[SPARK-14579][SQL] Fix the race condition in StreamExecution.processA…

…llAvailable again

## What changes were proposed in this pull request?

apache#12339 didn't fix the race condition. MemorySinkSuite is still flaky: https://amplab.cs.berkeley.edu/jenkins/job/spark-master-test-maven-hadoop-2.2/814/testReport/junit/org.apache.spark.sql.streaming/MemorySinkSuite/registering_as_a_table/

Here is an execution order to reproduce it.

| Time        |Thread 1           | MicroBatchThread  |
|:-------------:|:-------------:|:-----:|
| 1 | |  `MemorySink.getOffset` |
| 2 | |  availableOffsets ++= newData (availableOffsets is not changed here)  |
| 3 | addData(newData)      |   |
| 4 | Set `noNewData` to `false` in  processAllAvailable |  |
| 5 | | `dataAvailable` returns `false`   |
| 6 | | noNewData = true |
| 7 | `noNewData` is true so just return | |
| 8 |  assert results and fail | |
| 9 |   | `dataAvailable` returns true so process the new batch |

This PR expands the scope of `awaitBatchLock.synchronized` to eliminate the above race.

## How was this patch tested?

test("stress test"). It always failed before this patch. And it will pass after applying this patch. Ignore this test in the PR as it takes several minutes to finish.

Author: Shixiong Zhu <shixiong@databricks.com>

Closes apache#12582 from zsxwing/SPARK-14579-2.

sql/core/src/main/scala/org/apache/spark/sql/execution/streaming/StreamExecution.scala

@@ -242,12 +242,12 @@ class StreamExecution(
     // method. See SPARK-14131.
     //
     // Check to see what new data is available.
-    val newData = microBatchThread.runUninterruptibly {
-      uniqueSources.flatMap(s => s.getOffset.map(o => s -> o))
-    }
-    availableOffsets ++= newData
-
     val hasNewData = awaitBatchLock.synchronized {
+      val newData = microBatchThread.runUninterruptibly {
+        uniqueSources.flatMap(s => s.getOffset.map(o => s -> o))
+      }
+      availableOffsets ++= newData
+
       if (dataAvailable) {
         true
       } else {

sql/core/src/test/scala/org/apache/spark/sql/streaming/MemorySinkSuite.scala

@@ -26,6 +26,15 @@ class MemorySinkSuite extends StreamTest with SharedSQLContext {
   import testImplicits._
 
   test("registering as a table") {
+    testRegisterAsTable()
+  }
+
+  ignore("stress test") {
+    // Ignore the stress test as it takes several minutes to run
+    (0 until 1000).foreach(_ => testRegisterAsTable())
+  }
+
+  private def testRegisterAsTable(): Unit = {
     val input = MemoryStream[Int]
     val query = input.toDF().write
       .format("memory")