From 50fc9d84a0390a7e6282bd2b4ce398fe122f607c Mon Sep 17 00:00:00 2001
From: cremet <cremet@epfl.ch>
Date: Thu, 25 Sep 2003 15:49:41 +0000
Subject: - Better implementation of Pilib with fewer thr...

- Better implementation of Pilib with fewer thread creations.
---
 sources/scala/concurrent/pilib.scala | 156 +++++++++++++++++++++++++++++++++++
 1 file changed, 156 insertions(+)

diff --git a/sources/scala/concurrent/pilib.scala b/sources/scala/concurrent/pilib.scala
index 6a90c46068..c3cf55bd2d 100644
--- a/sources/scala/concurrent/pilib.scala
+++ b/sources/scala/concurrent/pilib.scala
@@ -1,5 +1,160 @@
 package scala.concurrent;
 
+/**
+* Library for using Pi-calculus concurrent primitives in Scala.
+*/
+object pilib with Monitor {
+
+  /////////////////////////// SPAWN //////////////////////////////
+
+  /**
+  * Run several processes in parallel using the following syntax:
+  * spawn < p_1 | ... | p_n >
+  */
+  trait Spawn {
+    def <(def p: unit): Spawn;
+    def |(def p: unit): Spawn;
+    def > : unit;
+  }
+  val spawn = new Spawn {
+  //  object spawn extends Spawn { BUG !
+    def <(def p: unit): Spawn = { ops.spawn(p); this }
+    def |(def p: unit): Spawn = { ops.spawn(p); this }
+    def > : unit = ()
+  }
+
+  //////////////////////// GUARDED PROCESSES /////////////////////////
+
+  type Name = AnyRef;
+
+  /** A guarded process.
+  * @param a         channel
+  * @param direction input (true) or output (false)
+  * @param v         transmitted value
+  * @param c         continuation
+  */
+  case class GP(a: Name, direction: boolean, v: Any, c: Any => unit);
+
+  ////////////////////////// CHANNELS //////////////////////////////
+
+  /**
+  * Name on which one can emit, receive or that can be emitted or received
+  * during a communication.
+    */
+  class Chan[a] with Function1[a, Product[a]] {
+
+    /** Creates an input guarded process. */
+    def input(c: a => unit) =
+      GP(this, true, (), v => c(v.asInstanceOf[a]));
+
+    /** Creates an input guarded process. */
+    def output(v: a, c: () => unit) =
+      GP(this, false, v, x => c());
+
+    /** Blocking read. */
+    def read = {
+      var res: a = _;
+      choice ( input(x => res = x) );
+      res
+    }
+
+    /** Blocking write. */
+    def write(x: a) =
+      choice ( output(x, () => ()) );
+
+    /** Syntactic sugar for input. */
+    def *(f: a => unit) =
+      input(f);
+
+    /** Syntactic sugar for output. */
+    def apply(v: a) =
+      new Product(this, v);
+  }
+
+  class Product[a](c: Chan[a], v: a) {
+    def *(def f: unit) = c.output(v, () => f);
+  }
+
+  //////////////////// SUM OF GUARDED PROCESSES //////////////////////
+
+  case class Sum(gs: List[GP]) with Monitor {
+
+    /** Continuation of the sum. */
+    var fun: Any => unit = _;
+    /** Argument of the continuation of the sum. */
+    var arg: Any = _;
+
+    var initialized = false;
+
+    /**
+    * Block if not initialized otherwise continue with the
+    * continuation.
+    */
+    def continue = synchronized {
+      if (!initialized) wait();
+      fun(arg)
+    }
+
+    /** Set the values of parameters and awake the sleeping sum. */
+    def set(f: Any => unit, x: Any) = synchronized {
+      fun = f;
+      arg = x;
+      initialized = true;
+      notify()
+    }
+  }
+
+  /////////////////////////// COMMUNICATION  //////////////////////////
+
+  private var sums: List[Sum] = Nil;
+
+  /** Test if two lists of guarded processes can communicate. */
+  private def matches(gs1: List[GP], gs2: List[GP]):
+  Option[Tuple4[Any, Any => unit, Any, Any => unit]] =
+    Pair(gs1, gs2) match {
+      case Pair(Nil, _) => None
+      case Pair(_, Nil) => None
+      case Pair(GP(a1, d1, v1, c1) :: rest1, GP(a2, d2, v2, c2) :: rest2) =>
+	if (a1 == a2 && d1 == !d2)
+	  Some(Tuple4(v1, c1, v2, c2))
+	else matches(gs1, rest2) match {
+	  case None => matches(rest1, gs2)
+	  case Some(t) => Some(t)
+	}
+    }
+
+  /**
+  * Test if the given sum can react with one of the pending sums.
+  * If yes then do the reaction otherwise append the sum at the end
+  * of the pending sums.
+  */
+  private def compare(s1: Sum, ss: List[Sum]): List[Sum] =
+    ss match {
+      case Nil => ss ::: List(s1)
+      case s2 :: rest => matches(s1.gs, s2.gs) match {
+	case None => s2 :: compare(s1, rest)
+	case Some(Tuple4(v1, c1, v2, c2)) => {
+	  s1.set(c1, v2);
+	  s2.set(c2, v1);
+	  rest
+	}
+      }
+    }
+
+  /** Pi-calculus non-deterministic choice. */
+  def choice(s: GP*): unit = {
+    val sum = Sum(s.asInstanceOf[List[GP]]);
+    synchronized { sums = compare(sum, sums) };
+    sum.continue
+  }
+
+
+}
+
+/* Former version.
+
+package scala.concurrent;
+
 /**
 * Library for using Pi-calculus concurrent primitives in Scala.
 */
@@ -168,3 +323,4 @@ object pilib with Monitor {
 
 }
 
+*/
-- 
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