Add the new file url-queue.el, which allows controlling the

parallelism when fetching web pages asynchronously.
parent 35813471
2011-05-02 Lars Magne Ingebrigtsen <larsi@gnus.org>
* url-queue.el: New file.
2011-04-16 Lars Magne Ingebrigtsen <larsi@gnus.org>
* url-http.el (url-http-wait-for-headers-change-function): Protect
......
;;; url-queue.el --- Fetching web pages in parallel
;; Copyright (C) 2011 Free Software Foundation, Inc.
;; Author: Lars Magne Ingebrigtsen <larsi@gnus.org>
;; Keywords: comm
;; 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 of the License, 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. If not, see <http://www.gnu.org/licenses/>.
;;; Commentary:
;; The point of this package is to allow fetching web pages in
;; parallel -- but control the level of parallelism to avoid DoS-ing
;; web servers and Emacs.
;;; Code:
(eval-when-compile (require 'cl))
(require 'browse-url)
(defcustom url-queue-parallel-processes 4
"The number of concurrent processes."
:type 'integer
:group 'url)
(defcustom url-queue-timeout 5
"How long to let a job live once it's started (in seconds)."
:type 'integer
:group 'url)
;;; Internal variables.
(defvar url-queue nil)
(defstruct url-queue
url callback cbargs silentp
process start-time)
(defun url-queue-retrieve (url callback &optional cbargs silent)
"Retrieve URL asynchronously and call CALLBACK with CBARGS when finished.
Like `url-retrieve' (which see for details of the arguments), but
controls the level of parallelism via the
`url-queue-parallel-processes' variable."
(setq url-queue
(append url-queue
(list (make-url-queue :url url
:callback callback
:cbargs cbargs
:silentp silent))))
(url-queue-run-queue))
(defun url-queue-run-queue ()
(url-queue-prune-old-entries)
(let ((running 0)
waiting)
(dolist (entry url-queue)
(if (url-queue-start-time entry)
(incf running)
(setq waiting entry)))
(when (and waiting
(< running url-queue-parallel-processes))
(setf (url-queue-start-time waiting) (float-time))
(url-queue-start-retrieve waiting))))
(defun url-queue-callback-function (status job)
(setq url-queue (delq job url-queue))
(url-queue-run-queue)
(apply (url-queue-callback job) (cons status (url-queue-cbargs job))))
(defun url-queue-start-retrieve (job)
(setf (url-queue-process job)
(ignore-errors
(url-retrieve (url-queue-url job)
#'url-queue-callback-function (list job)
(url-queue-silentp job)))))
(defun url-queue-prune-old-entries ()
(let (dead-jobs)
(dolist (job url-queue)
;; Kill jobs that have lasted longer than five seconds.
(when (and (url-queue-start-time job)
(> (- (float-time) (url-queue-start-time job))
url-queue-timeout))
(push job dead-jobs)))
(dolist (job dead-jobs)
(when (processp (url-queue-process job))
(ignore-errors
(delete-process (url-queue-process job)))
(ignore-errors
(kill-buffer (process-buffer (url-queue-process job))))
(setq url-queue (delq job url-queue))))))
(provide 'url-queue)
;;; url-queue.el ends here
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