Re: [PATCH] Make xmalloc and xrealloc thread-safe

> By providing a hook for the routine responsible for trying to free some
> memory on malloc failure, we can ensure that the  called routine is
> protected by the appropriate locks when threads are in play.
>
> The obvious offender here was pack-objects which was calling xmalloc()
> within threads while release_pack_memory() is not thread safe.
>
> Signed-off-by: Nicolas Pitre <nico@fluxnic.net>
> ---
>
> On Wed, 24 Mar 2010, Shawn Pearce wrote:
>
>> On Wed, Mar 24, 2010 at 11:54 AM, Nicolas Pitre <nico@fluxnic.net> wrote:
>> > Another solution could be for xmalloc() to use a function pointer for
>> > the method to use on malloc error path, which would default to a
>> > function calling release_pack_memory(size, -1).  Then pack-objects.c
>> > would override the default with its own to acquire the read_mutex around
>> > the call to release_pack_memory().  That is probably the easiest
>> > solution for now.
>>
>> Yea, that sounds like the most reasonable solution right now.
>
> So here it is.
>
> Note: there was a dubious usage of fd when calling release_pack_memory()
> in xmmap() which is now removed.
>
> diff --git a/builtin/pack-objects.c b/builtin/pack-objects.c
> index 9780258..65f797f 100644
> --- a/builtin/pack-objects.c
> +++ b/builtin/pack-objects.c
> @@ -1522,6 +1522,13 @@ static void find_deltas(struct object_entry **list, unsigned *list_size,
>
>  #ifndef NO_PTHREADS
>
> +static void try_to_free_from_threads(size_t size)
> +{
> +       read_lock();
> +       release_pack_memory(size, -1);
> +       read_unlock();
> +}
> +