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Strategy tester, DLLs, and FreeLibrary()

  • #1
  • First Post: Edited 1:45am Nov 16, 2011 1:02am | Edited 1:45am
I have seen this issue mentioned here and there, especially by 7bit, but I was never able to get around this problem:

The strategy tester does not properly decrement the reference count of the loaded library during deinit(). Because of this, the DLL file stays loaded in the system, and crashes when you attempt to run the tester again.

I tried to use GetModuleHandle() and FreeLibrary(), but that did not seem to solve the problem.

Inserted Code
if (IsTesting()) {
int dll_handle = DLLHandle("C:\Program Files (x86)\MT\experts\libraries\SQLBridgeV2.dll");
Print(dll_handle);
if (dll_handle>0) FreeLibrary(dll_handle);
}
CORRECTION:
dll_handle returns a non-0 number, and FreeLibrary decrements it.

If I check GetModuleHandle() again, I get 0 - which should mean the library is unloaded.

However if I start the tester again it still crashes.

This is getting pretty annoying because I cannot use the optimization feature.

What exactly happens? Is it that the DLL's global variables remain initialized and polluted by the last run's data? Or does an error occur during the attempt to initialize a DLL over an already-initialized DLL?
  • #2
  • Last Post: Nov 16, 2011 6:11am Nov 16, 2011 6:11am
Quoting mfurlend

However if I start the tester again it still crashes.

This is getting pretty annoying because I cannot use the optimization feature.

What exactly happens? Is it that the DLL's global variables remain initialized and polluted by the last run's data? Or does an error occur during the attempt to initialize a DLL over an already-initialized DLL?

This points to issues within your DLL. It is not correctly destroying / freeing all memory / objects, or -more likely given its causing a crash- at some point during reinit on the second attempt you are using a pointer or a reference to something that no longer exists.

Its impossible to say exactly what this is without looking at the DLL. But you'll need to :

1)pay attention to the init / deint of your DLL
2) DLL_entry_point() function will not be called the second time round since the DLL wasnt unloaded so DONT USE IT. Place code from here into the function you call from MT4 to init the DLL.
3) ensure any memory / objects created outside the init routine are dealt with during Deinit


Try modifying your DLL init / deint in a manner approximating the following :

Inserted Code
Global vars
objptr : pointer = nil; // object pointer initialized to nil
memptr : pointer = nil;

func DLL_INIT() // called by you from MT4 init()
{
   if (objptr == nil) objptr = somobject.create(); // create object 
}

func DLL_some routine() // called by you from mt4 somewhere in the EA
{
    memptr = getmem(somememory);
    
   // do something with the memory ... we wont free the memory 
   //at the    end of this function !
 
}

func DLL_Deint() // called by you from mt4 deinit()
{
  if (objptr != nil) 
    {
        objptr->free;
        objptr = nil;
    }

   if (memptr != nil)
     {
        freemem(memptr, somememory);
        memptr = nil;
     }
}

If you create / allocate all your memory / objs / dynamic vars in this manner you should avoid referencing something that doesnt exist.
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