[Caml-list] Attn: Development Editor, Latest OCaml Weekly News

Alan Schmitt
2020-07-07T10:04:52Z

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Hello

Here is the latest OCaml Weekly News, for the week of June 30 to July
07, 2020.

Table of Contents
─────────────────

Releases of ringo
Multicore OCaml: June 2020
Time expression demo
Interactive OCaml development with utop in Emacs
Old CWN

Releases of ringo
═════════════════

Archive: [https://discuss.ocaml.org/t/ann-releases-of-ringo/5605/5]

Continuing this thread, Raphaël Proust said
───────────────────────────────────────────

Ringo provides bounded-size key-value stores. More specifically, it
provides a functor similar to `Hastbl.Make' except that the number of
bindings held by the tables is limited: inserting additional bindings
when the limit has been reached causes some previously inserted
binding to be removed.

More more specifically, Ringo provides a function `map_maker' that
takes parameters to customise the policies that determine the
behaviour of the cache when supernumerary bindings are inserted, and
returns the functor described above. Once a module `Cache' is
instantiated using this functor, it can be used as follows:

┌────
│ let cache = Cache.create size
│ let fetch_data uri =
│ match Cache.find_opt cache uri with
│ | Some data -> data
│ | None ->
│ let data = really_fetch_data uri in
│ Cache.replace cache uri data;
│ data
└────

The cache will only hold up to [size] bindings, which avoids leaking
memory. Additionally, the parameters for `map_maker' allow you to
customise:

• The replacement policy: which binding is removed when a
supernumerary is inserted (currently supports least-recently used
and first-in first-out).
• The overflow policy: whether the cache can weakly hold some
supernumerary elements (if so, the cache may hold more but the GC
can always collect them if space is lacking).
• The accounting precision: whether to keep precise track of
removed/replaced elements.

In addition, Ringo also provide set-caches: i.e., sets (rather than
maps) with bounded size and all the same properties as above.

Also note Ringo-Lwt (`ringo-lwt') provides Lwt wrappers around Ringo
caches.

If you have suggestions for a different concise synopsis for `opam',
feel free to send them this way.

Use cases are, I guess, caches. In particular those that might receive
many elements not all of which you can hold in memory. We use it in a
few places in the Tezos project to hold resources (blocks, operations,
etc.) that are fetched from the P2p layer: it avoids having to fetch
them again from the network.

I think `anycache', `lru', and `lru-cache' are all alternatives
available on opam.

Raphaël Proust later added
──────────────────────────

The documentation is now available online at
[https://nomadic-labs.gitlab.io/ringo/index.html]

Of particular interest:
• [The signature for a `ringo' key-value cache]
• [The entry point for the `ringo' library] (allowing you to
instantiate modules with the above signature as well as simple value
caches)
• [The signature for `ringo-lwt' cache]

[The signature for a `ringo' key-value cache]
https://nomadic-labs.gitlab.io/ringo/ringo/Ringo/module-type-CACHE_MAP/index.html

[The entry point for the `ringo' library]
https://nomadic-labs.gitlab.io/ringo/ringo/Ringo/index.html

[The signature for `ringo-lwt' cache]
https://nomadic-labs.gitlab.io/ringo/ringo-lwt/Ringo_lwt/Sigs/module-type-CACHE_MAP/index.html

Multicore OCaml: June 2020
══════════════════════════

Archive:
[https://discuss.ocaml.org/t/multicore-ocaml-june-2020/6047/1]

Anil Madhavapeddy announced
───────────────────────────

Welcome to the June 2020 [Multicore OCaml] report! As with [previous
updates], many thanks to @shakthimaan and @kayceesrk for collating the
updates for the month of June 2020. /This is an incremental update;
new readers may find it helpful to flick through the previous posts
first./

This month has seen a tremendous surge of activity on the upstream
OCaml project to prepare for multicore integration, as @xavierleroy
and the core team have driven a number of initiatives to prepare the
OCaml project for the full multicore featureset. To reflect this,
from next month we will have a status page on the ocaml-multicore wiki
with the current status of both our multicore branch and the upstream
OCaml project itself.

