Debugging Script: Dumping out ASP.NET Session Contents

6 minute read

In my last post I wrote a script to dump out all the ASP.NET requests on the heap. Since one of the most common memory issues I encounter is too much cache or session state I figured that showing you how to retrieve session data would be good.

A word of caution, since this script uses !dumpheap (to dump out the objects on the heap) and !objsize (to figure out the size of an object including the size of its member variables) it may take a long time to execute if you have a very large dump, which is typically the case when you are worried about how much you store in session state.

There is a lot more data that you can get, other than what I am displaying, and the script can pretty easily be modified to display cache objects instead so if you find some cool use or modification of it, please post it in the comments so all of us can benefit from it.

Note: This script only works if you use in-proc session state since it is doing its magic by dumping out all the System.Web.SessionState.InProcSessionState items on the heap. On the other hand, if you have high memory usage due to session state it is probably the in-proc session state items you will be worried about. Btw, if this is what you are running into, check out the post index for other posts on ASP.NET Session memory issues.

Output and comments on output

This script is divided into two parts.

DumpSessions

Displays all the System.Web.SessionState.InProcSessionState items with the session address as a DML (Debugger Markup Language) link so that you can click it to get more detailed info.

DumpSessionVar

Dumps out more detailed information about each sessions, i.e. the session variables for that particular session and this is what gets executed when you click the DML link.

An idea for a modification of the script would be to print out all the session variables at once, or add some parsing to get the total size of all sessions. Oh well, there is endless possibilities here.

Finding the data

All in-proc sessions are represented on the heap as System.Web.SessionState.InProcSessionState objects.

0:013> !do 03093d38
Name: System.Web.SessionState.InProcSessionState
MethodTable: 663ac580
EEClass: 663ac510
Size: 48(0x30) bytes
GC Generation: 1
 (C:\WINDOWS\assembly\GAC_32\System.Web\2.0.0.0__b03f5f7f11d50a3a\System.Web.dll)
Fields:
      MT    Field   Offset                 Type VT     Attr    Value Name
663ecfbc  4001edc        4 ...ateItemCollection  0 instance 03093b18 _sessionItems
663a3390  4001edd        8 ...ObjectsCollection  0 instance 00000000 _staticObjects
791018e0  4001ede        c         System.Int32  1 instance       20 _timeout
79107584  4001edf       18       System.Boolean  1 instance        0 _locked
791084f8  4001ee0       1c      System.DateTime  1 instance 03093d54 _utcLockDate
791018e0  4001ee1       10         System.Int32  1 instance        1 _lockCookie
663aad40  4001ee2       24 ...ReadWriteSpinLock  1 instance 03093d5c _spinLock
791018e0  4001ee3       14         System.Int32  1 instance        0 _flags

given a particular System.Web.SessionState.InProcSessionState object we can get to the information we want like this.

Size of the session

0:013> !objsize 03093d38
sizeof(03093d38) =  268,437,272 (  0x10000718) bytes (System.Web.SessionState.InProcSessionState)

Individual Session Variables

We get to the individual session variables by dumping out the _sessionItems member variable, following the steps below…

Note: the number of session variables in the session is available from the _size member variable of the ArrayList

