fix 90452 threading by subject slow when threads are very large, sr=mscott, a=bsmedberg

mailnews/db/msgdb/src/nsMsgThread.cpp

@@ -290,6 +290,19 @@ NS_IMETHODIMP nsMsgThread::AddChild(nsIMsgDBHdr *child, nsIMsgDBHdr *inReplyTo,
   
   PRBool hdrMoved = PR_FALSE;
   nsCOMPtr <nsIMsgDBHdr> curHdr;
+
+  // This is an ugly but simple fix for a difficult problem. Basically, when we add
+  // a message to a thread, we have to run through the thread to see if the new
+  // message is a parent of an existing message in the thread, and adjust things
+  // accordingly. If you thread by subject, and you have a large folder with
+  // messages w/ all the same subject, this code can take a really long time. So the
+  // pragmatic thing is to say that for threads with more than 1000 messages, it's
+  // simply not worth dealing with the case where the parent comes in after the
+  // child. Threads with more than 1000 messages are pretty unwieldy anyway.
+  // See Bug 90452
+
+  if (numChildren < 1000)
+  {
     for (childIndex = 0; childIndex < numChildren; childIndex++)
     {
       nsMsgKey msgKey;
@@ -334,10 +347,11 @@ NS_IMETHODIMP nsMsgThread::AddChild(nsIMsgDBHdr *child, nsIMsgDBHdr *inReplyTo,
           // OK, this is a reparenting - need to send notification
           if (announcer)
             announcer->NotifyParentChangedAll(msgKey, oldThreadParent, newHdrKey, nsnull);
-#ifdef DEBUG_bienvenu1
+  #ifdef DEBUG_bienvenu1
           if (newHdrKey != m_threadKey)
             printf("adding second level child\n");
-#endif
+  #endif
+        }
       }
     }
   }