support procedural process-trap-exit handler

Support a procedural handler as the value for process-trap-exit
so that a process blocked in a gen-server call can perform some
clean-up if killed.

This commit also fixes an obscure bug in the case where a receive
form has a guard that calls receive.

Rework the interactive console so that:
 - we can interrupt the REPL via ^C on Windows again,
 - we can wait until interrupts are enabled before invoking the
   keyboard-interrupt-handler, and
 - a script can start an interactive REPL that handles ^C as Swish does

User visible changes to the behavior of the interactive console include:
 - trying to read from the console in a spawned process returns #!eof,

doc/swish/erlang.tex

@@ -973,11 +973,41 @@
 \begin{parameter}
   \code{process-trap-exit}
 \end{parameter}
-\hasvalue{} boolean
+\hasvalue{} boolean or a procedure
 
 The \code{process-trap-exit} parameter specifies whether or not the
-calling process traps exit signals as messages. Processes start with
-this parameter set to \code{\#f}.
+calling process traps exit signals as messages.
+Processes do not trap exit signals by default; therefore,
+processes start with this parameter set to \code{\#f}.
+To trap exit signals as messages, a process sets this parameter
+to \code{\#t} or a procedure.
+A gen-server can set the parameter to \code{\#t} and handle exit messages
+via its \code{handle-info} callback; see Section~\ref{sec:gen-server-callback} for details.
+Other processes can handle these messages via \code{receive}.
+
+A process may set the \code{process-trap-exit} parameter to a \var{handler}
+procedure that accepts one argument, \var{msg}.
+When the scheduler resumes that process, it checks whether \code{kill} or
+\code{link} has delivered an exit signal as a message.
+If so, it retrieves the first exit message, invokes \var{handler} on that
+message, and repeats this until it has consumed the available exit messages.\footnote{An exit message delivered via \code{send} will not trigger \var{handler} on its own, but \var{handler} may consume that message if
+the scheduler invokes \var{handler}.}
+A \var{handler} procedure may be useful, for example, to perform some cleanup
+in case an exit signal arrives while a process is blocked awaiting a reply in
+\code{gen-server:call}.
+
+% ----------------------------------------------------------------------------
+\defineentry{raise-on-exit}
+\begin{procedure}
+  \code{(raise-on-exit \var{msg})}
+\end{procedure}
+\returns{} see below
+
+The \code{raise-on-exit} procedure expects an exit message \var{msg}
+matching \code{`(EXIT \var{pid} \var{reason})}.
+If \var{reason} is \code{normal}, \code{raise-on-exit} returns
+an unspecified value.
+Otherwise, it raises an exception involving \var{reason}.
 
 % ----------------------------------------------------------------------------
 \defineentry{self}
@@ -991,6 +1021,21 @@
 global variable cannot be used directly because library bindings are
 immutable.
 
+% ----------------------------------------------------------------------------
+\defineentry{with-interrupts-disabled-for-io}
+\begin{syntax}
+  \code{(with-interrupts-disabled-for-io \var{body$_1$} \var{body$_2$} \etc)}
+\end{syntax}
+\expandsto{} see below
+
+The \code{with-interrupts-disabled-for-io} macro is like
+\code{with-interrupts-disabled} except that, just before returning, it checks
+for trapped exit messages.
+The system handles trapped exit messages at this time only if
+\code{process-trap-exit} is set to a procedure.
+This macro is intended for use in code that calls \code{wait-for-io} and
+\code{complete-io} with interrupts disabled.
+
 % ----------------------------------------------------------------------------
 \subsection{Miscellaneous}
 

doc/swish/gen-server.tex

@@ -346,7 +346,7 @@
   \argrow{reply}{the server's reply or \code{\#f}}
 \end{pubevent}
 
-\section {Callback Interface}
+\section {Callback Interface}\label{sec:gen-server-callback}
 
 A programmer implements the callback interface to define a particular
 server's behavior. All callback functions are called from within the

src/swish/app-core.ss

@@ -197,6 +197,7 @@
           (set! started? #t)
           (base-exception-handler app-exception-handler)
           (random-seed (+ (remainder (erlang:now) (- (ash 1 32) 1)) 1))
+          (trap-signals handle-signal)
           (hook-console-input)
           (call/cc
            (lambda (bail)
@@ -211,7 +212,6 @@
              (when stand-alone?
                (app:name who)
                (app:path who))
-             (trap-signals handle-signal)
              (set! Charon
                (spawn
                 (let ([me self])

src/swish/app.ss

@@ -180,17 +180,6 @@
           (try-import)
           (parameterize ([waiter-prompt-string (if (opt 'quiet) "" ">")]
                          [repl-level (+ (repl-level) 1)])
-            (define (trap-CTRL-C handler)
-              (meta-cond
-               [windows?
-                (signal-handler SIGBREAK handler)
-                (signal-handler SIGINT handler)]
-               [else
-                (signal-handler SIGINT handler)]))
-            (when (interactive?)
-              (trap-CTRL-C
-               (let ([p self])
-                 (lambda (n) (keyboard-interrupt p)))))
             (for-each load filenames)
             (new-cafe)))]
        [else                            ; script