From acb8ef5d18cc3976bf580a8e6925cb5641acd401 Mon Sep 17 00:00:00 2001
From: Anthony Ramine <n.oxyde@gmail.com>
Date: Mon, 6 May 2013 20:09:39 +0200
Subject: Fix receive support in erl_eval with a BEAM module

Using the low-level BEAM instructions, we can loop over each message in
the process queue and removes the first message that matches, without
receiving them all to later send them back to itself.

The function prim_eval:'receive'/2 is equivalent to the
following pseudo-code:

  'receive'(F, T) ->
    RESET MESSAGE QUEUE POINTER,
    LOOP:
      case PEEK CURRENT MESSAGE WITH TIMEOUT T of
        {ok,Msg} ->
          case F(Msg) of
            nomatch ->
              DECREMENT TIMEOUT T,
              ADVANCE MESSAGE QUEUE POINTER,
              GOTO LOOP;
            Result ->
              RESET MESSAGE QUEUE POINTER,
              Result
          end;
        timeout ->
          RESET MESSAGE QUEUE POINTER,
          timeout
      end.

To not break Dialyzer and other tools, we use a stub Erlang module which
abstract code is forcefully inserted into prim_inet.erl afterwards
compilation.
---
 lib/stdlib/doc/src/erl_eval.xml |  5 +---
 lib/stdlib/src/erl_eval.erl     | 64 +++++++----------------------------------
 2 files changed, 12 insertions(+), 57 deletions(-)

(limited to 'lib/stdlib')

diff --git a/lib/stdlib/doc/src/erl_eval.xml b/lib/stdlib/doc/src/erl_eval.xml
index d0622594d9..24940f8396 100644
--- a/lib/stdlib/doc/src/erl_eval.xml
+++ b/lib/stdlib/doc/src/erl_eval.xml
@@ -288,10 +288,7 @@ Func(FuncSpec, Arguments)        </code>
 
   <section>
     <title>Bugs</title>
-    <p>The evaluator is not complete. <c>receive</c> cannot be
-      handled properly.
-      </p>
-    <p>Any undocumented functions in <c>erl_eval</c> should not be used.</p>
+    <p>Undocumented functions in <c>erl_eval</c> should not be used.</p>
   </section>
 </erlref>
 
diff --git a/lib/stdlib/src/erl_eval.erl b/lib/stdlib/src/erl_eval.erl
index 0b57af1b6d..73b8da335a 100644
--- a/lib/stdlib/src/erl_eval.erl
+++ b/lib/stdlib/src/erl_eval.erl
@@ -245,10 +245,10 @@ expr({'case',_,E,Cs}, Bs0, Lf, Ef, RBs) ->
 expr({'try',_,B,Cases,Catches,AB}, Bs, Lf, Ef, RBs) ->
     try_clauses(B, Cases, Catches, AB, Bs, Lf, Ef, RBs);
 expr({'receive',_,Cs}, Bs, Lf, Ef, RBs) ->
-    receive_clauses(Cs, Bs, Lf, Ef, [], RBs);
+    receive_clauses(Cs, Bs, Lf, Ef, RBs);
 expr({'receive',_, Cs, E, TB}, Bs0, Lf, Ef, RBs) ->
     {value,T,Bs} = expr(E, Bs0, Lf, Ef, none),
-    receive_clauses(T, Cs, {TB,Bs}, Bs0, Lf, Ef, [], RBs);
+    receive_clauses(T, Cs, {TB,Bs}, Bs0, Lf, Ef, RBs);
 expr({'fun',_Line,{function,Mod0,Name0,Arity0}}, Bs0, Lf, Ef, RBs) ->
     {[Mod,Name,Arity],Bs} = expr_list([Mod0,Name0,Arity0], Bs0, Lf, Ef),
     F = erlang:make_fun(Mod, Name, Arity),
@@ -807,66 +807,24 @@ case_clauses(Val, Cs, Bs, Lf, Ef, RBs) ->
     end.
 
 %%
-%% receive_clauses(Clauses, Bindings, LocalFuncHnd,ExtFuncHnd, Messages, RBs) 
+%% receive_clauses(Clauses, Bindings, LocalFuncHnd,ExtFuncHnd, RBs)
 %%
-receive_clauses(Cs, Bs, Lf, Ef, Ms, RBs) ->
-    receive
-	Val ->
-	    case match_clause(Cs, [Val], Bs, Lf, Ef) of
-		{B, Bs1} ->
-		    merge_queue(Ms),
-		    exprs(B, Bs1, Lf, Ef, RBs);
-		nomatch ->
-		    receive_clauses(Cs, Bs, Lf, Ef, [Val|Ms], RBs)
-	    end
-    end.
+receive_clauses(Cs, Bs, Lf, Ef, RBs) ->
+    receive_clauses(infinity, Cs, unused, Bs, Lf, Ef, RBs).
 %%
 %% receive_clauses(TimeOut, Clauses, TimeoutBody, Bindings, 
 %%                 ExternalFuncHandler, LocalFuncHandler, RBs)
 %%
-receive_clauses(T, Cs, TB, Bs, Lf, Ef, Ms, RBs) ->
-    {_,_} = statistics(runtime),
-    receive
-	Val ->
-	    case match_clause(Cs, [Val], Bs, Lf, Ef) of
-		{B, Bs1} ->
-		    merge_queue(Ms),
-		    exprs(B, Bs1, Lf, Ef, RBs);
-		nomatch ->
-		    {_,T1} = statistics(runtime),
-		    if
-			T =:= infinity ->
-			    receive_clauses(T, Cs, TB,Bs,Lf,Ef,[Val|Ms],RBs);
-			T-T1 =< 0 ->
-			    receive_clauses(0, Cs, TB,Bs,Lf,Ef,[Val|Ms],RBs);
-			true ->
-			    receive_clauses(T-T1, Cs,TB,Bs,Lf,Ef,[Val|Ms],RBs)
-		    end
-	    end
-    after T ->
-	    merge_queue(Ms),
+receive_clauses(T, Cs, TB, Bs, Lf, Ef, RBs) ->
+    F = fun (M) -> match_clause(Cs, [M], Bs, Lf, Ef) end,
+    case prim_eval:'receive'(F, T) of
+	{B, Bs1} ->
+	    exprs(B, Bs1, Lf, Ef, RBs);
+	timeout ->
 	    {B, Bs1} = TB,
 	    exprs(B, Bs1, Lf, Ef, RBs)
     end.
 
-merge_queue([]) -> 
-    true;
-merge_queue(Ms) ->
-    send_all(recv_all(Ms), self()).
-
-recv_all(Xs) ->
-    receive
-	X -> recv_all([X|Xs])
-    after 0 ->
-	    reverse(Xs)
-    end.
-
-send_all([X|Xs], Self) ->
-    Self ! X,
-    send_all(Xs, Self);
-send_all([], _) -> true.
-
-
 %% match_clause -> {Body, Bindings} or nomatch
 
 -spec(match_clause(Clauses, ValueList, Bindings, LocalFunctionHandler) ->
-- 
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