guile/doc/ref/api-foreign-objects.texi

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@c This is part of the GNU Guile Reference Manual.
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@c   Free Software Foundation, Inc.
@c See the file guile.texi for copying conditions.

@node Foreign Objects
@section Foreign Objects

@cindex foreign object

This chapter contains reference information related to defining and
working with foreign objects.  @xref{Defining New Foreign Object Types},
for a tutorial-like introduction to foreign objects.

@deftp {C Type} scm_t_struct_finalize
This function type returns @code{void} and takes one @code{SCM}
argument.
@end deftp

@deftypefn {C Function} SCM scm_make_foreign_object_type (SCM name, SCM slots, scm_t_struct_finalize finalizer)
Create a fresh foreign object type.  @var{name} is a symbol naming the
type.  @var{slots} is a list of symbols, each one naming a field in the
foreign object type.  @var{finalizer} indicates the finalizer, and may
be @code{NULL}.
@end deftypefn

@cindex finalizer
@cindex finalization

We recommend that finalizers be avoided if possible.  @xref{Foreign
Object Memory Management}.  Finalizers must be async-safe and
thread-safe.  Again, @pxref{Foreign Object Memory Management}.  If you
are embedding Guile in an application that is not thread-safe, and you
define foreign object types that need finalization, you might want to
disable automatic finalization, and arrange to call
@code{scm_manually_run_finalizers ()} yourself.

@deftypefn {C Function} int scm_set_automatic_finalization_enabled (int enabled_p)
Enable or disable automatic finalization.  By default, Guile arranges to
invoke object finalizers automatically, in a separate thread if
possible.  Passing a zero value for @var{enabled_p} will disable
automatic finalization for Guile as a whole.  If you disable automatic
finalization, you will have to call @code{scm_run_finalizers ()}
periodically.

Unlike most other Guile functions, you can call
@code{scm_set_automatic_finalization_enabled} before Guile has been
initialized.

Return the previous status of automatic finalization.
@end deftypefn

@deftypefn {C Function} int scm_run_finalizers (void)
Invoke any pending finalizers.  Returns the number of finalizers that
were invoked.  This function should be called when automatic
finalization is disabled, though it may be called if it is enabled as
well.
@end deftypefn

@deftypefn {C Function} void scm_assert_foreign_object_type (SCM type, SCM val)
When @var{val} is a foreign object of the given @var{type}, do nothing.
Otherwise, signal an error.
@end deftypefn

@deftypefn {C Function} SCM scm_make_foreign_object_0 (SCM type)
@deftypefnx {C Function} SCM scm_make_foreign_object_1 (SCM type, void *val0)
@deftypefnx {C Function} SCM scm_make_foreign_object_2 (SCM type, void *val0, void *val1)
@deftypefnx {C Function} SCM scm_make_foreign_object_3 (SCM type, void *val0, void *val1, void *val2)
@deftypefnx {C Function} SCM scm_make_foreign_object_n (SCM type, size_t n, void *vals[])
Make a new foreign object of the type with type @var{type} and
initialize the first @var{n} fields to the given values, as appropriate.

The number of fields for objects of a given type is fixed when the type
is created.  It is an error to give more initializers than there are
fields in the value.  It is perfectly fine to give fewer initializers
than needed; this is convenient when some fields are of non-pointer
types, and would be easier to initialize with the setters described
below.
@end deftypefn

@deftypefn {C Function} void* scm_foreign_object_ref (SCM obj, size_t n);
@deftypefnx {C Function} scm_t_bits scm_foreign_object_unsigned_ref (SCM obj, size_t n);
@deftypefnx {C Function} scm_t_signed_bits scm_foreign_object_signed_ref (SCM obj, size_t n);
Return the value of the @var{n}th field of the foreign object @var{obj}.
The backing store for the fields is as wide as a @code{scm_t_bits}
value, which is at least as wide as a pointer.  The different variants
handle casting in a portable way.
@end deftypefn

@deftypefn {C Function} void scm_foreign_object_set_x (SCM obj, size_t n, void *val);
@deftypefnx {C Function} void scm_foreign_object_unsigned_set_x (SCM obj, size_t n, scm_t_bits val);
@deftypefnx {C Function} void scm_foreign_object_signed_set_x (SCM obj, size_t n, scm_t_signed_bits val);
Set the value of the @var{n}th field of the foreign object @var{obj} to
@var{val}, after portably converting to a @code{scm_t_bits} value, if
needed.
@end deftypefn

One can also access foreign objects from Scheme.  @xref{Foreign Objects
and Scheme}, for some examples.

@example
(use-modules (system foreign-object))
@end example

@deffn {Scheme Procedure} make-foreign-object-type name slots [#:finalizer=#f] [#:supers='()]

Make a new foreign object type.  See the above documentation for
@code{scm_make_foreign_object_type}; these functions are exactly
equivalent, except for the way in which the finalizer gets attached to
instances (an internal detail), and the fact that this function accepts
an optional list of superclasses, which will be paseed to
@code{make-class}.

The resulting value is a GOOPS class.  @xref{GOOPS}, for more on classes
in Guile.
@end deffn

@deffn {Scheme Syntax} define-foreign-object-type name constructor (slot ...) [#:finalizer=#f]
A convenience macro to define a type, using
@code{make-foreign-object-type}, and bind it to @var{name}.  A
constructor will be bound to @var{constructor}, and getters will be
bound to each of @var{slot...}.
@end deffn

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