[fpc-pascal]Constructor failing...

[James Mills]

On Fri, Mar 21, 2003 at 02:04:39PM +0100, Michael Van Canneyt wrote:
> 
> 
> On Fri, 21 Mar 2003, Anton Tichawa wrote:
> 
> > On Friday 21 March 2003 13:09, you wrote:
> > > > On Friday 21 March 2003 12:29, you wrote:
> > > >> >> > But, when I use fail in my simple example program, it returns
> > > >> >>
> > > >> >> NIL okay but
> > > >> >>
> > > >> >> > the Heaptrace function tells me I have two unfreed memory blocks
> > > >>
> > > >> (36
> > > >>
> > > >> >> > bytes).
> > > >> >> > I can't see a memory leak anywhere else in that program, what
> > > >> >>
> > > >> >> could cause
> > > >> >>
> > > >> >> > this? (Heaptrace output is as follows: I am using FPC 1.0.6 btw)
> > > >> >>
> > > >> >> [snip heap dump]
> > > >> >>
> > > >> >> That is the exception frame that is left on the heap. I don't have
> > > >>
> > > >> the
> > > >>
> > > >> >> time to analyze what the cause is that the exception frame is not
> > > >> >> removed.
> > > >> >
> > > >> > It may be a bug in 1.0.6 which has subsequently been fixed. I
> > > >>
> > > >> downloaded
> > > >>
> > > >> > and
> > > >> > installed the 1.1 snapshots and compiled the same source code, and the
> > > >> > memory leak vanishes....
> > > >>
> > > >> The reason why 1.1 has no leak is that it uses the stack to store the
> > > >> exception frames. The real problem is still there, because exception
> > > >> stack
> > > >> is still not updated
> > > >
> > > > some months ago i had a discussion with a friend, converning global
> > > > (static,
> > > > absolute) variables. his point of view was that they're not necessary
> > > > when using oop; mine was, sometimes they're absoulutely necessary.
> > > >
> > > > if we have just one level of exception processing above normal program
> > > > execution (i. e. while an exception is being processed, no other
> > > > exception will gain control), we can use absolute variables for the
> > > > exception frame.
> > > >
> > > > it's even possible to define a fixed whole number of exception layers and
> > > > allocate absolute memory for N exception levels.
> > > >
> > > > that memory space would not get lost, as it can be saved by allocating
> > > > the 'normal' stack or 'normal' heap more tightly - the old system has to
> > > > reserve
> > > > exception spae implicitely on the stack or on the heap.
> > > >
> > > > what do you think about that?
> > >
> > > It does not fix the problem, the frame is then still left on the stack.
> > >
> > > The allocation on the heap has already been changed to allocation on the
> > > stack in 1.1, because hat is much faster. Using a predefined storage of N
> > > exception levels is adding a limit and that is something we want to
> > > prevent.
> >
> > but also the power-switch, the data bus width, and the exception vectors in
> > ROM now are limits. i think limits cannot be prevented, but they can be
> > chosen knowingly, harmonic, and safe or so. every limit should include the
> > overhead to overcome it later, as things get better.
> 
> Not in this case. For instance recursive routines will get in trouble.
> There is no way to know how deep the stack can be nested, so you cannot
> foresee this. Putting a limit on that is out of the question.

Agreed. If you put a limit on that, you will disallow algorithms that
use resursive loops. There are many that do ...

cheers
James

> 
> Michael.
> 
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