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use "collections"
// Chandy-Misra solution to the dining philosophers problem in Pony
// R. Sean Bowman, July 2016
actor Philosopher
// our name (for printing) and a stream to log info on
let _name: String
let _out: OutStream
// how many times to eat
var _how_hungry: U32
// forks we need in order to eat
let _missing_forks: Array[Philosopher] = Array[Philosopher]
// forks we have already requested but not yet received
let _requested_forks: Array[Philosopher] = Array[Philosopher]
// forks we hold that are clean
let _clean_forks: Array[Philosopher] = Array[Philosopher]
// others waiting for us to finish with a fork
let _waiting: Array[Philosopher] = Array[Philosopher]
new create(name: String, how_hungry: U32, out: OutStream) =>
_name = name
_out = out
_how_hungry = how_hungry
fun ref log(msg: String) =>
_out.print(_name + ": " + msg)
fun ref _add_missing(missing: Philosopher) =>
_missing_forks.push(missing)
fun ref _remove_requested(missing: Philosopher) =>
try
_requested_forks.delete(_requested_forks.find(missing))
else
log("Couldn't remove requested fork!")
end
fun ref _can_eat(): Bool =>
(_missing_forks.size() == 0) and (_requested_forks.size() == 0)
fun ref eat() =>
_clean_forks.clear()
log("Eating! hunger " + _how_hungry.string())
for i in Range(0, _waiting.size()) do
try
_waiting(i).receive_fork(this)
_add_missing(_waiting(i))
else
log("COULDN'T SEND TO WAITING ")
end
end
_waiting.clear()
_how_hungry = _how_hungry - 1
hunger()
// initially we may be missing forks; this behavior says so
be add_missing(missing: Philosopher) =>
_add_missing(missing)
// request a fork from the receiver
be request_fork(requester: Philosopher) =>
if _clean_forks.contains(requester) then
_waiting.push(requester)
log("queuing")
else
requester.receive_fork(this)
_add_missing(requester)
log("sending fork to ")
end
// receive a fork from another actor
be receive_fork(giver: Philosopher) =>
_remove_requested(giver)
_clean_forks.push(giver)
let num_missing = _missing_forks.size() + _requested_forks.size()
log("received fork, missing " + num_missing.string())
if _can_eat() then
eat()
else
hunger()
end
// try to eat unless we've eaten enough times
be hunger() =>
if _how_hungry > 0 then
if _can_eat() then
eat()
else
if _missing_forks.size() > 0 then
for missing in _missing_forks.values() do
log("requesting fork")
missing.request_fork(this)
_requested_forks.push(missing)
end
_missing_forks.clear()
end
end
end
actor Main
new create(env: Env) =>
let n_hungers: U32 = 8
let out_stream = env.out
let p1 = Philosopher("A", n_hungers, out_stream)
let p2 = Philosopher("B", n_hungers, out_stream)
let p3 = Philosopher("C", n_hungers, out_stream)
let p4 = Philosopher("D", n_hungers, out_stream)
let p5 = Philosopher("E", n_hungers, out_stream)
// fork dependencies must form a DAG initially; p_1 holds both forks,
// p_n holds neither, all others hold exactly one fork
p2.add_missing(p1)
p3.add_missing(p2)
p4.add_missing(p3)
p5.add_missing(p1)
p5.add_missing(p4)
let ps = [p2, p3, p1, p5, p4]
for p in ps.values() do
p.hunger()
end