Enable SPI functionality in GraalVM native mode

[pivovarit]

This change introduces a GraalVM substitution for ServiceLoader#getServiceDefinitions so that discovered classpath resources are properly discovered, read and not accidentally discarded.

Motivation

Hazelcast SPI relies on the classpath presence of multiple META-INF/services/com.foo.Bar files (for example, com.hazelcast.spi.discovery.multicast.DiscoveryStrategyFactory).

The internal implementation of ServiceLoader processes and collects URLs to the classpath resources:

https://github.com/hazelcast/hazelcast/blob/d54fa6df9a88c59f7479744c2b46158f10b2df7f/hazelcast/src/main/java/com/hazelcast/internal/util/ServiceLoader.java#L101-L124

However, this implementation doesn't play along with GraalVM's native images since Substrate doesn't really feature a normal classpath nor classloading but a mere simulation of these.

URLs to classpath resources located in different jars normally look like:

jar:file:/work/application/lib/com.hazelcast.hazelcast-4.0.1.jar!/META-INF/services/com.hazelcast.spi.discovery.DiscoveryStrategyFactory
jar:file:/work/application/lib/com.hazelcast.hazelcast-kubernetes-2.0.1.jar!/META-INF/services/com.hazelcast.spi.discovery.DiscoveryStrategyFactory

but under Substrate, they become resources and share the same URL (but URL#openStream leads to different content) which requires special handling:

resource:META-INF/services/com.hazelcast.spi.discovery.DiscoveryStrategyFactory
resource:META-INF/services/com.hazelcast.spi.discovery.DiscoveryStrategyFactory

So, not only extra processing and conversions are not welcome:
https://github.com/hazelcast/hazelcast/blob/d54fa6df9a88c59f7479744c2b46158f10b2df7f/hazelcast/src/main/java/com/hazelcast/internal/util/ServiceLoader.java#L109-L112

But also storing URLs in a set causes rejection of valid URLs:
https://github.com/hazelcast/hazelcast/blob/d54fa6df9a88c59f7479744c2b46158f10b2df7f/hazelcast/src/main/java/com/hazelcast/internal/util/ServiceLoader.java#L106

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fixes #18

[leszko]

Thanks for the PR. Added a few comments. Also, would it be possible to add unit tests for the classes you added?

[leszko]

Could you mention how it's limited? Does Kubernetes work? Do custom SPIs work?

[pivovarit]

To be honest, it's hard to define. The code from parse method is effectively a normal IMDG code stripped from some magic needed for the sake of OSGi and Glassfish compatibility so I expect some problems in these areas provided that you can make GraalVM work with that.

Naturally, all standard SPI-enabled extensions provided at build time do work properly

[leszko]

1. Could you add javadoc explaining what this method does? Or maybe make this method name more explanatory?
2. Wouldn't it be worth to add some unit tests for his class and other you added?

[pivovarit]

I will add docs around the Graal substitution and explain the problem there as well.

I'm working on tests at the moment. Unit testing is useless, we need an integration test that loads a custom extension via SPI

[pivovarit]

Actually, this is covered by Hasan's test suite

[hasancelik]

Finally we have got green build 💚 🙂 👍
http://jenkins.hazelcast.com/view/Integration%20Tests/job/kubernetes-quarkus-client-extension-aggregate-spis-branch/6/

15:21:13 Entry added into map succesfully!
15:21:14 Extracted entry value is correct.
15:21:14 {"podName":"hazelcast-client-0","value":"value_1"}
15:21:16 {"podName":"hazelcast-client-2","value":"value_1"}
15:21:19 {"podName":"hazelcast-client-2","value":"value_1"}
15:21:21 {"podName":"hazelcast-client-2","value":"value_1"}
15:21:23 {"podName":"hazelcast-client-0","value":"value_1"}
15:21:25 Stopping Docker container after build completion
15:21:26 Finished: SUCCESS