[Mono-dev] Webapp stuck with "Key duplication when adding: httpModules"

[Etienne Champetier]

After some more investigation, reading many lines of code with a collegue,
we came to the conclusion that this exception is impossible :)
(yet the web is stuck on it)

m_ItemsContainer is an hashtable, and a private field of
NameObjectCollectionBase
class (new HashTable(0,StringComparer.Ordinal)).
The exception tell us that there is already a key 'httpModules' in
m_ItemsContainer.
Reading the code the only way we go from BaseSet to BaseAdd is if
FindFirstMatchedItem('httpModules'), so if (_Item)m_ItemsContainer[
'httpModules'] is null,
so if the value is null (the key exists, we got an exception to prove it :))

if i'm right, we are sure that we have ('httpModules',null) in
m_ItemsContainer.


Now m_ItemsContainer only modifications are:
0) m_ItemsContainer = new Hashtable (m_defCapacity, equality_comparer);

1) m_ItemsContainer.Clear ();

2) _Item newitem=new _Item(name, value);
   m_ItemsContainer.Add(name,newitem);

3) m_ItemsContainer.Remove(name);

So there is no way there is ('httpModules',null) in m_ItemsContainer


Please someone tell me where i'm wrong

https://github.com/mono/mono/blob/master/mcs/class/System/System.Collections.Specialized/NameObjectCollectionBase.cs

Thanks
Etienne


2014-10-21 14:54 GMT+02:00 Etienne Champetier <champetier.etienne at gmail.com>
:

> Hi,
>
> At my firm we are running multiple webapplication using mono (nginx +
> fastcgi-mono-server2.exe) on a cluster of 4 VM, 2 vcpus.
> One of them is restarted every day at 1h45 (small memory leak).
> 3 weeks ago we went from 8VM with 1vcpu (no restart problem) to 4VM with
> 2vcpus, and now,
> it's the 3rd time in 2 weeks that on one VM, the restart doesn't work well
> and we have:
>
> [System.ArgumentException]: Key duplication when adding: httpModules
>   at System.Collections.Hashtable.PutImpl (System.Object key,
> System.Object value, Boolean overwrite) [0x00000] in <filename unknown>:0
>   at System.Collections.Hashtable.Add (System.Object key, System.Object
> value) [0x00000] in <filename unknown>:0
>   at System.Collections.Specialized.NameObjectCollectionBase.BaseAdd
> (System.String name, System.Object value) [0x00000] in <filename unknown>:0
>   at System.Collections.Specialized.NameObjectCollectionBase.BaseSet
> (System.String name, System.Object value) [0x00000] in <filename unknown>:0
>   at System.Configuration.ConfigurationSectionCollection.get_Item
> (System.String name) [0x00000] in <filename unknown>:0
>   at System.Configuration.Configuration.GetSection (System.String path)
> [0x00000] in <filename unknown>:0
>   at System.Web.Configuration.WebConfigurationManager.GetSection
> (System.String sectionName, System.String path, System.Web.HttpContext
> context) [0x00000] in <filename unknown>:0
>   at System.Web.Configuration.WebConfigurationManager.GetSection
> (System.String sectionName, System.String path) [0x00000] in <filename
> unknown>:0
>   at
> System.Web.Configuration.WebConfigurationManager.GetWebApplicationSection
> (System.String sectionName) [0x00000] in <filename unknown>:0
>   at System.Web.HttpApplication.InitOnce (Boolean full_init) [0x00000] in
> <filename unknown>:0
>
>
> The really cool stuff is that even if it's a 500 error, the returned http
> code is 200 :)
>
> I've already checked and all files are equal (dll, exe, conf), all VM conf
> are equal (vcpu, memory, ...), ...
>
> I'm not able to reproduce the bug (restart under high load (ab -c 50 -n
> 100000)) so can't tell if the bug is there in the newest version.
>
> We are using a version of mono before 3.2.7
> (92887027be801b012846866208e6b4e362a4fc24) and fastcgi-mono-server2 (xsp)
> version 2.10.2-1 (old version build on 14/09/12 by someone at my firm)
> I know we are using old version but it seems that the bug is still there:
> https://bugzilla.xamarin.com/show_bug.cgi?id=18303
>
> I've run lsof on the processes (the stuck one and one working), and by
> comparing the 2, i see that App_global.asax_XXXXXXX.dll
> is here in both case, but not  App_Web_XXXXXXXX.dll (only on the working
> one) (see attachment)
>
> I have root access on the VM with the stuck process, and i'm on irc right
> now (champtar), so if you have some ideas to gather more info to kill this
> bug
>
> Thanks in advance
>
> Etienne
>
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