malloc failures in java/util/zip/Deflater

[Mario Torre]

Il 08/07/2009 20:52, Roman Kennke ha scritto:
> Hi Mario,
>
>> According to the specs, malloc may return either a valid pointer that
>> can be passed to free, or NULL, while generally NULL is considered to be
>> a failure. Linux and Solaris, albeit non specifying it, return always a
>> valid pointer, as far as I know
>
> I think NULL is returned in an out of memory situation, which is very
> rare on modern OSes, but I think it's still possible. The right thing to
> do here is check for NULL and (try to) throw an OOME. Which is what is
> beeing done already (AFAICS). What are you trying to solve by
> additionally checking for len>  0?
>
> /Roman

Hi Roman,

The OutOfMemory is thrown correctly in case of failure (it wasn't up to 
some builds ago, though :).

The problem is when passing a 0 length argument to malloc (from the man 
page):

malloc()  allocates  size  bytes and returns a pointer to the allocated
           memory.  The memory is not  cleared.   If  size  is  0, then
           malloc() returns  either  NULL, or a unique pointer value
           that can later be successfully passed to free().

Linux and Solaris AFAIK return a pointer to valid memory, but this is 
not specified, and the code only checks for NULL as in failure. So it 
may be the case that this changes in future. In my case I have a 
not-so-modern OS that returns NULL in such case.

So, to decide if we have a memory error or not, we need the additional 
len > 0 check.

Cheers,
Mario