Merge pull request scala#2563 from soc/SI-7474

SI-7474 Parallel collections: End the exception handling madness

Author: JamesIry

src/library/scala/collection/parallel/Tasks.scala

@@ -72,11 +72,13 @@ trait Task[R, +Tp] {
   }
 
   private[parallel] def mergeThrowables(that: Task[_, _]) {
-    if (this.throwable != null && that.throwable != null) {
-      // merge exceptions, since there were multiple exceptions
-      this.throwable = this.throwable alongWith that.throwable
-    } else if (that.throwable != null) this.throwable = that.throwable
-      else this.throwable = this.throwable
+    // TODO: As soon as we target Java >= 7, use Throwable#addSuppressed
+    // to pass additional Throwables to the caller, e. g.
+    // if (this.throwable != null && that.throwable != null)
+    //   this.throwable.addSuppressed(that.throwable)
+    // For now, we just use whatever Throwable comes across “first”.
+    if (this.throwable == null && that.throwable != null)
+      this.throwable = that.throwable
   }
 
   // override in concrete task implementations to signal abort to other tasks

src/library/scala/collection/parallel/package.scala

@@ -114,7 +114,9 @@ package parallel {
     def toParArray: ParArray[T]
   }
 
+  @deprecated("This trait will be removed.", "2.11.0")
   trait ThrowableOps {
+    @deprecated("This method will be removed.", "2.11.0")
     def alongWith(that: Throwable): Throwable
   }
 
@@ -133,9 +135,8 @@ package parallel {
   }
 
   /** Composite throwable - thrown when multiple exceptions are thrown at the same time. */
-  final case class CompositeThrowable(
-                                       throwables: Set[Throwable]
-  ) extends Exception(
+  @deprecated("This class will be removed.", "2.11.0")
+  final case class CompositeThrowable(throwables: Set[Throwable]) extends Exception(
     "Multiple exceptions thrown during a parallel computation: " +
       throwables.map(t => t + "\n" + t.getStackTrace.take(10).++("...").mkString("\n")).mkString("\n\n")
   )

test/files/run/t5375.check

@@ -1 +1 @@
-Composite throwable
+Runtime exception

test/files/run/t5375.scala

@@ -1,19 +1,8 @@
-
-
-
-import collection.parallel.CompositeThrowable
-
-
-
-object Test {
-  
-  def main(args: Array[String]) {
-    val foos = (1 to 1000).toSeq
-    try {
-      foos.par.map(i => if (i % 37 == 0) sys.error("i div 37") else i)
-    } catch {
-      case CompositeThrowable(thr) => println("Composite throwable")
-    }
+object Test extends App {
+  val foos = (1 to 1000).toSeq
+  try
+    foos.par.map(i => if (i % 37 == 0) sys.error("i div 37") else i)
+  catch {
+    case ex: RuntimeException => println("Runtime exception")
   }
-  
 }