wip: fix behavior of CCPool when min_size>0

problem is a deadlock occurs when some threads die (too early?)
when P.min_size>0

src/threads/CCPool.ml

@@ -20,8 +20,9 @@ exception Stopped
 
 (*$inject
   module P = Make(struct let min_size = 0 let max_size = 30 end)
+  module P2 = Make(struct let min_size = 1 let max_size = 15 end)
   module Fut = P.Fut
-  open Fut.Infix
+  module Fut2 = P2.Fut
 *)
 
 (** {2 Thread pool} *)
@@ -81,14 +82,16 @@ module Make(P : PARAM) = struct
   (* thread: seek what to do next (including dying).
      Assumes the pool is locked. *)
   let get_next_ pool =
-    if pool.stop
+    (*Printf.printf "get_next (cur=%d, min=%d, idle=%d, stop=%B)\n%!" pool.cur_size P.min_size pool.cur_idle pool.stop;*)
-    || (Queue.is_empty pool.jobs && pool.cur_size > P.min_size) then (
+    if pool.stop || (Queue.is_empty pool.jobs && pool.cur_size > P.min_size) then (
       (* die: the thread would be idle otherwise  *)
       assert (pool.cur_size > 0);
+      (*Printf.printf "time… to die (cur=%d, min=%d, idle=%d, stop=%B)\n%!" pool.cur_size P.min_size pool.cur_idle pool.stop;*)
       decr_size_ pool;
       Die
-    ) else if Queue.is_empty pool.jobs then Wait
+    ) else if Queue.is_empty pool.jobs then (
-    else (
+      Wait
+    ) else (
       let job = Queue.pop pool.jobs in
       Process job
     )
@@ -120,7 +123,11 @@ module Make(P : PARAM) = struct
       begin try ignore (f x y z w) with e -> pool.exn_handler e end; serve pool
 
   (* create a new worker thread *)
-  let launch_worker_ pool = ignore (Thread.create serve pool)
+  let launch_worker_ pool =
+    with_lock_ pool
+      (fun pool ->
+         incr_size_ pool;
+         ignore (Thread.create serve pool))
 
   (* launch the minimum required number of threads *)
   let () =
@@ -137,8 +144,7 @@ module Make(P : PARAM) = struct
     with_lock_ pool
       (fun pool ->
          if pool.stop then raise Stopped;
-         if Queue.is_empty pool.jobs && can_start_thread_ pool && pool.cur_idle = 0
+         if Queue.is_empty pool.jobs && can_start_thread_ pool && pool.cur_idle = 0 then (
-         then (
            (* create the thread now, on [job], as it will not break order of
               jobs. We do not want to wait for the busy threads to do our task
               if we are allowed to spawn a new thread. *)
@@ -147,10 +153,11 @@ module Make(P : PARAM) = struct
          ) else (
            (* cannot start thread, push and wait for some worker to pick it up *)
            Queue.push job pool.jobs;
-           Condition.signal pool.cond; (* wake up some worker, if any *)
+           Condition.broadcast pool.cond; (* wake up some worker, if any *)
            (* might want to process in the background, if all threads are busy *)
-           if pool.cur_idle = 0 && can_start_thread_ pool then (
+           if not (Queue.is_empty pool.jobs)
-             incr_size_ pool;
+              && pool.cur_idle = 0
+              && can_start_thread_ pool then (
              launch_worker_ pool;
            )
          ))
@@ -283,6 +290,23 @@ module Make(P : PARAM) = struct
         [ 10; 300; ]
     *)
 
+    (*$R
+      List.iter
+        (fun n ->
+          let l = Sequence.(1 -- n) |> Sequence.to_list in
+          let l = List.rev_map (fun i ->
+            Fut2.make
+              (fun () ->
+                Thread.delay 0.01;
+                1
+            )) l in
+          let l' = List.map Fut2.get l in
+          OUnit.assert_equal n (List.fold_left (+) 0 l');
+        )
+        [ 10; 300; ]
+    *)
+
+
     let make2 f x y =
       let cell = create_cell() in
       run4 run_and_set2 cell f x y;
@@ -379,6 +403,13 @@ module Make(P : PARAM) = struct
       OUnit.assert_equal 1 (Fut.get c)
     *)
 
+    (*$R
+      let a = Fut2.make (fun () -> 1) in
+      let b = Fut2.map (fun x -> x+1) a in
+      let c = Fut2.map (fun x -> x-1) b in
+      OUnit.assert_equal 1 (Fut2.get c)
+    *)
+
     let app_ ~async f x = match f, x with
       | Return f, Return x ->
         if async
@@ -525,6 +556,43 @@ module Make(P : PARAM) = struct
       OUnit.assert_equal 10_000 (List.length l');
     *)
 
+    (*$R
+      let l = CCList.(1 -- 50) in
+      let l' = l
+        |> List.map
+          (fun x -> Fut2.make (fun () -> Thread.delay 0.1; x*10))
+        |> Fut2.sequence_l
+        |> Fut2.map (List.fold_left (+) 0)
+      in
+      let expected = List.fold_left (fun acc x -> acc + 10 * x) 0 l in
+      OUnit.assert_equal expected (Fut2.get l')
+    *)
+
+    (*$R
+      let l = CCList.(1 -- 50) in
+      let l' = l
+        |> List.map
+          (fun x -> Fut2.make (fun () -> Thread.delay 0.1; if x = 5 then raise Exit; x))
+        |> Fut2.sequence_l
+        |> Fut2.map (List.fold_left (+) 0)
+      in
+      OUnit.assert_raises Exit (fun () -> Fut2.get l')
+    *)
+
+    (*$R
+      let rec fib x = if x<2 then 1 else fib (x-1)+fib(x-2) in
+      let l =
+        CCList.(1--10_000)
+        |> List.rev_map
+          (fun x-> Fut2.make (fun () -> Thread.yield(); fib (x mod 20)))
+        |> Fut2.(map_l (fun x->x>|= fun x->x+1))
+      in
+      OUnit.assert_bool "not done" (Fut2.state l = Waiting);
+      let l' = Fut2.get l in
+      OUnit.assert_equal 10_000 (List.length l');
+    *)
+
+
     let choose_
       : type a. a t array_or_list -> a t
       = fun aol ->
@@ -560,6 +628,17 @@ module Make(P : PARAM) = struct
       OUnit.assert_bool "some_parallelism" (stop -. start < float_of_int n *. pause);
     *)
 
+    (*$R
+      let start = Unix.gettimeofday () in
+      let pause = 0.2 and n = 10 in
+      let l = CCList.(1 -- n)
+        |> List.map (fun _ -> Fut2.make (fun () -> Thread.delay pause))
+      in
+      List.iter Fut2.get l;
+      let stop = Unix.gettimeofday () in
+      OUnit.assert_bool "some_parallelism" (stop -. start < float_of_int n *. pause);
+    *)
+
     module Infix = struct
       let (>>=) x f = flat_map f x
       let (>>) a f = and_then a f