Implement decreasing read count on release

Author: lhotari

managed-ledger/src/main/java/org/apache/bookkeeper/mledger/impl/AbstractEntryImpl.java

@@ -133,6 +133,7 @@ public void onDeallocate(Runnable r) {
 
     @Override
     protected final void deallocate() {
+        beforeDeallocate();
         // This method is called whenever the ref-count of the EntryImpl reaches 0, so that now we can recycle it
         if (onDeallocate != null) {
             try {
@@ -153,6 +154,15 @@ protected final void deallocate() {
         recyclerHandle.recycle(self());
     }
 
+    /**
+     * This method is called just before the object is deallocated.
+     * Subclasses can override this method to run actions before the fields
+     * of the object are cleared and the object gets recycled.
+     */
+    protected void beforeDeallocate() {
+        // No-op
+    }
+
     /**
      * This method is called just before the object is recycled. Subclasses can override this methods to cleanup
      * the object before it is returned to the pool.

managed-ledger/src/main/java/org/apache/bookkeeper/mledger/impl/EntryImpl.java

@@ -34,6 +34,8 @@ protected EntryImpl newObject(Handle<EntryImpl> handle) {
         }
     };
 
+    private boolean decreaseReadCountOnRelease;
+
     public static EntryImpl create(LedgerEntry ledgerEntry, int expectedReadCount) {
         EntryImpl entry = RECYCLER.get();
         entry.timestamp = System.nanoTime();
@@ -91,10 +93,29 @@ public static EntryImpl create(Entry other) {
         entry.readCountHandler = (EntryReadCountHandlerImpl) other.getReadCountHandler();
         entry.setDataBuffer(other.getDataBuffer().retainedDuplicate());
         entry.setRefCnt(1);
+        entry.decreaseReadCountOnRelease = true;
         return entry;
     }
 
     private EntryImpl(Recycler.Handle<EntryImpl> recyclerHandle) {
         super(recyclerHandle);
     }
+
+    @Override
+    protected void beforeDeallocate() {
+        super.beforeDeallocate();
+        if (decreaseReadCountOnRelease && readCountHandler != null) {
+            readCountHandler.markRead();
+        }
+    }
+
+    @Override
+    protected void beforeRecycle() {
+        super.beforeRecycle();
+        decreaseReadCountOnRelease = false;
+    }
+
+    public void setDecreaseReadCountOnRelease(boolean enabled) {
+        decreaseReadCountOnRelease = enabled;
+    }
 }

managed-ledger/src/main/java/org/apache/bookkeeper/mledger/impl/cache/PendingReadsManager.java

@@ -287,6 +287,8 @@ public void attach(CompletableFuture<List<Entry>> handle) {
                             callback.callback.readEntriesComplete(copy, callback.ctx);
                         }
                         for (Entry entry : entriesToReturn) {
+                            // don't decrease the read count when these entries are released
+                            ((EntryImpl) entry).setDecreaseReadCountOnRelease(false);
                             entry.release();
                         }
                     }

managed-ledger/src/main/java/org/apache/bookkeeper/mledger/impl/cache/RangeEntryCacheImpl.java

@@ -405,6 +405,7 @@ void doAsyncReadEntriesByPosition(ReadHandle lh, Position firstPosition, Positio
             }
             callback.readEntriesComplete(entriesToReturn, ctx);
         } else {
+            // TODO: consider reusing the partially cached entries and only reading the missing ones
             if (!cachedEntries.isEmpty()) {
                 cachedEntries.forEach(entry -> entry.release());
             }