Remove java wrapper altogether or mostly

[wkozaczuk]

This is the next and controversial step after we address #1168. For a long time, we have been able to run unmodified java from a host including bin/java regardless if it is a PIE or position dependant executable. Given that, the only reason to have OSv specific java wrapper (see modules/java-base/java.cc and modules/java-base/runjava-*) after we address #1168, is to support java ballooning once we fix it :-) (see #1038). Well, the other tiny issue is that we have to add ! to force terminating lingering Java threads.

I believe we can eliminate all java code ( modules/java-base/runjava-*) and either delete java.cc AND use alternative mechanism to pass -Xmx to java OR change java.cc to be a tiny front-end app that would calculate the value of -Xmx and launch native bin/java with -Xmx. Currently, the java.cc parses all arguments and calls JNI_CreateJavaVM directly, which creates many problems for modern Java as many arguments have changed since Java 7/8 or become obsolete. More "pass-through" tiny wrapper would better work.

The only complication is that the ballon C++ code relies on OSv java code - modules/java-base/runjava-common/src/main/java/io/osv/OSvGCMonitor.java (see https://github.com/cloudius-systems/osv/blob/master/modules/java-base/balloon/jvm_balloon.cc#L417-L443). But maybe that would not be a big deal, as OSvGCMonitor.java seems to be a standalone Java code that does not depend on other run-java java code.

Finally doing this would help us close many java-wrapper-related issues - java-wrapper .

[nyh]

I agree that if the Java executable works, we should use that (or a small executable which runs it) and not the shared library. I agree that since the balloon code is not in a working situation, and nobody wants to work on it, we don't need to worry about it. Moreover, I think that even if we run the unmodified Java executable, and in the future we'll want to return the ballooning stuff, there is probably/hopefully still a way to do this from another thread, using JNI.

[kmahapatra530]

Hi, my name is Koshik and I am a student at UT Austin. I'd like to work on this issue as part of my virtualization class assignment.

[wkozaczuk]

Hi, @kmahapatra530.

Welcome to the OSv community! You are very welcome to work on this issue. Please bear in mind it depends on #1168.

Solving this one and #1168 will require solid knowledge of Java and Python and makefile. I do not think we want to delete all relevant code but mostly disable it where necessary.

I would suggest you study this issue and #1168 and Java-related modules and come up with a more detailed strategy. I can help you with then.

BTW reading this 5-years old comment might help as well - #953 (comment).