Re: [HACKERS] [COMMITTERS] pgsql: Add new function dsa_allocate0.

On Thu, Feb 16, 2017 at 10:09 PM, Michael Paquier
<michael.paquier@gmail.com> wrote:
> On Fri, Feb 17, 2017 at 12:03 PM, Thomas Munro
> <thomas.munro@enterprisedb.com> wrote:
>> On Fri, Feb 17, 2017 at 11:34 AM, Thomas Munro
>> <thomas.munro@enterprisedb.com> wrote:
>>> On Fri, Feb 17, 2017 at 7:02 AM, Robert Haas <rhaas@postgresql.org> wrote:
>>>> http://git.postgresql.org/pg/commitdiff/9acb85597f1223ac26a5b19a9345849c43d0ff54
>>> Hmm.  This will segfault if you're out of memory.
>>
>> Or to provide a more useful response... maybe this should be like the
>> attached?  Or maybe people think that dsa_allocate should throw on
>> failure to allocate, like palloc?
>
>      dp = dsa_allocate(area, size);
> -    object = dsa_get_address(area, dp);
> -    memset(object, 0, size);
> +    if (DsaPointerIsValid(dp))
> +        memset(dsa_get_address(area, dp), 0, size);
> What you are proposing here looks like the right answer to me. Like
> dsa_allocate, dsa_allocate0 should allow users to fallback to other
> methods if what is returned is InvalidDsaPointer for consistency.

I'm thinking we should change this to look more like the
MemoryContextAlloc interface.  Let's have DSA_ALLOC_HUGE,
DSA_ALLOC_NO_OOM, and DSA_ALLOC_ZERO, just like the corresponding
MCXT_* flags, and a function dsa_allocate_extended() that takes a
flags argument.  Then, dsa_allocate(x,y) can be a macro for
dsa_allocate_extended(x,y,0) and dsa_allocate0(x,y) can be a macro for
dsa_allocate_extended(x,y,DSA_ALLOC_ZERO).  What this goof on my (and
Dilip's) part illustrates to me is that having this interface behave
significantly differently from the MemoryContextAlloc interface is
going to cause mistakes.

-- 
Robert Haas
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