register-foreign-callable

Arguments: name &optional index-or-reuse convert-to-c-types

The name argument must be a symbol defined with defun-foreign-callable.

The index-or-reuse argument can be a fixnum to select a specific table entry to replace, or the symbol :reuse to specify that if a function with the same name is already registered, the function will be replaced at the same index.

If convert-to-c-types is specified, then an attempt will be made to convert the return value to a foreign value, otherwise the return value is returned unchanged. It is important to note that though the default is nil, most often the desired effect is obtained by setting this option to t. The default of nil is retained for compatibility reasons. This is described in a little more detail in the description of defun-foreign-callable.

This function returns 5 values:

• an integer address which can be passed to C and used as the address of the function. This address is valid even after a gc and after a dumplisp and so is always be valid; see Calling Lisp functions from C: lisp_call_address() and lisp_call() in foreign-functions.htm for further information.
• a table-index value
• the previous table entry
• a fixnum representing the calling convention
• the number of bytes of stack space needed for this function's arguments

In versions using the :os-threads model of multiprocessing, the callback from foreign code to the foreign-callable function name may be made from a thread started outside Lisp. This is not supported in a version of Lisp using the non :os-threads model of multiprocessing. trying it will likely cause Lisp to fail. See Foreign functions and multiprocessing in foreign-functions.htm.

See ftype.htm for information on foreign types in Allegro CL and foreign-functions.htm for general information on foreign functions in Allegro CL.

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This page was not revised from the 10.0 page.
Created 2019.8.20.