[mapguide-internals] Found at least one memory leaks in Mapguide API

Bruno Scott bscott at geomapgis.com
Wed Jul 8 04:20:50 EDT 2009

I found the big one, but i will need some help to fix it.
Let me explain what is happening
I will describe the problem with the m_toolbar member but the same problem
apply to m_taskPane and m_contextMenu

There is a relationship between 

m_toolbar contains a collection of MgWebWidget
m_commands is a collection of MgWebCommand
m_cmdWidgets is a map of MgWebCommandWidget
MgWebCommandWidget is derived from MgWebWidget plus a MgWebCommand

After the first step for parsing a weblayout 
  - m_commands contains all MgWebCommand with refcount = 1
  - m_toolbar contains all MgWebWidget with refcount = 1
  - m_cmdWidgets contains all MgWebCommandWidget with refCount = 1 and
MgWebCommand = null
The last step is to 
  - loop on each MgWebCommandWidget of the m_cmdWidgets 
      - find the MgWebCommand in the m_commands
      - Copy this MgWebCommand into the MgWebCommandWidget (MgWebCommand
refcount becomes 2)
  - Finally clear the m_cmdWidgets 

When Disposing the WebLayout
  m_commands will be also disposed , this set all MgWebCommand refcount to 1
  m_cmdWidgets is already cleared
  and when m_toolbar is disposed it's the MgWebWidget destructor that is
actually called, leaving the underneath MgWebCommand not disposed.

There is many ways to fixe this Leak

First Idea
    this is the actual code that leaks
    for( all items in m_cmdWidgets )
        Ptr<MgWebCommand> cmd = m_commands->GetItem(cmdName);
    It's the GetItem that increment the refCount, so we could decrease it
    for( all items in m_cmdWidgets )
        Ptr<MgWebCommand> cmd = m_commands->GetItem(cmdName);
    it's simple but not a very clean solution

Second idea
  the m_toolbar member could be a MgWebCommandWidgetCollection instead of a
  So the destruction of the m_toobar would fire the desctructions of all
underneath WebCommand.
  This would require more work as we need to create a new class
(MgWebCommandWidgetCollection )

There is probably other way for fixing this.


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