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IMA at DeleteXMLNode
Posted: Thu Oct 20, 2011 10:09 am
by auser
Somebody have an Idea why this creates an Invalid Memory Access? PreviousXMLNode returns a value greater 0 which I would delete with DeleteXMLNode afterwards. I was using that PreviousXMLNode to avoid "deltenode(thisnode) -> nextnode(thisnode_is_deleted_already)"
Code: Select all
*ChildNode = ChildXMLNode(*CurrentNode)
While *ChildNode <> 0
If FilterXML(*ChildNode,CurrentSublevel + 1,*grp_stack, username.s) = 1
*DeleteNode = *ChildNode
*ChildNode = NextXMLNode(*ChildNode) ;
If *ChildNode
*DeleteNode = PreviousXMLNode(*ChildNode)
If *DeleteNode
DeleteXMLNode(*DeleteNode) ; <------------ IMA here
EndIf
Else
If *DeleteNode
DeleteXMLNode(*DeleteNode)
Break
EndIf
EndIf
Else
*ChildNode = NextXMLNode(*ChildNode)
EndIf
Wend
Re: IMA at DeleteXMLNode
Posted: Thu Oct 20, 2011 10:15 am
by Kiffi
@auser: can you provide a simple xml to reproduce the IMA?
Greetings ... Kiffi
Re: IMA at DeleteXMLNode
Posted: Thu Oct 20, 2011 10:28 am
by auser
The IMA is sporadically. It works for example 100 times... then it crashes. I start the app again (with the same file) and it works again. At first I've done a deltexmlnode and then used nextxmlnode on that (already deleted) one... it even worked most time but then it crashed with IMA as well (so I thought it's maybe bad to use a node for NextXMLNode(*AlreadyDeleted) that is deleted in a previous step already). But it seems (even when it tastes somewhat wrong to me anyway) that this was not the real problem. The XML is basicaly structured in that way:
Code: Select all
<?xml version="1.0" encoding="utf-8"?>
<main>
<maingroup name="Example" group="testuser">
<subentry name="Example" group="testuser">
<server name="example" group="testuser">
<type>example</type>
</server>
</subentry>
</maingroup>
</main>
Re: IMA at DeleteXMLNode
Posted: Thu Oct 20, 2011 12:37 pm
by kenmo
I feel like we're missing some info.
Is that original code inside a recursive procedure? If so, are you using Protected variables? If not, what does FilterXML() do?
It is definitely a good idea to grab the Next node pointer before deleting the current node. I'm not sure why you have this line though, it seems unnecessary (though harmless...):
Code: Select all
*DeleteNode = PreviousXMLNode(*ChildNode)
Other than that, unless anyone else is aware of any bug with DeleteXMLNode(), I guess we would need a reproducible example of the crash...
I'm using the XML library extensively in my current project, including recursive parsing/cleanup procedures, and have not encountered any crashes. Are you using the latest PB 4.60?
Re: IMA at DeleteXMLNode
Posted: Thu Oct 20, 2011 1:19 pm
by auser
kenmo: Sorry, yes there is more (and yes it's recursive)... but since PreviousXMLNode returned non-zero I thought it's maybe enough. I don't think that "*DeleteNode = PreviousXMLNode(*ChildNode)" is useless because I check if that value is nonzero one line below. I'm using PB 4.51... I had the crash twice on linux yesterday once and today once (after changing to PreviousXMLNode) - but did not found the crash on Windows so far (anyway... I've just started testing on windows today and it even works on Linux lots of times).
Code: Select all
Procedure FilterXML(*CurrentNode,CurrentSublevel,*grp_stack, username.s)
Protected *ChildNode
Protected *DeleteNode
Protected keepalive.i
Protected retval
Protected parse.s = ""
Protected x.i = 0
Protected fields.i = 0
If CurrentSublevel = 0
keepalive = 1
EndIf
If XMLNodeType(*CurrentNode) = #PB_XML_Normal
If ExamineXMLAttributes(*CurrentNode)
While NextXMLAttribute(*CurrentNode)
Select XMLAttributeName(*CurrentNode)
Case "user", "owner", "admin"
parse.s = XMLAttributeValue(*CurrentNode)
fields = CountString(parse.s,",")
If fields = 0
fields = 1
EndIf
For x = 1 To fields
If Trim(StringField(parse.s,x,",")) = username.s
keepalive = 1
EndIf
Next
Case "group", "owner_grp", "admin_grp"
parse.s = XMLAttributeValue(*CurrentNode)
fields = CountString(parse.s,",")
If fields = 0
fields = 1
EndIf
For x = 1 To fields
If IsInGroup(Trim(StringField(parse.s,x,",")),*grp_stack)
keepalive = 1
EndIf
Next
EndSelect
Wend
EndIf
EndIf
If keepalive = 0
ProcedureReturn(1)
EndIf
If CurrentSublevel = 3 ; no permission checks below that sublevel anymore
ProcedureReturn(0)
EndIf
*ChildNode = ChildXMLNode(*CurrentNode)
While *ChildNode <> 0
If FilterXML(*ChildNode,CurrentSublevel + 1,*grp_stack, username.s) = 1
*DeleteNode = *ChildNode
*ChildNode = NextXMLNode(*ChildNode)
If *ChildNode
*DeleteNode = PreviousXMLNode(*ChildNode)
If *DeleteNode
DeleteXMLNode(*DeleteNode)
EndIf
Else
If *DeleteNode
DeleteXMLNode(*DeleteNode)
Break
EndIf
EndIf
Else
*ChildNode = NextXMLNode(*ChildNode)
EndIf
Wend
EndProcedure
Re: IMA at DeleteXMLNode
Posted: Thu Oct 20, 2011 5:40 pm
by kenmo
Oh... maybe it's a bug in the Linux version of the XML library? I've only been using it on Windows.
I haven't looked over your function yet but I will try to.
I just meant that
Code: Select all
*DeleteNode = PreviousXMLNode(*ChildNode)
was unnecessary because it immediately follows
Code: Select all
*DeleteNode = *ChildNode
*ChildNode = NextXMLNode(*ChildNode)
so ideally, *DeleteNode should already have the same correct pointer, right?
Re: IMA at DeleteXMLNode
Posted: Fri Oct 21, 2011 8:08 am
by auser
kenmo wrote:
so ideally, *DeleteNode should already have the same correct pointer, right?
...mhhh...
- yes I think you are right, thanks for pointing me to that. Anyway I'm afraid that would not make a difference at all. But for sure I would change it (and hope
)
Greetings,
auser
Re: IMA at DeleteXMLNode
Posted: Mon Oct 24, 2011 2:53 pm
by auser
I think I've found the bug and created a report (it may be very well even the case on Win64bit and seems to only occur if your XMLtree got a big returnvalue via #PB_Any in CatchXML - maybe even LoadXML):
http://www.purebasic.fr/english/viewtop ... 23&t=47982
Greetings,
auser