Why not from this month? Well, there's good news and bad news. [Last
month], I observed that we are a PR away from most of the opam
ecosystem working with the multicore branch. The good news is that we
are still a single PR away from it working, but it's a different one
:-) The retrofitting of the `Threads' library has brought up [some
design complexities], and so rather than putting in a "bandaid" fix,
we are integrating a comprehensive solution that will work with system
threads, domains and (eventually) fibres. That work has taken some
time to get right, and I hope to be able to update you all on an
opam-friendly OCaml 4.10.0+multicore in a few weeks.

Aside from this, there have been a number of other improvements going
into the multicore branches: [mingw Windows support], [callstack
improvements], [fixing the Unix module] and so on. The full list is in
the detailed report later in this update.

[Multicore OCaml] https://github.com/ocaml-multicore/ocaml-multicore

[previous updates] https://discuss.ocaml.org/tag/multicore-monthly

[Last month]
https://discuss.ocaml.org/t/multicore-ocaml-may-2020-update/5898

[some design complexities]
https://github.com/ocaml-multicore/ocaml-multicore/pull/342

[mingw Windows support]
https://github.com/ocaml-multicore/ocaml-multicore/pull/351

[callstack improvements]
https://github.com/ocaml-multicore/ocaml-multicore/pull/363

[fixing the Unix module]
https://github.com/ocaml-multicore/ocaml-multicore/pull/346

Sandmark benchmarks
╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌

A major milestone in this month has been the upgrade to the latest
dune.2.6.0 to build Multicore OCaml 4.10.0 for the Sandmark
benchmarking project. A number of new OPAM packages have been added,
and the existing packages have been upgraded to their latest
versions. The Multicore OCaml code base has seen continuous
performance improvements and enhancements which can be observed from
the various PRs mentioned in the report.

We would like to thank:

• @xavierleroy for working on a number of multicore-prequisite PRs to
make stock OCaml ready for Multicore OCaml.
• @camlspotter has reviewed and accepted the camlimages changes and
made a release of camlimages.5.0.3 required for Sandmark.
• @dinosaure for updating the decompress test benchmarks for Sandmark
to build and run with dune.2.6.0 for Multicore OCaml 4.10.0.

A chapter on Parallel Programming in Multicore OCaml with topics on
task pool, channels section, profiling with code examples is being
written. We shall provide an early draft version of the document to
the community for your valuable feedback.

Papers
╌╌╌╌╌╌

Our "Retrofitting Parallism onto OCaml" paper has been officially
accepted at [ICFP 2020] which will be held virtually between August
23-28, 2020. A [preprint] of the paper was made available earlier, and
will be updated in a few days with the camera-ready version for ICFP.
Please do feel free to send on comments and queries even after the
paper is published, of course.

Excitingly, another multicore-related paper on [Cosmo: A Concurrent
Separation Logic for Multicore OCaml] will also be presented at the
same conference.

The Multicore OCaml updates are first listed in our report, which are
followed by improvements to the Sandmark benchmarking
project. Finally, the changes made to upstream OCaml which include
both the ongoing and completed tasks are mentioned for your reference.

[ICFP 2020]
https://icfp20.sigplan.org/track/icfp-2020-papers#event-overview

[preprint] https://arxiv.org/abs/2004.11663

[Cosmo: A Concurrent Separation Logic for Multicore OCaml]
http://gallium.inria.fr/~fpottier/publis/mevel-jourdan-pottier-cosmo-2020.pdf

Multicore OCaml
╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌

◊ Ongoing

• [ocaml-multicore/ocaml-multicore#339] Proposal for domain-local
storage

An RFC proposal to implement a domain-local storage in Multicore
OCaml. Kindly review the idea and share your feedback!

• [ocaml-multicore/ocaml-multicore#342] Implementing the threads
library with Domains

An effort to rebase @jhwoodyatt's implementation of the Thread
library for Domains.

