misc

documents/Programmierparadigmen/scripts/scala/erasthostenes-parallel.scala

@@ -0,0 +1,35 @@
+import scala.actors.Futures._
+/** @author Axel Busch */
+object EratosthenesFutures {
+    def parallel(end : Int, threads: Int) : Array[Boolean] = {
+        val sieve = Array.fill[Boolean](end+1)(true)
+        for (i <- 2 to scala.math.sqrt(end).toInt) {
+            if (sieve(i)) {
+                val nextComposite = i*i
+                val compositesPerThread = (end-nextComposite+1)/(threads*i)
+                val tasks = for (t <- 0 until threads) yield future {
+                    val begin = nextComposite + t * i *
+                                compositesPerThread
+                    val finish = if (t+1 == threads) end 
+                                 else nextComposite + (t+1) * i *
+                                        compositesPerThread
+                    assert (begin % i == 0)
+                    for (composite <- begin to finish by i) {
+                        sieve(composite) = false
+                    }
+                }
+                awaitAll(20000L, tasks: _*);
+            }
+        }
+        sieve
+    }
+    def main(args: Array[String]) = {
+        val end = 100000000
+        for (threads <- List(1,2,4,8)) {
+            val startTime = System.currentTimeMillis();
+            parallel(end,threads);
+            val endTime = System.currentTimeMillis();
+            println(threads + " thread: " + (endTime - startTime) + " ms");
+        }
+    }
+}