[Caml-list] Long running finalizers and global lock

[Caml-list] Long running finalizers and global lock

[Pedro Borges]

Hi again,

the reference manual states:

 > Note: the finalize, compare, hash, serialize and deserialize
functions attached to custom block
 > descriptors must never trigger a garbage collection. Within these
functions, do not call any of
 > the Caml allocation functions, and do not perform a callback into
Caml code. Do not use
 > CAMLparam to register the parameters to these functions, and do not
use CAMLreturn to return the result.

I have a long running function inse a finalizer is it safe to release
and acquire the runtime lock ?

Best Regards

Re: [Caml-list] Long running finalizers and global lock

[Goswin von Brederlow]

Pedro Borges <pdhb.lists@gmail.com> writes:

> Hi again,
>
> the reference manual states:
>
>  > Note: the finalize, compare, hash, serialize and deserialize
> functions attached to custom block
>  > descriptors must never trigger a garbage collection. Within these
> functions, do not call any of
>  > the Caml allocation functions, and do not perform a callback into
> Caml code. Do not use
>  > CAMLparam to register the parameters to these functions, and do not
> use CAMLreturn to return the result.
>
> I have a long running function inse a finalizer is it safe to release
> and acquire the runtime lock ?
>
> Best Regards

If you release the lock then any ocaml values might get relocated by the
GC at any time and then your code would reference the wrong address. If
your code uses any ocaml values (CAMLparam or CAMLlocal or registered
roots) you will need to aquire the lock every time you access
them.

On the other hand I'm not sure it is allowed to release the lock in a
finalizer. Given the warning the GC seems to be in an inconsitent state
when the finalizer is run and releasing the lock would mean some other
thread would certinly allocate something and crash your program.

So overall I consider it highly unlikely. Say I'm 99% sure you can't
release the lock but I would be happy to be tought otherwise.

MfG
        Goswin

Re: [Caml-list] Long running finalizers and global lock

[Damien Doligez]

On 2011-04-05, at 19:10, Pedro Borges wrote:

> I have a long running function inse a finalizer is it safe to release
> and acquire the runtime lock ?


NOT safe.  In fact, it will almost certainly crash immediately.

-- Damien