 | ( | sint16 | SHORT INTEGER | |
| uint32 | ( | uint32 | CARDINAL | |
| sint32 | ( | sint32 | INTEGER | |
| uint64 | ( | uint64 | LONG CARDINAL | does not work on all platforms |
| sint64 | ( | sint64 | LONG INTEGER | does not work on all platforms |
SINGLE-FLOAT | SINGLE-FLOAT | float | ||
DOUBLE-FLOAT | DOUBLE-FLOAT | double |
NIL is accepted as a FFI:C-POINTER and
treated as NULL; when a function wants to return a NULL
FFI:C-POINTER, it actually returns NIL.
(FFI:C-POINTER
c-type)c-type *: a pointer to a single item of the given
c-type. It differs from (FFI:C-PTR-NULL
c-type) (see below) in that no conversion to and from
Lisp will occur (beyond the usual one of the C NULL pointer
to or from Lisp NIL). Instead, an object of type FFI:FOREIGN-VARIABLE
is used to represent the foreign place. It is assimilable to a typed
pointer.(FFI:C-STRUCT class
(ident1 c-type1) ... (identn c-typen))This type is equivalent to what C calls
struct { c-type1 ident1; ...; c-typen identn; }.
Its Lisp equivalent is: if class is VECTOR, a
SIMPLE-VECTOR; if class is LIST, a proper list;
if class is a symbol naming a structure or CLOS class, an
instance of this class, with slots of names
ident1, ..., identn.
class may also be a CONS of a SYMBOL (as above) and
a LIST of FFI:DEF-C-STRUCT options.
(FFI:C-UNION
(ident1 c-type1) ... (identn c-typen))c-type1 ident1; ...; c-typen identn; }.
Conversion to and from Lisp assumes that a value is to be viewed as
being of c-type1.
(FFI:C-ARRAY
c-type dim1)(FFI:C-ARRAY c-type (dim1
... dimn))c-type [dim1] ... [dimn].
Note that when an array is passed as an argument to a function in
C, it is actually passed as a pointer; you therefore have to
write (FFI:C-PTR (FFI:C-ARRAY ...)) for this
argument's type.(FFI:C-ARRAY-MAX
c-type maxdimension)c-type [maxdimension], an array containing up to
maxdimension elements.
The array is zero-terminated if it contains less than maxdimension elements.
Conversion from Lisp of an array with more than maxdimension elements
silently ignores the extra elements.
(FFI:C-FUNCTION (:ARGUMENTS
{(argument a-c-type
[PARAM-MODE [ALLOCATION]])}*)
(:RETURN-TYPE r-c-type [ALLOCATION])
(:LANGUAGE language))(r-c-type (*)
(a-c-type1, ...)).
Conversion between C functions and Lisp functions
is transparent, and NULL/NIL is recognized and
accepted.(FFI:C-PTR c-type)c-type *: a pointer to a single item of the given
c-type.(FFI:C-PTR-NULL c-type)c-type *: a pointer to a single item of the given
c-type, with the exception that C NULL corresponds to
Lisp NIL.(FFI:C-ARRAY-PTR c-type)c-type (*)[]: a pointer to a zero-terminated array of
items of the given c-type.The conversion of FFI:C-STRING,
(FFI:C-ARRAY ,
CHARACTER dim1)(FFI:C-ARRAY-MAX ,
CHARACTER maxdimension)(FFI:C-ARRAY-PTR
is governed by CHARACTER)CUSTOM:*FOREIGN-ENCODING* and dimensions are given
in bytes.
The conversion of CHARACTER, and as such of
(FFI:C-PTR , or
CHARACTER)(FFI:C-PTR-NULL , as well as
that of multi-dimensional arrays CHARACTER)(FFI:C-ARRAY , are governed by CHARACTER
(dim1 ... dimn))CUSTOM:*FOREIGN-ENCODING* if
the latter is a “1:1” encoding, or by the ASCII encoding otherwise.
Remember that the C type char is
a numeric type and does not use CHARACTER
EXT:ENCODINGs.
