package moonpool-lwt

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Event loop for moonpool based on Lwt-engine (experimental)


Dune Dependency






  • breaking: remove Immediate_runner (bug prone and didn't handle effects). Moonpool_fib.main can be used to handle effects in the main function.

  • remove deprecated alias Moonpool.Pool

  • feat: add structured concurrency sub-library moonpool.fib with fibers. Fibers can use await and spawn other fibers that will be appropriately cancelled when their parent is.

  • feat: add add moonpool-lwt as an experimental bridge between moonpool and lwt. This allows moonpool runners to be used from within Lwt to perform background computations, and conversely to call Lwt from moonpool with some precautions.

  • feat: task-local storage in the main moonpool runners, available from fibers and regular tasks.

  • feat: add Exn_bt to core

  • feat: add Runner.dummy

  • make moonpool.forkjoin optional (only on OCaml >= 5.0)

  • feat: add Fut.Advanced.barrier_on_abstract_container_of_futures

  • feat: add Fut.map_list

  • refactor: split off domain pool to moonpool.dpool

  • fix too early exit in Ws_pool


  • fix Ws_pool: workers would exit before processing all remaining tasks upon shutdown



  • add Bb_queue.transfer

  • add Bb_queue.to_{iter,gen,seq}

  • add Fifo_pool, a simple pool with a single blocking queue for workloads with coarse granularity tasks that value latency (e.g. a web server)

  • add a work-stealing pool for heavy compute workloads that feature a lot of await/fork-join, with a lot of help from Vesa Karvonen (@polytypic)

  • add Fut.spawn_on_current_runner

  • add Runner.{spawn_on_current_runner, await}

  • add a few more toplevel aliases in Moonpool itself

  • add No_runner: a runner that runs tasks synchronously in the caller

  • on shutdown, pools will finish running all present tasks before closing. New tasks are immediately rejected.

  • use an optional dependency on thread-local-storage to implement work stealing and spawn_on_current_runner


  • use the main domain to spawn threads on it. This means we can really use all cores, not all but one.

  • in Fork_join.both, only one of the two sides schedules a task, the other runs in the current thread. This reduces scheduling overhead.

  • compare to domainslib in benchmarks. With the WS pool we're now slightly ahead in terms of overhead on the recursive fib benchmark.


  • deprecate Pool, now an alias to Fifo_pool

  • the Fut.Infix_local and Fut.infix are gone, replaced with a simpler Fut.Infix module that tries to use the current runner for intermediate tasks.


  • add Fut.{reify_error,bind_reify_error}

  • full lifecycle for worker domains, where a domain will shutdown if no thread runs on it, after a short delay.

  • fix: generalize type of create_arg

  • perf: in Bb_queue, only signal condition on push if queue was empty


  • add Fork_join for parallelizing computations. This is only available on OCaml 5.x because it relies on effects.

  • add Fork_join.{for_,map_array,map_list}

  • add Fork_join.all_{list,init}

  • add Pool.with_

  • add a channel module

  • add Runner, change Pool to produce a Runner.t

  • add a Lock module

  • add support for domain-local-await when installed

  • add Fut.await for OCaml >= 5.0

  • fix: Fork_join.both_ignore now has a more general type

  • expose Suspend_ and its internal effect with an unstability alert. This is intended for implementors of Runner only.

  • port from containers, replace previous codegen with it. This will provide better flexibility for supporting multiple versions of OCaml in the future.

  • add Pool.run_wait_block; rename into Pool.run_async

  • fix: in blocking queue, pop works on a non empty closed queue


  • add Fut.for_list

  • add around_task to Pool.create

  • add Pool.shutdown_without_waiting

  • add Pool.num_tasks

  • add Fut.is_done

  • add Blocking_queue.size

  • add Fut.for_array to easily iterate on an array in parallel

  • add Fut.get_or_fail{,_exn}

  • perf: limit number of work queues in pool

  • perf: use multiple queues and non-blocking work-stealing from them, in pool this improves the behavior for many small tasks by reducing contention on each queue

  • fix: fut: actually run all map/bind callbacks in pool if provided


  • fix(fut): fix bug when calling wait_list []

  • fix: join_array on arrays of length=1 had a bound error


initial release


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