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+;;;
+;;; Code freely lifted from various places with compatible license
+;;; terms.  Most of this code is copyright Daniel Barlow
+;;; <dan@metacircles.com> or Gilbert Baumann
+;;; <unk6@rz.uni-karlsruhe.de>.  The bugs are copyright Walter
+;;; C. Pelissero <walter@pelissero.de>.
+;;;
+
+;;; This library is free software; you can redistribute it and/or
+;;; modify it under the terms of the GNU Library General Public
+;;; License as published by the Free Software Foundation; either
+;;; version 2 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
+;;; Library General Public License for more details.
+;;;
+;;; You should have received a copy of the GNU Library General Public
+;;; License along with this library; if not, write to the 
+;;; Free Software Foundation, Inc., 59 Temple Place - Suite 330, 
+;;; Boston, MA  02111-1307  USA.
+
+(in-package :sclf)
+
+(defstruct (process
+             (:constructor %make-process)
+             (:predicate processp))
+  name
+  state
+  whostate
+  function
+  thread)
+
+(defvar *current-process*
+  (%make-process
+   :name "initial process" :function nil
+   :thread
+   #+#.(cl:if (cl:find-symbol "THREAD-NAME" "SB-THREAD") '(and) '(or))
+   sb-thread:*current-thread*
+   #-#.(cl:if (cl:find-symbol "THREAD-NAME" "SB-THREAD") '(and) '(or))
+   (sb-thread:current-thread-id)))
+
+(defvar *all-processes* (list *current-process*))
+
+(defvar *all-processes-lock*
+  (sb-thread:make-mutex :name "Lock around *ALL-PROCESSES*"))
+
+;; we implement disable-process by making the disablee attempt to lock
+;; *permanent-queue*, which is already locked because we locked it
+;; here.  enable-process just interrupts the lock attempt.
+
+(defmacro get-mutex (mutex &optional (wait t))
+  `(
+    #+#.(cl:if (cl:find-symbol "GRAB-MUTEX" "SB-THREAD") '(and) '(or))
+        sb-thread:grab-mutex
+        #-#.(cl:if (cl:find-symbol "GRAB-MUTEX" "SB-THREAD") '(and) '(or))
+        sb-thread:get-mutex
+        ,mutex :waitp ,wait))
+
+(defvar *permanent-queue*
+  (sb-thread:make-mutex :name "Lock for disabled threads"))
+(unless (sb-thread:mutex-owner *permanent-queue*)
+  (get-mutex *permanent-queue* nil))
+
+(defun make-process (function &key name)
+  (let ((p (%make-process :name name
+                          :function function)))
+    (sb-thread:with-mutex (*all-processes-lock*)
+      (pushnew p *all-processes*))
+    (restart-process p)))
+
+(defun process-kill-thread (process)
+  (let ((thread (process-thread process)))
+    (when (and thread
+               (sb-thread:thread-alive-p thread))
+      (assert (not (eq thread sb-thread:*current-thread*)))
+      (sb-thread:terminate-thread thread)
+      ;; Wait until all the clean-up forms are done.
+      (sb-thread:join-thread thread :default nil))
+    (setf (process-thread process) nil)))
+
+(defun process-join (process)
+  (sb-thread:join-thread (process-thread process)))
+
+(defun restart-process (p)
+  (labels ((boing ()
+             (let ((*current-process* p)
+                   (function (process-function p)))
+               (when function
+                 (funcall function)))))
+    (process-kill-thread p)
+    (when (setf (process-thread p)
+                (sb-thread:make-thread #'boing :name (process-name p)))
+      p)))
+
+(defun destroy-process (process)
+  (sb-thread:with-mutex (*all-processes-lock*)
+    (setf *all-processes* (delete process *all-processes*)))
+  (process-kill-thread process))
+
+(defun current-process ()
+  *current-process*)
+
+(defun all-processes ()
+  ;; we're calling DELETE on *ALL-PROCESSES*.  If we look up the value
+  ;; while that delete is executing, we could end up with nonsense.
+  ;; Better use a lock (or call REMOVE instead in DESTROY-PROCESS).
