RFR[10]: 8187658: Bigger buffer for GetAdaptersAddresses

[Ivan Gerasimov]

Thank you Roger for review!


On 9/25/17 11:47 AM, Roger Riggs wrote:
> Hi Ivan,
>
> Looks ok to me.
>
> I don't see a reason to skimp on the additional size since it is 
> allocated and then freed immediately.
> The increment might as well be as big as the initial size.
>
Right.  Let's use the same value of 15K, which reduces the number of 
variables to operate with.

> I don't see a reason to retry if the buffer gets close to ULONG_MAX; 
> I'd just break the for loop
> and let it fail. (but the new code is just doing what the old code did 
> and retry even if the buffer did not increase).
>
If len is close to ULONG_MAX, it is still larger value of len returned 
by the previous call to GetAdaptersAddresses (otherwise we wouldn't have 
gotten ERROR_BUFFER_OVERFLOW.)
So, if we're in the loop, there's no way the buffer will not increase 
(unless there's a failure due to OOM, of course.)

> Also, please introduce a constant for the number of retries; it will 
> make it clearer
> and not need to hard code it in two places.
Done!

Would you please take a look at the updated webrev:

http://cr.openjdk.java.net/~igerasim/8187658/01/webrev/

With kind regards,
Ivan

> (I would probably have coded the retry count counting down to zero but 
> its the same effect).
>
> Regards, Roger
>
>
> On 9/25/2017 1:03 PM, Ivan Gerasimov wrote:
>> Ping.
>>
>> Please review the proposed change at your convenience.
>>
>> The fix will greatly reduce the possibility of a need to reallocate 
>> the buffer to retrieve the results (something that the documentation 
>> strongly suggests to avoid), and, if such reallocation still occurs 
>> to be necessary, will increase number of retries.
>>
>> With kind regards,
>> Ivan
>>
>>
>> On 9/19/17 10:50 AM, Ivan Gerasimov wrote:
>>> Hello!
>>>
>>> When retrieving information about network interfaces on Windows we 
>>> make up to 2 attempts to call GetAdaptersAddresses().
>>>
>>> It was reported that in very rare cases it may not be sufficient, 
>>> and even the second attempt can fail with ERROR_BUFFER_OVERFLOW.
>>>
>>> I suggest that we follow the recommendation given in MSDN [1]: 
>>> increase the initial buffer size to 15K and do up to 3 attempts to 
>>> call GetAdaptersAddresses().
>>>
>>> BUGURL: https://bugs.openjdk.java.net/browse/JDK-8187658
>>> WEBREV: http://cr.openjdk.java.net/~igerasim/8187658/00/webrev/
>>>
>>> Would you please help review the fix?
>>>
>>> [1] 
>>> https://msdn.microsoft.com/en-us/library/windows/desktop/aa365915(v=vs.85).aspx
>>>
>>
>
>

-- 
With kind regards,
Ivan Gerasimov