Re: Memory leak with CAsyncSocket::Create

"Doug Harrison [MVP]" <>
Tue, 10 Jul 2007 20:50:33 -0500
On Tue, 10 Jul 2007 13:45:46 -0700, "Michael K. O'Neill"
<> wrote:

"r norman" <> wrote in message

I have traced a memory leak problem to CAsyncSocket::Create(). Is
this a known problem? Is there a workaround/solution/fix? Here is
sample code:

  for (int i=0; i<m_nReopenCount; ++i) {
    CAsyncSocket *pAS = new CAsyncSocket;
    delete pAS;

Running this 1000 times uses up 1200 KBytes of memory, or just over 1
KByte per call. Commenting out the Create() leaves memory clean. (And
please don't complain about my bracketing style -- I like it.)

This is a known problem, acknowledged by Microsoft.

Apparently, when using CAsyncSocket in a GUI app that also has XP visual
styles (themes), there is a memory leak. The problem seems to be
OS-dependent, and it might exist only under XP (running themes). It did not
manifest itself under Win 2000, and it might be gone now from Vista.

For one report, see "CSocket Consuming Memory Uncontrollably" at . I am fairly certain
that this is the same problem that you are seeing, since this report also
includes the exact same number for the amount of leaked memory (i.e., 1200
bytes per call to Create()).

There is a parallel posting in the newsgroups at "HELP!! CSocket and
CAsyncSocket Consumes Memory Uncontrollably" in the
microsoft.public.win32.programmer.networks newsgroup, at

The "solution", if you can call it that, is to disable themes. See
"CAsynCSocket Memory Leak Fix" at

Interesting! The problem appears to be the creation of a top-level,
non-child window by CAsyncSocket::AttachHandle. For example, if I replace
norman's loop body with the following, I observe the same "leak" in Process

      CWnd* p = new CSocketWnd;
#if 1
      p->CreateEx(0, AfxRegisterWndClass(0), 0,
            WS_OVERLAPPED, CRect(), 0, 0);
      p->Create(AfxRegisterWndClass(0), 0,
            WS_CHILD, CRect(), AfxGetMainWnd(), 0);
      delete p;

If I use #if 0, a child window is created instead, and I don't observe the

Doug Harrison
Visual C++ MVP

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