FFI:C-FUNCTION, FFI:DEF-CALL-IN, FFI:DEF-CALL-OUT take a :LANGUAGE argument.
The language is either :C (denotes K&R C) or :STDC
(denotes ANSI C) or :STDC-STDCALL (denotes ANSI C
with the stdcall calling convention).
It specifies whether the C function (caller or callee) has been
compiled by a K&R C compiler or by an ANSI C compiler,
and possibly the calling convention.
The default language is set using the macro
FFI:DEFAULT-FOREIGN-LANGUAGE
.
If this macro has not been called in the current compilation unit
(usually a file), a warning is issued and :STDC is used for the rest
of the unit.
Foreign variables are variables whose
storage is allocated in the foreign language module.
They can nevertheless be evaluated and modified through SETQ,
just as normal variables can, except that the range of allowed values
is limited according to the variable's foreign type.
For a foreign variable x the form ( is not necessarily true, since every time EQL x
x)x is
evaluated its foreign value is converted to a fresh Lisp value.
Ergo, ( modifies this
fresh Lisp value (immediately discarded), not the foreign data.
Use SETF (AREF x n) y)FFI:ELEMENT et al instead, see Section 32.3.6, “Operations on foreign places”.
Foreign variables are defined using FFI:DEF-C-VAR and FFI:WITH-C-VAR.
A FFI:FOREIGN-VARIABLE name defined by FFI:DEF-C-VAR, FFI:WITH-C-VAR
or FFI:WITH-C-PLACE defines a place,
i.e., a form which can also be used as argument to SETF.
(An “lvalue” in C terminology.)
The following operations are available on foreign places:
FFI:ELEMENT | FFI:C-VAR-ADDRESS |
FFI:DEREF | FFI:C-VAR-OBJECT |
FFI:SLOT | FFI:TYPEOF |
FFI:CAST | FFI:SIZEOF |
FFI:OFFSET | FFI:BITSIZEOF |
Foreign functions are functions which are defined in the foreign language.
There are named foreign functions
(imported via FFI:DEF-CALL-OUT or created via FFI:DEF-CALL-IN) and
anonymous foreign functions; they arise through conversion of function
pointers using FFI:FOREIGN-FUNCTION.
A call-out function is a foreign function called from Lisp: control flow temporarily leaves Lisp. A call-in function (AKA callback) is a Lisp function called from the foreign language: control flow temporary enters Lisp.
The following operators define foreign functions:
FFI:DEF-CALL-IN |
FFI:DEF-CALL-OUT |
FFI:FOREIGN-FUNCTION |
Callbacks (C function calling Lisp function) create so-called trampolines. A trampoline is a piece of C code which knows how to call a particular Lisp function. (That is how all foreign language interfaces work, not just ours). The C pointer that the foreign library receives is the pointer to this piece of code. These are not subject to garbage-collection, as there is no protocol to tell the garbage collector when a given callback is not needed anymore (unlike with Lisp objects).
With callbacks to named functions (i.e.,
created by a FFI:DEF-CALL-IN form where function is a function name) this is
mostly harmless, since function is unlikely to be redefined.
With callbacks to anonymous functions (i.e.,
created by FFI:FOREIGN-FUNCTION or a FFI:DEF-CALL-IN form where function
argument is a lambda expression), this might become an issue when they are
produced dynamically and en masse, e.g. inside a loop, so that many
trampolines are generated.
You can use FFI:FOREIGN-FREE to free the trampoline associated with a
FFI:FOREIGN-FUNCTION object, but when you pass a lambda expression to a
FFI:DEF-CALL-OUT as an argument of type FFI:C-FUNCTION, such a trampoline
is allocated, but you do not get hold of the associated trampoline
object, and thus you cannot (trivially) free it.
Thus you may find it easier to create the FFI:FOREIGN-FUNCTION object
first, pass it to the FFI:DEF-CALL-OUT, and then call FFI:FOREIGN-FREE
manually.
When passed to and from functions, allocation of arguments and results is handled as follows:
Values of SIMPLE-C-TYPE, FFI:C-POINTER are passed on the stack,
with dynamic extent. The ALLOCATION is effectively ignored.
