Code review request for 8012044: Give more information about self-suppression from Throwable.addSuppressed

[Joe Darcy]

On 04/14/2013 07:36 PM, Joe Darcy wrote:
> On 04/12/2013 07:29 PM, Jason Mehrens wrote:
>> Joe,
>> You'll have guard ise.addSuppressed against null.  Looks good otherwise.
>>
>> private static void initCauseNull() {
>>       Throwable t1 = new Throwable();
>>       t1.initCause(null);
>>       try {
>>         t1.initCause(null);
>>       } catch(IllegalStateException expect) {
>>       }
>> }
>
> Right you are; check added and test updated in:
>
>     http://cr.openjdk.java.net/~darcy/8012044.2/
>
> Full patch to Throwable:

[snip]

One more iteration; I've changed the initCause logic to suppress both 
exceptions rather than using one as the cause:

      http://cr.openjdk.java.net/~darcy/8012044.2

Patch to throwable:

--- old/src/share/classes/java/lang/Throwable.java    2013-04-14 
19:33:23.000000000 -0700
+++ new/src/share/classes/java/lang/Throwable.java    2013-04-14 
19:33:23.000000000 -0700
@@ -452,10 +452,15 @@
       * @since  1.4
       */
      public synchronized Throwable initCause(Throwable cause) {
-        if (this.cause != this)
-            throw new IllegalStateException("Can't overwrite cause");
+        if (this.cause != this) {
+            IllegalStateException ise =
+                new IllegalStateException("Can't overwrite cause", this);
+            if (cause != null)
+                ise.addSuppressed(cause);
+            throw ise;
+        }
          if (cause == this)
-            throw new IllegalArgumentException("Self-causation not 
permitted");
+            throw new IllegalArgumentException("Self-causation not 
permitted", this);
          this.cause = cause;
          return this;
      }
@@ -1039,7 +1044,7 @@
       */
      public final synchronized void addSuppressed(Throwable exception) {
          if (exception == this)
-            throw new IllegalArgumentException(SELF_SUPPRESSION_MESSAGE);
+            throw new 
IllegalArgumentException(SELF_SUPPRESSION_MESSAGE, exception);

          if (exception == null)
              throw new NullPointerException(NULL_CAUSE_MESSAGE);

The suppression mechanism is typically, but not exclusively, used by the 
try-with-resources statement.

Thanks,

-Joe