RFR[10]: 8187658: Bigger buffer for GetAdaptersAddresses

[Roger Riggs]

Hi Ivan,

Looks fine,

Thanks, Roger

On 9/25/2017 4:58 PM, Ivan Gerasimov wrote:
> 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
>>>>
>>>
>>
>>
>

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