Memory management problem

[Brandon Langley]

I have this structure that I am using in conjunction with
NetLocalGroupAd dMembers:

[StructLayout(La youtKind.Sequen tial, CharSet=CharSet .Unicode)]
public struct LOCALGROUP_MEMB ERS_INFO_3
{
[MarshalAs(Unman agedType.LPWStr )] public string lgrmi3_domainan dname;
}

I am having failures that stinky hugely of either memory allocation being
incorrectly sized, or simply using the wrong allocation method. To test
this, I snipped the code somewhat and threw it into nUnit. This is what I
have:

/// <summary>
/// Hammers memory allocation to try to force a failure
/// </summary>
[Test]
public void TestMemoryAlloc ation()
{
System.Console. Write("\n\n");
System.Console. Write("Testing memory issue...\n");
for (int i=1; i<=15; i++)
{
System.Console. Write("Count: "+ i.ToString());
CatchAndRelease ();
System.Console. Write(".\n");
}
}

/// <summary>
/// Allocates and clears memory
/// </summary>
public void CatchAndRelease ()
{
try
{
LOCALGROUP_MEMB ERS_INFO_3 MemberToAdd;
LOCALGROUP_MEMB ERS_INFO_3[] MembersToAdd;
IntPtr bufPtr=IntPtr.Z ero;

// Initialize Variables
MemberToAdd.lgr mi3_domainandna me = "DOMAIN\\USERNA ME";
MembersToAdd = new LOCALGROUP_MEMB ERS_INFO_3[1] { MemberToAdd };

// Allocate memory and convert data into pointer
bufPtr =
Marshal.AllocHG lobal(Marshal.S izeOf(typeof(LO CALGROUP_MEMBER S_INFO_3)) *
MembersToAdd.Le ngth);
Marshal.Structu reToPtr(Members ToAdd[0], bufPtr, true);

// Free memory and zero out the pointer
Marshal.FreeHGl obal(bufPtr);
bufPtr = IntPtr.Zero;
}

catch (Exception e)
{
System.Windows. Forms.MessageBo x.Show("Excepti on thrown " + e.Message );

}
}
}

Seems to work okay with a repeat count of < 3. It either explodes or throws
an OutofMemoryExce ption when I repeat the fucntion 3 or more times.

If someone could educate me on whatever i'm doing wrong here, I would muchly
appreciate!

Thanks,
Brandon

[Martin Dechev]

Hi,

I tested your code and the bottleneck seems to be the call to
Marshal.Structu reToPtr. It seems to throw this exception when the pointer
points to an empty allocated buffer and you call it with fDeleteOld=true . I
can't explain where this exception comes from. I suppose they loop through
the managed references to see if there is a reference pointing to this
address and the exception is thrown in this loop. Maybe someone (MSFT) could
shed some light.

As it is stated in the remarks section in
http://msdn.microsoft.com/library/en...ToPtrTopic.asp
If not otherwise specified (read: if fDeleteOld=fals e) the function
allocates a new block of memory, fills it with the data in the passed
structure and hooks it up to the pointer. So here's the best I could come up
with:

// Allocate memory and convert data into pointer
// Here we just create a valid pointer:
IntPtr bufPtr = Marshal.AllocHG lobal(0);
// Call StructureToPtr with fDeleteOld=fals e
Marshal.Structu reToPtr(Members ToAdd[0], bufPtr, false);

Hope this helps
Martin Dechev
ASP.NET MVP
"Brandon Langley" <Br************ @discussions.mi crosoft.com> wrote in
message news:34******** *************** ***********@mic rosoft.com...

I have this structure that I am using in conjunction with
NetLocalGroupAd dMembers:

[StructLayout(La youtKind.Sequen tial, CharSet=CharSet .Unicode)]
public struct LOCALGROUP_MEMB ERS_INFO_3
{
[MarshalAs(Unman agedType.LPWStr )] public string lgrmi3_domainan dname;
}

I am having failures that stinky hugely of either memory allocation being
incorrectly sized, or simply using the wrong allocation method. To test
this, I snipped the code somewhat and threw it into nUnit. This is what I
have:

/// <summary>
/// Hammers memory allocation to try to force a failure
/// </summary>
[Test]
public void TestMemoryAlloc ation()
{
System.Console. Write("\n\n");
System.Console. Write("Testing memory issue...\n");
for (int i=1; i<=15; i++)
{
System.Console. Write("Count: "+ i.ToString());
CatchAndRelease ();
System.Console. Write(".\n");
}
}

/// <summary>
/// Allocates and clears memory
/// </summary>
public void CatchAndRelease ()
{
try
{
LOCALGROUP_MEMB ERS_INFO_3 MemberToAdd;
LOCALGROUP_MEMB ERS_INFO_3[] MembersToAdd;
IntPtr bufPtr=IntPtr.Z ero;

// Initialize Variables
MemberToAdd.lgr mi3_domainandna me = "DOMAIN\\USERNA ME";
MembersToAdd = new LOCALGROUP_MEMB ERS_INFO_3[1] { MemberToAdd };

// Allocate memory and convert data into pointer
bufPtr =
Marshal.AllocHG lobal(Marshal.S izeOf(typeof(LO CALGROUP_MEMBER S_INFO_3)) *
MembersToAdd.Le ngth);
Marshal.Structu reToPtr(Members ToAdd[0], bufPtr, true);

// Free memory and zero out the pointer
Marshal.FreeHGl obal(bufPtr);
bufPtr = IntPtr.Zero;
}

catch (Exception e)
{
System.Windows. Forms.MessageBo x.Show("Excepti on thrown " + e.Message );

}
}
}

Seems to work okay with a repeat count of < 3. It either explodes or throws an OutofMemoryExce ption when I repeat the fucntion 3 or more times.

If someone could educate me on whatever i'm doing wrong here, I would muchly appreciate!

Thanks,
Brandon