Values of type FFI:C-STRING, FFI:C-PTR, FFI:C-PTR-NULL, FFI:C-ARRAY-PTR
need storage. The ALLOCATION specifies the allocation policy:
If no ALLOCATION is specified, the default ALLOCATION is
:NONE for most types, but :ALLOCA for FFI:C-STRING and FFI:C-PTR and
FFI:C-PTR-NULL and FFI:C-ARRAY-PTR and for :OUT arguments.
The :MALLOC-FREE policy provides the ability to pass
arbitrarily nested structures within a single conversion.
:MALLOC-FREEmalloc and
never deallocates it. The C function is supposed to call
free when done with it.:ALLOCA:NONELisp assumes that the pointer already points to a valid area of the proper size and puts the result value there.
This is dangerous and deprecated.
:MALLOC-FREEfree on it when done.
:NONEPassing FFI:C-STRUCT, FFI:C-UNION,
FFI:C-ARRAY, FFI:C-ARRAY-MAX values as arguments (not via pointers) is
only possible to the extent the C compiler supports it.
Most C compilers do it right, but some C compilers
(such as gcc on hppa,
x86_64 and Win32)
have problems with this.
The recommended workaround is to pass pointers; this is fully supported.
See also clisp-devel
(Gmane/devel/10089/https://sourceforge.net/p/clisp/mailman/message/12562038/).
A function parameter's PARAM-MODE may be
:IN (means: read-only)::OUT (means: write-only):ALLOCATION = :ALLOCA.:IN-OUT (means: read-write)::OUT value is returned as an additional return value.
The default is :IN.
List of Examples
gethostname from CLISPExample 32.2. Simple declarations and access
The C declaration
struct foo {
int a;
struct foo * b[100];
};
corresponds to
(FFI:DEF-C-STRUCT foo
(a int)
(b (c-array (c-ptr foo) 100)))
The element access
struct foo f; f.b[7].a
corresponds to
(declare (type foo f))
(foo-a (aref (foo-b f) 7)) ; or
(slot-value (aref (slot-value f 'b) 7) 'a)
Example 32.3. External C variable and some accesses
struct bar {
short x, y;
char a, b;
int z;
struct bar * n;
};
extern struct bar * my_struct;
my_struct->x++;
my_struct->a = 5;
my_struct = my_struct->n;
corresponds to
(FFI:DEF-C-STRUCTbar (x short) (y short) (a char) (b char) ; or (b character) if it represents a character, not a number (z int) (n (c-ptr bar))) (FFI:DEF-C-VARmy_struct (:type (c-ptr bar))) (setq my_struct (let ((s my_struct)) (incf (slot-value s 'x)) s)) ; or (incf (slot my_struct 'x)) (setq my_struct (let ((s my_struct)) (setf (slot-value s 'a) 5) s)) ; or (setf (slot my_struct 'a) 5) (setq my_struct (slot-value my_struct 'n)) ; or (setq my_struct (deref (slot my_struct 'n)))
Example 32.4. Calling an external function
On ANSI C systems, <stdlib.h>
contains the declarations:
typedef struct {
int quot; /* Quotient */
int rem; /* Remainder */
} div_t;
extern div_t div (int numer, int denom);
This translates to
(FFI:DEF-C-STRUCT(div_t :typedef) (quot int) (rem int)) (FFI:DEFAULT-FOREIGN-LANGUAGE:stdc) (FFI:DEF-CALL-OUTdiv (:ARGUMENTS(numer int) (denom int)) (:RETURN-TYPEdiv_t))
Sample call from within Lisp (after running clisp-link):
(div 20 3)
⇒ #S(DIV_T :QUOT 6 :REM 2)
