COM provides
IMalloc,
IMallocSpy,
Experiment shows that on Windows 2000/XP some memory still remains
allocated even after COM has been shut down by calling
Behavior on Windows XP is the same.
This makes detection of COM memory leaks difficult. At no moment in our program we can say "OK, all COM memory should be released by now. If anything is not released, it is definitely a leak".
Life used to be easier on Windows NT. On Windows NT
Windows 2000 introduces a new system DLL named clbcatq.dll.
This DLL is loaded by COM runtime when you call clbcatq.dll
startup code located in clbcatq.dll
shutdown code, also in
The caveat is that clbcatq.dll! This appears to contradict
statements from
CoUninitialize
closes the COM library on the current thread,
unloads all DLLs loaded by the thread, frees any other
resources that the thread maintains, and forces all
RPC connections on the thread to close.
|
Anyway, clbcatq.dll DLL gets unloaded
by
MallocSpyTest is a console application.
It tries to create an instance of a COM coclass specified on the command
line. It also implements IMallocSpyinterface and prints
to standard output information about all COM alocations and deallocations.
After
Test project can be invoked as follows:
MallocSpyTest ADODB.Recordset
You can use any COM coclass you like instead of ADODB.Recordset.
C:\TEMP>MallocSpyTest.exe ADODB.Recordset CoInitialize() returns 0x00000000 CoRegisterMallocSpy() returns 0x00000000 CLSIDFromProgID() returns 0x00000000 MALLOC SPY: 0x00139E90 - 216 bytes allocated MALLOC SPY: 0x00138650 - 16 bytes allocated MALLOC SPY: 0x00139F70 - 16 bytes allocated CoCreateInstance() returns 0x00000000 Object released MALLOC SPY: 0x00138650 - freed, 2 blocks remaining MALLOC SPY: 0x00139F70 - freed, 1 blocks remaining MALLOC SPY: 0x00139E90 - freed, 0 blocks remaining Called CoUninitialize() CoRevokeMallocSpy() returns 0x00000000 C:\TEMP> |
However, results on Windows 2000 are astonishing:
C:\Ivan\cpp\MallocSpyTest>MallocSpyTest ADODB.Recordset CoInitialize() returns 0x00000000 CoRegisterMallocSpy() returns 0x00000000 MALLOC SPY: 0x0013BBB0 - 28 bytes allocated more allocations... CLSIDFromProgID() returns 0x00000000 [...] CoCreateInstance() returns 0x00000000 Object released [...] MALLOC SPY: 0x0013C150 - freed, 18 blocks remaining [...] Called CoUninitialize() CoRevokeMallocSpy() returns 0x80070005 MALLOC SPY: detected memory leaks! 0x0013A8F8 - 44 bytes: 98 B1 5A 77 08 BC 13 00 01 00 00 00 01 00 11 00 ..Zw............ more leaks... MALLOC SPY: 0x0013C0C0 - freed, 11 blocks remaining [...] MALLOC SPY: 0x0013BED0 - freed, 1 blocks remaining |
Take a note of two things:
CoUninitialize() CoRevokeMallocSpy() 0x8007005 which stands for E_ACCESSDENIED. I.e., we are
not allowed to revoke the spy, despite the fact that COM has been shut down. This obviously
makes using spy very problematic.
Since our spy continues to work while the program is being
terminated, and continues to call MallocSpyTest to a file (as in
MallocSpyTest ADODB.Recordset >out.txt ),
last lines of output won't go to the file.
Results on XP are similar to those on 2000, main difference is more allocations.