package rpc_parallel

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Type-safe parallel library built on top of Async_rpc


Dune Dependency






  • Take away @@deriving bin_io for managed workers.

  • Introduce a spawn_in_foreground function that returns a Process.t along with the worker.

    Also use this opportunity to clean up the handling of file descriptors in the spawn case as well.

  • Add a couple features to Rpc_parallel to make debugging connection issues easier.

    • Add Worker.Connection.close_reason

    • Add Worker.Connection.sexp_of_t

  • Add some extra security around making Rpc calls to workers.

    Because we do not expose the port of a worker, unless you do really hacky things, you are going to go through Rpc_parallel when running Rpcs. When Rpc_parallel connects to a worker, it initializes a connection state (that includes the worker state). This initialization would raise if the worker did not have a server listening on the port that the client was talking to. Add some security by enforcing unification of worker_ids instead of ports (which will be reused by the OS).

  • Make an Rpc_parallel test case deterministic


  • Adding the mandatory arguments redirect_stderr and redirect_stdout to Map_reduce so it is easier to debug your workers. Also removed spawn_exn in favor of only exposing spawn_config_exn. If you want to spawn a single worker, make a config of one worker.

  • Cleans up the implementation-side interface for aborting Pipe_rpcs.


    The aborted Deferred.t that got passed to Pipe_rpc implementations is gone. The situations where it would have been determined now close the reading end of the user-supplied pipe instead.


    Previously, when an RPC dispatcher decided to abort a query, the RPC implementation would get its aborted Deferred.t filled in, but would remain free to write some final elements to the pipe.

    This is a little bit more flexible than the new interface, but it's also problematic in that the implementer could easily just not pay attention to aborted. (They're not obligated to pay attention to when the pipe is closed, either, but at least they can't keep writing to it.) We don't think the extra flexibility was used at all.

    In the future, we may also simplify the client side to remove the abort function on the dispatch side (at least when not using dispatch_iter). For the time being it remains, but closing the received pipe is the preferred way of aborting the query.

    There are a couple of known ways this might have changed behavior from before. Both of these appear not to cause problems in the jane repo.

    • In the past, an implementation could write to a pipe as long as the client didn't disconnect, even if it closed its pipe. Now writes will raise after a client closes its pipe (or calls abort), since the implementor's pipe will also be closed in this case. Doing this was already unsafe, though, since the pipe was closed if the RPC connection was closed.

    • aborted was only determined if a client aborted the query or the connection was closed. The new alternative, Pipe.closed called on the returned pipe, will also be determined if the implementation closes the pipe itself. This is unlikely to cause serious issues but could potentially cause some confusing logging.

  • Deal with an fd leak in Managed worker connections

  • There was a race condition where spawn would return a Worker.t even though the worker had not daemonized yet. This manifested itself in a spurious test case failure.

    This also allowed for running the worker initialization code before we daemonize.

  • Reuse the master rpc settings when the worker connects using the Heartbeater module

  • Make all global state and rpc servers lazy.


    1. Toplevel hashtables are initialized with size 1 to reduce overhead due to linking with Rpc_parallel

    2. The master rpc server is only started upon the first call to spawn

  • Fixed a Rpc_parallel bug that caused a Master to Worker call to never return.

  • Add new functions spawn_and_connect and spawn_and_connection_exn which return back the worker and a connection to the worker.

    Also, move all the example code off of the managed module

  • Some refactoring:

    1. Take serve out of the Connection module. It shouldn't be in there because it does nothing with the Connection.t type

    2. Remove some unnecessary functions defined on Connection.t's. E.g. no longer expose close_reason because all the exception handling will be done with the registered exn handlers.

    3. Move Rpc_settings module

    4. Separate global_state into as_worker and as_master

    5. Some cleanup with how we are managing worker ids

    6. create a record type for Init_connection_state_rpc.query


  • Switched to PPX.

  • Expose the connection_timeout argument in rpc_parallel. This argument exists in Rpc_parallel_core.Parallel, but it is not exposed in Rpc_parallel.Parallel.

  • Allow custom handling of missed async_rpc heartbeats.

  • Give a better error message when redirecting output on a remote box to a file path that does not exist.

  • remove unncessary chmod 700 call on the remote executable

  • Give a clear error message for the common mistake of not making the Parallel.Make_worker() functor application top-level

  • Make errors/exceptions in Rpc_parallel more observable

    • Make stderr and stdout redirection mandatory in order to encourage logging stderr

    • Clean up the use of monitors across Rpc_parallel

    • Fix bug with exceptions that are sent directly to Monitor.main (e.g. Async_log does this)

  • Add the ability to explicitly initialize as a master and use some subcommand for the worker. This would allow writing programs with complex command structures that don't have to invoke a bunch of Rpc_parallel logic and start RPC servers for every command.

  • Add the ability to get log messages from a worker sent back to the master. In fact, any worker can register for the log messages of any other workers.


  • Fixed a file-descriptor leak

    There was a file descriptor leak when killing workers. Their stdin, stdout, and stderr remain open. We now close them after the worker process exits.


  • Added Parallel.State.get function, to check whether Rpc_parallel has been initialized correctly.

  • Added Map_reduce module, which is an easy-to-use parallel map/reduce library.

    It can be used to map/fold over a list while utilizing multiple cores on multiple machines.

    Also added support for workers to keep their own inner state.

  • Fixed bug in which zombie process was created per spawned worker.

    Also fixed shutdown on remote workers

  • Made it possible for workers to spawn other workers, i.e. act as masters.

  • Made the connection timeout configurable and bumped the default to 10s.


  • Follow changes in Async RPC


Initial import.