[Mono-bugs] [Bug 77824][Nor] Changed - im: crash when calling PaintEventArgs.Graphics.Transform in OnPaint()

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Changed by peter at novonyx.com.

http://bugzilla.ximian.com/show_bug.cgi?id=77824

--- shadow/77824	2006-05-21 16:29:18.000000000 -0400
+++ shadow/77824.tmp.32042	2006-05-22 18:03:35.000000000 -0400
@@ -1,13 +1,13 @@
 Bug#: 77824
 Product: Mono: Class Libraries
 Version: 1.1
 OS: unknown
 OS Details: 
-Status: REOPENED   
-Resolution: 
+Status: RESOLVED   
+Resolution: NOTABUG
 Severity: Unknown
 Priority: Normal
 Component: Windows.Forms
 AssignedTo: peter at novonyx.com                            
 ReportedBy: matt at use.net               
 QAContact: mono-bugs at ximian.com
@@ -235,6 +235,25 @@
 
 Personally I dislike the g_return_val_if_fail calls - in part because
 they mess up the unit tests display, coverity has a hard time dealing
 with them (and reporting false alarms) and, in some case, introduced
 problem when dealing with errors (e.g. missing free). But removing
 them won't fix your problem (only the display ;-)
+
+------- Additional Comments From peter at novonyx.com  2006-05-22 18:03 -------
+After lots of analyzing here's what I found:
+
+Inside it's OnPaint(paint_event) handler the application does:
+new PaintEventArgs(paint_event.Graphics, rectangle)
+
+That causes the graphics object to be copied into a new 
+PaintEventArgs object, and when the GC cleans up that object, the 
+graphics object will be disposed. In some cases, this object, 
+however, is represending the double buffer context and may not be 
+disposed. If it is anyways, we get a later crash since it's native 
+object is now 0.
+
+The problem is that just creating new PaintEventArgs is not really 
+legal, even on MS. If the GC on MS were to kick in at the right time, 
+the graphics object would be disposed there, too, and the app would 
+crash. Since we reuse our graphics object it just is more obvious on 
+Mono.