Re: 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