Make ~num_domains in Task.setup_pool optional

CHANGES.md

@@ -1,3 +1,7 @@
+## Unreleased
+
+* Make ~num_domains argument for Task.setup_pool optional (#87, #91)
+
 ## v0.5.0
 
 This release includes:

README.md

@@ -21,8 +21,8 @@ We can parallelise this program using Domainslib:
 
 ```ocaml
 (* fib_par.ml *)
-let num_domains = try int_of_string Sys.argv.(1) with _ -> 1
-let n = try int_of_string Sys.argv.(2) with _ -> 1
+let n = try int_of_string Sys.argv.(1) with _ -> 1
+let num_domains = try Some (int_of_string Sys.argv.(2) - 1) with _ -> None
 
 (* Sequential Fibonacci *)
 let rec fib n = 
@@ -40,7 +40,7 @@ let rec fib_par pool n =
     fib n
 
 let main () =
-  let pool = T.setup_pool ~num_domains:(num_domains - 1) () in
+  let pool = T.setup_pool ?num_domains () in
   let res = T.run pool (fun _ -> fib_par pool n) in
   T.teardown_pool pool;
   Printf.printf "fib(%d) = %d\n" n res
@@ -51,28 +51,28 @@ let _ = main ()
 The parallel program scales nicely compared to the sequential version. The results presented below were obtained on a 2.3 GHz Quad-Core Intel Core i7 MacBook Pro with 4 cores and 8 hardware threads.
 
 ```bash
-$ hyperfine './fib.exe 42' './fib_par.exe 2 42' \
-            './fib_par.exe 4 42' './fib_par.exe 8 42'
+$ hyperfine './fib.exe 42' './fib_par.exe 42 2' \
+            './fib_par.exe 42 4' './fib_par.exe 42 8'
 Benchmark 1: ./fib.exe 42
   Time (mean ± sd):     1.217 s ±  0.018 s    [User: 1.203 s, System: 0.004 s]
   Range (min … max):    1.202 s …  1.261 s    10 runs
 
-Benchmark 2: ./fib_par.exe 2 42
+Benchmark 2: ./fib_par.exe 42 2
   Time (mean ± sd):    628.2 ms ±   2.9 ms    [User: 1243.1 ms, System: 4.9 ms]
   Range (min … max):   625.7 ms … 634.5 ms    10 runs
 
-Benchmark 3: ./fib_par.exe 4 42
+Benchmark 3: ./fib_par.exe 42 4
   Time (mean ± sd):    337.6 ms ±  23.4 ms    [User: 1321.8 ms, System: 8.4 ms]
   Range (min … max):   318.5 ms … 377.6 ms    10 runs
 
-Benchmark 4: ./fib_par.exe 8 42
+Benchmark 4: ./fib_par.exe 42 8
   Time (mean ± sd):    250.0 ms ±   9.4 ms    [User: 1877.1 ms, System: 12.6 ms]
   Range (min … max):   242.5 ms … 277.3 ms    11 runs
 
