RFR: JDK-8256844: Make NMT late-initializable

[Thomas Stuefe]

On Thu, 29 Jul 2021 23:03:46 GMT, Coleen Phillimore <coleenp at openjdk.org> wrote:

> This is an interesting and it seems a better way to solve this problem. Where were you all those years ago?? I hope @zhengyu123 has a chance to review it.

Thank you! I was here, but we were not yet doing much upstream :) To be fair, this problem got quite involved and did cost me some cycles and false starts. I fully understand that the first solution uses the environment variable approach.

I spend some time investigating different ideas with this one; at first I did not use a hash-table but a static pre-allocated buffer from which I fed early allocations. But the code got too complex, and Kim's suggestion with the side table turned out just to be a lot simpler.

> Also interesting is that we were wondering how we could return malloc'd memory on JVM creation failure, and this might partially help with that larger problem.

Yes, this would be trivial now, to return that memory. Though I am afraid it would be a small part only. But NMT may be instrumental in releasing all memory, since it knows everything. Only, its not always enabled.

Is that a real-life problem? Are there cases where the launcher would want to live on if the JVM failed to load?

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PR: https://git.openjdk.java.net/jdk/pull/4874