Example 32.5. Another example for calling an external function
Suppose the following is defined in a file cfun.c:
struct cfunr { int x; char *s; };
struct cfunr * cfun (int i,char *s,struct cfunr * r,int a[10]) {
int j;
struct cfunr * r2;
printf("i = %d\n", i);
printf("s = %s\n", s);
printf("r->x = %d\n", r->x);
printf("r->s = %s\n", r->s);
for (j = 0; j < 10; j++) printf("a[%d] = %d.\n", j, a[j]);
r2 = (struct cfunr *) malloc (sizeof (struct cfunr));
r2->x = i+5;
r2->s = "A C string";
return r2;
}
It is possible to call this function from Lisp using the file
callcfun.lisp (do not call it
cfun.lisp - COMPILE-FILE will
overwrite
cfun.c) whose contents is:
(DEFPACKAGE"TEST-C-CALL" (:use “COMMON-LISP” “FFI”)) (IN-PACKAGE"TEST-C-CALL") (EVAL-WHEN(compile) (setqFFI:*OUTPUT-C-FUNCTIONS*t)) (FFI:DEF-C-STRUCTcfunr (x int) (s c-string)) (FFI:DEFAULT-FOREIGN-LANGUAGE:stdc) (FFI:DEF-CALL-OUTcfun (:RETURN-TYPE(c-ptr cfunr)) (:ARGUMENTS(i int) (s c-string) (r (c-ptr cfunr) :in :alloca) (a (c-ptr (c-array int 10)) :in :alloca))) (defun call-cfun () (cfun 5 "A Lisp string" (make-cfunr :x 10 :s "Another Lisp string") '#(0 1 2 3 4 5 6 7 8 9)))
Use the module facility:
$clisp-link create cfun callcfun.c$cc -O -c cfun.c$cd cfun$ln -s ../cfun.o cfun.o Add cfun.o to NEW_LIBS and NEW_FILES in link.sh.$cd ..$base/lisp.run-Mbase/lispinit.mem-ccallcfun.lisp$clisp-link add base base+cfun cfun$base+cfun/lisp.run-Mbase+cfun/lispinit.mem-icallcfun > (test-c-call::call-cfun) i = 5 s = A Lisp string r->x = 10 r->s = Another Lisp string a[0] = 0. a[1] = 1. a[2] = 2. a[3] = 3. a[4] = 4. a[5] = 5. a[6] = 6. a[7] = 7. a[8] = 8. a[9] = 9. #S(TEST-C-CALL::CFUNR :X 10 :S "A C string") >$rm -r base+cfun
Note that there is a memory leak here: The return value
r2 of cfun() is
malloced but never freed. Specifying
(:RETURN-TYPE (c-ptr cfunr) :malloc-free)
is not an alternative because this would also
free(r2->x) but r2->x is a
pointer to static data.
The memory leak can be avoided using
(:RETURN-TYPE (c-pointer cfunr))
instead, in conjunction with
(defun call-cfun ()
(let ((data (cfun ...)))
(UNWIND-PROTECT (FFI:FOREIGN-VALUE data)
(FFI:FOREIGN-FREE data :FULL nil))))
Example 32.6. Accessing cpp macros
Suppose you are interfacing to a library mylib.so
which defines types, macros and inline functions
in mylib.h:
#define FOO(x) .....
#define BAR ...
struct zot { ... }
inline int bar (int x) { ... }
To make them available from CLISP, write these forms into the lisp
file my.lisp:
(FFI:C-LINES"#include <mylib.h> int my_foo (int x) { return FOO(x); } int my_bar (int x) { return bar(x); }~%") (FFI:DEF-C-CONSTbar) (FFI:DEF-C-CONSTzot-size (:name "sizeof(struct zot)") (:guard nil)) (FFI:DEF-CALL-OUTmy-foo (:NAME"my_foo") (:ARGUMENTS(x ffi:int)) (:RETURN-TYPEffi:int)) (FFI:DEF-CALL-OUTmy-bar (:NAME"my_bar") (:ARGUMENTS(x ffi:int)) (:RETURN-TYPEffi:int))
Compiling this file will produce my.c
and my.fas and you have two options:
Compile my.c
into my.o with
$ gcc -c my.c -lmyliband use clisp-link to create a new CLISP linking set.
