Dr. Memory identifies Windows handles that are left open and reports them as handle leaks. The type of handle (kernel, user, or GDI) is listed along with the callstack where it was opened. For example:

Error #1: HANDLE LEAK: KERNEL handle 0x000000a8 and 1 similar handle(s) were opened but not closed:
# 0 system call NtOpenFile
# 1 KERNELBASE.dll!FindFirstFileExW     (0x751ca6bc <KERNELBASE.dll+0x1a6bc>) modid:7
# 2 KERNELBASE.dll!FindFirstFileA       (0x751caaf7 <KERNELBASE.dll+0x1aaf7>) modid:7
# 3 test_file_handles       [d:\src\cygwin\home\zhaoqin\workspace\drmemory\drmemory.git\tests\handle.cpp:107] (0x010a14f7 <handle.exe+0x14f7>) modid:1
# 4 main                    [d:\src\cygwin\home\zhaoqin\workspace\drmemory\drmemory.git\tests\handle.cpp:239] (0x010a11f3 <handle.exe+0x11f3>) modid:1
Note: @0:00:03.232 in thread 7196
Note: handles created with the same callstack are closed here:
Note: # 0 system call NtClose
Note: # 1 KERNELBASE.dll!FindClose      (0x751ca46d <KERNELBASE.dll+0x1a46d>) modid:7
Note: # 2 test_file_handles [d:\src\cygwin\home\zhaoqin\workspace\drmemory\drmemory.git\tests\handle.cpp:169] (0x010a16a7 <handle.exe+0x16a7>) modid:1
Note: # 3 main              [d:\src\cygwin\home\zhaoqin\workspace\drmemory\drmemory.git\tests\handle.cpp:239] (0x010a11f3 <handle.exe+0x11f3>) modid:1

Another common example of a handle leak error is calling DuplicateHandle and passing NULL as TargetHandle. This will be reported as:

Error #2: HANDLE LEAK: Syscall NtDuplicateObject leaks handle with NULL handle pointer in its own process 0xffffffff.
# 0 system call NtDuplicateObject
# 1 KERNELBASE.dll!DuplicateHandle             (0x751bc4d9 <KERNELBASE.dll+0xc4d9>) modid:7
# 2 KERNEL32.dll!DuplicateHandleImplementation (0x753118a2 <KERNEL32.dll+0x118a2>)  modid:9
# 3 test_file_handles  [d:\src\cygwin\home\zhaoqin\workspace\drmemory\drmemory.git\tests\handle.cpp:157] (0x010a163d <handle.exe+0x163d>) modid:1
# 4 main               [d:\src\cygwin\home\zhaoqin\workspace\drmemory\drmemory.git\tests\handle.cpp:239] (0x010a11f3 <handle.exe+0x11f3>) modid:1

Detection of these errors can be disabled with the -no_check_handle_leaks runtime option.

Handle leak detection is currently an experimental feature, tuned conservatively with a filter on the error to avoid false positives. Call stacks with system libraries at the top, or handle leaks that do not occur very often, are not reported in the main list of errors. The full list of suspected handle leaks can be found in potential_errors.txt (see Application Versus System Library Errors). In the future we hope to improve the distinction between application and system handle leaks and directly report all relevant errors.