• [ocaml-multicore/ocaml-multicore#357] Implementation of systhreads
with pthreads

Exploring the possibilty of implementing systhreads with pthreads,
while still maintaining compatibility with the existing solution.

• [ocaml/dune#3548] Dune fails to pick up secondary compiler

The `ocaml-secondary-compiler' fails to install with
dune.2.6.0. This is required as Multicore OCaml cannot build the
latest dune without systhreads support.

[ocaml-multicore/ocaml-multicore#339]
https://github.com/ocaml-multicore/ocaml-multicore/issues/339

[ocaml-multicore/ocaml-multicore#342]
https://github.com/ocaml-multicore/ocaml-multicore/pull/342

[ocaml-multicore/ocaml-multicore#357]
https://github.com/ocaml-multicore/ocaml-multicore/issues/357

[ocaml/dune#3548] https://github.com/ocaml/dune/issues/3548

◊ Completed

• [ocaml-multicore/multicore-opam#22] Update dune to 2.6.0

The dune version in the Multicore OPAM repository is now updated to
use the latest 2.6.0.

• [ocaml-multicore/ocaml-multicore#338] Introduce Lazy.try_force and
Lazy.try_force_val

An implementation of `Lazy.try_force' and `Lazy.try_force_val'
functions to implement concurrent lazy abstractions.

• [ocaml-multicore/ocaml-multicore#340] Fix Atomic.exchange in
concurrent_minor_gc

A patch that introduces `Atomic.exchange' through `Atomic.get' that
provides the appropriate read barrier for correct exchange semantics
for `caml_atomic_exchange' in `memory.c'.

• [ocaml-multicore/ocaml-multicore#343] Fix extcall noalloc DWARF

The DWARF information emitted for `extcall noalloc' had broken
backtraces and this PR fixes the same.

• [ocaml-multicore/ocaml-multicore#345] Absolute exception stack

The representation of the exception stack is changed from relative
addressing to absolute addressing and the results are promising. The
Sandmark serial benchmark results after the change is illustrated in
the following graph:

[https://aws1.discourse-cdn.com/standard11/uploads/ocaml/optimized/2X/b/b385409b3f9e44cbfef98de668b0b4d0ed403472_2_1380x436.png]

• [ocaml-multicore/ocaml-multicore#347] Turn on -Werror by default

Adds a `--enable-warn-error' option to `configure' to treat C
compiler warnings as errors.

• [ocaml-multicore/ocaml-multicore#353] Poll for interrupts in
cpu_relax without locking

Use `Caml_check_gc_interrupt' first to poll for interrupts without
locking, and then proceeding to handle the interrupt with the lock.

• [ocaml-multicore/ocaml-multicore#354] Add Caml_state_field to
domain_state.h

The `Caml_state_field' macro definition in domain_state.h is
required for base-v0.14.0 to build for Multicore OCaml 4.10.0 with
dune.2.6.0.

• [ocaml-multicore/ocaml-multicore#355] One more location to poll for
interrupts without lock

Another use of `Caml_check_gc_interrupt' first to poll for
interrupts without lock, similar to
[ocaml-multicore/ocaml-multicore#353].

• [ocaml-multicore/ocaml-multicore#356] Backup threads for domain

Introduces `backup threads' to perform GC and handle service
interrupts when the domain is blocked in the kernel.

• [ocaml-multicore/ocaml-multicore#358] Fix up bad CFI information in
amd64.S

Add missing `CFI_ADJUST' directives in `runtime/amd64.S' for
`caml_call_poll' and `caml_allocN'.

• [ocaml-multicore/ocaml-multicore#359] Inline caml_domain_alone

The PR makes `caml_domain_alone' an inline function to improve
performance for `caml_atomic_cas_field' and other atomics in
`memory.c'.

• [ocaml-multicore/ocaml-multicore#360] Parallel minor GC inline mask
rework

The inline mask rework for the promotion path to the
`parallel_minor_gc' branch gives a 3-5% performance improvement for
`test_decompress' sandmark benchmark, and a decrease in the executed
instructions for all other benchmarks.

