C / C++ / MFC

Calling DLL method from multi-thread

8-Dec-17 7:48

This class may provide all the functionality of a DDV macro

shakumar_215-Dec-17 23:23

shakumar_21

5-Dec-17 23:23

HI,
I'm updating my C++ application in to multi thread application in VisualStudio 2013.
In main(), thread's was created by CreateThread()and inside the thread's classA ObjA(); was created & called the function.
In the classA it call another dll method.
Dll was include in to the project through properties->Linker.

Problem was when objA called dll method , application throws access violation reading location.
But without multi-thread it works normal.

Accessing dll method from multi-thread is same way as normal or any other things needed for accessing.

Thanks in Advance.

Re: Calling DLL method from multi-thread

Richard MacCutchan5-Dec-17 23:54

Richard MacCutchan

5-Dec-17 23:54

You need to use the debugger to check exactly what caused the access violation. Are you sure the DLL is totally thread-safe?

Re: Calling DLL method from multi-thread

Victor Nijegorodov6-Dec-17 8:23

Victor Nijegorodov

6-Dec-17 8:23

What is a type of your project?
What is a type of a DLL?

Why -nan values appear

User 135094504-Dec-17 6:49

User 13509450

4-Dec-17 6:49

I perform some experiments with the cpp code and I got -nan values. Can anybody tell why I might get these values

modified 29-Jan-21 21:01pm.

Jochen Arndt4-Dec-17 7:01

Jochen Arndt

4-Dec-17 7:01

Because the math operations performed by your code result in a NaN?
You cast an integer with at least the relevant most signficant bits set to float or double?
You have a buffer overflow writing such a value to the memory of a float or double?

Without seeing code, we can't tell you for sure.

k50544-Dec-17 7:05

k5054

4-Dec-17 7:05

2 most likely reasons:

Invalid math e.g. division by zero, or use of uninitialized variables. Without seeing your code, and input, we can't know.

Peter_in_27805-Dec-17 12:50

Peter_in_2780

5-Dec-17 12:50

ahem... Division by zero in general produces a (signed) Inf, not a NaN.

Software rusts. Simon Stephenson, ca 1994. So does this signature. me, 2012

David Crow4-Dec-17 8:58

David Crow

4-Dec-17 8:58

Because what ever you are doing, the result is not a number.

"One man's wage rise is another man's price increase." - Harold Wilson

"Fireproof doesn't mean the fire will never come. It means when the fire comes that you will be able to withstand it." - Michael Simmons

"You can easily judge the character of a man by how he treats those who can do nothing for him." - James D. Miles

CPallini4-Dec-17 22:26

CPallini

4-Dec-17 22:26

Have a look at IEEE 754-1985 - Wikipedia[^].

Storage Allocation

ForNow3-Dec-17 6:13

3-Dec-17 6:13

Hi
I have some questions regarding storage allocations. I know there is default heap value every exe or DLL gets. You can make that bigger or smaller /HEAP

I am guessing this is where the "new" operator gets storage.

using GetProcessHeap gets storage from this heap

If I don't want to bump heads with that I do a HeapAlloc initially the three paramters all zeros

But I "THINK" even if I do a HeapAlloc for 20 byes it really gets 1K

if I see that during my processing I need more I do a HeapRealloc using the same pointer for return value and 1st parameter I get more storage

I don't know if this better than using new

would anyone have any input ?

CPallini3-Dec-17 9:35

CPallini

3-Dec-17 9:35

There are differences between HeapAlloc and new (and malloc).
See, for instance:
Comparing Memory Allocation Methods (Windows)[^].
new operator - How do you 'realloc' in C++? - Stack Overflow[^].
c++ - malloc() vs. HeapAlloc() - Stack Overflow[^].

jschell5-Dec-17 11:51

jschell

5-Dec-17 11:51

ForNow wrote:
But I "THINK" even if I do a HeapAlloc for 20 byes it really gets 1K

I don't know if this better than using new

There is a very specific reason for using HeapAlloc and nothing you posted suggests you need that.

And not a good idea to attempt to circumvent C++ compiler allocations unless you have identified a specific need and you understand exactly how allocations work.

If you have some limited need or just want to mess around then you can override allocations for a specific class (one class only) and control it in fine detail. And do so knowing that you are not as likely to mess up the rest of the application doing it.

Alternatively find several open source allocators and heaps and examine how they are implemented first to understand what happens with heaps.

