root/trunk/lisp/gnus/gnus-async.el

;;; gnus-async.el --- asynchronous support for Gnus

;; Copyright (C) 1996, 1997, 1998, 1999, 2000, 2001, 2002, 2003, 2004,
;;   2005, 2006, 2007, 2008 Free Software Foundation, Inc.

;; Author: Lars Magne Ingebrigtsen <larsi@gnus.org>
;; Keywords: news

;; This file is part of GNU Emacs.

;; GNU Emacs is free software; you can redistribute it and/or modify
;; it under the terms of the GNU General Public License as published by
;; the Free Software Foundation; either version 3, or (at your option)
;; any later version.

;; GNU Emacs 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 General Public License for more details.

;; You should have received a copy of the GNU General Public License
;; along with GNU Emacs; see the file COPYING.  If not, write to the
;; Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor,
;; Boston, MA 02110-1301, USA.

;;; Commentary:

;;; Code:

(eval-when-compile (require 'cl))

(require 'gnus)
(require 'gnus-sum)
(require 'nntp)

(eval-when-compile
  (when (featurep 'xemacs)
    (require 'timer-funcs)))

(defgroup gnus-asynchronous nil
  "Support for asynchronous operations."
  :group 'gnus)

(defcustom gnus-use-article-prefetch 30
  "*If non-nil, prefetch articles in groups that allow this.
If a number, prefetch only that many articles forward;
if t, prefetch as many articles as possible."
  :group 'gnus-asynchronous
  :type '(choice (const :tag "off" nil)
                 (const :tag "all" t)
                 (integer :tag "some" 0)))

(defcustom gnus-asynchronous nil
  "*If nil, inhibit all Gnus asynchronicity.
If non-nil, let the other asynch variables be heeded."
  :group 'gnus-asynchronous
  :type 'boolean)

(defcustom gnus-prefetched-article-deletion-strategy '(read exit)
  "List of symbols that say when to remove articles from the prefetch buffer.
Possible values in this list are `read', which means that
articles are removed as they are read, and `exit', which means
that all articles belonging to a group are removed on exit
from that group."
  :group 'gnus-asynchronous
  :type '(set (const read) (const exit)))

(defcustom gnus-use-header-prefetch nil
  "*If non-nil, prefetch the headers to the next group."
  :group 'gnus-asynchronous
  :type 'boolean)

(defcustom gnus-async-prefetch-article-p 'gnus-async-unread-p
  "Function called to say whether an article should be prefetched or not.
The function is called with one parameter -- the article data.
It should return non-nil if the article is to be prefetched."
  :group 'gnus-asynchronous
  :type 'function)

;;; Internal variables.

(defvar gnus-async-prefetch-article-buffer " *Async Prefetch Article*")
(defvar gnus-async-article-alist nil)
(defvar gnus-async-article-semaphore '(nil))
(defvar gnus-async-fetch-list nil)
(defvar gnus-async-hashtb nil)
(defvar gnus-async-current-prefetch-group nil)
(defvar gnus-async-current-prefetch-article nil)
(defvar gnus-async-timer nil)

(defvar gnus-async-prefetch-headers-buffer " *Async Prefetch Headers*")
(defvar gnus-async-header-prefetched nil)

;;; Utility functions.

(defun gnus-group-asynchronous-p (group)
  "Say whether GROUP is fetched from a server that supports asynchronicity."
  (gnus-asynchronous-p (gnus-find-method-for-group group)))

;;; Somewhat bogus semaphores.

(defun gnus-async-get-semaphore (semaphore)
  "Wait until SEMAPHORE is released."
  (while (/= (length (nconc (symbol-value semaphore) (list nil))) 2)
    (sleep-for 1)))

(defun gnus-async-release-semaphore (semaphore)
  "Release SEMAPHORE."
  (setcdr (symbol-value semaphore) nil))

(defmacro gnus-async-with-semaphore (&rest forms)
  `(unwind-protect
       (progn
         (gnus-async-get-semaphore 'gnus-async-article-semaphore)
         ,@forms)
     (gnus-async-release-semaphore 'gnus-async-article-semaphore)))

(put 'gnus-async-with-semaphore 'lisp-indent-function 0)
(put 'gnus-async-with-semaphore 'edebug-form-spec '(body))

;;;
;;; Article prefetch
;;;

(gnus-add-shutdown 'gnus-async-close 'gnus)
(defun gnus-async-close ()
  (gnus-kill-buffer gnus-async-prefetch-article-buffer)
  (gnus-kill-buffer gnus-async-prefetch-headers-buffer)
  (setq gnus-async-hashtb nil
        gnus-async-article-alist nil
        gnus-async-header-prefetched nil))

(defun gnus-async-set-buffer ()
  (nnheader-set-temp-buffer gnus-async-prefetch-article-buffer t)
  (unless gnus-async-hashtb
    (setq gnus-async-hashtb (gnus-make-hashtable 1023))))

