reddycharan commented on a change in pull request #1281: Issue #570: 
Introducing EntryLogManager.
URL: https://github.com/apache/bookkeeper/pull/1281#discussion_r180670849
 
 

 ##########
 File path: 
bookkeeper-server/src/main/java/org/apache/bookkeeper/bookie/EntryLogger.java
 ##########
 @@ -499,176 +576,163 @@ void createNewLog() throws IOException {
     EntryLoggerAllocator getEntryLoggerAllocator() {
         return entryLoggerAllocator;
     }
-    /**
-     * Append the ledger map at the end of the entry log.
-     * Updates the entry log file header with the offset and size of the map.
-     */
-    private void appendLedgersMap(BufferedLogChannel entryLogChannel) throws 
IOException {
-        long ledgerMapOffset = entryLogChannel.position();
-
-        ConcurrentLongLongHashMap ledgersMap = entryLogChannel.getLedgersMap();
-        int numberOfLedgers = (int) ledgersMap.size();
-
-        // Write the ledgers map into several batches
-
-        final int maxMapSize = LEDGERS_MAP_HEADER_SIZE + 
LEDGERS_MAP_ENTRY_SIZE * LEDGERS_MAP_MAX_BATCH_SIZE;
-        final ByteBuf serializedMap = 
ByteBufAllocator.DEFAULT.buffer(maxMapSize);
-
-        try {
-            ledgersMap.forEach(new BiConsumerLong() {
-                int remainingLedgers = numberOfLedgers;
-                boolean startNewBatch = true;
-                int remainingInBatch = 0;
-
-                @Override
-                public void accept(long ledgerId, long size) {
-                    if (startNewBatch) {
-                        int batchSize = Math.min(remainingLedgers, 
LEDGERS_MAP_MAX_BATCH_SIZE);
-                        int ledgerMapSize = LEDGERS_MAP_HEADER_SIZE + 
LEDGERS_MAP_ENTRY_SIZE * batchSize;
-
-                        serializedMap.clear();
-                        serializedMap.writeInt(ledgerMapSize - 4);
-                        serializedMap.writeLong(INVALID_LID);
-                        serializedMap.writeLong(LEDGERS_MAP_ENTRY_ID);
-                        serializedMap.writeInt(batchSize);
-
-                        startNewBatch = false;
-                        remainingInBatch = batchSize;
-                    }
-                    // Dump the ledger in the current batch
-                    serializedMap.writeLong(ledgerId);
-                    serializedMap.writeLong(size);
-                    --remainingLedgers;
-
-                    if (--remainingInBatch == 0) {
-                        // Close current batch
-                        try {
-                            entryLogChannel.write(serializedMap);
-                        } catch (IOException e) {
-                            throw new RuntimeException(e);
-                        }
-
-                        startNewBatch = true;
-                    }
-                }
-            });
-        } catch (RuntimeException e) {
-            if (e.getCause() instanceof IOException) {
-                throw (IOException) e.getCause();
-            } else {
-                throw e;
-            }
-        } finally {
-            serializedMap.release();
-        }
-        // Flush the ledger's map out before we write the header.
-        // Otherwise the header might point to something that is not fully 
written
-        entryLogChannel.flush();
-
-        // Update the headers with the map offset and count of ledgers
-        ByteBuffer mapInfo = ByteBuffer.allocate(8 + 4);
-        mapInfo.putLong(ledgerMapOffset);
-        mapInfo.putInt(numberOfLedgers);
-        mapInfo.flip();
-        entryLogChannel.fileChannel.write(mapInfo, 
LEDGERS_MAP_OFFSET_POSITION);
-    }
 
     /**
      * An allocator pre-allocates entry log files.
      */
     class EntryLoggerAllocator {
 
         private long preallocatedLogId;
-        private Future<BufferedLogChannel> preallocation = null;
+        Future<BufferedLogChannel> preallocation = null;
         private ExecutorService allocatorExecutor;
-        private final Object createEntryLogLock = new Object();
-        private final Object createCompactionLogLock = new Object();
 
