RFR: 8339538: Wrong timeout computations in DnsClient

[Jaikiran Pai]

On Fri, 6 Sep 2024 16:28:36 GMT, Aleksei Efimov <aefimov at openjdk.org> wrote:

> This PR proposes the following changes to address wrong timeout computations in the `com.sun.jndi.dns.DnsClient`:
> - The `DnsClient` has been updated to use a monotonic high-resolution (nano) clock. The existing `Timeout` test has also been updated to use the nano clock to measure observed timeout value.
> 
> - The left timeout computation has been fixed to decrease the timeout value during each retry attempt. A new test, `TimeoutWithEmptyDatagrams`, has been added to test it.
> 
> - The `DnsClient.blockingReceive` has been updated:
>     - to detect if any data is received
>     - to avoid contention with `Selector.close()` that could be called by a cleaner thread
> 
> - The expected timeout calculation in the `Timeout` test has been updated to take into account the minimum retry timeout (50ms). Additionally, the max allowed difference between the observed timeout and the expected one has been increased from 50% to 67%. Taking into account 50 ms retry timeout decrease the maximum allowed difference is effectively set to 61%. This change is expected to improve the stability of the `Timeout` test which has been seen to fail [intermittentlly](https://bugs.openjdk.org/browse/JDK-8220213). If no objections, I'm planning to close [JDK-8220213](https://bugs.openjdk.org/browse/JDK-8220213) as duplicate of this one.
> 
> JNDI/DNS jtreg tests has been executed multiple times (500+) to check if the new and the modified tests are stable. No failures been observed (so far?).

src/jdk.naming.dns/share/classes/com/sun/jndi/dns/DnsClient.java line 478:

> 476:                     long elapsedMillis = Math.max(1,
> 477:                             TimeUnit.NANOSECONDS.toMillis(end - start));
> 478:                     timeoutLeft = timeoutLeft - (int) elapsedMillis;

Hello Aleksei, should this `int` cast take into account potential integer value overflow? In theory (and probably even in practice depending on what the initial timeout value was configured to), the `elapsedMillis`, I think can be a value greater than `Integer.MAX_VALUE`, in which case this cast to `int` can cause unexpected computation of `timeoutLeft`.

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PR Review Comment: https://git.openjdk.org/jdk/pull/20892#discussion_r1748082435