Add ( to the :LIBRARY "my.dll")FFI:DEF-CALL-OUT
forms, compile my.c into my.so
(or my.dll on Win32) with
$ gcc -shared -o my.so my.c -lmylib and
load my.fas.
Of course, you could have created my1.c
containing
#include <mylib.h>
int my_foo (int x) { return FOO(x); }
int my_bar (int x) { return bar(x); }
manually, but FFI:C-LINES allows you to keep the
definitions of my_foo and my-foo
close together for easier maintenance.
Example 32.7. Calling Lisp from C
To sort an array of double-floats using the Lisp function SORT
instead of the C library function
qsort, one can use the
following interface code sort1.c.
The main problem is to pass a variable-sized array.
extern void lispsort_begin (int);
void* lispsort_function;
void lispsort_double (int n, double * array) {
double * sorted_array;
int i;
lispsort_begin(n); /* store #'sort2 in lispsort_function */
sorted_array = ((double * (*) (double *)) lispsort_function) (array);
for (i = 0; i < n; i++) array[i] = sorted_array[i];
free(sorted_array);
}
This is accompanied by sort2.lisp:
(DEFPACKAGE"FFI-TEST" (:use “COMMON-LISP” “FFI”)) (IN-PACKAGE"FFI-TEST") (EVAL-WHEN(compile) (SETQFFI:*OUTPUT-C-FUNCTIONS*t)) (FFI:DEF-CALL-INlispsort_begin (:ARGUMENTS(n int)) (:RETURN-TYPEnil) (:LANGUAGE:stdc)) (FFI:DEF-C-VARlispsort_function (:type c-pointer)) (DEFUNlispsort_begin (n) (SETF(FFI:CASTlispsort_function `(FFI:C-FUNCTION (:ARGUMENTS(v (c-ptr (c-array double-float ,n)))) (:RETURN-TYPE(c-ptr (c-array double-float ,n)) :malloc-free))) #'sort2)) (DEFUNsort2 (v) (declare (type vector v)) (sort v #'<))
To test this, use the following test file sorttest.lisp:
(EVAL-WHEN(compile) (setqFFI:*OUTPUT-C-FUNCTIONS*t)) (FFI:DEF-CALL-OUTsort10 (:NAME"lispsort_double") (:LANGUAGE:stdc) (:ARGUMENTS(n ffi:int) (array (FFI:C-PTR (FFI:C-ARRAY ffi:double-float 10)) :in-out)))
Now try
$clisp-link create sort sort2.c sorttest.c$cc -O -c sort1.c$cd sort$ln -s ../sort1.o sort1.o
Add sort1.o to NEW_LIBS
and NEW_FILES in link.sh.
Create a file package.lisp containing the form
(MAKE-PACKAGE "FFI-TEST" :use '(“COMMON-LISP” “FFI”))
and add package.lisp to TO_PRELOAD in link.sh.
Proceed:
$cd ..$base/lisp.run-Mbase/lispinit.mem-csort2.lisp-csorttest.lisp$clisp-link add base base+sort sort$base+sort/lisp.run-Mbase+sort/lispinit.mem-isort2 sorttest > (sort10 10 '#(0.501d0 0.528d0 0.615d0 0.550d0 0.711d0 0.523d0 0.585d0 0.670d0 0.271d0 0.063d0)) #(0.063d0 0.271d0 0.501d0 0.523d0 0.528d0 0.55d0 0.585d0 0.615d0 0.67d0 0.711d0)$rm -r base+sort
Example 32.8. Calling Lisp from C dynamically
Create a dynamic library lispdll
(#P".dll" on Win32,
#P".so" on UNIX)
with the following function:
typedef int (*LispFunc)(int parameter);
int CallInFunc(LispFunc f) {
return f(5)+11;
}
and call it from Lisp:
(ffi:def-call-out callout (:NAME"CallInFunc") (:LIBRARY"lispdll.dll") (:ARGUMENTS(function-arg (FFI:C-FUNCTION (:ARGUMENTS(number ffi:int)) (:RETURN-TYPEffi:int) (:LANGUAGE:stdc)))) (:RETURN-TYPEffi:int) (:LANGUAGE:stdc)) (defun f (x) (* x 2)) ⇒F(callout #'f) ⇒21
Example 32.9. Variable size arguments:
calling gethostname from CLISP
The standard UNIX function
follows a typical pattern of C “out”-parameter
convention: it expects a pointer to a buffer it is going to fill.
