Github user andrewor14 commented on a diff in the pull request:
https://github.com/apache/spark/pull/42#discussion_r10616539
--- Diff:
core/src/main/scala/org/apache/spark/storage/BlockManagerStatusListener.scala
---
@@ -0,0 +1,63 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements. See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License. You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.apache.spark.storage
+
+import scala.collection.mutable.ArrayBuffer
+
+import org.apache.spark.scheduler._
+
+/**
+ * A listener for BlockManager status updates.
+ *
+ * This listener provides a way to post executor storage status
information as soon as it
+ * is available (i.e. immediately after the associated BlockManager has
registered with the
+ * driver). This is necessary because the SparkContext is only notified
when an executor is
+ * launched, but by then the storage information is not ready yet.
+ *
+ * Further, it is possible for a BlockManager be registered before the
listener bus on the
+ * driver is initialized (e.g. the driver's own BlockManager), in which
case the corresponding
+ * event should be buffered.
+ */
+private[spark] class BlockManagerStatusListener extends SparkListener {
--- End diff --
This would require creating the event bus and the scheduler before
SparkEnv, since SparkEnv creates all the block manager classes. This is not
possible, however, since the DAGScheduler depends on the block manager and the
map output tracker.
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