the handle is invalid

i am getting this message intermittently during runtime with a new control i developed. the control is pretty straightforward. i don't understand what's causing this at all.

i haven't come across this before. i know it's something from windows, but from googling, this appears to happen in such a broad variety of situations that i can't find anything that's actually helping me narrow down the possible causes, let alone a solution.

please help.

If you expect us to figure it out from that description, you're probably dreaming.

Do you know how to use your debugger?

i know that's not a lot of information, but i don't have anything more myself. i can't isolate it to a particular line, only somewhere in the control...

and yes, i tried stepping through it over and over again, but i could never get it to occur when i was doing that.

Can't you break execution when the error occurs? What debugger are you using?

i use borland C++ builder.

anyway, i changed the control to use different (non-COM) subcomponents and now the error isn't happening anymore.

i'd still like to know a lot more about using the debugger tools more effectively, and how to ensure that i obtain handles safely and allocating on the stack/heap/etc...

Practice using the debugger on a program you know works.

Add known "errors" to your program, say stepping off the end of an array, and use the debugger to "find" the problem.

Like anything else, actual practical experience is how you learn this stuff. And trying to learn it in the middle of a crisis doesn't help.

Quote:

---

Originally Posted by Salem

Like anything else, actual practical experience is how you learn this stuff. And trying to learn it in the middle of a crisis doesn't help.

---

Amen! However, being in the middle of a crisis tends to focus my concentration like nothing else. :o

Coffee, whoie, coffee...

ok, well it's not as resolved as i thought.

the problem here is that when this error occurs, the debugger doesn't resolve to any line. it just brings me to wherever i was in the IDE, but doesn't highlight any line or anything.

Did you compile the program with debugging information enabled?

yes.

Look in the call stack, is there anything there? Can you find some part of your code and go to that?

never used that before. i'll give it a try!

thanks! i'm totally open to any and all suggestions. i have a rather nice system message system worked out now, i'd hate to replace it with a stupid, featureless memo.



the only thing that sticks out is that i did the following:

Code:

---

__fastcall systemMessage::systemMessage(TSystemMessageScreen *Owner,String msg) :
        TPanel(Owner),
        owner(Owner),
        memo(new TLabel(this))
{
//...etc.
}

---

is it unsafe to invoke the this pointer in a constructor list like this?

>> is it unsafe to invoke the this pointer in a constructor list like this?
Potentially. If the systemMessage object is used in the TLabel constructor (or indirectly in the memo constructor) then it would be a problem.

hmm...yes i belive it is.

the "Owner" property is used for garbage disposal in BCB; but that's WAAAY up in the inheritance tree, so anything used in that function should be totally initialized at that point.

anyway, i changed it to memo=new TLabel, and it still occurred.

i wrapped all the new systemMessage statements with try/catch blocks, where the catch just retries to instatntiate the message, and it's working pretty well. i've gotten a lot of messages displayed with no problems.

here's the complete code. if someone sees something, please let me know!

Code:

---

//---------------------------------------------------------------------------

#ifndef SystemMessageScreenH
#define SystemMessageScreenH
//---------------------------------------------------------------------------
#include <SysUtils.hpp>
#include <Classes.hpp>
#include <Controls.hpp>
#include <Forms.hpp>
#include <ComCtrls.hpp>
//---------------------------------------------------------------------------
class TSystemMessageScreen;
class systemMessage : public TPanel
{
        protected:
                TLabel *memo;
                bool READ;
                TSystemMessageScreen *owner;
                String __fastcall gettime()
                {
                        String timeString;
                        TDateTime timeStamp = Now();
                        DateTimeToString(timeString,"yyyy-mm-dd hh:nn:ss.zz",timeStamp);
                        return timeString;
                }

                __property String timeStamp={read=gettime};
        public:
                __property bool read={read=READ};
                __fastcall systemMessage(TSystemMessageScreen *Owner,String msg);
};

class urgentMessage : public systemMessage
{
        protected:
                virtual void __fastcall acknowledgeClick(TObject *Sender);
        public:
                __fastcall urgentMessage(TSystemMessageScreen *Owner,String msg);
};

class warningMessage : public urgentMessage
{
        public:
                __fastcall warningMessage(TSystemMessageScreen *Owner,String msg);
};

class alarmMessage : public urgentMessage
{
        public:
                __fastcall alarmMessage(TSystemMessageScreen *Owner,String msg);
};

class PACKAGE TSystemMessageScreen : public TScrollBox
{
        private:
                DynamicArray<systemMessage *>messages;
                unsigned int UNREAD;
        protected:
        public:
                __fastcall TSystemMessageScreen(TComponent* Owner);

