with-signal-handler

Arguments: (signo function) &rest body

This macro installs a handler using function for signal number signo for the dynamic extent of the execution of body.

The handling of operating system dependent signals generated during program execution is not part of Common Lisp. A signal is a small integer. The list of valid signals is given in a system dependent file, usually on UNIX something like /usr/include/signals.h. Signals are either synchronous or asynchronous, but there is no distinction made in this interface--the handling of both types of signals is the same. A handler for a signal is a function of two arguments, signal number and t. If there is no handler for a particular signal, then some default action is invoked, which is usually to signal an error. Signals handlers should return a true value if they handle the signal, so that other, nested handlers are not invoked to handle the signal. A signal that is posted during a gc is processed immediately after the gc finishes.

;; This macro is defined in terms of the other signal handling
;; primitives, with some protection for multiprocessing as well:
(defmacro with-signal-handler ((signo function) &rest body)
  (let ((cellvar (gensym "cell")))
    `(let ((,cellvar (cons ,signo ,function)))
       (progn 
         (push-atomic ,cellvar (globalq *signals*)))
       (unwind-protect
           (progn ,@body)
         (delete-signal-handler ,cellvar)))))

See also add-signal-handler (which has an example), set-signal-handler, *signals*, and remove-signal-handler.

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