So you must view this parameter as either :OUT or :IN-OUT.
Additionally, one must tell the function the size of the buffer.
Here length is just an :IN parameter.
Sometimes this will be an :IN-OUT parameter, returning the
number of bytes actually filled in.
So name is actually a pointer to an array of up to length
characters, regardless of what the poor char* C
prototype says, to be used like a C string
(NULL-termination). UNIX specifies that “host names are
limited to HOST_NAME_MAX bytes”, which is,
of course, system dependent, but it appears that 256 is sufficient.
In the present example, you can use allocation :ALLOCA, like
you would do in C: stack-allocate a temporary:
(FFI:DEF-CALL-OUTgethostname (:ARGUMENTS(name (FFI:C-PTR (FFI:C-ARRAY-MAX ffi:char 256)):OUT:ALLOCA) (length ffi:int)) (:LANGUAGE:stdc) (:LIBRARY:default) (:RETURN-TYPEffi:int)) ⇒GETHOSTNAME(defun myhostname () (multiple-value-bind (success name) ;:OUTand:IN-OUTparameters are returned as multiple values (gethostname 256) (if (zerop success) name (error "~S: ~S: ~S" 'myhostname (os:errno) (os:strerror))))) ; See Section 33.2.15, “Error handling” ⇒MYHOSTNAME(myhostname) ⇒#(97 98 97 122 111 110 107)
It is a SIMPLE-VECTOR, not a STRING, because the name
argument is an array of char (an INTEGER type, see
Section 32.3.3, “(Foreign) C types”), not character.
(FFI:DEF-CALL-OUTgethostname (:ARGUMENTS(name (FFI:C-PTR (FFI:C-ARRAY-MAX character 256)):OUT:ALLOCA) (length ffi:int)) (:LANGUAGE:stdc) (:LIBRARY:default) (:RETURN-TYPEffi:int)) ⇒GETHOSTNAME(myhostname) ⇒"abazonk"
Now we have a different problem:
if gethostname fails, then the buffer
allocated for name will be filled with garbage, but it will still go
through the string conversion before we can check
the success status.
If CUSTOM:*FOREIGN-ENCODING* is CHARSET:ISO-8859-1, this is not a problem since no real
conversion is happening, but with CHARSET:UTF-8 an ERROR may be SIGNALed.
A safe approach is to pass to the foreign function our own
stack-allocated buffer, and only convert the buffer to a string when the
foreign function succeeds:
(FFI:DEF-CALL-OUTgethostname (:ARGUMENTS(name FFI:C-POINTER) (length ffi:int)) (:LANGUAGE:stdc) (:LIBRARY:default) (:RETURN-TYPEffi:int)) ⇒GETHOSTNAME(defun myhostname () (FFI:WITH-FOREIGN-OBJECT(name '(FFI:C-ARRAY-MAX character 256)) (let ((success (gethostname name 256))) (if (zerop success) (FFI:FOREIGN-VALUEname) (error "~S: ~S: ~S" 'myhostname (os:errno) (os:strerror)))))) ⇒MYHOSTNAME(myhostname) ⇒"abazonk"
Note that the type argument of FFI:WITH-FOREIGN-OBJECT is evaluated,
so we do not have to make any assumptions
about HOST_NAME_MAX:
(defun myhostname () (let ((host-name-max (os:sysconf :host-name-max))) (FFI:WITH-FOREIGN-OBJECT(name `(FFI:C-ARRAY-MAX character ,host-name-max)) (let ((success (gethostname name host-name-max))) (if (zerop success) (FFI:FOREIGN-VALUEname) (error "~S: ~S: ~S" 'myhostname (os:errno) (os:strerror))))))) ⇒MYHOSTNAME(myhostname) ⇒"abazonk"
Example 32.10. Accessing variables in shared libraries
Suppose one wants to access and modify variables that reside in shared libraries:
struct bar {
double x, y;
double out;
};
struct bar my_struct = {10.0, 20.5, 0.0};
double test_dll(struct bar *ptr)
{
return ptr->out = ptr->out + ptr->x + ptr->y;
}
This is compiled to libtest.so (or
libtest.dll, depending on your platform).
