.. _server-protocol: Server Protocol =============== A Futhark program can be compiled to a *server executable*. Such a server maintains a Futhark context and presents a line-oriented interface (over stdin/stdout) for loading and dumping values, as well as calling the entry points in the program. The main advantage over the plain executable interface is that program initialisation is done only *once*, and we can work with opaque values. The server interface is not intended for human consumption, but is useful for writing tools on top of Futhark programs, without having to use the C API. Futhark's built-in benchmarking and testing tools use server executables. A server executable is started like any other executable, and supports most of the same command line options (:ref:`executable-options`). Basics ------ Each command is sent as a *single line* on standard input. A command consists of space-separated *words*. A word is either a sequence of non-space characters (``foo``), *or* double quotes surrounding a sequence of non-newline and non-quote characters (``"foo bar"``). The response is sent on standard output. The server will print ``%%% OK`` on a line by itself to indicate that a command has finished. It will also print ``%%% OK`` at startup once initialisation has finished. If initialisation fails, the process will terminate. If a command fails, the server will print ``%%% FAILURE`` followed by the error message, and then ``%%% OK`` when it is ready for more input. Some output may also precede ``%%% FAILURE``, e.g. logging statements that occured before failure was detected. Fatal errors that lead to server shutdown may be printed to stderr. Variables --------- Some commands produce or read variables. A variable is a mapping from a name to a Futhark value. Values can be both transparent (arrays and primitives), but they can also be *opaque* values. These can be produced by entry points and passed to other entry points, but cannot be directly inspected. Types ----- All variables have types, and all entry points accept inputs and produce outputs of defined types. The notion of transparent and opaque types are the same as in the C API: primitives and array of primitives are directly supported, and everything else is treated as opaque. See also :ref:`valuemapping`. When printed, types follow basic Futhark type syntax *without* sizes (e.g. ``[][]i32``). Uniqueness is not part of the types, but is indicated with an asterisk in the ``inputs`` and ``outputs`` commands (see below). Consumption and aliasing ------------------------ Since the server protocol closely models the C API, the same rules apply to entry points that consume their arguments (see :ref:`api-consumption`). In particular, consumed variables must still be freed with the ``free`` command - but this is the only operation that may be used on consumed variables. Commands -------- The following commands are supported. General Commands ~~~~~~~~~~~~~~~~ ``types`` ......... Print the names of available types, one per line. ``entry_points`` ................ Print the names of available entry points. ``call`` *entry* *o1* ... *oN* *i1* ... *iM* ............................................ Call the given entry point with input from the variables *i1* to *iM*. The results are stored in *o1* to *oN*, which must not already exist. ``restore`` *file* *v1* *t1* ... *vN* *tN* .......................................... Load *N* values from *file* and store them in the variables *v1* to *vN* of types *t1* to *tN*, which must not already exist. ``store`` *file* *v1* ... *vN* .............................. Store the *N* values in variables *v1* to *vN* in *file*. ``free`` *v1* ... *vN* ...................... Delete the given variables. ``rename`` *oldname* *newname* .............................. Rename the variable *oldname* to *newname*, which must not already exist. ``inputs`` *entry* .................. Print the types of inputs accepted by the given entry point, one per line. If the given input is consumed, the type is prefixed by `*`. ``outputs`` *entry* ................... Print the types of outputs produced by the given entry point, one per line. If the given output is guaranteed to be unique (does not alias any inputs), the type is prefixed by `*`. ``clear`` ......... Clear all internal caches and counters maintained by the Futhark context. Corresponds to :c:func:`futhark_context_clear_caches`. ``pause_profiling`` ................... Corresponds to :c:func:`futhark_context_pause_profiling`. ``unpause_profiling`` ..................... Corresponds to :c:func:`futhark_context_unpause_profiling`. ``report`` .......... Corresponds to :c:func:`futhark_context_report`. ``set_tuning_param`` *param* *value* .................................... Corresponds to :c:func:`futhark_context_config_set_tuning_param`. ``tuning_params`` *entry* ......................... For each tuning parameters relevant to the given entry point, print its name, then a space, then its class. This is similar to on :c:func:`futhark_tuning_params_for_sum`, but note that this command prints *names* and not *integers*. ``tuning_param_class`` *param* .............................. Corresponds to :c:func:`futhark_get_tuning_param_class`. Record Commands ~~~~~~~~~~~~~~~ ``fields`` *type* ................. If the given type is a record, print a line for each field of the record. The line will contain the name of the field, followed by a space, followed by the type of the field. Note that the type name can contain spaces. The order of fields is significant, as it is the one expected by the ``new_record`` command. ``new`` *v0* *type* *v1* ... *vN* ................................. Create a new variable *v0* of type *type*, which must be a record type with *N* fields, where *v1* to *vN* are variables with the corresponding field types (the expected order is given by the ``fields`` command). ``project`` *to* *from* *field* ............................... Create a new variable *to* whose value is the field *field* of the record-typed variable *from*. Environment Variables --------------------- ``FUTHARK_COMPILER_DEBUGGING`` ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Turns on debugging output for the server when set to 1.