Re: [MLton] strange gc message

[Bernard B. <be...@la...>]

On 11/18/15 4:48 PM, Matthew Fluet wrote:
>
>> As I mentionned in my previous post, the application makes use of ffi,
>> and allocates some storage in C using mmap. At first, I was suspecting
>> a collision between the storage allocated in C and that allocated by mlton.
>> But how this could happen ?
> ...
> Unfortunately, the semantics of mmap is that if there is already a
> mapping at a given address, then that previous mapping is removed and
> a new one created.  So, if MLton's sweep of high/low addresses happens
> to hit upon the same address returned by a previous mmap, then it
> might take that as an ML heap.  But, I've never seen this happen.
> But, I guess that we could look more closely at the strace to see if
> this is happening.
According to the mmap man page, removal of an old mapping may only
happen if flag MAP_FIXED was passed to mmap (or the analogue for mremap),
what mlton does not seem to do.

> Another possibility is if the application passes an ML pointer to C
> code via the FFI, which is retained by the C code and then accessed
> later (e.g., during a subsequent FFI call).

Not the case. The application could call SML from C, but it does not in
that particular run.


I'll prepare asap a stripped version of my source code, for further 
investigations.

Thanks for your help,
   Bernard.