sijie commented on a change in pull request #1281: Issue #570: Introducing 
EntryLogManager.
URL: https://github.com/apache/bookkeeper/pull/1281#discussion_r181630491
 
 

 ##########
 File path: 
bookkeeper-server/src/main/java/org/apache/bookkeeper/bookie/EntryLogger.java
 ##########
 @@ -788,89 +810,392 @@ private long readLastLogId(File f) {
         }
     }
 
-    /**
-     * Flushes all rotated log channels. After log channels are flushed,
-     * move leastUnflushedLogId ptr to current logId.
-     */
-    void checkpoint() throws IOException {
-        flushRotatedLogs();
+    interface EntryLogManager {
+
+        /*
+         * add entry to the corresponding entrylog and return the position of
+         * the entry in the entrylog
+         */
+        long addEntry(long ledger, ByteBuf entry, boolean rollLog) throws 
IOException;
+
+        /*
+         * gets the active logChannel with the given entryLogId. null if it is
+         * not existing.
+         */
+        BufferedLogChannel getCurrentLogIfPresent(long entryLogId);
+
+        /*
+         * Returns eligible writable ledger dir for the creation next entrylog
+         */
+        File getDirForNextEntryLog(List<File> writableLedgerDirs);
+
+        /*
+         * Do the operations required for checkpoint.
+         */
+        void checkpoint() throws IOException;
+
+        /*
+         * flush both current and rotated logs.
+         */
+        void flush() throws IOException;
+
+        /*
+         * close current logs.
+         */
+        void close() throws IOException;
+
+        /*
+         * force close current logs.
+         */
+        void forceClose();
+
         /*
-         * In the case of entryLogPerLedgerEnabled we need to flush both
-         * rotatedlogs and currentlogs. This is needed because syncThread
-         * periodically does checkpoint and at this time all the logs should
-         * be flushed.
          *
-         * TODO: When EntryLogManager is introduced in the subsequent 
sub-tasks of
-         * this Issue, I will move this logic to individual implamentations of
-         * EntryLogManager and it would be free of this booalen flag based 
logic.
+         */
+        void prepareSortedLedgerStorageCheckpoint(long numBytesFlushed) throws 
IOException;
+
+        /*
+         * this method should be called before doing entrymemtable flush, it
+         * would save the state of the entrylogger before entrymemtable flush
+         * and commitEntryMemTableFlush would take appropriate action after
+         * entrymemtable flush.
+         */
+        void prepareEntryMemTableFlush();
+
+        /*
+         * this method should be called after doing entrymemtable flush,it 
would
+         * take appropriate action after entrymemtable flush depending on the
+         * current state of the entrylogger and the state of the entrylogger
+         * during prepareEntryMemTableFlush.
+         *
+         * It is assumed that there would be corresponding
+         * prepareEntryMemTableFlush for every commitEntryMemTableFlush and 
both
+         * would be called from the same thread.
          *
+         * returns boolean value indicating whether EntryMemTable should do 
checkpoint
+         * after this commit method.
          */
-        if (entryLogPerLedgerEnabled) {
-            flushCurrentLog();
-        }
+        boolean commitEntryMemTableFlush() throws IOException;
     }
 
-    void flushRotatedLogs() throws IOException {
-        List<BufferedLogChannel> channels = null;
-        long flushedLogId = INVALID_LID;
-        synchronized (this) {
-            channels = logChannelsToFlush;
-            logChannelsToFlush = null;
+    abstract class EntryLogManagerBase implements EntryLogManager {
+        final List<BufferedLogChannel> rotatedLogChannels;
+
+        EntryLogManagerBase() {
+            rotatedLogChannels = new 
CopyOnWriteArrayList<BufferedLogChannel>();
 
 Review comment:
   > LinkedList iterator will fail because "if the list is structurally 
modified at any time after the iterator is created, in any way except through 
the Iterator's own remove or add methods, the iterator will throw a 
ConcurrentModificationException."
   
   I see the access to `rotatedLogChannels` are under synchronized block. so I 
am not sure when this `ConcurrentModificationException` can happen. If it can 
happen, please write a test to reproduce it and show your fix actually work.

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