;;;; 	Copyright (C) 1996, 1998, 2001, 2002, 2003, 2006, 2010, 2011,
;;;;      2012, 2018 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
;;;;
;;;; ----------------------------------------------------------------
;;;; threads.scm -- User-level interface to Guile's thread system
;;;; 4 March 1996, Anthony Green <green@cygnus.com>
;;;; Modified 5 October 1996, MDJ <djurfeldt@nada.kth.se>
;;;; Modified 6 April 2001, ttn
;;;; ----------------------------------------------------------------
;;;;

;;; Commentary:

;; This module is documented in the Guile Reference Manual.

;;; Code:

(define-module (ice-9 threads)
  #:use-module (ice-9 match)
  ;; These bindings are marked as #:replace because when deprecated code
  ;; is enabled, (ice-9 deprecated) also exports these names.
  ;; (Referencing one of the deprecated names prints a warning directing
  ;; the user to these bindings.)  Anyway once we can remove the
  ;; deprecated bindings, we should use #:export instead of #:replace
  ;; for these.
  #:replace (call-with-new-thread
             yield
             cancel-thread
             join-thread
             thread?
             make-mutex
             make-recursive-mutex
             lock-mutex
             try-mutex
             unlock-mutex
             mutex?
             mutex-owner
             mutex-level
             mutex-locked?
             make-condition-variable
             wait-condition-variable
             signal-condition-variable
             broadcast-condition-variable
             condition-variable?
             current-thread
             all-threads
             thread-exited?
             total-processor-count
             current-processor-count)
  #:export (begin-thread
            make-thread
            with-mutex
            monitor

            parallel
            letpar
            par-map
            par-for-each
            n-par-map
            n-par-for-each
            n-for-each-par-map
            %thread-handler))

;; Note that this extension also defines %make-transcoded-port, which is
;; not exported but is used by (rnrs io ports).

(eval-when (expand eval load)
  (load-extension (string-append "libguile-" (effective-version))
                  "scm_init_ice_9_threads"))



(define-syntax-rule (with-mutex m e0 e1 ...)
  (let ((x m))
    (dynamic-wind
      (lambda () (lock-mutex x))
      (lambda () (begin e0 e1 ...))
      (lambda () (unlock-mutex x)))))

(define cancel-tag (make-prompt-tag "cancel"))
(define (cancel-thread thread . values)
  "Asynchronously interrupt the target @var{thread} and ask it to
terminate, returning the given @var{values}.  @code{dynamic-wind} post
thunks will run, but throw handlers will not.  If @var{thread} has
already terminated or been signaled to terminate, this function is a
no-op."
  (system-async-mark
   (lambda ()
     (catch #t
       (lambda ()
         (apply abort-to-prompt cancel-tag values))
       (lambda _
         (error "thread cancellation failed, throwing error instead???"))))
   thread))

(define thread-join-data (make-object-property))
(define %thread-results (make-object-property))

(define* (call-with-new-thread thunk #:optional handler)
  "Call @code{thunk} in a new thread and with a new dynamic state,
returning a new thread object representing the thread.  The procedure
@var{thunk} is called via @code{with-continuation-barrier}.

When @var{handler} is specified, then @var{thunk} is called from within
a @code{catch} with tag @code{#t} that has @var{handler} as its handler.
This catch is established inside the continuation barrier.

