RFR: 8290714: Make com.sun.jndi.dns.DnsClient virtual threads friendly [v2]

[Aleksei Efimov]

On Mon, 7 Nov 2022 15:41:40 GMT, Aleksei Efimov <aefimov at openjdk.org> wrote:

>> src/jdk.naming.dns/share/classes/com/sun/jndi/dns/DnsClient.java line 185:
>> 
>>> 183:     public void close() {
>>> 184:         try {
>>> 185:             udpChannelSelector.close();
>> 
>> Do you think we should now maintain a `closed` boolean flag in this class to keep track of whether this underlying selector has been closed? 
>> 
>> The javadoc of `Selector.close()` states that any subsequent use of the selector will throw a `ClosedSelectorException`. A `ClosedSelectorException` is a `RuntimeException`, so if a closed `DnsClient` gets used (for example a `query()` gets triggered) then from what I can see it will end up propagating this `ClosedSelectorException` out of these class methods instead of the declared compile time exceptions.
>> 
>> Maintaining a `closed` flag could allow us to use that flag to check in these methods (where we use the selector) and throw a more appropriate exception.
>
> Good point - planning to address the closed selector in the `blockingReceive` method by calling `udpChannelSelector.isOpen()`.

Addressed it by catching `ClosedSelectorException` and wrapping it into JNDI's `CommunicationException` in 55dd0a4a

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PR: https://git.openjdk.org/jdk/pull/11007