(defun gnus-async-halt-prefetch ()
  "Stop prefetching."
  (setq gnus-async-fetch-list nil))

(defun gnus-async-prefetch-next (group article summary)
  "Possibly prefetch several articles starting with the article after ARTICLE."
  (when (and (gnus-buffer-live-p summary)
             gnus-asynchronous
             (gnus-group-asynchronous-p group))
    (save-excursion
      (set-buffer gnus-summary-buffer)
      (let ((next (caadr (gnus-data-find-list article))))
        (when next
          (if (not (fboundp 'run-with-idle-timer))
              ;; This is either an older Emacs or XEmacs, so we
              ;; do this, which leads to slightly slower article
              ;; buffer display.
              (gnus-async-prefetch-article group next summary)
            (when gnus-async-timer
              (ignore-errors
                (nnheader-cancel-timer 'gnus-async-timer)))
            (setq gnus-async-timer
                  (run-with-idle-timer
                   0.1 nil 'gnus-async-prefetch-article
                   group next summary))))))))

(defun gnus-async-prefetch-article (group article summary &optional next)
  "Possibly prefetch several articles starting with ARTICLE."
  (if (not (gnus-buffer-live-p summary))
      (gnus-async-with-semaphore
        (setq gnus-async-fetch-list nil))
    (when (and gnus-asynchronous
               (gnus-alive-p))
      (when next
        (gnus-async-with-semaphore
          (pop gnus-async-fetch-list)))
      (let ((do-fetch next)
            (do-message t))             ;(eq major-mode 'gnus-summary-mode)))
        (when (and (gnus-group-asynchronous-p group)
                   (gnus-buffer-live-p summary)
                   (or (not next)
                       gnus-async-fetch-list))
          (gnus-async-with-semaphore
            (unless next
              (setq do-fetch (not gnus-async-fetch-list))
              ;; Nix out any outstanding requests.
              (setq gnus-async-fetch-list nil)
              ;; Fill in the new list.
              (let ((n gnus-use-article-prefetch)
                    (data (gnus-data-find-list article))
                    d)
                (while (and (setq d (pop data))
                            (if (numberp n)
                                (natnump (decf n))
                              n))
                  (unless (or (gnus-async-prefetched-article-entry
                               group (setq article (gnus-data-number d)))
                              (not (natnump article))
                              (not (funcall gnus-async-prefetch-article-p d)))
                    ;; Not already fetched -- so we add it to the list.
                    (push article gnus-async-fetch-list)))
                (setq gnus-async-fetch-list
                      (nreverse gnus-async-fetch-list))))

            (when do-fetch
              (setq article (car gnus-async-fetch-list))))

          (when (and do-fetch article)
            ;; We want to fetch some more articles.
            (save-excursion
              (set-buffer summary)
              (let (mark)
                (gnus-async-set-buffer)
                (goto-char (point-max))
                (setq mark (point-marker))
                (let ((nnheader-callback-function
                       (gnus-make-async-article-function
                        group article mark summary next))
                      (nntp-server-buffer
                       (get-buffer gnus-async-prefetch-article-buffer)))
                  (when do-message
                    (gnus-message 9 "Prefetching article %d in group %s"
                                  article group))
                  (setq gnus-async-current-prefetch-group group)
                  (setq gnus-async-current-prefetch-article article)
                  (gnus-request-article article group))))))))))

(defun gnus-make-async-article-function (group article mark summary next)
  "Return a callback function."
  `(lambda (arg)
     (gnus-async-article-callback arg ,group ,article ,mark ,summary ,next)))

(defun gnus-async-article-callback (arg group article mark summary next)
  "Function called when an async article is done being fetched."
  (save-excursion
    (setq gnus-async-current-prefetch-article nil)
    (when arg
      (gnus-async-set-buffer)
      (gnus-async-with-semaphore
        (setq
         gnus-async-article-alist
         (cons (list (intern (format "%s-%d" group article)
                             gnus-async-hashtb)
                     mark (set-marker (make-marker) (point-max))
                     group article)
               gnus-async-article-alist))))
    (if (not (gnus-buffer-live-p summary))
        (gnus-async-with-semaphore
          (setq gnus-async-fetch-list nil))
      (gnus-async-prefetch-article group next summary t))))

(defun gnus-async-unread-p (data)
  "Return non-nil if DATA represents an unread article."
  (gnus-data-unread-p data))

(defun gnus-async-request-fetched-article (group article buffer)
  "See whether we have ARTICLE from GROUP and put it in BUFFER."
  (when (numberp article)
    (when (and (equal group gnus-async-current-prefetch-group)
               (eq article gnus-async-current-prefetch-article))
      (gnus-async-wait-for-article article))
    (let ((entry (gnus-async-prefetched-article-entry group article)))
      (when entry
        (save-excursion
          (gnus-async-set-buffer)
          (copy-to-buffer buffer (cadr entry) (caddr entry))
          ;; Remove the read article from the prefetch buffer.
          (when (memq 'read gnus-prefetched-article-deletion-strategy)
            (gnus-async-delete-prefetched-entry entry))
          t)))))