Once @var{thunk} or @var{handler} returns, the return value is made the
@emph{exit value} of the thread and the thread is terminated."
  (let ((cv (make-condition-variable))
        (mutex (make-mutex))
        (thunk (if handler
                   (lambda () (catch #t thunk handler))
                   thunk))
        (thread #f))
    (define (call-with-backtrace thunk)
      (let ((err (current-error-port)))
        (catch #t
          (lambda () (%start-stack 'thread thunk))
          (lambda _ (values))
          (lambda (key . args)
            ;; Narrow by three: the dispatch-exception,
            ;; this thunk, and make-stack.
            (let ((stack (make-stack #t 3)))
              (false-if-exception
               (begin
                 (when stack
                   (display-backtrace stack err))
                 (let ((frame (and stack (stack-ref stack 0))))
                   (print-exception err frame key args)))))))))
    (with-mutex mutex
      (%call-with-new-thread
       (lambda ()
         (call-with-values
             (lambda ()
               (call-with-prompt cancel-tag
                 (lambda ()
                   (lock-mutex mutex)
                   (set! thread (current-thread))
                   ;; Rather than use the 'set!' syntax here, we use the
                   ;; underlying 'setter' generic function to set the
                   ;; 'thread-join-data' property on 'thread'.  This is
                   ;; because 'set!' will try to resolve 'setter' in the
                   ;; '(guile)' module, which means acquiring the
                   ;; 'autoload' mutex.  If the calling thread is
                   ;; already holding that mutex, this will result in
                   ;; deadlock.  See <https://bugs.gnu.org/62691>.
                   ((setter thread-join-data) thread (cons cv mutex))
                   (signal-condition-variable cv)
                   (unlock-mutex mutex)
                   (call-with-unblocked-asyncs
                    (lambda () (call-with-backtrace thunk))))
                 (lambda (k . args)
                   (apply values args))))
           (lambda vals
             (lock-mutex mutex)
             ;; Probably now you're wondering why we are going to use
             ;; the cond variable as the key into the thread results
             ;; object property.  It's because there is a possibility
             ;; that the thread object itself ends up as part of the
             ;; result, and if that happens we create a cycle whereby
             ;; the strong reference to a thread in the value of the
             ;; weak-key hash table used by the object property prevents
             ;; the thread from ever being collected.  So instead we use
             ;; the cv as the key.  Weak-key hash tables, amirite?
             (set! (%thread-results cv) vals)
             (broadcast-condition-variable cv)
             (unlock-mutex mutex)
             (apply values vals)))))
      (let lp ()
        (unless thread
          (wait-condition-variable cv mutex)
          (lp))))
    thread))

(define* (join-thread thread #:optional timeout timeoutval)
  "Suspend execution of the calling thread until the target @var{thread}
terminates, unless the target @var{thread} has already terminated."
  (match (thread-join-data thread)
    (#f (error "foreign thread cannot be joined" thread))
    ((cv . mutex)
     (lock-mutex mutex)
     (let lp ()
       (cond
        ((%thread-results cv)
         => (lambda (results)
              (unlock-mutex mutex)
              (apply values results)))
        ((if timeout
             (wait-condition-variable cv mutex timeout)
             (wait-condition-variable cv mutex))
         (lp))
        (else
         (unlock-mutex mutex)
         timeoutval))))))

(define* (try-mutex mutex)
  "Try to lock @var{mutex}.  If the mutex is already locked, return
@code{#f}.  Otherwise lock the mutex and return @code{#t}."
  (lock-mutex mutex 0))



;;; Macros first, so that the procedures expand correctly.

(define-syntax-rule (begin-thread e0 e1 ...)
  (call-with-new-thread
   (lambda () e0 e1 ...)
   %thread-handler))

(define-syntax-rule (make-thread proc arg ...)
  (call-with-new-thread
   (lambda () (proc arg ...))
   %thread-handler))

(define monitor-mutex-table (make-hash-table))

(define monitor-mutex-table-mutex (make-mutex))

(define (monitor-mutex-with-id id)
  (with-mutex monitor-mutex-table-mutex
    (or (hashq-ref monitor-mutex-table id)
        (let ((mutex (make-mutex)))
          (hashq-set! monitor-mutex-table id mutex)
          mutex))))

(define-syntax monitor
  (lambda (stx)
    (syntax-case stx ()
      ((_ body body* ...)
       (let ((id (datum->syntax #'body (gensym))))
         #`(with-mutex (monitor-mutex-with-id '#,id)
             body body* ...))))))