+  (sb-thread:with-mutex (*all-processes-lock*)
+    *all-processes*))
+
+(defun process-yield ()
+  (sb-thread:thread-yield))
+
+(defun process-wait (reason predicate)
+  (let ((old-state (process-whostate *current-process*)))
+    (unwind-protect
+         (progn
+           (setf old-state (process-whostate *current-process*)
+                 (process-whostate *current-process*) reason)
+           (until (funcall predicate)
+             (process-yield)))
+      (setf (process-whostate *current-process*) old-state))))
+
+(defun process-wait-with-timeout (reason timeout predicate)
+  (let ((old-state (process-whostate *current-process*))
+        (end-time (+ (get-universal-time) timeout)))
+    (unwind-protect
+         (progn
+           (setf old-state (process-whostate *current-process*)
+                 (process-whostate *current-process*) reason)
+           (loop 
+              for result = (funcall predicate)
+              until (or result
+                        (> (get-universal-time) end-time))
+              do (process-yield)
+              finally (return result)))
+      (setf (process-whostate *current-process*) old-state))))
+
+(defun process-interrupt (process function)
+  (sb-thread:interrupt-thread (process-thread process) function))
+
+(defun disable-process (process)
+  (sb-thread:interrupt-thread
+   (process-thread process)
+   (lambda ()
+     (catch 'interrupted-wait (get-mutex *permanent-queue*)))))
+
+(defun enable-process (process)
+  (sb-thread:interrupt-thread
+   (process-thread process) (lambda () (throw 'interrupted-wait nil))))
+
+(defmacro without-scheduling (&body body)
+  (declare (ignore body))
+  (error "WITHOUT-SCHEDULING is not supported on this platform."))
+
+(defparameter *atomic-lock*
+  (sb-thread:make-mutex :name "atomic incf/decf"))
+
+(defmacro atomic-incf (place)
+  `(sb-thread:with-mutex (*atomic-lock*)
+    (incf ,place)))
+
+(defmacro atomic-decf (place) 
+  `(sb-thread:with-mutex (*atomic-lock*)
+    (decf ,place)))
+
+;;; 32.3 Locks
+
+(defun make-lock (&optional name)
+  (sb-thread:make-mutex :name name))
+
+(defmacro with-lock-held ((place &key state (wait t) timeout) &body body)
+  (declare (ignore timeout))
+  (let ((old-state (gensym "OLD-STATE")))
+    `(sb-thread:with-mutex (,place :wait-p ,wait)
+       (let (,old-state)
+         (unwind-protect
+              (progn
+                (when ,state
+                  (setf ,old-state (process-state *current-process*))
+                  (setf (process-state *current-process*) ,state))
+                ,@body)
+           (setf (process-state *current-process*) ,old-state))))))
+
+
+(defun make-recursive-lock (&optional name)
+  (sb-thread:make-mutex :name name))
+
+(defmacro with-recursive-lock-held ((place &optional state (wait t) timeout) &body body)
+  (declare (ignore wait timeout))
+  (let ((old-state (gensym "OLD-STATE")))
+  `(sb-thread:with-recursive-lock (,place)
+    (let (,old-state)
+      (unwind-protect
+           (progn
+             (when ,state
+               (setf ,old-state (process-state *current-process*))
+               (setf (process-state *current-process*) ,state))
+             ,@body)
+        (setf (process-state *current-process*) ,old-state))))))
+
+(defun make-condition-variable () (sb-thread:make-waitqueue))
+
+(defun condition-wait (cv lock &optional timeout)
+  (if timeout
+      (handler-case 
+          (sb-ext:with-timeout timeout
+            (sb-thread:condition-wait cv lock)
+            t)
+        (sb-ext:timeout (c)
+          (declare (ignore c))
+          nil))
+      (progn (sb-thread:condition-wait cv lock) t)))
+
+(defun condition-notify (cv)
+  (sb-thread:condition-notify cv))
+
+
+(defvar *process-plists* (make-hash-table)
+  "Hash table mapping processes to a property list.  This is used by
+PROCESS-PLIST.")
+
+(defun process-property-list (process)
+  (gethash process *process-plists*))
+
+(defun (setf process-property-list) (value process)
+  (setf (gethash process *process-plists*) value))
+
+(defun process-execute (process function)
+  (setf (process-function process) function)
+  (restart-process process))
+
+(defun process-alive-p (process)
+  (sb-thread:thread-alive-p (process-thread process)))