• [ocaml-multicore/ocaml-multicore#361] Mark stack push work credit

The PR improves the Multicore mark work accounting to be in line
with stock OCaml.

• [ocaml-multicore/ocaml-multicore#362] Iloadmut does not clobber rax
and rdx when we do not have a read barrier

A code clean-up to free the registers `rax' and `rdx' for OCaml code
when `Iloadmut' is used.

[ocaml-multicore/multicore-opam#22]
https://github.com/ocaml-multicore/multicore-opam/pull/22

[ocaml-multicore/ocaml-multicore#338]
https://github.com/ocaml-multicore/ocaml-multicore/pull/338

[ocaml-multicore/ocaml-multicore#340]
https://github.com/ocaml-multicore/ocaml-multicore/pull/340

[ocaml-multicore/ocaml-multicore#343]
https://github.com/ocaml-multicore/ocaml-multicore/pull/343

[ocaml-multicore/ocaml-multicore#345]
https://github.com/ocaml-multicore/ocaml-multicore/pull/345

[ocaml-multicore/ocaml-multicore#347]
https://github.com/ocaml-multicore/ocaml-multicore/pull/347

[ocaml-multicore/ocaml-multicore#353]
https://github.com/ocaml-multicore/ocaml-multicore/pull/353

[ocaml-multicore/ocaml-multicore#354]
https://github.com/ocaml-multicore/ocaml-multicore/pull/354

[ocaml-multicore/ocaml-multicore#355]
https://github.com/ocaml-multicore/ocaml-multicore/pull/355

[ocaml-multicore/ocaml-multicore#356]
https://github.com/ocaml-multicore/ocaml-multicore/pull/356

[ocaml-multicore/ocaml-multicore#358]
https://github.com/ocaml-multicore/ocaml-multicore/pull/358

[ocaml-multicore/ocaml-multicore#359]
https://github.com/ocaml-multicore/ocaml-multicore/pull/359

[ocaml-multicore/ocaml-multicore#360]
https://github.com/ocaml-multicore/ocaml-multicore/pull/360

[ocaml-multicore/ocaml-multicore#361]
https://github.com/ocaml-multicore/ocaml-multicore/pull/361

[ocaml-multicore/ocaml-multicore#362]
https://github.com/ocaml-multicore/ocaml-multicore/pull/362

Benchmarking
╌╌╌╌╌╌╌╌╌╌╌╌

◊ Ongoing

• [ocaml-bench/sandmark#8] Ability to run compiler variants in
Sandmark

A feature to specify configure options when building compiler
variants such as `flambda' is useful for development and
testing. This feature is being worked upon.

• [ocaml-bench/sandmark#107] Add Coq benchmarks

We are continuing to add more benchmarks to Sandmark for Multicore
OCaml and investigating adding the [Coq] benchmarks to our
repertoire!

• [ocaml-bench/sandmark#124] User configurable paramwrapper added to
Makefile

A `PARAMWRAPPER' environment variable can be passed as an argument
by specifying the `--cpu-list' to be used for parallel benchmark
runs.

• [ocaml-bench/sandmark#131] Update decompress benchmarks

Thanks to @dinosaure for updating the decompress benchmarks in order
to run them with dune.2.6.0 for Multicore OCaml 4.10.0.

• [ocaml-bench/sandmark#132] Update dependency packages to use
dune.2.6.0 and Multicore OCaml 4.10.0

Sandmark has been running with dune.1.11.4, and we need to move to
the latest dune.2.6.0 for using Multicore OCaml 4.10.0 and beyond,
as mentioned in [Promote dune to > 2.0]. The PR updates over 30
dependency packages and successfully builds both serial and parallel
benchmarks!

