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Universal Construction
open Marvel
open System.Collections.Concurrent
open System.Collections.Generic
type Pid = int
type Op = {
op : string
sn : SN
}
and SN = int
and Exec = {
op : string
pid : Pid
}
let start
(pid:Pid) (N:int)
(s:'s) (d:'s -> string -> 's * 'o)
(LAST_OP:IDictionary<Pid, Op>) /// a MRSW shared variable containg the last operation invoked by each process
(CONS:IDictionary<int, _>) /// a sequence of consensus objects indexed by round
= async {
/// A list of all processes
let procs : Pid list = undef
/// The last sequence number
let lastSN : IDictionary<Pid, SN> = undef
/// A local variable containing the result of the operation
let res = MVar.create ()
let helper = async {
let k = ref 0 // the round number
let s = ref s // the current object state
while true do
// the proposal is the list of operations that
// invoked by processes who's sequence number is greater
// than the last sequence number known by the calling process
let prop =
procs
|> List.choose (fun p ->
if LAST_OP.[p].sn > lastSN.[p] then
Some LAST_OP.[p].op
else
None)
match prop with
| [] -> ()
| prop ->
incr k
let execs : Exec list = CONS.[!k] prop
for exec in execs do
let (s',r) = d !s exec.op
s := s'
lastSN.[exec.pid] <- lastSN.[exec.pid] + 1
if (exec.pid = pid) then
do! MVar.put r res |> Async.Ignore
}
Async.Start helper
let perform args = async {
LAST_OP.[pid] <- { Op.op = "" ; sn = lastSN.[pid] + 1 }
return! res |> MVar.take }
return perform
}
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