8143397: It looks like InetAddress.isReachable(timeout) works incorrectly

[Mark Sheppard]

Hi Rob,
     change looks fine and handles the MS idiosyncrasies neatly
     change works fine ... consistent responses and failing test returns 
expected results


regards
Mark

On 09/12/2015 01:44, Rob McKenna wrote:
> The intention of the 2nd revision of the fix is to make the 
> undocumented 1000ms problem a non issue.
>
> If a user calls this function with a timeout of 200ms that timeout is 
> automatically substituted for 1000ms in the IcmpSendEcho call. Once 
> the response is received its RTT is checked to make sure it is lower 
> than 200ms. If not the method returns false.
>
> That being the case though the call could potentially take up to 
> 1000ms to complete where a host is not reachable even though a smaller 
> timeout is specified. The return value of isReachable() will correctly 
> say whether the host was reachable or not within the actual timeout 
> specified by the user however.
>
> In order to avoid the older (and less reliable) way of testing 
> reachability I feel that this small corner case is a worthwhile tradeoff.
>
>     -Rob
>
> On 09/12/15 01:31, Xuelei Fan wrote:
>> Is it nice to say in the spec that it is not reliable if the timeout is
>> too small?  At least 1000ms timeout by default may be not acceptable in
>> some circumstances.
>>
>> Xuelei
>>
>> On 12/9/2015 12:31 AM, Rob McKenna wrote:
>>> Testing has shown that when a timeout < 1000ms is specified the
>>> IcmpSendEcho calls fail (apparently) randomly. Once the timeout is
>>> 1000ms or greater it works as expected. Therefore I've updated the fix
>>> to use 1000ms as a minimum. The existing logic ensures that the ttl is
>>> less than the specified timeout in any case:
>>>
>>> http://cr.openjdk.java.net/~robm/8143397/webrev.02/
>>>
>>>      -Rob
>>>
>>> On 01/12/15 14:59, Rob McKenna wrote:
>>>> It appears that there is an undocumented minimum timeout in the
>>>> IcmpSendEcho* functions. If the timeout parameter is set to a number
>>>> below this minimum timeout it is effectively ignored. Thus if you 
>>>> wanted
>>>> to ensure that you could ping a particular host within a certain 
>>>> timeout
>>>> less than the undocumented minimum, you could potentially receive a
>>>> false positive. (i.e. if you set the timeout to 20ms but the ping 
>>>> takes
>>>> 30ms, IcmpSendEcho will still succeed)
>>>>
>>>> The following fix checks the icmp reply packet and compares the round
>>>> trip time to the requested timeout parameter before deciding 
>>>> whether the
>>>> call was successful or not:
>>>>
>>>> http://cr.openjdk.java.net/~robm/8143397/webrev.01/
>>>>
>>>>       -Rob
>>