[GitHub] athanatos commented on a change in pull request #1931: (WIP) GetListOfEntriesOfLedger implementation

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athanatos commented on a change in pull request #1931: (WIP) GetListOfEntriesOfLedger implementation
URL: https://github.com/apache/bookkeeper/pull/1931#discussion_r253228615
 
 

 ##########
 File path: bookkeeper-server/src/main/java/org/apache/bookkeeper/bookie/EntryMemTable.java
 ##########
 @@ -456,4 +459,95 @@ boolean isEmpty() {
     public void close() throws Exception {
         // no-op
     }
+
+    /*
+     * returns the Iterator of EntryKeys of a ledger available in this
+     * EntryMemTable. It would be in the ascending order and this Iterator is
+     * weakly consistent.
+     */
+    Iterator<EntryKey> getEntriesOfALedger(long ledgerId) {
+        EntryKey thisLedgerFloorEntry = new EntryKey(ledgerId, 0);
+        EntryKey thisLedgerCeilingEntry = new EntryKey(ledgerId, LONG_MAX_VALUE);
+        Iterator<EntryKey> thisLedgerEntriesInKVMap;
+        Iterator<EntryKey> thisLedgerEntriesInSnapshot;
+        this.lock.readLock().lock();
+        try {
+            /*
+             * Gets a view of the portion of this map that corresponds to
+             * entries of this ledger.
+             *
+             * Here 'kvmap' is of type 'ConcurrentSkipListMap', so its 'subMap'
+             * call would return a view of the portion of this map whose keys
+             * range from fromKey to toKey and it would be of type
+             * 'ConcurrentNavigableMap'. ConcurrentNavigableMap's 'keySet' would
+             * return NavigableSet view of the keys contained in this map. This
+             * view's iterator would be weakly consistent -
+             * https://docs.oracle.com/javase/8/docs/api/java/util/concurrent/
+             * package-summary.html#Weakly.
+             *
+             * 'weakly consistent' would guarantee 'to traverse elements as they
+             * existed upon construction exactly once, and may (but are not
+             * guaranteed to) reflect any modifications subsequent to
+             * construction.'
+             *
+             */
+            thisLedgerEntriesInKVMap = this.kvmap.subMap(thisLedgerFloorEntry, thisLedgerCeilingEntry).keySet()
+                    .iterator();
+            thisLedgerEntriesInSnapshot = this.snapshot.subMap(thisLedgerFloorEntry, thisLedgerCeilingEntry).keySet()
+                    .iterator();
+        } finally {
+            this.lock.readLock().unlock();
+        }
+        return new Iterator<EntryKey>() {
+            private EntryKey curKVMapEntry = null;
+            private EntryKey curSnapshotEntry = null;
+            private boolean hasToPreFetch = true;
+
+            @Override
+            public boolean hasNext() {
+                if (hasToPreFetch) {
+                    if (curKVMapEntry == null) {
+                        curKVMapEntry = thisLedgerEntriesInKVMap.hasNext() ? thisLedgerEntriesInKVMap.next() : null;
+                    }
+                    if (curSnapshotEntry == null) {
+                        curSnapshotEntry = thisLedgerEntriesInSnapshot.hasNext() ? thisLedgerEntriesInSnapshot.next()
+                                : null;
+                    }
+                }
+                hasToPreFetch = false;
+                return (curKVMapEntry != null || curSnapshotEntry != null);
+            }
+
+            @Override
+            public EntryKey next() {
+                if (hasNext()) {
+                    EntryKey returnEntryKey = null;
+                    if (curKVMapEntry != null && curSnapshotEntry != null) {
 
 Review comment:
   Agreed.

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