Re: Memory leak with CAsyncSocket::Create

r norman <>
Tue, 10 Jul 2007 13:08:46 -0400
On Tue, 10 Jul 2007 11:45:00 -0500, "AliR \(VC++ MVP\)"
<AliR@online.nospam> wrote:

Incidentally, the first time I create and delete CAsyncSocket, it uses
312K of system memory. After that it uses only 1K each time. I am
not concerned about one-time memory usage, only about continuous
nibbles eating away system memory.

hummm, I ran a sample that created 1000 sockets and closed them. The memory
usage went up 1 Meg, I watched it for an hour to see when the memory would
be released, it didn't.

I put a call to WSACleanup right after the loop and no more increase in
memory. Seems like whatever memory is allocated by the sockets gets cleaned
up on after WSACleanup is called!

Ok I'm baffled.


"r norman" <> wrote in message

On Tue, 10 Jul 2007 10:33:26 -0500, "AliR \(VC++ MVP\)"
<AliR@online.nospam> wrote:

As far as the memory being returned, it will eventually, when the system
thinks that the program won't need it anymore.
With the example I posted, before the loop my sample app is using 3676K of
memory after the loop the program is using 4024K of memory but there is no
memory leak.

As far as Create not being reentrant goes, I am not really sure what could
be causing that. There are some many possibilities as to why it doesn't
work the way he wants it. Is Close being called before the next call to
Create? Is the socket being passed from one thread to another? Maybe
a corrupted install of Visual Studio.

I think that the OP should try and recreate the problem with one socket in
the main thread. And go from there.

I responded to Joe's post about the concurrency problem and explained
what I was doing there. It was multiple instances of CAsyncSocket
that was the problem, not successive Creates on the same instance or
sockets shared between threads. And I found a workaround by
serializing the calls to Create so I left it at that.

I still worry about Windows memory management and whether it is solid
enough to support embedded programs that run continuously for month
after month. I know for a fact that older versions of Visual C
programs (version 3.0 or 4.0 if my memory serves me well) running on
16 bit MS-DOS failed miserably -- memory became so fragmented that it
was unusable even if the total available byte count was maintained. At
that time, I had to go to a commercial third party memory manager. I
only reluctantly migrated from C to C++ because of my fears of the
object oriented code's proclivity to create and delete objects at
will, thereby stressing the memory manager to its limits. My roots
are in 8 bit embedded systems with really severe memory constraints
and I still have a probably unfounded fear of that problem.


"Joseph M. Newcomer" <> wrote in message

I would have thought it *would* be returned.

I'm also concerned about the concurrency problem, because I've not seen
that particular
problem in MFC before. I'm wondering if there is some storage damage
is causing both
apparent problems.

On Tue, 10 Jul 2007 09:45:46 -0500, "AliR \(VC++ MVP\)"
<AliR@online.nospam> wrote:

I couldn't find a memory leak. What you are most likely seeing is
memory managment doing its work. The Create method is creating a socket
object, when when it's freed the memory is not given back to the system
right away.

(I used this method to detect a leak)

// Declare the variables needed
#ifdef _DEBUG
  CMemoryState oldMemState, newMemState, diffMemState;

  for (int i=0; i<10; ++i)
     CAsyncSocket *pAS = new CAsyncSocket;
     delete pAS;

#ifdef _DEBUG
  if( diffMemState.Difference( oldMemState, newMemState ) )
     TRACE( "Memory leaked!\n" );


"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.)

I have Visual Studio 2005 Professional version 8.0.

Incidentally, I also discovered that the call to Create() is not
re-entrant. My application involves connecting to some 10 to 20
external devices and my normal code creates a CWinThread to support
each socket, where the socket is created and destroyed only within
the thread routine. Creating all the threads and starting them up
simultaneously meant having multiple instances of
CAsyncSocket::Create() being called at the same time, crashing my
system (memory access faults). That one I found and fixed with
sentries. Now I am left with the memory leak.

The problem is that I have an rather intricate communication protocol
system all self contained so that adding a new hardware device simply
means creating a new instance of the whole works. It runs fine until
the external hardware goes haywire, in which case I destruct the whole
instance and start a new one which breaks and reconnects the socket
with a clean start and, most of the time, results in a good
connection; the external device resets itself through the disconnect.
One faulty device, though, generated thousand upon thousand of
disconnects over a number of days and, after a few hundred thousand of
these I my own system crashed due, I have now found out, to a lack of
memory caused by this leak.

My application must run essentially as an embedded system, unattended
week after week, month after month so I cannot tolerate a memory leak.
Does anybody know about this? Is there a simple clean way to force a
socket disconnection on a CAsyncSocket and then reconnect? My
application is the connect() end of the socket, not the listen() end.

Joseph M. Newcomer [MVP]
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