Project Panama: Interconnecting JVM and native code

We are improving and enriching the connections between the Java virtual machine and well-defined but “foreign” (non-Java) APIs, including many interfaces commonly used by C programmers.
To this end, Project Panama will include most or all of these components:

native function calling from JVM (C, C++), specifically per JEP 191
native data access from JVM or inside JVM heap
new data layouts in JVM heap
native metadata definition for JVM
header file API extraction tools (see below)
native library management APIs
native-oriented interpreter and runtime “hooks”
class and method resolution “hooks”
native-oriented JIT optimizations
tooling or wrapper interposition for safety
exploratory work with difficult-to-integrate native libraries

Community
This Project is sponsored by the Hotspot Group.

Mailing lists
    panama-dev — the usual developer list
    panama-spec-experts — moderated, restricted to specification discussions only
Bloggers
    Charles Nutter
    John Rose
Links
    Panama bindings/jextract tutorial
    design document: State of the Isthmus
    new project CFV for Panama
    JEP 191: Foreign Function Interface
    JNR example code: Java Native Runtime
    early problem space overview: the isthmus in the VM

Repository organization
Project Panama is designed to incubate a series of components for eventual inclusion in the JDK, via curated merge. Following the experience of Project Amber, and Project Valhalla, we have our sanbox-like repository, whose default branch is kept in sync with jdk/jdk, and where each experimental feature is developed in its own branch.
Here’s a list of the branches under active development:

foreign, this branch provides a native binder which greatly reduces the impedence mismatch between native libraries and the JVM;
foreign-memaccess, this branch adds support for foreign memory access;
vectorIntrinsics, this branch adds vectorization support in Java through JVM intriniscs.

When first cloning the panama repository, it is necessary to update it to the desired experimental branch; this can be achieved using the hg update ${branch} command.
For an up-to-date list of the available branches, you might also want to run the hg branches command. For more information regarding each branch, please refer to the README.${branch} file in that branch (if that file does not exist, usual OpenJDK build instruction apply).
The legacy Panama repository is also available here, although we do not expect to carry out further work there; as such this repository should not be used (and in the future we might make this more explicit by marking the legacy repository as read-only). Repository workflow
The repository will be managed as follows (note, this process is local and subject to change):

No changes will be pushed to the default branch of the Panama repository. This branch should in fact always be in sync with the upstream repository (jdk/jdk) to facilitate automatic integration of upstream changes, as well as to allow developers to generate diffs against upstream in an easy and predictable fashion (see below).
Create and update JIRA issues to informally describe chunks of work, using repo-panama as the value of the Fix Version field. Additionally, labels are used to identify the branch to which the issue refers to, as shown here;
Commit rough changesets to JDK and/or JVM code, with ad hoc review, change set format, and testing. A typical example of review process for Panama changesets can be found here
Automated infrastructure will take care of performing regular test runs when new changes are pushed to any of the Panama branches; additionally, the infrastructure might automatically propagate changesets from the default branch to other experimental branches (not all branches might opt in on this feature given the subtlety of some of the changes involved).
Infrequently, create a “curated” change set targeted at the upstream JDK repository; properly review, test, integrate. For an example of how this integration process might work, see here. Developers can easily generate a diff against upstream using the hg diff --rev default command from any experimental branch.

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