src/Pure/Concurrent/multithreading.ML

clarified modules;

(*  Title:      Pure/Concurrent/multithreading.ML
    Author:     Makarius

Multithreading in Poly/ML, see also
  - $ML_SOURCES/basis/Thread.sml: numPhysicalProcessors
  - $ML_SOURCES/libpolyml/processes.cpp: PolyThreadNumPhysicalProcessors
*)

signature MULTITHREADING =
sig
  val num_processors: unit -> int
  val max_threads: unit -> int
  val max_threads_update: int -> unit
  val parallel_proofs: int ref
  val sync_wait: Time.time option -> Thread.ConditionVar.conditionVar -> Thread.Mutex.mutex ->
    bool Exn.result
  val trace: int ref
  val tracing: int -> (unit -> string) -> unit
  val tracing_time: bool -> Time.time -> (unit -> string) -> unit
  val synchronized: string -> Thread.Mutex.mutex -> (unit -> 'a) -> 'a
end;

structure Multithreading: MULTITHREADING =
struct

(* physical processors *)

fun num_processors () =
  Int.max
    (case Thread.Thread.numPhysicalProcessors () of
      SOME n => n
    | NONE => Thread.Thread.numProcessors (), 1);


(* max_threads *)

local

fun max_threads_result m =
  if Thread_Data.is_virtual then 1
  else if m > 0 then m
  else Int.min (num_processors (), 8);

val max_threads_state = ref 1;

in

fun max_threads () = ! max_threads_state;
fun max_threads_update m = max_threads_state := max_threads_result m;

end;


(* parallel_proofs *)

val parallel_proofs = ref 1;


(* synchronous wait *)

fun sync_wait time cond lock =
  Thread_Attributes.with_attributes
    (Thread_Attributes.sync_interrupts (Thread_Attributes.get_attributes ()))
    (fn _ =>
      (case time of
        SOME t => Exn.Res (Thread.ConditionVar.waitUntil (cond, lock, t))
      | NONE => (Thread.ConditionVar.wait (cond, lock); Exn.Res true))
      handle exn => Exn.Exn exn);


(* tracing *)

val trace = ref 0;

fun tracing level msg =
  if ! trace < level then ()
  else Thread_Attributes.uninterruptible_body (fn _ =>
    (TextIO.output (TextIO.stdErr, (">>> " ^ msg () ^ "\n")); TextIO.flushOut TextIO.stdErr)
      handle _ (*sic*) => ());

fun tracing_time detailed time =
  tracing
   (if not detailed then 5
    else if time >= seconds 1.0 then 1
    else if time >= seconds 0.1 then 2
    else if time >= seconds 0.01 then 3
    else if time >= seconds 0.001 then 4 else 5);


(* synchronized evaluation *)

fun synchronized name lock e =
  Exn.release (Thread_Attributes.uninterruptible_body (fn run =>
    if ! trace > 0 then
      let
        val immediate =
          if Thread.Mutex.trylock lock then true
          else
            let
              val _ = tracing 5 (fn () => name ^ ": locking ...");
              val timer = Timer.startRealTimer ();
              val _ = Thread.Mutex.lock lock;
              val time = Timer.checkRealTimer timer;
              val _ = tracing_time true time (fn () => name ^ ": locked after " ^ Time.toString time);
            in false end;
        val result = Exn.capture0 (run e) ();
        val _ = if immediate then () else tracing 5 (fn () => name ^ ": unlocking ...");
        val _ = Thread.Mutex.unlock lock;
      in result end
    else
      let
        val _ = Thread.Mutex.lock lock;
        val result = Exn.capture0 (run e) ();
        val _ = Thread.Mutex.unlock lock;
      in result end));

end;