Use the following lisp code:
(USE-PACKAGE“FFI”) (FFI:DEF-C-STRUCTbar (x double-float) (y double-float) (out double-float)) (FFI:DEF-CALL-OUTget-own-c-float (:LIBRARY"libtest.so") (:LANGUAGE:stdc) (:NAME"test_dll") (:ARGUMENTS(ptr c-pointer :in :alloca)) (:RETURN-TYPEdouble-float)) (FFI:DEF-C-VARmy-c-var (:name "my_struct") (:LIBRARY"libtest.so") (:type (c-ptr bar)))
Note that get-own-c-float takes a
FFI:C-POINTER, not a (FFI:C-PTR bar) as the
argument.
Now you can access call get-own-c-float on
my-c-var:
(FFI:C-VAR-ADDRESSmy-c-var) ⇒#<FOREIGN-ADDRESS #x282935D8>(get-own-c-float (FFI:C-VAR-ADDRESSmy-c-var)) ⇒30.5d0(get-own-c-float (FFI:C-VAR-ADDRESSmy-c-var)) ⇒61.0d0(get-own-c-float (FFI:C-VAR-ADDRESSmy-c-var)) ⇒91.5d0(get-own-c-float (FFI:C-VAR-ADDRESSmy-c-var)) ⇒122.0d0
Example 32.11. Controlling validity of resources
FFI:SET-FOREIGN-POINTER is useful in conjunction with ( to limit the extent of external resources.
Closing twice can be avoided by checking SETF
FFI:VALIDP)FFI:VALIDP.
All pointers depending on this resource can be disabled at once upon
close by sharing their FFI:FOREIGN-POINTER using FFI:SET-FOREIGN-POINTER.
(FFI:DEF-C-TYPEPGconn c-pointer) ; opaque pointer (FFI:DEF-CALL-OUTPQconnectdb (:RETURN-TYPEPGconn) (:ARGUMENTS(conninfo c-string))) (defun sql-connect (conninfo) (let ((conn (PQconnectdb conninfo))) (unless conn (error "NULL pointer")) ;; may wish to useEXT:FINALIZEas well (FFI:SET-FOREIGN-POINTERconn:COPY))) (defun sql-dependent-resource (conn arg1) (FFI:SET-FOREIGN-POINTER(PQxxx conn arg1) conn)) (defun sql-close (connection) (when (FFI:VALIDPconnection) (PQfinish connection) (setf (FFI:VALIDPconnection) nil) T))
Sharing FFI:FOREIGN-POINTER goes both ways: invalidating
the dependent resource will invalidate the primary one.
An alternative approach to resource management,
more suitable to non-“FFI” modules,
is implemented in the berkeley-db module,
see Section 33.7.2, “Closing handles”.
Example 32.12. Floating point arrays
Save this code into sum.c:
double sum (int len, double *vec) {
int i;
double s=0;
for (i=0; i<len; i++) s+= vec[i];
return s;
}
and compile it with
$ gcc -shared -o libsum.so sum.cNow you can sum doubles:
(FFI:DEF-CALL-OUTsum (:NAME"sum") (:LIBRARY"libsum.so") (:LANGUAGE:stdc) (:RETURN-TYPEffi:double-float) (:ARGUMENTS(len ffi:int) (vec (FFI:C-ARRAY-PTR ffi:double-float)))) (sum 3 #(1d0 2d0 3d0)) ⇒6d0
You can find more information and examples of the CLISP “FFI” in the following clisp-list messages:
Even more examples can be found in the file
tests/ffi.tst
in the CLISP source distribution.
| These notes document CLISP version 2.49.93+ | Last modified: 2018-02-19 |
| |