(defun gnus-async-wait-for-article (article)
  "Wait until ARTICLE is no longer the currently-being-fetched article."
  (save-excursion
    (gnus-async-set-buffer)
    (let ((proc (nntp-find-connection (current-buffer)))
          (nntp-server-buffer (current-buffer))
          (nntp-have-messaged nil)
          (tries 0))
      (condition-case nil
          ;; FIXME: we could stop waiting after some
          ;; timeout, but this is the wrong place to do it.
          ;; rather than checking time-spent-waiting, we
          ;; should check time-since-last-output, which
          ;; needs to be done in nntp.el.
          (while (eq article gnus-async-current-prefetch-article)
            (incf tries)
            (when (nntp-accept-process-output proc)
              (setq tries 0))
            (when (and (not nntp-have-messaged)
                       (= tries 3))
              (gnus-message 5 "Waiting for async article...")
              (setq nntp-have-messaged t)))
        (quit
         ;; if the user interrupted on a slow/hung connection,
         ;; do something friendly.
         (when (> tries 3)
           (setq gnus-async-current-prefetch-article nil))
         (signal 'quit nil)))
      (when nntp-have-messaged
        (gnus-message 5 "")))))

(defun gnus-async-delete-prefetched-entry (entry)
  "Delete ENTRY from buffer and alist."
  (ignore-errors
    (delete-region (cadr entry) (caddr entry))
    (set-marker (cadr entry) nil)
    (set-marker (caddr entry) nil))
  (gnus-async-with-semaphore
    (setq gnus-async-article-alist
          (delq entry gnus-async-article-alist))))

(defun gnus-async-prefetch-remove-group (group)
  "Remove all articles belonging to GROUP from the prefetch buffer."
  (when (and (gnus-group-asynchronous-p group)
             (memq 'exit gnus-prefetched-article-deletion-strategy))
    (let ((alist gnus-async-article-alist))
      (save-excursion
        (gnus-async-set-buffer)
        (while alist
          (when (equal group (nth 3 (car alist)))
            (gnus-async-delete-prefetched-entry (car alist)))
          (pop alist))))))

(defun gnus-async-prefetched-article-entry (group article)
  "Return the entry for ARTICLE in GROUP if it has been prefetched."
  (let ((entry (save-excursion
                 (gnus-async-set-buffer)
                 (assq (intern (format "%s-%d" group article)
                               gnus-async-hashtb)
                       gnus-async-article-alist))))
    ;; Perhaps something has emptied the buffer?
    (if (and entry
             (= (cadr entry) (caddr entry)))
        (progn
          (ignore-errors
            (set-marker (cadr entry) nil)
            (set-marker (caddr entry) nil))
          (setq gnus-async-article-alist
                (delq entry gnus-async-article-alist))
          nil)
      entry)))

;;;
;;; Header prefetch
;;;

(defun gnus-async-prefetch-headers (group)
  "Prefetch the headers for group GROUP."
  (save-excursion
    (let (unread)
      (when (and gnus-use-header-prefetch
                 gnus-asynchronous
                 (gnus-group-asynchronous-p group)
                 (listp gnus-async-header-prefetched)
                 (setq unread (gnus-list-of-unread-articles group)))
        ;; Mark that a fetch is in progress.
        (setq gnus-async-header-prefetched t)
        (nnheader-set-temp-buffer gnus-async-prefetch-headers-buffer t)
        (erase-buffer)
        (let ((nntp-server-buffer (current-buffer))
              (nnheader-callback-function
               `(lambda (arg)
                  (setq gnus-async-header-prefetched
                        ,(cons group unread)))))
          (gnus-retrieve-headers unread group gnus-fetch-old-headers))))))

(defun gnus-async-retrieve-fetched-headers (articles group)
  "See whether we have prefetched headers."
  (when (and gnus-use-header-prefetch
             (gnus-group-asynchronous-p group)
             (listp gnus-async-header-prefetched)
             (equal group (car gnus-async-header-prefetched))
             (equal articles (cdr gnus-async-header-prefetched)))
    (save-excursion
      (nnheader-set-temp-buffer gnus-async-prefetch-headers-buffer t)
      (nntp-decode-text)
      (copy-to-buffer nntp-server-buffer (point-min) (point-max))
      (erase-buffer)
      (setq gnus-async-header-prefetched nil)
      t)))

(provide 'gnus-async)

;;; arch-tag: fee61de5-3ea2-4de6-8578-2f90ce89391d
;;; gnus-async.el ends here