                __property unsigned int unread={read=UNREAD};

                void __fastcall ShowMessage(String msg);
                void __fastcall ShowWarning(String msg);
                void __fastcall ShowAlarm(String msg);                               
                void __fastcall setAcknowledged(systemMessage *msg);

        __published:
};
//---------------------------------------------------------------------------
#endif

---

Code:

---

//---------------------------------------------------------------------------

#include <vcl.h>

#pragma hdrstop

#include "SystemMessageScreen.h"
#pragma package(smart_init)
//---------------------------------------------------------------------------
// ValidCtrCheck is used to assure that the components created do not have
// any pure virtual functions.
//

static inline void ValidCtrCheck(TSystemMessageScreen *)
{
        new TSystemMessageScreen(NULL);
}
//---------------------------------------------------------------------------
__fastcall TSystemMessageScreen::TSystemMessageScreen(TComponent* Owner)
        : TScrollBox(Owner),
        UNREAD(0)
{
        AutoScroll = true;
}
//---------------------------------------------------------------------------
namespace Systemmessagescreen
{
        void __fastcall PACKAGE Register()
        {
                TComponentClass classes[1] = {__classid(TSystemMessageScreen)};
                RegisterComponents("custom", classes, 0);
        }
}
//---------------------------------------------------------------------------


void __fastcall TSystemMessageScreen::ShowMessage(String msg)
{
        try
        {
                systemMessage *m = new systemMessage(this,msg);
                m->Align = alTop;
                messages.Length++;
                messages[messages.High]=m;

        }
        catch(...)
        {
                ShowMessage(msg);       
        }
}

void __fastcall TSystemMessageScreen::setAcknowledged(systemMessage *s)
{
        UNREAD--;
}


void __fastcall TSystemMessageScreen::ShowWarning(String msg)
{
        try
        {
                systemMessage *m = new warningMessage(this,msg);
                m->Align = alTop;
                messages.Length++;
                messages[messages.High]=m;
                UNREAD++;

        }
        catch(...)
        {
                ShowWarning(msg);
        }
}

void __fastcall TSystemMessageScreen::ShowAlarm(String msg)
{
        try
        {
                systemMessage *m = new alarmMessage(this,msg);
                m->Align = alTop;
                messages.Length++;
                messages[messages.High]=m;
                UNREAD++;

        }
        catch(...)
        {
                ShowAlarm(msg);
        }
}

__fastcall systemMessage::systemMessage(TSystemMessageScreen *Owner,String msg) :
        TPanel(Owner),
        owner(Owner)
{
        try
        {
                memo=new TLabel(this);
                msg = timeStamp+": "+msg;

                Width = Owner->Width-1;

                Parent = Owner;
                Align = alTop;
                Height = 64;

                int numchars = Width/Canvas->TextWidth("0");

                TSysCharSet bchars;
                bchars << '.' << '-' << ' ';
                msg = WrapText(msg, "\n", bchars, numchars);

                memo->Transparent = true;
                memo->Parent = this;
                memo->Align = alTop;
                memo->Height = Height-1;
                memo->Caption = msg;

        }
        catch(...){}

}

void __fastcall urgentMessage::acknowledgeClick(TObject *Sender)
{
        READ = true;
        Color = clWhite;
        owner->setAcknowledged(this);
}

__fastcall urgentMessage::urgentMessage(TSystemMessageScreen *Owner,String msg) :
        systemMessage(Owner,msg)
{
        memo->OnClick= acknowledgeClick;
        OnClick= acknowledgeClick;
}


__fastcall warningMessage::warningMessage(TSystemMessageScreen *Owner,String msg) :
        urgentMessage(Owner,msg)
{
        Color= clYellow;
}


__fastcall alarmMessage::alarmMessage(TSystemMessageScreen *Owner,String msg) :
        urgentMessage(Owner,msg)
{
        Color= clRed;
}

---

hmmm....

i just got "Access is Denied"; the last things in the call stack are:

7C812A5B: C:\\Windows\system32\kernel32.dll
400B77A0 C:\\Windows\system32\vcl.bpl

i have no idea wtf to do with this information.

alright, well, i'm positive i've gotten it now.

it was totally coincidence; it had nothing to do with this message system.

it was a threading conflict, trying to draw on a bitmap.

http://www.forumammo.com/cpg/albums/...o-facepalm.jpg