From b40fe867e021bc365df1a904c2b1ed2068208f13 Mon Sep 17 00:00:00 2001
From: Robin Haberkorn <robin.haberkorn@googlemail.com>
Date: Mon, 23 Feb 2015 02:54:41 +0100
Subject: implemented to undo stack memory limiting

 * acts as a safe-guard against uninterrupted infinite loops
   or other operations that are costly to undo in interactive mode.
   If we're out of memory, it is usually too late to react properly.
   This implementation tries to avoid OOMs due to SciTECO behaviour.
   We cannot fully exclude the chance of an OOM error.
 * The undo stack size is only approximated using the
   UndoToken::get_size() method.
   Other ways to measure the exact amount of allocated heap
   (including size fields in every heap object or using sbrk(0) and
   similar) are either costly in terms of memory or platform-specific.
   This implementation does not need any additional memory per heap
   object or undo token but exploits the fact that undo tokens
   are virtual already. The size of an undo token is determined
   at compile time.
 * Default memory limit of 500mb should be OK for most people.
 * The current limit can be queried with "2EJ" and set with <x>,2EJ.
   This also works interactively (a bit tricky!)
 * Limiting can be disabled. In this case, undo token processing
   is a bit faster.
 * closes #3
---
 src/parser.cpp | 56 +++++++++++++++++++++++++++++++++++++++++++++++++-------
 1 file changed, 49 insertions(+), 7 deletions(-)

(limited to 'src/parser.cpp')

diff --git a/src/parser.cpp b/src/parser.cpp
index 384c42d..97876b0 100644
--- a/src/parser.cpp
+++ b/src/parser.cpp
@@ -1896,31 +1896,69 @@ StateECommand::custom(gchar chr)
 	 * If \fIkey\fP is omitted, the prefix sign is implied
 	 * (1 or -1).
 	 * With two arguments, it sets property \fIkey\fP to
-	 * \fIvalue\fP and returns nothing. Currently, there
-	 * are no properties that can be set.
+	 * \fIvalue\fP and returns nothing. Properties may be
+	 * read-only.
 	 *
 	 * The following property keys are defined:
 	 * .IP 0 4
 	 * The current user interface: 1 for Curses, 2 for GTK
+	 * (\fBread-only\fP)
 	 * .IP 1
 	 * The current numbfer of buffers: Also the numeric id
 	 * of the last buffer in the ring. This is implied if
 	 * no argument is given, so \(lqEJ\(rq returns the number
 	 * of buffers in the ring.
+	 * (\fBread-only\fP)
+	 * .IP 2
+	 * The current undo stack memory limit in bytes.
+	 * This limit helps to prevent dangerous out-of-memory
+	 * conditions (e.g. resulting from infinite loops) by
+	 * approximating the memory used by \*(ST's undo stack and is only
+	 * effective in interactive mode.
+	 * Commands which would exceed that limit fail instead.
+	 * When getting, a zero value indicates that memory limiting is
+	 * disabled.
+	 * Setting a value less than or equal to 0 as in
+	 * \(lq0,2EJ\(rq disables the limit.
+	 * \fBWarning:\fP Disabling memory limiting may provoke
+	 * uncontrollable out-of-memory errors in long running
+	 * or infinite loops.
+	 * Setting a new limit may fail if the current undo stack
+	 * is too large for the new limit \(em if this happens
+	 * you may have to clear your command-line first.
+	 * Undo stack memory limiting is enabled by default.
 	 */
 	case 'J': {
 		BEGIN_EXEC(&States::start);
 
+		enum {
+			EJ_USER_INTERFACE = 0,
+			EJ_BUFFERS,
+			EJ_UNDO_MEMORY_LIMIT
+		};
 		tecoInt property;
 
 		expressions.eval();
 		property = expressions.pop_num_calc();
-		if (expressions.args() > 0)
-			throw Error("Cannot set property %" TECO_INTEGER_FORMAT
-			            " for <EJ>", property);
+		if (expressions.args() > 0) {
+			/* set property */
+			tecoInt value = expressions.pop_num_calc();
+
+			switch (property) {
+			case EJ_UNDO_MEMORY_LIMIT:
+				undo.set_memory_limit(MAX(0, value));
+				break;
+
+			default:
+				throw Error("Cannot set property %" TECO_INTEGER_FORMAT
+				            " for <EJ>", property);
+			}
+
+			break;
+		}
 
 		switch (property) {
-		case 0: /* user interface */
+		case EJ_USER_INTERFACE:
 #ifdef INTERFACE_CURSES
 			expressions.push(1);
 #elif defined(INTERFACE_GTK)
@@ -1930,10 +1968,14 @@ StateECommand::custom(gchar chr)
 #endif
 			break;
 
-		case 1: /* number of buffers */
+		case EJ_BUFFERS:
 			expressions.push(ring.get_id(ring.last()));
 			break;
 
+		case EJ_UNDO_MEMORY_LIMIT:
+			expressions.push(undo.memory_limit);
+			break;
+
 		default:
 			throw Error("Invalid property %" TECO_INTEGER_FORMAT
 			            " for <EJ>", property);
-- 
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