0:013> !do 03093b18
Name: System.Web.SessionState.SessionStateItemCollection
MethodTable: 66411bb4
EEClass: 66411b3c
Size: 60(0x3c) bytes
GC Generation: 2
 (C:\WINDOWS\assembly\GAC_32\System.Web\2.0.0.0__b03f5f7f11d50a3a\System.Web.dll)
Fields:
      MT    Field   Offset                 Type VT     Attr    Value Name
79107584  4001173       24       System.Boolean  1 instance        0 _readOnly
79105cd4  4001174        4 ...ections.ArrayList  0 instance 03093b60 _entriesArray
791138d4  4001175        8 ...IEqualityComparer  0 instance 03049ce0 _keyComparer
79101634  4001176        c ...ections.Hashtable  0 instance 03093b78 _entriesTable
7a761668  4001177       10 ...e+NameObjectEntry  0 instance 00000000 _nullKeyEntry
7a78e3b0  4001178       14 ...se+KeysCollection  0 instance 00000000 _keys
7910ec98  4001179       18 ...SerializationInfo  0 instance 00000000 _serializationInfo
791018e0  400117a       20         System.Int32  1 instance        4 _version
790fc35c  400117b       1c        System.Object  0 instance 00000000 _syncRoot
79115538  400117c      538 ...em.StringComparer  0   shared   static defaultComparer
    >> Domain:Value  0019b498:NotInit  001cc780:NotInit  <<
79107584  4001f2b       25       System.Boolean  1 instance        1 _dirty
664228fc  4001f2c       28 ...n+KeyedCollection  0 instance 00000000 _serializedItems
79100f74  4001f2d       2c     System.IO.Stream  0 instance 00000000 _stream
791018e0  4001f2e       34         System.Int32  1 instance        0 _iLastOffset
790fc35c  4001f2f       30        System.Object  0 instance 03093b54 _serializedItemsLock
79101634  4001f2a      c54 ...ections.Hashtable  0   shared   static s_immutableTypes
    >> Domain:Value  0019b498:NotInit  001cc780:0708be1c <<
0:013> !do 03093b60
Name: System.Collections.ArrayList
MethodTable: 79105cd4
EEClass: 79105c28
Size: 24(0x18) bytes
GC Generation: 2
 (C:\WINDOWS\assembly\GAC_32\mscorlib\2.0.0.0__b77a5c561934e089\mscorlib.dll)
Fields:
      MT    Field   Offset                 Type VT     Attr    Value Name
7912ad90  40008df        4      System.Object[]  0 instance 03093c90 _items
791018e0  40008e0        c         System.Int32  1 instance        3 _size
791018e0  40008e1       10         System.Int32  1 instance        3 _version
790fc35c  40008e2        8        System.Object  0 instance 00000000 _syncRoot
7912ad90  40008e3      1c0      System.Object[]  0   shared   static emptyArray
    >> Domain:Value  0019b498:03031ff8 001cc780:030371e4 <<
0:013> dc 03093c90
03093c90  7912ad90 00000004 790fc35c 03093c80  ...y....\..y.<..
03093ca0  03093cb0 03093ce4 00000000 00000000  .<...<..........
03093cb0  7a761668 030939c8 03093c64 00000000  h.vz.9..d<......
03093cc0  79105cd4 31180038 00000000 020bb7a8  .\.y8..1........
03093cd0  020bb7a8 00000000 00194d40 00000000  ........@M......
03093ce0  00000000 7a761668 03093a14 03093cc0  ....h.vz.:...<..
03093cf0  00000000 790fcb30 0000001a 00000019  ....0..y........
03093d00  0061006a 006e0030 00710078 007a006e  j.a.0.n.x.q.n.z.
0:013> !do 03093c80
Name: System.Collections.Specialized.NameObjectCollectionBase+NameObjectEntry
MethodTable: 7a761668
EEClass: 7a7ce36c
Size: 16(0x10) bytes
GC Generation: 2
 (C:\WINDOWS\assembly\GAC_MSIL\System\2.0.0.0__b77a5c561934e089\System.dll)
Fields:
      MT    Field   Offset                 Type VT     Attr    Value Name
790fcb30  400117d        4        System.String  0 instance 030939a4 Key
790fc35c  400117e        8        System.Object  0 instance 03093c40 Value
0:013> !do 030939a4
Name: System.String
MethodTable: 790fcb30
EEClass: 790fca90
Size: 34(0x22) bytes
GC Generation: 2
 (C:\WINDOWS\assembly\GAC_32\mscorlib\2.0.0.0__b77a5c561934e089\mscorlib.dll)
String: UserName
Fields:
      MT    Field   Offset                 Type VT     Attr    Value Name
791018e0  4000096        4         System.Int32  1 instance        9 m_arrayLength
791018e0  4000097        8         System.Int32  1 instance        8 m_stringLength
790fe534  4000098        c          System.Char  1 instance       55 m_firstChar
790fcb30  4000099       10        System.String  0   shared   static Empty
    >> Domain:Value  0019b498:790d81bc 001cc780:790d81bc <<
7912b1d8  400009a       14        System.Char[]  0   shared   static WhitespaceChars
    >> Domain:Value  0019b498:030303f4 001cc780:03034558 <<
0:013> !do 03093c40
Name: System.String
MethodTable: 790fcb30
EEClass: 790fca90
Size: 36(0x24) bytes
GC Generation: 2
 (C:\WINDOWS\assembly\GAC_32\mscorlib\2.0.0.0__b77a5c561934e089\mscorlib.dll)
String: Joe Smith
Fields:
      MT    Field   Offset                 Type VT     Attr    Value Name
791018e0  4000096        4         System.Int32  1 instance       10 m_arrayLength
791018e0  4000097        8         System.Int32  1 instance        9 m_stringLength
790fe534  4000098        c          System.Char  1 instance       4a m_firstChar
790fcb30  4000099       10        System.String  0   shared   static Empty
    >> Domain:Value  0019b498:790d81bc 001cc780:790d81bc <<
7912b1d8  400009a       14        System.Char[]  0   shared   static WhitespaceChars
    >> Domain:Value  0019b498:030303f4 001cc780:03034558 <<