Keep in mind that if you do attempt to control your own allocations you can completely destroy the application (runtime) because you can end up overwriting memory that has nothing to do with what you think it should. So do it very carefully.

ForNow5-Dec-17 12:52

5-Dec-17 12:52

The run time has it own heap I think the default heap

When I create my heap I’m segragting the allocations

jschell8-Dec-17 6:58

jschell

8-Dec-17 6:58

ForNow wrote:
The run time has it own heap I think the default heap

Modern OSes generally have at least two allocators. So in C++ the OS provides space to the app and then C++ itself manages that heap with its own allocator. Same is true for Java and C#.

ForNow wrote:
When I create my heap I’m segragting the allocations

Not sure that what that means.

An heap already represents a segregation. The C++ heap (every one I have looked at going back decades) dynamically manages blocks that it requested from the OS. Then on top of that it lays down a simple (or even complex) traditional heap. Then when you use 'new' (presuming you do not otherwise provide an allocator) it uses that existing API to request an amount of space appropriate for usage. Generally the allocation is exact to the structure.

The structure might have padding but that is intrinsic to the structure and not the allocation.

ForNow8-Dec-17 8:08

8-Dec-17 8:08

New works well when you now Exactly howvmuch storage you want I.e a object or class

In my case I am capturing user input and not quite sure thus HeapReAlloc

Exception in CListBox::Addstring

jschell8-Dec-17 13:07

jschell

8-Dec-17 13:07

ForNow wrote:
New works well when you now Exactly howvmuch storage you want I.e a object or class

That is not true.

For an object in C++ you must ALWAYS allocate at least as much space is needed for the object. You can allocate more but it will be wasted.

One can force C++ to use space that is less but that would be nothing but bad programming.

ForNow wrote:
In my case I am capturing user input and not quite sure thus HeapReAlloc

All that means is that you are dynamically allocating the space. Which is something that C++ allows directly. You do not need to use a system API method to do that.

As I previously pointed out HeapReAlloc has a specific purpose. And what you just described here is an inappropriate use of that. And one that could lead to resource (memory) starvation if you are not careful how you use it.

ForNow1-Dec-17 2:07

1-Dec-17 2:07

My Addstring works fine its in OinitDialog

except when I make it ownerdraw then I get an exception however even out it I mean Addstring

DrawItem never gets control

Jochen Arndt1-Dec-17 2:47

Jochen Arndt

1-Dec-17 2:47

It would be helpful to know which kind of exception and where it occurs.

However, has your owner drawn list box also the LBS_HASSTRINGS style?
If not, that is probably the reason:

LB_ADDSTRING message (Windows)[^]:
If the list box has an owner-drawn style but not the LBS_HASSTRINGS style, this parameter is stored as item data instead of a string. You can send the LB_GETITEMDATA and LB_SETITEMDATA messages to retrieve or modify the item data.

ForNow1-Dec-17 2:58

1-Dec-17 2:58

I have that "LBS_HASSSTRINGS" actually just stepping thru the code on ClistBox::AddString the VS debugger

comes up with a DialogBox "BreakPoint hit" a message indicating some sort of exception

I am wondering if I cannt do AddString in OnitDialog for a OwneDraw litbox ?

Jochen Arndt1-Dec-17 4:18

Jochen Arndt

1-Dec-17 4:18

Calling AddString() itself should not raise an exception (provided that the list box window exists) because that just sends the LB_ADDSTRING message. I guess it is happening later when other list box operations are performed.

ForNow1-Dec-17 5:04

1-Dec-17 5:04

I made a custom DDX to create the list box

C++

DDX_TextVAL(pDX, IDC_STORAGE_AREAS, storage_area);

C++

HWND tempwin = ::GetDlgItem(pDX->m_pDlgWnd->m_hWnd, nIDC);
      LPTSTR temptr = (LPTSTR)new char[10];
      ::GetClassName(tempwin, temptr, 10);
      if (strcmp((char *)temptr, "Edit") == 0)
         value.Attach(pDX->PrepareEditCtrl(nIDC));
      else
        value.Attach(pDX->PrepareCtrl(nIDC));

      delete temptr;

CListBox storage_area

Victor Nijegorodov1-Dec-17 9:34

Victor Nijegorodov

1-Dec-17 9:34

ForNow wrote:
I made a custom DDX to create the list box

And what for?
IMHO, it is not a good idea...