CR feedback (clarify comment and log statement)

Author: holdenk

core/src/main/scala/org/apache/spark/executor/CoarseGrainedExecutorBackend.scala

@@ -289,7 +289,7 @@ private[spark] class CoarseGrainedExecutorBackend(
 
   private def decommissionSelf(): Boolean = {
     if (!decommissioned) {
-      logInfo("Decommissioning self w/sync")
+      logInfo("Decommissioning self and starting background thread to exit when done.")
       try {
         decommissioned = true
         // Tell master we are are decommissioned so it stops trying to schedule us

core/src/main/scala/org/apache/spark/executor/Executor.scala

@@ -230,10 +230,10 @@ private[spark] class Executor(
   private[executor] def numRunningTasks: Int = runningTasks.size()
 
   /**
-   * Mark an executor for decommissioning and avoid launching new tasks.
+   * Mark an executor for decommissioning.
    */
   private[spark] def decommission(): Unit = {
-    logInfo("Executor asked to decommission. Starting shutdown thread.")
+    logInfo("Executor asked to decommission.")
     decommissioned = true
   }
 

core/src/main/scala/org/apache/spark/storage/BlockManager.scala

@@ -1890,6 +1890,8 @@ private[spark] class BlockManager(
    * Note: this does not delete the shuffle files in-case there is an in-progress fetch
    * but rather shadows them.
    * Requires an Indexed based shuffle resolver.
+   *
+   * @return true if we have not migrated all shuffle blocks, false otherwise.
    */
   def offloadShuffleBlocks(): Boolean = {
     // Update the queue of shuffles to be migrated