(define (thread-handler tag . args)
  (let ((n (length args))
	(p (current-error-port)))
    (display "In thread:" p)
    (newline p)
    (if (>= n 3)
        (display-error #f
                       p
                       (car args)
                       (cadr args)
                       (caddr args)
                       (if (= n 4)
                           (cadddr args)
                           '()))
        (begin
          (display "uncaught throw to " p)
          (display tag p)
          (display ": " p)
          (display args p)
          (newline p)))
    #f))

;;; Set system thread handler
(define %thread-handler thread-handler)

(use-modules (ice-9 futures))

(define-syntax parallel
  (lambda (x)
    (syntax-case x ()
      ((_ e0 ...)
       (with-syntax (((tmp0 ...) (generate-temporaries (syntax (e0 ...)))))
         #'(let ((tmp0 (future e0))
                 ...)
             (values (touch tmp0) ...)))))))

(define-syntax-rule (letpar ((v e) ...) b0 b1 ...)
  (call-with-values
      (lambda () (parallel e ...))
    (lambda (v ...)
      b0 b1 ...)))

(define (par-mapper mapper cons)
  (lambda (proc . lists)
    (let loop ((lists lists))
      (match lists
        (((heads tails ...) ...)
         (let ((tail (future (loop tails)))
               (head (apply proc heads)))
           (cons head (touch tail))))
        (_
         '())))))

(define par-map (par-mapper map cons))
(define par-for-each (par-mapper for-each (const *unspecified*)))

(define (n-par-map n proc . arglists)
  (let* ((m (make-mutex))
	 (threads '())
	 (results (make-list (length (car arglists))))
	 (result results))
    (do ((i 0 (+ 1 i)))
	((= i n)
	 (for-each join-thread threads)
	 results)
      (set! threads
	    (cons (begin-thread
		   (let loop ()
		     (lock-mutex m)
		     (if (null? result)
			 (unlock-mutex m)
			 (let ((args (map car arglists))
			       (my-result result))
			   (set! arglists (map cdr arglists))
			   (set! result (cdr result))
			   (unlock-mutex m)
			   (set-car! my-result (apply proc args))
			   (loop)))))
		  threads)))))

(define (n-par-for-each n proc . arglists)
  (let ((m (make-mutex))
	(threads '()))
    (do ((i 0 (+ 1 i)))
	((= i n)
	 (for-each join-thread threads))
      (set! threads
	    (cons (begin-thread
		   (let loop ()
		     (lock-mutex m)
		     (if (null? (car arglists))
			 (unlock-mutex m)
			 (let ((args (map car arglists)))
			   (set! arglists (map cdr arglists))
			   (unlock-mutex m)
			   (apply proc args)
			   (loop)))))
		  threads)))))

;;; The following procedure is motivated by the common and important
;;; case where a lot of work should be done, (not too much) in parallel,
;;; but the results need to be handled serially (for example when
;;; writing them to a file).
;;;
(define (n-for-each-par-map n s-proc p-proc . arglists)
  "Using N parallel processes, apply S-PROC in serial order on the results
of applying P-PROC on ARGLISTS."
  (let* ((m (make-mutex))
	 (threads '())
	 (no-result '(no-value))
	 (results (make-list (length (car arglists)) no-result))
	 (result results))
    (do ((i 0 (+ 1 i)))
	((= i n)
	 (for-each join-thread threads))
      (set! threads
	    (cons (begin-thread
		   (let loop ()
		     (lock-mutex m)
		     (cond ((null? results)
			    (unlock-mutex m))
			   ((not (eq? (car results) no-result))
			    (let ((arg (car results)))
			      ;; stop others from choosing to process results
			      (set-car! results no-result)
			      (unlock-mutex m)
			      (s-proc arg)
			      (lock-mutex m)
			      (set! results (cdr results))
			      (unlock-mutex m)
			      (loop)))
			   ((null? result)
			    (unlock-mutex m))
			   (else
			    (let ((args (map car arglists))
				  (my-result result))
			      (set! arglists (map cdr arglists))
			      (set! result (cdr result))
			      (unlock-mutex m)
			      (set-car! my-result (apply p-proc args))
			      (loop))))))
		  threads)))))


;; Now that thread support is loaded, make module autoloading
;; thread-safe.
(set! (@ (guile) call-with-module-autoload-lock)
  (let ((mutex (make-mutex 'recursive)))
    (lambda (thunk)
      (with-mutex mutex
        (thunk)))))

;;; threads.scm ends here
