EnterCriticalSection() is corrupting my heap

[Arsalan Ahmad]

Hi all,

I have developed a static library which I am using in one of my application.
In my library I have created my own heap and all the objects (class objects)
in my application are created in that heap. What I have observed is that in
my library at a certain place when I call EnterCriticalSection() to an
object allocated at my heap, it is corrupting my heap. I am using Windows XP
and visual studio 8.0. Any hint how can I solve this problem?

Thanks,

Arsalan

[Oleg Starodumov]

I have developed a static library which I am using in one of my application.
In my library I have created my own heap and all the objects (class objects)
in my application are created in that heap. What I have observed is that in
my library at a certain place when I call EnterCriticalSection() to an
object allocated at my heap, it is corrupting my heap. I am using Windows XP
and visual studio 8.0. Any hint how can I solve this problem?

How exactly do you create and use the heap?
Do you use HeapCreate/HeapAlloc/etc., or some other approach?
How do you detect the heap corruption?
How do you allocate memory for the CRITICAL_SECTION structure?
How do you pass this CRITICAL_SECTION to EnterCriticalSection?

Code samples would be helpful.

Regards,
Oleg
[VC++ MVP http://www.debuginfo.com/]

[Arsalan Ahmad]

Hi,

Yes i use HeapCreate() and HeapAlloc().

I have a class object which is created on the heap and I have a member
variable in this class of type CRITICALSECTION (say m_cs). Inside one of my
class function when I call EnterCriticalSection(&m_cs) then this problem
occurs. Ok may be its not because of critical section because at the place
in code where EnterCriticalSection() was being called I create and
CAutoLock() object and pass my pointer to CRITICALSECTION object to it
(CAutoLock just call EnterCriticalSection in its constructor and
LeaveCriticalSection in its destructor). In the constructor when I try to
save pointer of critical section to the class member (CRITICALSECTION
*m_pCS) of CAutoLock then although it is pointer assignment but after
assignement the class member has some garbage data.

In my outside code:

{
CAutoLock(&m_cs);

// Some code
}

CAutoLock::CAutoLock(CRITICALSECTION *pCS)
{
m_pCS = pCS; <= This assignement is not working correctly and after
assignment m_pCS points to some garbage memory location
EnterCriticalSection(m_pCS);
}

So any idea what is wrong?

Thanks,

Arsalan


Any idea whats wrong?
"Oleg Starodumov" <com-dot-debuginfo-at-oleg> wrote in message
news:es**************@TK2MSFTNGP03.phx.gbl...

I have developed a static library which I am using in one of my
application.
In my library I have created my own heap and all the objects (class
objects)
in my application are created in that heap. What I have observed is that
in
my library at a certain place when I call EnterCriticalSection() to an
object allocated at my heap, it is corrupting my heap. I am using Windows
XP
and visual studio 8.0. Any hint how can I solve this problem?

How exactly do you create and use the heap?
Do you use HeapCreate/HeapAlloc/etc., or some other approach?
How do you detect the heap corruption?
How do you allocate memory for the CRITICAL_SECTION structure?
How do you pass this CRITICAL_SECTION to EnterCriticalSection?

Code samples would be helpful.

Regards,
Oleg
[VC++ MVP http://www.debuginfo.com/]

[Oleg Starodumov]

In my outside code:

{
CAutoLock(&m_cs);

// Some code
}

CAutoLock::CAutoLock(CRITICALSECTION *pCS)
{
m_pCS = pCS; <= This assignement is not working correctly and after
assignment m_pCS points to some garbage memory location
EnterCriticalSection(m_pCS);
}

So any idea what is wrong?

There can be a problem with the way the function is called (I mean the function
that instantiates CAutoLock object). It could be that it is called via a bad object
pointer, as a result "this" pointer passed to the function contains wrong value,
and so on. The next time you reproduce the problem, take a look at the value
of "this" passed to that function, and check if it's correct.

I mean something like this:

class CObj
{
...
CRITICAL_SECTION m_cs;
void YourFunc(); // instantiates CAutoLock and passes it &m_cs
}

CObj pObj; // not initialized, for example
pObj->YourFunc(); // when it is called, "this" pointer is bad, and thus pointers to
// its data members will also be bad

Generic safety checks for heap corruptions with PageHeap would not harm too,
try to enable it as described here:
http://www.debuginfo.com/tips/userbpntdll.html

Oleg

[Arsalan Ahmad]

As far as CAutoLock is concerned, I am creating its object in stack as
follows:

{
CAutoLock lock(&m_cs);

// Some code
}

So still no idea what is wrong.

Regards,

Arsalan

"Oleg Starodumov" <com-dot-debuginfo-at-oleg> wrote in message
news:O6**************@TK2MSFTNGP04.phx.gbl...

In my outside code:

{
CAutoLock(&m_cs);

// Some code
}

CAutoLock::CAutoLock(CRITICALSECTION *pCS)
{
m_pCS = pCS; <= This assignement is not working correctly and after
assignment m_pCS points to some garbage memory location
EnterCriticalSection(m_pCS);
}

So any idea what is wrong?

There can be a problem with the way the function is called (I mean the
function
that instantiates CAutoLock object). It could be that it is called via a
bad object
pointer, as a result "this" pointer passed to the function contains wrong
value,
and so on. The next time you reproduce the problem, take a look at the
value
of "this" passed to that function, and check if it's correct.

