Question

I have a Silverlight 3 application which seems to be leaking DispatcherTimer objects. At least, over time when the application runs I find more of them on the heap:

!dumpheap -type DispatcherTimer

returns an increating number of them.

I’d like to find the Tick event handler method for these so I can identify where they’re created in my code.

When I try dumping one of these in windbg, I get something like:

!do 098b9980
Name:        System.Windows.Threading.DispatcherTimer
MethodTable: 0bfd4ba0
EEClass:     0bc98d18
Size:        20(0x14) bytes
File:        C:\Program Files (x86)\Microsoft Silverlight\4.0.50524.0\System.Windows.dll
Fields:
      MT    Field   Offset                 Type VT     Attr    Value Name
0bfd1538  40008be        4 ...eObjectSafeHandle  0 instance 098b9994 m_nativePtr
0bfd3d0c  40008bf        8 ...reTypeEventHelper  0 instance 098b99ac _coreTypeEventHelper
506a07e4  40008c0        c       System.Boolean  1 instance        1 _isEnabled
0bfd3c68  40008c1      cec ...ependencyProperty  0   shared   static IntervalProperty
    >> Domain:Value  086d3f38:NotInit  086daeb8:098b99b8 <<

But from here, I don’t know how to find the method handling the Tick event. I suspect it’s something to do with _coreTypeEventHelper, but when I dump that, I get:

!do 098b99ac 
Name:        MS.Internal.CoreTypeEventHelper
MethodTable: 0bfd3d0c
EEClass:     0bc98420
Size:        12(0xc) bytes
File:        C:\Program Files (x86)\Microsoft Silverlight\4.0.50524.0\System.Windows.dll
Fields:
      MT    Field   Offset                 Type VT     Attr    Value Name
00000000  40009f5        4                       0 instance 098b9ae4 _eventAndDelegateTable
506a0e94  40009f4      514         System.Int32  1   shared   static _nextAvailableTableIndex
    >> Domain:Value  086d3f38:NotInit  086daeb8:669 <<

then I dump the _eventAndDelegateTable:

Name:        System.Collections.Generic.Dictionary`2[[System.Int32, mscorlib],[MS.Internal.CoreTypeEventHelper+EventAndDelegate, System.Windows]]
MethodTable: 0bfcc0a0
EEClass:     5026c744
Size:        52(0x34) bytes
File:        C:\Program Files (x86)\Microsoft Silverlight\4.0.50524.0\mscorlib.dll
Fields:
      MT    Field   Offset                 Type VT     Attr    Value Name
5068f2d0  4000648        4       System.Int32[]  0 instance 098b9b18 buckets
50691060  4000649        8 ...non, mscorlib]][]  0 instance 098b9b30 entries
506a0e94  400064a       20         System.Int32  1 instance        1 count
506a0e94  400064b       24         System.Int32  1 instance        1 version
506a0e94  400064c       28         System.Int32  1 instance       -1 freeList
506a0e94  400064d       2c         System.Int32  1 instance        0 freeCount
50697f08  400064e        c ...Int32, mscorlib]]  0 instance 098b9650 comparer
506ccfb0  400064f       10 ...Canon, mscorlib]]  0 instance 00000000 keys
506ceaac  4000650       14 ...Canon, mscorlib]]  0 instance 00000000 values
506a02e4  4000651       18        System.Object  0 instance 00000000 _syncRoot
506895d8  4000652       1c ...SerializationInfo  0 instance 00000000 m_siInfo

And then I’m kind of lost!

Answer 1

Before attempting to find the relevant event handler, you could also search for the source of the leak by investigating why the DispatcherTimer instances doesn’t get released.
After you have the output of the !dumpheap -type DispatcherTimer, execute the !gcroot command on a couple of instances of DispatcherTimer. You should be able to see which object holds a reference to the timer.
Also, you could place appropriate breakpoints (using !bpmd), in order to obtain helpful stacktraces.