counter

An asynchronous, shared counter. This example shows something subtle: a way to safely "share mutable data" by dedicating a data owner, then communicating with that owner.

How to Compile

With a minimal Pony installation, in the same directory as this README file run ponyc. You should see content building the necessary packages, which ends with:

...
Generating
 Reachability
 Selector painting
 Data prototypes
 Data types
 Function prototypes
 Functions
 Descriptors
Optimising
Writing ./counter.o
Linking ./counter

How to Run

Once counter has been compiled, in the same directory as this README file run ./counter. You should see your count:

$ ./counter 100
100

Program Modifications

If you want to prove to yourself that the counter is running in realtime (rather than pre-computing the result), you can add the following behaviors to see more output.

actor Counter
...
  be is_running(main: Main) =>
    main.still_running()
...

actor Main
...
    for i in Range[U32](0, count) do
      counter.increment()
      counter.is_running(this)
    end
...
  be still_running() =>
    _env.out.print("Your message here")

Doing this will print "Your message here" after each increment().

As an exercise, modify the program so you display(...) the current count after each counter.increment() -- hint: you need to add a parameter to the increment() behavior.