 Summary
-  './fib_par2.exe 8 42' ran
-    1.35 ± 0.11 times faster than './fib_par.exe 4 42'
-    2.51 ± 0.10 times faster than './fib_par.exe 2 42'
+  './fib_par.exe 42 8' ran
+    1.35 ± 0.11 times faster than './fib_par.exe 42 4'
+    2.51 ± 0.10 times faster than './fib_par.exe 42 2'
     4.87 ± 0.20 times faster than './fib.exe 42'
 ```
 

lib/task.ml

@@ -106,7 +106,8 @@ let run (type a) pool (f : unit -> a) : a =
 let named_pools = Hashtbl.create 8
 let named_pools_mutex = Mutex.create ()
 
-let setup_pool ?name ~num_domains () =
+(* Domain.recommended_domain_count is guaranteed to be at least 1 *)
+let setup_pool ?name ?(num_domains = Domain.recommended_domain_count () - 1) () =
   if num_domains < 0 then
     invalid_arg "Task.setup_pool: num_domains must be at least 0"
   else

lib/task.mli

@@ -7,10 +7,11 @@ type !'a promise
 type pool
 (** Type of task pool *)
 
-val setup_pool : ?name:string -> num_domains:int -> unit -> pool
+val setup_pool : ?name:string -> ?num_domains:int -> unit -> pool
 (** Sets up a task execution pool with [num_domains] new domains. If [name] is
     provided, the pool is mapped to [name] which can be looked up later with
-    [lookup_pool name].
+    [lookup_pool name]. [~num_domains] defaults to
+    [Domain.recommended_domain_count () - 1].
 
     When [num_domains] is 0, the new pool will be empty, and when an empty
     pool is in use, every function in this module will run effectively

test/LU_decomposition_multicore.ml

@@ -1,6 +1,8 @@
 module T = Domainslib.Task
-let num_domains = try int_of_string Sys.argv.(1) with _ -> 1
-let mat_size = try int_of_string Sys.argv.(2) with _ -> 1200
+let mat_size = try int_of_string Sys.argv.(1) with _ -> 1200
+let num_domains =
+  try int_of_string Sys.argv.(2)
+  with _ -> Domain.recommended_domain_count ()
 
 let k = Domain.DLS.new_key Random.State.make_self_init
 

test/enumerate_par.ml

@@ -1,10 +1,10 @@
-let num_domains = try int_of_string Sys.argv.(1) with _ -> 1
-let n = try int_of_string Sys.argv.(2) with _ -> 100
+let n = try int_of_string Sys.argv.(1) with _ -> 100
+let num_domains = try Some (int_of_string Sys.argv.(2) - 1) with _ -> None
 
 module T = Domainslib.Task
 
 let _ =
-  let p = T.setup_pool ~num_domains:(num_domains - 1) () in
+  let p = T.setup_pool ?num_domains () in
   T.run p (fun _ ->
     T.parallel_for p ~start:0 ~finish:(n-1) ~chunk_size:16 ~body:(fun i ->
       print_string @@ Printf.sprintf "[%d] %d\n%!" (Domain.self () :> int) i));

test/fib_par.ml

@@ -1,5 +1,5 @@
-let num_domains = try int_of_string Sys.argv.(1) with _ -> 1
-let n = try int_of_string Sys.argv.(2) with _ -> 43
+let n = try int_of_string Sys.argv.(1) with _ -> 43
+let num_domains = try Some (int_of_string Sys.argv.(2) - 1) with _ -> None
 
 module T = Domainslib.Task
 
@@ -15,7 +15,7 @@ let rec fib_par pool n =
     T.await pool a + T.await pool b
 
 let main =
-  let pool = T.setup_pool ~num_domains:(num_domains - 1) () in
+  let pool = T.setup_pool ?num_domains () in
   let res = T.run pool (fun _ -> fib_par pool n) in
   T.teardown_pool pool;
   Printf.printf "fib(%d) = %d\n" n res

test/game_of_life_multicore.ml

@@ -1,6 +1,6 @@
-let num_domains = try int_of_string Sys.argv.(1) with _ -> 1
-let n_times = try int_of_string Sys.argv.(2) with _ -> 20
-let board_size = try int_of_string Sys.argv.(3) with _ -> 16
+let n_times = try int_of_string Sys.argv.(1) with _ -> 20
+let board_size = try int_of_string Sys.argv.(2) with _ -> 16
+let num_domains = try Some (int_of_string Sys.argv.(3) - 1) with _ -> None
 
 module T = Domainslib.Task
 
@@ -62,7 +62,7 @@ let rec repeat pool n =
   | _-> next pool; repeat pool (n-1)
 
 let ()=
-  let pool = T.setup_pool ~num_domains:(num_domains - 1) () in
+  let pool = T.setup_pool ?num_domains () in
   print !rg;
   T.run pool (fun _ -> repeat pool n_times);
   print !rg;

test/spectralnorm2_multicore.ml

@@ -6,8 +6,10 @@
  * Modified by Mauricio Fernandez
  *)
 
-let num_domains = try int_of_string Sys.argv.(1) with _ -> 1
-let n = try int_of_string Sys.argv.(2) with _ ->  2000
+let n = try int_of_string Sys.argv.(1) with _ -> 2000
+let num_domains =
+  try int_of_string Sys.argv.(2)
+  with _ -> Domain.recommended_domain_count ()
 
 module T = Domainslib.Task
 

test/sum_par.ml

@@ -1,5 +1,7 @@
-let num_domains = try int_of_string Sys.argv.(1) with _ -> 2
 let n = try int_of_string Sys.argv.(2) with _ -> 100
+let num_domains =
+  try int_of_string Sys.argv.(2)
+  with _ -> Domain.recommended_domain_count ()
 
 module T = Domainslib.Task
 

test/summed_area_table.ml

@@ -1,6 +1,6 @@
 module T = Domainslib.Task
-let num_domains = try int_of_string Sys.argv.(1) with _ -> 4
-let size = try int_of_string Sys.argv.(2) with _ -> 100
+let size = try int_of_string Sys.argv.(1) with _ -> 100
+let num_domains = try Some (int_of_string Sys.argv.(2) - 1) with _ -> None
 
 let transpose a =
   let r = Array.length a in
@@ -29,7 +29,7 @@ let calc_table pool mat =
 let _ =
   let m = Array.make_matrix size size 1 (*Array.init size (fun _ -> Array.init size (fun _ -> Random.int size))*)
   in
-  let pool = T.setup_pool ~num_domains:(num_domains - 1) () in
+  let pool = T.setup_pool ?num_domains () in
   let _ = T.run pool (fun _ -> calc_table pool m) in
 
   (* for i = 0 to size-1 do

test/task_throughput.ml

@@ -1,7 +1,9 @@
 
-let n_domains = try int_of_string Sys.argv.(1) with _ -> 1
-let n_iterations = try int_of_string Sys.argv.(2) with _ -> 1024
-let n_tasks = try int_of_string Sys.argv.(3) with _ -> 1024
+let n_iterations = try int_of_string Sys.argv.(1) with _ -> 1024
+let n_tasks = try int_of_string Sys.argv.(2) with _ -> 1024
+let n_domains =
+  try int_of_string Sys.argv.(3)
+  with _ -> Domain.recommended_domain_count ()
 
 module T = Domainslib.Task