[GitHub] [incubator-uniffle] jerqi commented on a diff in pull request #16: [Bug] Fix NPE problem when process the event if application was cleared already

[GitBox <gi...@apache.org>]

jerqi commented on code in PR #16:
URL: https://github.com/apache/incubator-uniffle/pull/16#discussion_r912895756


##########
server/src/main/java/org/apache/uniffle/server/ShuffleFlushManager.java:
##########
@@ -135,59 +139,62 @@ public void addToFlushQueue(ShuffleDataFlushEvent event) {
 
   private void flushToFile(ShuffleDataFlushEvent event) {
 
-    Storage storage = storageManager.selectStorage(event);
-    if (!storage.canWrite()) {
-      addPendingEvents(event);
-      return;
-    }
-
     long start = System.currentTimeMillis();
     List<ShufflePartitionedBlock> blocks = event.getShuffleBlocks();
     boolean writeSuccess = false;
     try {
-      if (blocks == null || blocks.isEmpty()) {
-        LOG.info("There is no block to be flushed: " + event);
-      } else if (!event.isValid()) {
-        //  avoid printing error log
-        writeSuccess = true;
-        LOG.warn("AppId {} was removed already, event {} should be dropped", event.getAppId(), event);
-      } else {
-        ShuffleWriteHandler handler = storage.getOrCreateWriteHandler(new CreateShuffleWriteHandlerRequest(
-            storageType,
-            event.getAppId(),
-            event.getShuffleId(),
-            event.getStartPartition(),
-            event.getEndPartition(),
-            storageBasePaths,
-            shuffleServerId,
-            hadoopConf,
-            storageDataReplica));
+      Storage storage = storageManager.selectStorage(event);
+      // storage info maybe null if the application cache was cleared already
+      if (storage != null) {
+        if (!storage.canWrite()) {
+          addPendingEvents(event);

Review Comment:
   Why do we put the code into 
   ```
   try {
   } catch {
   } finally {
   }
   ```
   We release memory in the finally block, when we add the event to PendingEvents, we shouldn't release the event memory.



##########
server/src/main/java/org/apache/uniffle/server/ShuffleFlushManager.java:
##########
@@ -285,7 +292,9 @@ void processPendingEvents() throws Exception {
           pendingEventTimeoutSec, event.getEvent());
       return;
     }
-    if (storage.canWrite()) {
+    // storage maybe null if the application cache was cleared already
+    // add event to flush queue, and it will be released
+    if (storage == null || storage.canWrite()) {

Review Comment:
   when storage equals `null`, why do we need add it to the FlushQueue?



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