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EventQueue for CPS

This is a dispatcher for CPS which is designed to serve as a reference for generic asynchronous I/O via selectors.

For more information on what this is and how you might use it, see https://github.com/disruptek/cps.

The dispatcher is based upon selectors, so you can see how the features of that module will support typical I/O operations with CPS.

Windows is not supported by the dispatcher yet due to the lack of native timer support in selectors, but an ioselectors package that supports Windows is in an advanced stage of development.

Example

# all cps programs need the cps macro to perform the transformation
import cps

# but each usage of the .cps. macro can have its own dispatcher
# implementation and continuation type, allowing you to implement
# custom forms of async or use an existing library implementation
from eventqueue import sleep, run, spawn, trampoline, Cont

# this procedure is written in a simple synchronous style, but when
# the .cps. is applied during compilation, it is rewritten to use
# the Cont type in a series of asynchronous continuations

proc tock(name: string; ms: int) {.cps: Cont.} =
  ## echo the `name` at `ms` millisecond intervals, ten times

  # a recent change to cps allows us to use type inference
  var count = 10

  # `for` loops are not supported yet
  while count > 0:

    dec count

    # the dispatcher supplied this primitive which receives the
    # continuation and returns control to the caller immediately
    sleep ms

    # subsequent control-flow is continues from the dispatcher
    # when it elects to resume the continuation
    echo name, " ", count

# NOTE: all the subsequent code is supplied by the chosen dispatcher

# the trampoline repeatedly invokes continuations until they
# complete or are queued in the dispatcher; this call does not block
trampoline tock("tick", ms = 300)

# you can also send a continuation directly to the dispatcher;
# this call does not block
spawn tock("tock", ms = 700)

# run the dispatcher to invoke its pending continuations from the queue;
# this is a blocking call that completes when the queue is empty
run()

...and when built with --define:cpsDebug, outputs something like...

The source to the tick-tock test.

Documentation

See the documentation for eventqueue as generated directly from the source. See also the documentation for the cps module.

Tests

The tests provide the best examples of usage and are a great starting point for your experiments.

A few tests of eventqueue:

License

MIT