Running the scripts

To run the scripts copy the text below and put it in two text files somewhere on your hard drive.

I’ve put mine in c:\tools\extensions\DumpSessions.wds and c:\tools\extensions\DumpSessionVar.wds.

If you put them somewhere else, make sure you change the path in the DumpSessions.wds script so that you get to the right script file when you click the DML links.

To run it, open up your dump in windbg and load sos.dll, and then run

$><c:\tools\extensions\DumpSessions.wdl

Script code

DumpSessions.wds

$$
$$ Dumps all sessions on the heap
$$
$$
$$ Written by: Tess
$$
$$ Run as: $><c:\tools\extensions\DumpSessions.wds
$$

$$ CLEAR ALL ALIASES (VARIABLES)
$$ ----------------------------------------------------------------------------------
ad /q *

r @$t0=0;
r @$t1=0;

$$ GET ALL SESSION ITEMS
.foreach (CurrentSession {!dumpheap -type System.Web.SessionState.InProcSessionState -short}){
    $$ Increment # of sessions
    r @$t0 = @$t0+1

    .printf /D "Session Address:\t<?dml?><exec cmd=\"$$>a< c:\\tools\\extensions\\DumpSessionVar.wds ${CurrentSession}\">${CurrentSession}</exec>\n";
    .printf "Session Timeout:\t%d\n", poi(${CurrentSession}+0xc);
    .foreach /pS 2 /ps 99 (token {!objsize ${CurrentSession}}){.printf "Session Size:\t${token} bytes\n"}
    .printf "_______________________________________________\n";
}

.printf "Number of Sessions: %d\n\n\n\n\n\n\n\n\n", @$t0;

DumpSessionVar.wds

$$
$$ Dumps details of a particular session
$$
$$
$$ Written by: Tess
$$
$$ Run as: $$>a<c:\tools\extensions\DumpSessionVar.wds SessionAddress
$$

.printf "Session:\t\t${$arg1}\n";
.foreach /pS 2 /ps 99 (token {!objsize ${$arg1}}){.printf "Session Size:\t${token} bytes\n"}

$$ Number of session variables
r @$t0 = poi(poi(poi(${$arg1}+0x4)+0x4)+0xc);


.for(r @$t1=0; @$t1 < @$t0; r @$t1=@$t1+1){
    .printf "\n================================================\n"
    .printf "Session Variable\n"
    .printf "================================================\n"

    $$ NameObject Entry (actual session variable)
    r @$t2 = poi(poi(poi(poi(${$arg1}+0x4)+0x4)+0x4)+0x8+0x4*(@$t1+1));
    $$ Size
    .foreach /pS 2 /ps 99 (token {!objsize @$t2}){.printf "Sessionvar Size:\t${token} bytes\n"}
    $$ Key
    .foreach /pS 5 (tk {.foreach /pS 9 (token {!do -nofields poi(@$t2+0x4)}){.printf "${token} "}}) {
        .printf /D "Session Key:\t<?dml?><col fg=\"emphfg\">${tk}</col>\n"
    };
    $$ Value
    .printf "Session Variable:\t%p\n****\n", poi(@$t2+0x8);
    !do poi(@$t2+0x8)
}

.printf "\n\n\n\n\n\n\n\n\n";
ad /q *

Final words

You can access all the scripts from this blog in the debugging scripts repo

If you have any ideas for scripts that you think would be useful please let me know and if I have the time and energy I will probably implement and post them…

Have fun,

Tess