Externals and Memory Leaks???

[chris bohnert]

Dave,

To my knowledge, Rev. makes a copy of the buffer when you do the SetVariable
call.  So in instances where you're making successive calls like this you
should never expect rev to send back a ptr that you've already
allocated..its probably safe enough to do something like this in your
external code

myExternalVariableInfo.buffer = theVariablePtr;
myExternalVariableInfo.length = theVariableSize;
SetVariableEx
(theVariableNamePtr,"",&myExternalVariableInfo,&myRunRevStatus);
if (myRunRevStatus == EXTERNAL_FAILURE)
       return(kRunRevVariableNotDefined);

 // added explicit free here as rev should have copied the buff in the
SetVariable Call
if( theVariable!=NULL)
  free theVariable;


In instances where you have allocated memory that needs to be persisted over
a long period of time in the external ( image buffer, multiple instances of
browser object and the like) you'll want to track them similar to previous
description.

--
cb

On 5/24/07, Dave <dave at looktowindward.com> wrote:
>
> Hi Chris,
>
> Thanks for the information, but I'm a bit confused! In the RunRev
> script I have the following code:
>
> local myBuffer
> local myNewData
>
> repeat until <some_condition>
>   get XGetData("myTempData")
> XProcessData(myTempData,"myNewData")
> end repeat
>
> In my externals I allocate a new buffer each time it's called, should
> I check if the variable already has something allocated to it and
> free it if so? I am guessing this is what you mean when you say store
> the Allocations in a list? So before allocating a new buffer check if
> the variable has a buffer assigned and then free it if (and only if)
> it's in the list?
>
> Thanks again
> All the Best
> Dave
>
> On 24 May 2007, at 15:58, chris bohnert wrote:
>
> > Dave,
> >
> > Yep..when you use SetVariableEx you're responsible for managing the
> > memory.
> > Normally I handle this by building a SafeAlloc function in C or by
> > creating
> > my own  new/delete in c++.
> >
> > This will let you store your allocs in a list and handle their
> > release as
> > necessary.  In my experience, releasing only what I know I have
> > allocated is
> > much safer than trying to free random memory blocks coming back
> > from rev.
> >
> > hope that helps.
> >
> > --
> > cb
> >
> > On 5/24/07, Dave < dave at looktowindward.com> wrote:
> >>
> >> Hi All,
> >>
> >> I have a Stack that uses two functions from an external:
> >>
> >> XGetData("myTempData")
> >> XProcessData(myTempData,"myNewData")
> >>
> >> XGetData() Gets the data into the correct format and stores it in the
> >> RunRev variable "myTempData".
> >>
> >> XProcessData() takes the data in "myTempData", processes it and puts
> >> the results into "myNewData".
> >>
> >> This all works well and produces good results, the only problem is
> >> that memory seems to be leaking by quite a lot and the two data
> >> buffers here are quite large.
> >>
> >> In the external, I use malloc() to allocate the buffers and then use
> >> "SetVariableEx()" to pass it back to RunRev. My question is, who is
> >> responsible for freeing the data?
> >>
> >> I am guessing that the on each subsequent call to the External
> >> Functions causes a new block to be allocated and overwrites the
> >> contents of the old RunRev "ExternalString" structure without first
> >> freeing it. How should I handle this? Do I need to check if the
> >> variable passed into my external already has data allocated and if so
> >> either free or re-use the data (the block sizes are likely to be the
> >> same).
> >>
> >> Any advice or help on this greatly appreciated.
> >>
> >> All the Best
> >> Dave
> >>
> >> PS
> >>
> >> I set the External Variable using the following function:
> >>
> >>
> >> OSStatus LTWLibraryUtilsSetExternalVariablePtr( char*
> >> theVariableNamePtr,
> >>
> >>                            const
> >> char*                     theVariablePtr,
> >>
> >>
> >>                            long
> >> theVariableSize)
> >> {
> >> ExternalString                          myExternalVariableInfo;
> >> int
> >> myRunRevStatus;
> >>
> >> //**
> >> //**    Get the External Variable
> >> //**
> >> myExternalVariableInfo.buffer = theVariablePtr;
> >> myExternalVariableInfo.length = theVariableSize;
> >> SetVariableEx
> >> (theVariableNamePtr,"",&myExternalVariableInfo,&myRunRevStatus);
> >> if (myRunRevStatus == EXTERNAL_FAILURE)
> >>         return(kRunRevVariableNotDefined);
> >>
> >> //**
> >> //**    Good Return
> >> //**
> >> return(noErr);
> >> }
> >>
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