[ocaml-bench/sandmark#8]
https://github.com/ocaml-bench/sandmark/issues/8

[ocaml-bench/sandmark#107]
https://github.com/ocaml-bench/sandmark/issues/107

[Coq] https://coq.inria.fr/

[ocaml-bench/sandmark#124]
https://github.com/ocaml-bench/sandmark/pull/124

[ocaml-bench/sandmark#131]
https://github.com/ocaml-bench/sandmark/pull/131

[ocaml-bench/sandmark#132]
https://github.com/ocaml-bench/sandmark/pull/132

[Promote dune to > 2.0]
https://github.com/ocaml-bench/sandmark/issues/106

◊ Completed

• [camlspotter/camlimages#1] Use dune-configurator instead of
configurator for camlimages

A new release of `camlimages.5.0.3' was made by @camlspotter after
accepting the changes to camlimages.opam in order to build with
dune.2.6.0.

• [ocaml-bench/sandmark#115] Task API Port: LU-Decomposition, Floyd
Warshall, Mandelbrot, Nbody

The changes to use the `Domainslib.Task' API for the listed
benchmarks have been merged.

• [ocaml-bench/sandmark#121] Mention sudo access for
run_all_parallel.sh script

The README.md file has been updated with the necessary `sudo'
configuration steps to execute the `run_all_parallel.sh' script for
nightly builds.

• [ocaml-bench/sandmark#125] Add cubicle benchmarks

The `German PFS' and `Szymanski's mutual exclusion algorithm'
cubicle benchmarks have been included in Sandmark.

• [ocaml-bench/sandmark#126] Update ocaml-versions README to reflect
4.10.0+multicore

The README has now been updated to reflect the latest 4.10.0
Multicore OCaml compiler and its variants.

• [ocaml-bench/sandmark#129] Add target to run parallel benchmarks in
the CI

The .drone.yml file used by the CI has been updated to run both the
serial and parallel benchmarks.

• [ocaml-bench/sandmark#130] Add missing dependencies in
multicore-numerical

The `domainslib' library has been added to the dune file for the
multicore-numerical benchmark.

[camlspotter/camlimages#1]
https://gitlab.com/camlspotter/camlimages/-/merge_requests/1

[ocaml-bench/sandmark#115]
https://github.com/ocaml-bench/sandmark/pull/115

[ocaml-bench/sandmark#121]
https://github.com/ocaml-bench/sandmark/pull/121

[ocaml-bench/sandmark#125]
https://github.com/ocaml-bench/sandmark/pull/125

[ocaml-bench/sandmark#126]
https://github.com/ocaml-bench/sandmark/pull/126

[ocaml-bench/sandmark#129]
https://github.com/ocaml-bench/sandmark/pull/129

[ocaml-bench/sandmark#130]
https://github.com/ocaml-bench/sandmark/pull/130

OCaml
╌╌╌╌╌

◊ Ongoing

• [ocaml/ocaml#9541] Add manual page for the instrumented runtime

The [instrumented runtime] has been merged to OCaml 4.11.0. A manual
for the same has been created and is under review.

• [sadigqj/ocaml#1] GC colours change

This PR removes the grey colour used in stock OCaml to match the
scheme used by the Multicore major collector. The performance and
considerations are included for review.

[ocaml/ocaml#9541] https://github.com/ocaml/ocaml/pull/9541

[instrumented runtime] https://github.com/ocaml/ocaml/pull/9082

[sadigqj/ocaml#1] https://github.com/sadiqj/ocaml/pull/1

◊ Completed

• [ocaml/ocaml#9619] A self-describing representation for function
closures

The PR provides a way to record the position of the environment for
each entry point for function closures.

• [ocaml/ocaml#9649] Marshaling for the new closure representation

The `output_value' marshaler has been updated to use the new closure
representation. There is no change required for the `input_value'
unmarshaler.

• [ocaml/ocaml#9655] Introduce type Obj.raw_data and functions
Obj.raw_field, Obj.set_raw_field to manipulate out-of-heap pointers

The PR introduces a type `Obj.bits', and functions `Obj.field_bits'
and `Obj.set_field_bits' to read and write bit representation of
block fields to support the no-naked-pointer operation.

