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From eribeiro <...@git.apache.org>
Subject [GitHub] zookeeper pull request #173: ZOOKEEPER-2691: recreateSocketAddresses may rec...
Date Fri, 17 Feb 2017 21:05:02 GMT
Github user eribeiro commented on a diff in the pull request:

    --- Diff: src/java/main/org/apache/zookeeper/server/quorum/QuorumPeer.java ---
    @@ -181,6 +197,33 @@ public void recreateSocketAddresses() {
    +        /**
    +         * Resolve the hostname to IP addresses, and find one reachable address.
    +         *
    +         * @param hostname the name of the host
    +         * @param timeout the time, in millseconds, before {@link InetAddress#isReachable}
    +         *                aborts
    +         * @return a reachable IP address. If no such IP address can be found,
    +         *         just return the first IP address of the hostname.
    +         *
    +         * @exception UnknownHostException
    +         */
    +        public InetAddress getReachableAddress(String hostname, int timeout) 
    +                throws UnknownHostException {
    +            InetAddress[] addresses = InetAddress.getAllByName(hostname);
    +            for (InetAddress a : addresses) {
    +                try {
    +                    if (a.isReachable(timeout)) {
    --- End diff --
    My main problem with this PR is that call to `isReachable(timeout)` for two reasons: 
    1) the most important one: `isReachable(timeout)` seems unreliable so there are plenty
cases where it returns false even tough the node is reachable or vice-versa! https://bugs.openjdk.java.net/browse/JDK-8159410
(google "InetAddress.isReachable not working" or "InetAddress.isReachable unreliable" to see
further cases).
    2) This timeout can add an arbitrary delay until a reachable node can be tested.
    IDK what a good compromise would be for both points above (leaving as it is today could
work, so no problem, even tough I am a bit concerned), but maybe we could use a solution similar
to ZOOKEEPER-2184 and return the next address in the array (using `next = ++next % addresses.length`
to prevent out of bound exceptions).

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