         EntryLoggerAllocator(long logId) {
             preallocatedLogId = logId;
             allocatorExecutor = Executors.newSingleThreadExecutor();
         }
 
-        BufferedLogChannel createNewLog() throws IOException {
-            synchronized (createEntryLogLock) {
-                BufferedLogChannel bc;
-                if (!entryLogPreAllocationEnabled){
-                    // create a new log directly
-                    bc = allocateNewLog();
-                    return bc;
-                } else {
-                    // allocate directly to response request
-                    if (null == preallocation){
-                        bc = allocateNewLog();
+        synchronized long getPreallocatedLogId(){
+            return preallocatedLogId;
+        }
+
+        synchronized BufferedLogChannel createNewLog() throws IOException {
+            BufferedLogChannel bc;
+            if (!entryLogPreAllocationEnabled || null == preallocation) {
+                // initialization time to create a new log
+                bc = allocateNewLog();
+            } else {
+                // has a preallocated entry log
+                try {
+                    /*
+                     * both createNewLog and allocateNewLog are synchronized on
+                     * EntryLoggerAllocator.this object. So it is possible that
+                     * a thread calling createNewLog would attain the lock on
+                     * this object and get to this point but preallocation
+                     * Future is starving for lock on EntryLoggerAllocator.this
+                     * to execute allocateNewLog. Here since we attained lock
+                     * for this it means preallocation future must have either
+                     * completed creating new log or still waiting for lock on
+                     * this object to execute allocateNewLog method. So we
+                     * should try to get result of the future without waiting.
+                     * If it fails with TimeoutException then call
+                     * allocateNewLog explicitly since we are holding the lock
+                     * on this anyhow.
+                     *
+                     */
+                    bc = preallocation.get(0, TimeUnit.MILLISECONDS);
+                } catch (ExecutionException ee) {
+                    if (ee.getCause() instanceof IOException) {
+                        throw (IOException) (ee.getCause());
                     } else {
-                        // has a preallocated entry log
-                        try {
-                            bc = preallocation.get();
-                        } catch (ExecutionException ee) {
-                            if (ee.getCause() instanceof IOException) {
-                                throw (IOException) (ee.getCause());
-                            } else {
-                                throw new IOException("Error to execute entry 
log allocation.", ee);
-                            }
-                        } catch (CancellationException ce) {
-                            throw new IOException("Task to allocate a new 
entry log is cancelled.", ce);
-                        } catch (InterruptedException ie) {
-                            Thread.currentThread().interrupt();
-                            throw new IOException("Intrrupted when waiting a 
new entry log to be allocated.", ie);
-                        }
+                        throw new IOException("Error to execute entry log 
allocation.", ee);
                     }
-                    // preallocate a new log in background upon every call
-                    preallocation = allocatorExecutor.submit(() -> 
allocateNewLog());
-                    return bc;
+                } catch (CancellationException ce) {
+                    throw new IOException("Task to allocate a new entry log is 
cancelled.", ce);
+                } catch (InterruptedException ie) {
+                    Thread.currentThread().interrupt();
+                    throw new IOException("Intrrupted when waiting a new entry 
log to be allocated.", ie);
+                } catch (TimeoutException e) {
+                    LOG.debug("Received TimeoutException while trying to get 
preallocation future result,"
+                            + " which means that Future is waiting for 
acquiring lock on EntryLoggerAllocator.this");
+                    bc = allocateNewLog();
                 }
             }
+            if (entryLogPreAllocationEnabled) {
+                /*
+                 * We should submit new callable / create new instance of 
future only if the previous preallocation is
+                 * null or if it is done. This is needed because previous 
preallocation has not completed its execution
+                 * since it is waiting for lock on EntryLoggerAllocator.this.
+                 */
+                if ((preallocation == null) || preallocation.isDone()) {
+                    preallocation = allocatorExecutor.submit(new 
Callable<BufferedLogChannel>() {
 
 Review comment:
   i think lambda expression was introduced recently in this code.

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