Save/load i2c2i adapters

[ashu-mehra]

This is an attempt to save and load i2c2i adapters along with the adapter handler table.
There are mainly two parts to this change:

1. Storing of adapter code in the SCCache or AOT code cache.
2. Storing of adapter handler table in the AOT cache.

Adapter handler table is a map from AdapterFingerPrint to AdapterHnadlerEntry. To store them in AOT cache, AdapterFingerPrint and AdapterHandlerEntry are updated to MetaspaceObj. Both these entities are discovered and added to the cache while processing the Method. When storing the adapter handler table, only the entries that have already been archived are considered. This allows pruning of AdapterHnadlerEntry that may be only reachable through a Method that is not eligible to be archived.

An AdapterHandlerEntry has pointer to the adapter code. Because the AdapterHandlerEntry and the adapter code are stored in separate archives, this link between the AdapterHandlerEntry and the adapter code needs to be removed (see AdapterHandlerEntry::remove_unshareable_info()).
During the production run, as the methods in the AOT cache are adopted, the AdapterHandlerEntry is linked back to the adapter code (see AdapterHandlerEntry::restore_unshareable_info).

All this code is guarded by -XX:[+-]ArchiveAdapters option which defaults to false, but is set to true in CDSConfig during the assembly phase.

Other changes worth mentioning:

1. Changes to the SCCache infrastructure to make it possible to store and load adapter code. (Thanks to @adinn)
2. Updating AdapterFingerPrint hashing algorithm to avoid collisions. If there is any collision, then it will prevent finding the adapter code in the SCCache. (Again courtesy of @adinn)

Thanks to @adinn for providing many of these changes.

Performance:
-Xlog:init shows time taken for linking of Methods and making adapters. An example output is:

ClassLoader:
  clinit:                             150us / 4612 events
  link methods:                     28980us / 176893 events
  method adapters:                  15378us / 697 events

Save/load of adapters seem to have improved these stats.

Quarkus	-ArchiveAdapters	+ArchiveAdapters
link methods	12214us / 58913 events	2700us / 58913 events
method adapters	7793us / 607 events	4402us / 38 events

Spring-petclinic	-ArchiveAdapters	+ArchiveAdapters
link methods	28980us / 176893 events	7485us / 176893 events
method adapters	15378us / 697 events	7050us / 13 events

However, testing with Quarkus app, I don't see any noticeable improvement in the startup time.

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Progress

• Change must not contain extraneous whitespace
• Change must be properly reviewed (1 review required, with at least 1 Committer)

Reviewing

Using git

Checkout this PR locally:
$ git fetch https://git.openjdk.org/leyden.git pull/25/head:pull/25
$ git checkout pull/25

Update a local copy of the PR:
$ git checkout pull/25
$ git pull https://git.openjdk.org/leyden.git pull/25/head

Using Skara CLI tools

Checkout this PR locally:
$ git pr checkout 25

View PR using the GUI difftool:
$ git pr show -t 25

Using diff file

Download this PR as a diff file:
https://git.openjdk.org/leyden/pull/25.diff

Using Webrev

Link to Webrev Comment

[bridgekeeper]

👋 Welcome back asmehra! A progress list of the required criteria for merging this PR into premain will be added to the body of your pull request. There are additional pull request commands available for use with this pull request.

[openjdk]

❗ This change is not yet ready to be integrated.
See the Progress checklist in the description for automated requirements.

[mlbridge]

Webrevs

• 02: Full - Incremental (59b65ef1)
• 01: Full - Incremental (b04ba154)
• 00: Full (04fb256b)

[vnkozlov]

Very nice changes. Few comments.

[vnkozlov]

Can you check next (opposite to check in the following assert)?:

 if (adapter() != nullptr && !adapter()->is_linked()) {

The assumption is that we have enough CodeCache when we loading adapters from APT cache. Otherwise we should bailout (did you test such case?).

Is is_linked() is specific for adapters from AOT cache?

[ashu-mehra]

is_linked() is being set for every AdapterHandlerEntry when its code is either generated or loaded from AOT cache.

Regarding the original block of code that this check pertains to:

  // If the code cache is full, we may reenter this function for the
  // leftover methods that weren't linked.
  if (adapter() != nullptr) {
    return;
  }

The comment seem to indicate that we may reenter this function for a Method* for which adapter code has already been generated. However I am not able to trace the code path that may result in re-entering this function. Can you please explain under what conditions is this possible? @vnkozlov

[openjdk]

@ashu-mehra this pull request can not be integrated into premain due to one or more merge conflicts. To resolve these merge conflicts and update this pull request you can run the following commands in the local repository for your personal fork:

git checkout premain-save-i2c2i-v3
git fetch https://git.openjdk.org/leyden.git premain
git merge FETCH_HEAD
# resolve conflicts and follow the instructions given by git merge
git commit -m "Merge premain"
git push