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+;;; tq.el --- utility to maintain a transaction queue
+
+;;; Copyright (C) 1992 Scott Draves (spot@cs.cmu.edu)
+;;; 
+;;; manages receiving a stream asynchronously, 
+;;; parsing it into transactions, and then calling
+;;; handler functions
+
+
+;;; Our basic structure is the queue/process/buffer triple.  Each entry
+;;; of the queue is a regexp/closure/function triple.  We buffer
+;;; bytes from the process until we see the regexp at the head of the
+;;; queue.  Then we call the function with the closure and the
+;;; collected bytes.
+
+
+(provide 'tq)
+
+(defun tq-create (process)
+  "Create and return a transaction queue.  PROCESS should be capable
+of sending and receiving streams of bytes.  It may be a local process,
+or it may be connected to a tcp server on another machine."
+  (let ((tq (cons nil (cons process
+                            (generate-new-buffer
+                             (concat " tq-temp-"
+                                     (process-name process)))))))
+    (set-process-filter process
+                        (`(lambda (proc string)
+                           (tq-filter  '(, tq) string))))
+    tq))
+
+;;; accessors
+(defun tq-queue   (tq) (car tq))
+(defun tq-process (tq) (car (cdr tq)))
+(defun tq-buffer  (tq) (cdr (cdr tq)))
+
+(defun tq-queue-add (tq re closure fn)
+  (setcar tq (nconc (tq-queue tq)
+                    (cons (cons re (cons closure fn)) nil)))
+  'ok)
+
+(defun tq-queue-head-regexp  (tq) (car (car (tq-queue tq))))
+(defun tq-queue-head-fn      (tq) (cdr (cdr (car (tq-queue tq)))))
+(defun tq-queue-head-closure (tq) (car (cdr (car (tq-queue tq)))))
+(defun tq-queue-empty        (tq) (not (tq-queue tq)))
+(defun tq-queue-pop          (tq) (setcar tq (cdr (car tq))) (null (car tq)))
+ 
+
+;;; must add to queue before sending!
+(defun tq-enqueue (tq question regexp closure fn)
+  "Add a transaction to TQ.  Send question to the process, and call FN
+with CLOSURE and and the answer, when it appears.  The end of the
+answer is identified by REGEXP."
+  (tq-queue-add tq regexp closure fn)
+  (process-send-string (tq-process tq) question))
+
+(defun tq-close (tq)
+  "Shut down the process, and destroy the evidence."
+  (delete-process (tq-process tq))
+  (kill-buffer (tq-buffer tq)))
+
+(defun tq-filter (tq string)
+  "Append STRING to the TQ's buffer; then process the new data."
+  (set-buffer (tq-buffer tq))
+  (goto-char (point-max))
+  (insert string)
+  (tq-process-buffer tq))
+
+(defun tq-process-buffer (tq)
+  "Check TQ's buffer for the regexp at the head of the queue."
+  (set-buffer (tq-buffer tq))
+  (if (= 0 (buffer-size)) ()
+    (if (tq-queue-empty tq)
+        (let ((buf (generate-new-buffer "*spurious*")))
+          (copy-to-buffer buf (point-min) (point-max))
+          (delete-region (point-min) (point))
+          (pop-to-buffer buf nil)
+          (error (concat "Spurious communication from process "
+                         (process-name (tq-process tq))
+                         ", see buffer *spurious*.")))
+      (goto-char (point-min))
+      (if (re-search-forward (tq-queue-head-regexp tq) nil t)
+          (let ((answer (buffer-substring (point-min) (point))))
+            (delete-region (point-min) (point))
+            (funcall (tq-queue-head-fn tq)
+                     (tq-queue-head-closure tq)
+                     answer)
+            (tq-queue-pop tq)
+            (tq-process-buffer tq))))))
+
+;;; tq.el ends here