RFR: 8290714: Make com.sun.jndi.dns.DnsClient virtual threads friendly [v3]

[Jaikiran Pai]

On Tue, 8 Nov 2022 00:26:56 GMT, Aleksei Efimov <aefimov at openjdk.org> wrote:

>> ### The Proposed Change
>> 
>> The proposed change updates JNDI's `DnsClient` internal implementation to use `DatagramChannel` (DC) as a replacement for `DatagramSocket` (DS).
>> The main motivation behind this change is to make JNDI/DNS lookups friendly to virtual-thread environments and update its underlying implementation to use efficient `DatagramChannel` APIs.
>>  The list of proposed changes:
>> - Replace DS usage with DC. That includes the `DNSDatagramSocketFactory` class updates to return DC instead of DS. The factory class was renamed to `DNSDatagramChannelFactory` to reflect that.
>> - Change DNS query timeouts implementation - the current version introduces a nio channels selector to implement timeouts. One selector is created for each instance of `DnsClient`.
>> - Adjust query retries logic to the new implementation of timeouts.
>> - Modify the `Timeout` test to create a bound UDP socket to simulate an unresponsive DNS server. Before this change, the test was using the '10.0.0.0' network address that doesn't belong to any host. The proposed change with a bound unresponsive UDP socket is better for test stability on different platforms.
>> 
>> 
>> ### Testing
>> `jdk-tier1` to `jdk-tier3 `tests are showing no failures related to the changes.
>> JNDI regression and JCK tests also didn't highlight any problems with the changes. 
>> 
>> Also, an app performing a DNS lookup from a virtual thread context executed with the following options `--enable-preview -Djdk.tracePinnedThreads=full` showed no pinned carrier threads. Before the proposed change the following pinned stack trace was observed:
>> ```    java.base/sun.nio.ch.DatagramChannelImpl.park(DatagramChannelImpl.java:486)
>>     java.base/sun.nio.ch.DatagramChannelImpl.trustedBlockingReceive(DatagramChannelImpl.java:734)
>>     java.base/sun.nio.ch.DatagramChannelImpl.blockingReceive(DatagramChannelImpl.java:661)
>>     java.base/sun.nio.ch.DatagramSocketAdaptor.receive(DatagramSocketAdaptor.java:241) <== monitors:1
>>     java.base/java.net.DatagramSocket.receive(DatagramSocket.java:714)
>>     jdk.naming.dns/com.sun.jndi.dns.DnsClient.doUdpQuery(DnsClient.java:430) <== monitors:1
>>     jdk.naming.dns/com.sun.jndi.dns.DnsClient.query(DnsClient.java:216)
>>     jdk.naming.dns/com.sun.jndi.dns.Resolver.query(Resolver.java:81)
>>     jdk.naming.dns/com.sun.jndi.dns.DnsContext.c_lookup(DnsContext.java:290)
>>     java.naming/com.sun.jndi.toolkit.ctx.ComponentContext.p_lookup(ComponentContext.java:542)
>>     java.naming/com.sun.jndi.toolkit.ctx.PartialCompositeContext.lookup(PartialCompositeContext.java:177)
>>     java.naming/com.sun.jndi.toolkit.ctx.PartialCompositeContext.lookup(PartialCompositeContext.java:166)
>>     java.naming/javax.naming.InitialContext.lookup(InitialContext.java:409)
>> 
>> After proposed changes - pinned threads are not detectable.
>
> Aleksei Efimov has updated the pull request incrementally with one additional commit since the last revision:
> 
>   Simplify openRandom

Marked as reviewed by jpai (Reviewer).

Thank you Aleksei for the changes. The latest revision looks good to me.

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