FIX: Memory Leak Reported in PLEX.CPP When Using CSocket

The information in this article applies to:

• The Microsoft Foundation Classes (MFC) included with: Microsoft Visual C++, 32-bit Edition, versions 2.1 and 2.2

SYMPTOMS

Running an application that uses the CSocket class causes a memory leak report to be generated when the application exits. The memory leak report will be similar to this:

   {1555} plex.cpp(28) : non-object block at $002ECC8C, 132 bytes long

CAUSE

The CSocket class will queue up socket notification messages while it waits for a particular socket operation to complete. These messages are stored in CPtrList (m_listSocketNotifications) on a per-thread basis. This object is destroyed when the thread-state information for that thread is cleaned-up. Unfortunately the thread-state information for the primary thread is not cleaned-up until after the memory leak detection is performed.

Because MFC does not take care to free the plex objects associated with this list before the list is destroyed, the perceived memory leak is reported.

Because the problem is related to the frequency and sequence of the socket notification messages being received, the memory leak message might not occur every time the program is executed. It might only be seen under certain circumstances.

RESOLUTION

This message will only occur when CSocket objects are used in the primary thread. The message can be safely ignored because the m_listSocketNotifications object is actually being safely deleted before the application exits, so the memory will be freed then.

STATUS

Microsoft has confirmed this to be a bug in the Microsoft products listed at the beginning of this article. This problem was fixed in Microsoft Visual C++, 32-bit Edition, version 4.0.