
Changes in JGroups to make it run natively in GraalVM
=====================================================

Author: Bela Ban
Date:   March 2019
JIRA:   https://issues.jboss.org/browse/JGRP-2332

The command to create a native image is JGroups/bin/compile.sh org.jgroups.tests.perf.ProgrammaticUPerf2.

Current limitations
===================
* Socket option SO_LINGER cannot be set due to CCE (see todos)
* Only java.util.logging logging is supported. To enable this:
  * Include resource logging.properties at compile time, e.g.: -H:IncludeResources=/home/bela/logging.properties
  * Force use of the JDK logger: -Djgroups.use.jdk_logger=true
* JMX cannot be used (flag -jmx is a no-go)
* reflection.json should include all classes/fields that are accessed via reflection; unused classes/fields should be
  removed
* ObjectOutputStream.writeObject() is not yet supported [4]. This is used by the RPC framework when a request or reply
  is an Object, but doesn't implement Streamable. A reply could be an Exception, which triggers writeObject().
* Invoking a method which takes a long with an int via reflection throws a CCE. The argument has to be 1L *not* 1.
* jg-protocol-ids.xml and jg-magic-map.xml are parsed to get mappings between protocols and their IDs, and classes and
  their magic IDs (for marshalling).
  * These files can be changed: unused protocols and classes can simply be removed


Changes
=======
* The accessors of some of the protocols changed, e.g. from void setX() to <P extends TP> P setX()
* Util.getAddress(AddressScope scope) has NetworkInterface.isUp() commented; this needs to be reverted when [1]
  has been fixed
* TP.timer is now created in TP.init(), but started (the threads) in TP.start(). As a requirement, start() is now
  called in the protocol stack from _bottom to top_ (used to be top to bottom).


Todos
=====
* Uncomment uses of NetworkInterface.isUp() when [1] has been resolved. The current port will return *all* interfaces,
  even ones that are down

* Try MulticastSockets (UDP). Currently, setting options fail: [2,3]

* Re-enable setting socket option SO_LINGER in {Tcp,Nio}Connection.setSocketParameters()



References
==========
[1] https://github.com/oracle/graal/pull/1076   // NetworkInterface.isUp0()

[2] https://github.com/oracle/graal/issues/1087 // Socket.setOption(SO_LINGER, -1) [FIXED]

[3] https://github.com/oracle/graal/issues/1082 // SO_REUSEADDR fails on MulticastSocket

[4] https://github.com/oracle/graal/issues/460 // Serialization not supported yet (ObjectOutputStream)
