Provide meaningful message for MultitargetException

Author: vsilaev

src/main/java/net/tascalate/concurrent/AggregatingPromise.java

@@ -175,7 +175,15 @@ void onComplete(int idx, T result, Throwable error) {
                         cancelPromises();
                     }
 
-                    failure(new MultitargetException(errors));
+                    failure(new MultitargetException(
+                        String.format(
+                            c == 1 ? 
+                            "Aggregated promise was completed exceptionally (1 out of %d)"
+                            :
+                            "Aggregated promises were completed exceptionally (%2$d out of %1$d)",
+                            promises.size(), c), 
+                        errors
+                    ));
                 }
             }
         }

src/main/java/net/tascalate/concurrent/MultitargetException.java

@@ -18,7 +18,6 @@
 import java.io.IOException;
 import java.io.PrintStream;
 import java.io.PrintWriter;
-import java.io.StringWriter;
 import java.util.Collections;
 import java.util.IdentityHashMap;
 import java.util.List;
@@ -34,7 +33,8 @@ public class MultitargetException extends Exception {
 
     private final List<Throwable> exceptions;
 
-    public MultitargetException(List<Throwable> exceptions) {
+    public MultitargetException(String message, List<Throwable> exceptions) {
+        super(message);
         this.exceptions = exceptions == null ? 
             Collections.emptyList() 
             : 
@@ -67,41 +67,6 @@ public List<Throwable> getExceptions() {
     Optional<Throwable> getFirstException() {
         return exceptions.stream().filter(Objects::nonNull).findFirst();
     }
-
-    public static MultitargetException of(final Throwable exception) {
-        return new MultitargetException(Collections.singletonList(exception));
-    }
-    
-    @Override
-    public String toString() {
-        // Exclude getMessage / getLocalizedMessage to avoid infinite recursion
-        return getClass().getName();
-    }
-    
-    @Override
-    public String getMessage() {
-        StringWriter w = new StringWriter();
-        printDetails(new PrintWriter(w), newDejavueSet());
-        return w.toString();
-    }
-    
-    void printDetails(PrintWriter w, Set<Throwable> visited) {
-        visited.add(this);
-        w.println(this);
-        printExceptions(w, (ex, padding) -> {
-            PrintWriter pw = new PrintWriter(new PaddedWriter(w, padding), true); 
-            if (visited.contains(ex)) {
-                pw.println("\t[CIRCULAR REFERENCE:" + ex + "]");
-            } else {
-                if (ex instanceof MultitargetException) {
-                    ((MultitargetException)ex).printDetails(pw, visited);
-                } else {
-                    pw.println(ex.toString());
-                }
-            }
-        });        
-        
-    }
 
     public void printExceptions() {
         printExceptions(System.err);

src/main/java/net/tascalate/concurrent/Promises.java

@@ -423,16 +423,14 @@ private static <T> Function<Promise<T>, Promise<T>> onCloseSource(Object source)
 
                 } catch (RuntimeException | Error ex) {
                     if (null != e) {
-                        e.addSuppressed(ex);
-                    } else {
-                        throw ex;
+                        ex.addSuppressed(e);
                     }
+                    throw ex;
                 } catch (Exception ex) {
                     if (null != e) {
-                        e.addSuppressed(ex);
-                    } else {
-                        throw new CompletionException(ex);
+                        ex.addSuppressed(e);
                     }
+                    throw new CompletionException(ex);
                 }
             }, true);
         } else {
@@ -1186,7 +1184,10 @@ private static <E extends Throwable> MultitargetException wrapMultitargetExcepti
         if (exception instanceof MultitargetException) {
             return (MultitargetException)exception;
         } else {
-            return MultitargetException.of(exception);
+            return new MultitargetException(
+                "Aggregated promise was completed exceptionally (1 out of 1)", 
+                Collections.singletonList(exception)
+            );
         }
     }
 

src/test/java/net/tascalate/concurrent/TestMultitargetExceptionTraces.java

@@ -11,9 +11,9 @@ public static void main(String[] argv) {
         //Throwable e = outer().initCause(err());
         //e.printStackTrace(new PrintWriter(System.err, true));
         e.printStackTrace();
-        System.out.println("--------------");
-        System.out.println(e.getLocalizedMessage());
-        System.out.println("--------------");
+        System.err.println("--------------");
+        System.err.println(e.getLocalizedMessage());
+        System.err.println("--------------");
         e.printExceptions();
     }
 
@@ -26,12 +26,12 @@ static Exception err() {
     }
 
     static Exception err_1() {
-        MultitargetException e = new MultitargetException(Arrays.asList(
+        MultitargetException e = new MultitargetException("First message", Arrays.asList(
             null, 
             null, 
             b(), null, 
             a(), null, 
-            new MultitargetException(Arrays.asList(c(), b()))
+            new MultitargetException("Another message", Arrays.asList(c(), b()))
         ));
         //e.fillInStackTrace();
         return e;