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;;; Cooperative REPL server
;; Copyright (C) 2014 Free Software Foundation, Inc.
;; This library is free software; you can redistribute it and/or
;; modify it under the terms of the GNU Lesser General Public
;; License as published by the Free Software Foundation; either
;; version 3 of the License, or (at your option) any later version.
;;
;; This library is distributed in the hope that it will be useful,
;; but WITHOUT ANY WARRANTY; without even the implied warranty of
;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
;; Lesser General Public License for more details.
;;
;; You should have received a copy of the GNU Lesser General Public
;; License along with this library; if not, write to the Free Software
;; Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
;; 02110-1301 USA
;;; Code:
(define-module (system repl coop-server)
#:use-module (ice-9 match)
#:use-module (ice-9 receive)
#:use-module (ice-9 threads)
#:use-module (ice-9 q)
#:use-module (srfi srfi-9)
#:use-module ((system repl repl)
#:select (start-repl* prompting-meta-read))
#:use-module ((system repl server)
#:select (run-server* make-tcp-server-socket
add-open-socket! close-socket!))
#:export (spawn-coop-repl-server
poll-coop-repl-server))
(define-record-type <coop-repl-server>
(%make-coop-repl-server mutex queue)
coop-repl-server?
(mutex coop-repl-server-mutex)
(queue coop-repl-server-queue))
(define (make-coop-repl-server)
(%make-coop-repl-server (make-mutex) (make-q)))
(define (coop-repl-server-eval coop-server opcode . args)
"Queue a new instruction with the symbolic name OPCODE and an arbitrary
number of arguments, to be processed the next time COOP-SERVER is polled."
(with-mutex (coop-repl-server-mutex coop-server)
(enq! (coop-repl-server-queue coop-server)
(cons opcode args))))
(define-record-type <coop-repl>
(%make-coop-repl mutex condvar thunk cont)
coop-repl?
(mutex coop-repl-mutex)
(condvar coop-repl-condvar) ; signaled when thunk becomes non-#f
(thunk coop-repl-read-thunk set-coop-repl-read-thunk!)
(cont coop-repl-cont set-coop-repl-cont!))
(define (make-coop-repl)
(%make-coop-repl (make-mutex) (make-condition-variable) #f #f))
(define (coop-repl-read coop-repl)
"Read an expression via the thunk stored in COOP-REPL."
(let ((thunk
(with-mutex (coop-repl-mutex coop-repl)
(unless (coop-repl-read-thunk coop-repl)
(wait-condition-variable (coop-repl-condvar coop-repl)
(coop-repl-mutex coop-repl)))
(let ((thunk (coop-repl-read-thunk coop-repl)))
(unless thunk
(error "coop-repl-read: condvar signaled, but thunk is #f!"))
(set-coop-repl-read-thunk! coop-repl #f)
thunk))))
(thunk)))
(define (store-repl-cont cont coop-repl)
"Save the partial continuation CONT within COOP-REPL."
(set-coop-repl-cont! coop-repl
(lambda (exp)
(coop-repl-prompt
(lambda () (cont exp))))))
(define (coop-repl-prompt thunk)
"Apply THUNK within a prompt for cooperative REPLs."
(call-with-prompt 'coop-repl-prompt thunk store-repl-cont))
(define (make-coop-reader coop-repl)
"Return a new procedure for reading user input from COOP-REPL. The
generated procedure passes the responsibility of reading input to
another thread and aborts the cooperative REPL prompt."
(lambda (repl)
(let ((read-thunk
;; Need to preserve the REPL stack and current module across
;; threads.
(let ((stack (fluid-ref *repl-stack*))
(module (current-module)))
(lambda ()
(with-fluids ((*repl-stack* stack))
(set-current-module module)
(prompting-meta-read repl))))))
(with-mutex (coop-repl-mutex coop-repl)
(when (coop-repl-read-thunk coop-repl)
(error "coop-reader: read-thunk is not #f!"))
(set-coop-repl-read-thunk! coop-repl read-thunk)
(signal-condition-variable (coop-repl-condvar coop-repl))))
(abort-to-prompt 'coop-repl-prompt coop-repl)))
(define (reader-loop coop-server coop-repl)
"Run an unbounded loop that reads an expression for COOP-REPL and
stores the expression within COOP-SERVER for later evaluation."
(coop-repl-server-eval coop-server 'eval coop-repl
(coop-repl-read coop-repl))
(reader-loop coop-server coop-repl))
(define (poll-coop-repl-server coop-server)
"Poll the cooperative REPL server COOP-SERVER and apply a pending
operation if there is one, such as evaluating an expression typed at the
REPL prompt. This procedure must be called from the same thread that
called spawn-coop-repl-server."
(let ((op (with-mutex (coop-repl-server-mutex coop-server)
(let ((queue (coop-repl-server-queue coop-server)))
(and (not (q-empty? queue))
(deq! queue))))))
(when op
(match op
(('new-repl client)
(start-repl-client coop-server client))
(('eval coop-repl exp)
((coop-repl-cont coop-repl) exp))))
*unspecified*))
(define (start-coop-repl coop-server)
"Start a new cooperative REPL process for COOP-SERVER."
;; Calling stop-server-and-clients! from a REPL will cause an
;; exception to be thrown when trying to read from the socket that has
;; been closed, so we catch that here.
(false-if-exception
(let ((coop-repl (make-coop-repl)))
(make-thread reader-loop coop-server coop-repl)
(start-repl* (current-language) #f (make-coop-reader coop-repl)))))
(define (run-coop-repl-server coop-server server-socket)
"Start the cooperative REPL server for COOP-SERVER using the socket
SERVER-SOCKET."
(run-server* server-socket (make-coop-client-proc coop-server)))
(define* (spawn-coop-repl-server
#:optional (server-socket (make-tcp-server-socket)))
"Create and return a new cooperative REPL server object, and spawn a
new thread to listen for connections on SERVER-SOCKET. Proper
functioning of the REPL server requires that poll-coop-repl-server be
called periodically on the returned server object."
(let ((coop-server (make-coop-repl-server)))
(make-thread run-coop-repl-server
coop-server
server-socket)
coop-server))
(define (make-coop-client-proc coop-server)
"Return a new procedure that is used to schedule the creation of a new
cooperative REPL for COOP-SERVER."
(lambda (client addr)
(coop-repl-server-eval coop-server 'new-repl client)))
(define (start-repl-client coop-server client)
"Run a cooperative REPL for COOP-SERVER within a prompt. All input
and output is sent over the socket CLIENT."
;; Add the client to the list of open sockets, with a 'force-close'
;; procedure that closes the underlying file descriptor. We do it
;; this way because we cannot close the port itself safely from
;; another thread.
(add-open-socket! client (lambda () (close-fdes (fileno client))))
(with-continuation-barrier
(lambda ()
(coop-repl-prompt
(lambda ()
(parameterize ((current-input-port client)
(current-output-port client)
(current-error-port client)
(current-warning-port client))
(with-fluids ((*repl-stack* '()))
(save-module-excursion
(lambda ()
(start-coop-repl coop-server)))))
;; This may fail if 'stop-server-and-clients!' is called,
;; because the 'force-close' procedure above closes the
;; underlying file descriptor instead of the port itself.
(false-if-exception
(close-socket! client)))))))
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