• [ocaml/ocaml#9678] Reimplement Obj.reachable_word using a hash table
to detect sharing

The `caml_obj_reachable_words' now uses a hash table instead of
modifying the mark bits of block headers to detect sharing. This is
required for compatibility with Multicore OCaml.

• [ocaml/ocaml#9680] Naked pointers and the bytecode interpreter

The bytecode interpreter implementation is updated to support the
no-naked-pointers mode operation as required by Multicore OCaml.

• [ocaml/ocaml#9682] Signal handling in native code without the page
table

The patch uses the code fragment table instead of a page table
lookup for signal handlers to know whether the signal came from
ocamlopt-generated code.

• [ocaml/ocaml#9683] globroots.c: adapt to no-naked-pointers mode

The patch considers out-of-heap pointers as major-heap pointers in
no-naked-pointers mode for global roots management.

• [ocaml/ocaml#9689] Generic hashing for the new closure
representation

The hashing functions have been updated to use the latest closure
representation from [ocaml/ocaml#9619] for the no-naked-pointers
mode.

• [ocaml/ocaml#9698] The end of the page table is near

The PR eliminates some of the use of the page tables in the runtime
system when built with no-naked-pointers mode.

Our thanks to all the OCaml developers and users in the community for
their continued support and contribution to the project. Stay safe!

[ocaml/ocaml#9619] https://github.com/ocaml/ocaml/pull/9619

[ocaml/ocaml#9649] https://github.com/ocaml/ocaml/pull/9649

[ocaml/ocaml#9655] https://github.com/ocaml/ocaml/pull/9655

[ocaml/ocaml#9678] https://github.com/ocaml/ocaml/pull/9678

[ocaml/ocaml#9680] https://github.com/ocaml/ocaml/pull/9680

[ocaml/ocaml#9682] https://github.com/ocaml/ocaml/pull/9682

[ocaml/ocaml#9683] https://github.com/ocaml/ocaml/pull/9683

[ocaml/ocaml#9689] https://github.com/ocaml/ocaml/pull/9689

[ocaml/ocaml#9698] https://github.com/ocaml/ocaml/pull/9698

Acronyms
╌╌╌╌╌╌╌╌

• API: Application Programming Interface
• CFI: Call Frame Information
• CI: Continuous Integration
• DWARF: Debugging With Attributed Record Formats
• GC: Garbage Collector
• ICFP: International Conference on Functional Programming
• OPAM: OCaml Package Manager
• PR: Pull Request
• RFC: Request for Comments

Time expression demo
════════════════════

Archive: [https://discuss.ocaml.org/t/time-expression-demo/6052/1]

Darren announced
────────────────

An interactive demo for a small part of our time stuff and schedule
handling library is available here:
[https://daypack-dev.github.io/time-expr-demo/]

Time expression is in essence a language for specifying time points or
time slots precisely and concisely, while trying to mimic natural
language.

The implementation of the demo core itself can be seen here:
[https://github.com/daypack-dev/time-expr-demo/blob/master/src/demo.ml]
, where the usage of Daypack-lib is shown.

Lastly, the library is still a prototype, so expect some faults in the
outputs of the demo here and there.

Interactive OCaml development with utop in Emacs
════════════════════════════════════════════════

Archive:
[https://discuss.ocaml.org/t/interactive-ocaml-development-with-utop-in-emacs/6058/1]

Samarth Kishor announced
────────────────────────

I made a [blog post] about REPL driven development with utop in Emacs
a few months ago. Please let me know if you found it useful or have
anything to add! I'm a bit new to OCaml so any feedback helps.

There was a [similar post about REPL driven development] last year and
my post addresses a lot of those points. I wish I'd seen that post
before I wrote this since there's a ton of useful information in the
comments.

[blog post]
https://samarthkishor.github.io/posts/interactive_ocaml_development/

[similar post about REPL driven development]
https://discuss.ocaml.org/t/ocaml-repl-driven-development/4068

Old CWN
═══════

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[Alan Schmitt]

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