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List:       openjdk-serviceability-dev
Subject:    Re: RFR: 8295044: Implementation of Foreign Function and Memory API (Second Preview)
From:       Maurizio Cimadamore <mcimadamore () openjdk ! org>
Date:       2022-10-27 20:55:35
Message-ID: rDhx7aLwHsyZdbzh_3bnwiu1QXHQm7LHh9nB2YYNXko=.6665a243-3366-471c-ad0b-244271db4241 () github ! com
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On Wed, 26 Oct 2022 13:11:50 GMT, Maurizio Cimadamore <mcimadamore@openjdk.org> \
wrote:

> This PR contains the API and implementation changes for JEP-434 [1]. A more \
> detailed description of such changes, to avoid repetitions during the review \
> process, is included as a separate comment. 
> [1] - https://openjdk.org/jeps/434

Here are the main API changes introduced in this round (there are also some JVM \
changes which will be integrated separately):

* The main change is the removal of `MemoryAddress` and `Addressable`. Instead, \
*zero-length memory segments* are used whenever the API needs to model "raw" \
addresses coming from native code. This simplifies the API, removing an ambiguous \
abstraction as well as some duplication in the API (see accessor methods in \
`MemoryAddress`);

* To allow for "unsafe" access of zero-length memory segments, a new method has been \
added to `ValueLayout.OfAddress`, namely `asUnbounded`. This new restricted method \
takes an address layout and creates a new unbounded address layout. When using an \
unbounded layout to dereference memory, or construct downcall method handles, the API \
will create memory segments with maximal length (i.e. `Long.MAX_VALUE`, rather than \
zero-length memory segments, which can therefore be accessed;

* The `MemoryLayout` hierarchy has been improved in several ways. First, the \
hierarchy is now defined in terms of sealed interfaces (intermediate abstract classes \
have been moved into the implementation package). The hierarchy is also exhaustive \
now, and works much better to pattern matching. More specifically, three new types \
have been added: `PaddingLayout`, `StructLayout` and `UnionLayout`, the latter two \
are a subtype of `GroupLayout`. Thanks to this move, several predicate methods \
(`isPadding`, `isStruct`, `isUnion`) have been dropped from the API;

* The `SymbolLookup::lookup` method has been renamed to `SymbolLookup::find` - to \
avoid using the same word `lookup` in both noun and verb form, which leads to \
confusion;

* A new method, on `ModuleLayer.Controller` has been added to enable native access on \
a module in a custom layer;

* The new interface `Linker.Option` has been introduced. This is a tag interface \
accepted in `Linker::downcallHandle`. At the moment, only a single option is \
provided, to specify variadic function calls (because of this, the \
`FunctionDescriptor` interface has been simplified, and is now a simple carrier of \
arguments/return layouts). More linker options will follow.

Javadoc: http://cr.openjdk.java.net/~mcimadamore/jdk/8295044/v1/javadoc/java.base/java/lang/foreign/package-summary.html


-------------

PR: https://git.openjdk.org/jdk/pull/10872


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