I am very pleased to announce that the core Ada 2022 “parallel” features have been implemented for mainline FSF GNAT as part of a successful Google Summer of Code project. The patch is now ready for beta testing.
We are preparing to formally submit this patch to the FSF GCC project, to have it incorporated into GCC trunk, and therefore all future FSF GCC releases. Before we make that submission, we hope to seek additional feedback from the Ada community.
This patch introduces most core capabilities for the parallel keyword, including:
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Parallel loops
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Parallel blocks
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Early exit
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Chunking
This patch does NOT yet support Parallel Iterators - but this is being actively worked on and hopefully will be completed soon.
The GSoC project work was hosted on the Ada Rapporteur Group’s own GCC mirror github repo, and the stable version of the parallel beta release currently lives at https://github.com/Ada-Rapporteur-Group/gcc-mirror/tree/devel/arg-proto/ada2022-parallel-release.
This branch can be built and bootstrapped as-is on most mainstream platforms using FSF GCC 15, with a standard build process. No additional libraries or build flags are needed, as the parallel features do not imply any new complier, runtime, or platform dependencies.
Additionally, Maxim Reznik has made available binary builds of the parallel support beta for most popular platforms. He also includes instructions on how to get going with Alire. Look for the “GCC with parallel PREVIEW” release at https://github.com/reznikmm/GNAT-FSF-builds/releases. Expand the “Assets” area at the bottom of the section to download binary builds for your platform.
By default, GNAT will expand parallel loops/blocks into sequential (regular) loops resp. blocks. To get actual parallelization of parallel constructs, the existence of an Ada “light weight threading” library (formally an Ada subsystem a la the Ada Reference Manual 10.1-3) is required. GNAT will detect the presence of the “LWT” subsystem at compile-time, and if “withed”, will generate calls to the LWT subsystem during expansion. It is therefore conventional that the unit containing the main subprogram “withs” LWT. Refer to the example programs included with the reference LWT subsystem to see how this works.
A reference LWT subsystem implementation currently lives under the Parasail language project (https://github.com/parasail-lang/parasail). This may be separated from the Parasail repository at a later time. This LWT implementation is also an official Alire crate of the same name, and Maxim’s instructions detail how to install LWT and use the beta toolchain under Alire.
The reference LWT subsystem could potentially be incorporated into the GNAT standard library (libgnat) at some point in the future, but it was decided to keep the first iteration as simple and digestible as possible.
This is only the first phase, and we look forward to additional refinements in the future!
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Note that Alire is NOT required to beta test this build, and simply making the sources of the LWT reference implementation available to the compiler is sufficient (using -I for gcc or gnatmake)
There are also some Ada 2022 parallel example programs under lwt/a22_examples, and these can be build and run with the vanilla FSF GNAT toolchain as follows (Linux/UNIX):
$ git clone https://github.com/parasail-lang/parasail
$ cd parasail/lwt/a22_examples
$ gnatmake -gnat2022 -I../ n_queens.adb
$ ./n_queens
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We would love to have more members of the Ada community try-out these features. Please let me know if you need any support getting set up, or if you have any other questions.