OCaml 5.1.1 released

In the last three months after the release of OCaml 5.1.0, three significant regressions have been discovered in OCaml 5.1.0. Those regressions concern the packaging of executables, the typechecking of OCaml programs, and the performance of numerical codes.

Since those regressions affect many users and could have lasting effects, we have published a patch release, OCaml 5.1.1, fixing those issues.

As a major exception to our policy for patch releases, OCaml 5.1.1 will contain one breaking change in the standard library: the Compression flag has been removed from the Marshal module.
This drastic measure has been taken because supporting zstd compression in the standard library made zstd a dependency of all OCaml executables. Since the compiler should not propagate its dependencies on end-users, the support for compressed marshalling has been moved to a compiler internal library in 5.1.1.

Accounting for the still experimental nature of the multicore runtime, this patch release 5.1.1 also contains safe fixes for subtle concurrency bugs in the OCaml runtime.

In brief, if you were using OCaml 5.1.0, I strongly recommend that you switch to 5.1.1 .

The full list of changes is available below for more details.


Installation Instructions

The base compiler can be installed as an opam switch with the following commands:

opam update
opam switch create 5.1.1

The source code for the release is also directly available on:


Changes in OCaml 5.1.1 (8 December 2023)

Standard Library:

  • (breaking change) #12562, #12734, #12783: Remove the Marshal.Compression flag to the
    Marshal.to_* functions introduced in 5.1 by #12006, as it cannot
    be implemented without risking to link -lzstd with all
    ocamlopt-generated executables. The compilers are still able to use
    ZSTD compression for compilation artefacts.
    (Xavier Leroy and David Allsopp, report by Kate Deplaix, review by
    Nicolás Ojeda Bär, Kate Deplaix, and Damien Doligez).

Bug Fixes:

  • #12623, fix the computation of variance composition
    (Florian Angeletti, report by Vesa Karvonen, review by Gabriel Scherer)

  • #12581, #12609: Fix error on uses of packed modules outside their pack
    to correctly handle nested packs
    (Vincent Laviron, report by Javier Chávarri, review by Pierre Chambart)

  • #12645, #12649 fix error messages for cyclic type definitions in presence of
    the -short-paths flag.
    (Florian Angeletti, report by Vesa Karvonen, review by Gabriel Scherer)

  • #12757: Fix ocamlnat (native toplevel) by registering frametables correctly
    (Stephen Dolan, Nick Barnes and Mark Shinwell,
    review by Vincent Laviron and Sébastien Hinderer)

  • #12791: extern is applied to definitions of caml_builtin_cprim
    and caml_names_of_builtin_cprim when linking bytecode ‘-custom’
    executables with a C++ linker.
    (Shayne Fletcher, review by Antonin Décimo and Xavier Leroy)

GC Performance Regression Fixes

  • #12318: GC: simplify the meaning of custom_minor_max_size: blocks with
    out-of-heap memory above this limit are now allocated directly in
    the major heap.
    (Damien Doligez, report by Stephen Dolan, review by Gabriel Scherer)

  • #12439: Finalize and collect dead custom blocks during minor collection
    (Damien Doligez, review by Xavier Leroy, Gabriel Scherer and KC
    Sivaramakrishnan)

  • #12590, #12595: Move caml_collect_gc_stats_sample in
    caml_empty_minor_heap_promote before barrier arrival.
    (B. Szilvasy, review by Gabriel Scherer)

  • #12491, #12493, #12500, #12754: Do not change GC pace when creating
    sub-arrays of bigarrays
    (Xavier Leroy, report by Ido Yariv, analysis by Gabriel Scherer,
    review by Gabriel Scherer and Fabrice Buoro)

Runtime Bug Fixes

  • #11800, #12707: fix an assertion race condition in install_backup_thread
    (Jan Midtgaard, review by Gabriel Scherer)

  • #12486, #12535: Fix delivery of unhandled effect exceptions on amd64 with
    –enable-frame-pointers
    (Miod Vallat, report by Jan Midtgaard, review by Gabriel Scherer)

  • #12712, #12742: fix an assertion boundary case in caml_reset_young_limit
    (Jan Midtgaard, review by Guillaume Munch-Maccagnoni)

  • #12713, #12715: disable common subexpression elimination for atomic loads
    (Gabriel Scherer and Vincent Laviron,
    review by Vincent Laviron, KC Sivaramakrishnan and Xavier Leroy,
    report by Vesa Karvonen and Carine Morel)

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