8374368: Invalid java.nio.channels.spi.SelectorProvider value results in ClassNotFoundException instead of falling back to default provider

[shruacha1234]

Fall back to the default SelectorProvider by logging an error when an invalid provider is specified via the java.nio.channels.spi.SelectorProvider system property.
The bug report for the same: https://bugs.openjdk.org/browse/JDK-8374368

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Integration blocker

 ⚠️ Title mismatch between PR and JBS for issue JDK-8374368

Issue

• JDK-8374368: SelectorProvider.provider() throws CNFE if system property java.nio.channels.spi.SelectorProvider set to bad value (Bug - P4) ⚠️ Title mismatch between PR and JBS.

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• 00: Full (6ecfdd06)

[shruacha1234]

Validated the fix with the personal build

SelectorTypeCheck.java

import java.nio.channels.Selector;
public class SelectorTypeCheck {
    public static void main(String[] args) throws Exception {
        try (Selector selector = Selector.open()) {
            System.out.println("Selector provider: " + selector.provider());
            System.out.println("Selector implementation class: " + selector.getClass().getName());
        }
    }
}

jdk/bin/java SelectorTypeCheck
Selector provider: sun.nio.ch.EPollSelectorProvider@68968cd4
Selector implementation class: sun.nio.ch.EPollSelectorImpl

jdk/bin/java -Djava.nio.channels.spi.SelectorProvider=abc SelectorTypeCheck

Invalid SelectorProvider specified: abc. Falling back to default provider.
Selector provider: sun.nio.ch.EPollSelectorProvider@7f1338e3
Selector implementation class: sun.nio.ch.EPollSelectorImpl

jdk/bin/java -Djava.nio.channels.spi.SelectorProvider=sun.nio.ch.PollSelectorProvider SelectorTypeCheck

Selector provider: sun.nio.ch.PollSelectorProvider@b3462c23
Selector implementation class: sun.nio.ch.PollSelectorImpl

Also I have triggred java_nio, java_io and jdk_net tests. All of them are passing

20:55:05  TEST TARGETS SUMMARY
20:55:05  ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
20:55:05  PASSED test targets:
20:55:05  	jdk_io_0 - Test results: passed: 395 
20:55:05  	jdk_io_1 - Test results: passed: 395 
20:55:05  	jdk_nio_0 - Test results: passed: 445 
20:55:05  	jdk_nio_1 - Test results: passed: 445 

[AlanBateman]

This is not a bug, the lookup is specified to fall if there is a configuration error.

[lmesnik]

This fix should have a regression test, based on the provided reproducer.
If it can't be implemented, then bug should have 'noreg-' label.