I mean something like this:

class CObj
{
...
CRITICAL_SECTION m_cs;
void YourFunc(); // instantiates CAutoLock and passes it &m_cs
}

CObj pObj; // not initialized, for example
pObj->YourFunc(); // when it is called, "this" pointer is bad, and thus
pointers to
// its data members will also be bad

Generic safety checks for heap corruptions with PageHeap would not harm
too,
try to enable it as described here:
http://www.debuginfo.com/tips/userbpntdll.html

Oleg

[Oleg Starodumov]

As far as CAutoLock is concerned, I am creating its object in stack as
follows:

{
CAutoLock lock(&m_cs);

// Some code
}

So still no idea what is wrong.

No, I mean the function that instantiates CAutoLock. E.g. if it is:

void SomeClass::SomeFunc()
{
CAutoLock lock(&m_cs);
// Some code
}

Check "this" pointer passed to SomeClass::SomeFunc, and how
the object of SomeClass is instantiated. (E.g. use Call Stack window
to activate the previous frame on the stack, and inspect "this"
in Watch window).

Oleg

[Arsalan Ahmad]

Still no luck. Just one assignment statement inside the constructor (in
which i am assigning one pointer to another is not working) and if i dont
use CAutoLock class at all then at the same line when EnterCriticalSeciton()
statement executes another pointer gets garbage value. This is the time when
I really think about switching to .NET but I cannot :(.

Regards,

Arsalan
"Oleg Starodumov" <com-dot-debuginfo-at-oleg> wrote in message
news:OB**************@TK2MSFTNGP05.phx.gbl...

As far as CAutoLock is concerned, I am creating its object in stack as
follows:

>> {
>> CAutoLock lock(&m_cs);
>>
>> // Some code
>> }

So still no idea what is wrong.

No, I mean the function that instantiates CAutoLock. E.g. if it is:

void SomeClass::SomeFunc()
{
CAutoLock lock(&m_cs);
// Some code
}

Check "this" pointer passed to SomeClass::SomeFunc, and how
the object of SomeClass is instantiated. (E.g. use Call Stack window
to activate the previous frame on the stack, and inspect "this"
in Watch window).

Oleg

[Stephen Kellett]

In message <eA**************@TK2MSFTNGP04.phx.gbl>, Arsalan Ahmad
<ar*****@hotmail.com> writes

CAutoLock::CAutoLock(CRITICALSECTION *pCS)
{
m_pCS = pCS; <= This assignement is not working correctly and after
assignment m_pCS points to some garbage memory location
EnterCriticalSection(m_pCS);
}

Do you call InitializeCriticalSection() anywhere? You must call this
once before you try entering the critical section. Doesn't look to me
like you are using MFC's CCriticalSection wrapper, so I assume you are
using the raw Win32 object. Hence you need to initialize it.

VOID InitializeCriticalSection(
LPCRITICAL_SECTION lpCriticalSection // critical section
);

Thread Validator from Software Verification would have identified this
error if you had run your code through it.

http://www.softwareverify.com/thread...tor/index.html

Stephen
--
Stephen Kellett
Object Media Limited http://www.objmedia.demon.co.uk/software.html
Computer Consultancy, Software Development
Windows C++, Java, Assembler, Performance Analysis, Troubleshooting

[Oleg Starodumov]

Still no luck. Just one assignment statement inside the constructor (in
which i am assigning one pointer to another is not working) and if i dont use CAutoLock class at all then at the same
line when EnterCriticalSeciton() statement executes another pointer gets garbage value. This is the time when I really
think about switching to .NET but I cannot :(.

Run the application under debugger and stop at the following line:

{
CAutoLock lock(&m_cs); <== STOP HERE
// Some code
}

Enter "this" into Watch window. What value will be shown?

Then F11 (step into) CAutoLock constructor:

CAutoLock::CAutoLock(CRITICALSECTION *pCS)
{
m_pCS = pCS;
EnterCriticalSection(m_pCS); <== STOP HERE
}

Enter "m_pCS" into Watch window. What value will be shown?

Oleg

[Doug Harrison [MVP]]

On Wed, 24 May 2006 15:19:27 +0200, "Arsalan Ahmad" <ar*****@hotmail.com>
wrote:

Hi,

Yes i use HeapCreate() and HeapAlloc().

I have a class object which is created on the heap and I have a member
variable in this class of type CRITICALSECTION (say m_cs). Inside one of my
class function when I call EnterCriticalSection(&m_cs) then this problem
occurs. Ok may be its not because of critical section because at the place
in code where EnterCriticalSection() was being called I create and
CAutoLock() object and pass my pointer to CRITICALSECTION object to it
(CAutoLock just call EnterCriticalSection in its constructor and
LeaveCriticalSection in its destructor). In the constructor when I try to
save pointer of critical section to the class member (CRITICALSECTION
*m_pCS) of CAutoLock then although it is pointer assignment but after
assignement the class member has some garbage data.

In my outside code:

{
CAutoLock(&m_cs);

// Some code
}

CAutoLock::CAutoLock(CRITICALSECTION *pCS)
{
m_pCS = pCS; <= This assignement is not working correctly and after
assignment m_pCS points to some garbage memory location
EnterCriticalSection(m_pCS);
}

So any idea what is wrong?

I see you corrected the above in a subsequent message, but it's worth
mentioning that the following will indeed compile, but it won't do what you
want:

{
CAutoLock(&m_cs);

// Some code
}

This will just create a temporary CAutoLock object and immediately destroy
it, so the code which follows it in the block will not execute in a
critical section.

--
Doug Harrison
Visual C++ MVP