Re: retry shm attach for windows (WAS: Re: OK, so culicidae is *still* broken)

On Thu, Jun 1, 2017 at 10:36 PM, Petr Jelinek
<petr(dot)jelinek(at)2ndquadrant(dot)com> wrote:
> On 01/06/17 15:25, Tom Lane wrote:
>> Robert Haas <robertmhaas(at)gmail(dot)com> writes:
>>> So, are you going to, perhaps, commit this? Or who is picking this up?
>>
>>> /me knows precious little about Windows.
>>
>> I'm not going to be the one to commit this either, but seems like someone
>> should.
>>
>
> The new code does not use any windows specific APIs or anything, it just
> adds retry logic for reattaching when we do EXEC_BACKEND which seems to
> be agreed way of solving this. I do have couple of comments about the
> code though.
>
> The new parameter retry_count in PGSharedMemoryReAttach() seems to be
> only used to decide if to log reattach issues so that we don't spam log
> when retrying, but this fact is not mentioned anywhere.
>

No, it is to avoid calling free of memory which is not reserved on
retry. See the comment:
+ * On the first try, release memory region reservation that was made by
+ * the postmaster.

Are you referring to the same function in sysv_shm.c, if so probably I
can say refer the same API in win32_shmem.c or maybe add a similar
comment there as well?

> Also, I am not excited about following coding style:
>> + if (!pgwin32_ReserveSharedMemoryRegion(pi.hProcess))
>> + continue;
>> + else
>> + {
>
> Amit, if you want to avoid having to add the curly braces for single
> line while still having else, I'd invert the expression in the if ()
> statement so that true comes first. It's much less ugly to have curly
> braces part first and the continue statement in the else block IMHO.
>

I felt that it is easier to understand the code in the way it is
currently written, but I can invert the check if you find it is easier
to read and understand that way.

--
With Regards,
Amit Kapila.
EnterpriseDB: http://www.enterprisedb.com