Stands for User Mode Dump Heap

Can be downloaded for free as part of the Windows 7 SDK (also works for Windows XP)

Helps you to find memory leaks in running processes!

1. Set the _NT_SYMBOL_PATH environment var to:

2. Append the path to your executable

srv*c:\symbols*http://msdl.microsoft.com/download/symbols;

1. Flag your process under test as being monitored:

2. Start your process under test:

3. Take an initial “snapshot” of allocated memory as Test.exe runs:

C:> gflags -i Test.exe +ust

C:> umdh -pn:Test.exe -f:C:\f1.txt

C:> Test.exe

4. Exercise your program in a way that you think may make it leak memory.

5. Take a second snapshot and save it with a different file name from the first.

6. Use UMDH to “diff” the first and last snapshots taken to get the best idea of what has leaked

C:> umdh -d f1.txt f2.txt > f12.txt

C:> umdh -pn:Test.exe -f:C:\f2.txt

The “diff” file shows a stack trace, and the

number/size of allocations that were allocated but not freed between two snapshots.

+ 483328 ( 487424 - 4096) 119 allocs BackTrace23FF

+ 118 ( 119 - 1) BackTrace23FF allocations

ntdll!RtlDebugAllocateHeap+000000E1

ntdll!RtlAllocateHeapSlowly+00000044

ntdll!RtlAllocateHeap+00000E64

kernel32!FindNextFileW+00000077

kernel32!FindNextFileA+00000028

MSVCR80D!findnext64i32+00000178

Test!readdir+00000075 (c:\myproject\util.cpp, 674)

…

+ 483328 ( 487424 - 4096) 119 allocs BackTrace23FF

+ 118 ( 119 - 1) BackTrace23FF allocations

ntdll!RtlDebugAllocateHeap+000000E1

ntdll!RtlAllocateHeapSlowly+00000044

ntdll!RtlAllocateHeap+00000E64

kernel32!FindNextFileW+00000077

kernel32!FindNextFileA+00000028

MSVCR80D!findnext64i32+00000178

Test!readdir+00000075 (c:\myproject\util.cpp, 674)

…

Bytes “leaked” between the two snapshots

Stacktrace showing where the “leaked”

memory was allocated.

At the very bottom of the file, there is an overall summary of how much memory was allocated but not freed. E.g.:

If used as part of an automated test, it is fairly easy to extract the “Total increase” number using a Perl script and graphs of memory allocations and usage over time.

Total increase == 13919896 requested + 830364 overhead = 14750260

UMDH is a useful tool for finding memory leaks in Windows applications.

Its output is a file listing outstanding memory allocations that can be read directly, or processed by another program or script.

http://msdn.microsoft.com/en-us/library/ff558947%28v=vs.85%29.aspx