Implement destroy for BlobByteBuffer, but dont invoke it yet

hollow/src/main/java/com/netflix/hollow/core/memory/FixedLengthDataFactory.java

@@ -22,11 +22,11 @@ public static FixedLengthData get(HollowBlobInput in, MemoryMode memoryMode, Arr
         }
     }
 
-    public static void destroy(FixedLengthData fld, ArraySegmentRecycler memoryRecycler) {
+    public static void destroy(FixedLengthData fld, ArraySegmentRecycler memoryRecycler) throws IOException {
         if (fld instanceof FixedLengthElementArray) {
             ((FixedLengthElementArray) fld).destroy(memoryRecycler);
         } else if (fld instanceof EncodedLongBuffer) {
-            LOG.warning("Destroy operation is a no-op in shared memory mode");
+            LOG.warning("Destroy operation is not implemented for shared memory mode");
         } else {
             throw new UnsupportedOperationException("Unknown type");
         }

hollow/src/main/java/com/netflix/hollow/core/memory/encoding/BlobByteBuffer.java

@@ -8,6 +8,7 @@
 import java.nio.ByteOrder;
 import java.nio.MappedByteBuffer;
 import java.nio.channels.FileChannel;
+import sun.nio.ch.DirectBuffer;
 
 /**
  * <p>A stitching of {@link MappedByteBuffer}s to operate on large memory mapped blobs. {@code MappedByteBuffer} is
@@ -31,13 +32,17 @@ public final class BlobByteBuffer {
     private final int shift;
     private final int mask;
 
+    // SNAP: TODO: potentially needed for destruction
+    private final FileChannel channel;
+    private final boolean original;
+
     private long position;              // within index 0 to capacity-1 in the underlying ByteBuffer
 
-    private BlobByteBuffer(long capacity, int shift, int mask, ByteBuffer[] spine) {
-        this(capacity, shift, mask, spine, 0);
+    private BlobByteBuffer(long capacity, int shift, int mask, ByteBuffer[] spine, FileChannel channel, boolean original) {
+        this(capacity, shift, mask, spine, 0, channel, original);
     }
 
-    private BlobByteBuffer(long capacity, int shift, int mask, ByteBuffer[] spine, long position) {
+    private BlobByteBuffer(long capacity, int shift, int mask, ByteBuffer[] spine, long position, FileChannel channel, boolean original) {
 
         if (!spine[0].order().equals(ByteOrder.BIG_ENDIAN)) {
             throw new UnsupportedOperationException("Little endian memory layout is not supported");
@@ -46,6 +51,8 @@ private BlobByteBuffer(long capacity, int shift, int mask, ByteBuffer[] spine, l
         this.capacity = capacity;
         this.shift = shift;
         this.mask = mask;
+        this.channel = channel;
+        this.original = original;
         this.position = position;
 
         // The following assignment is purposefully placed *after* the population of all segments (this method is called
@@ -60,7 +67,7 @@ private BlobByteBuffer(long capacity, int shift, int mask, ByteBuffer[] spine, l
      * @return a new {@code BlobByteBuffer} which is view on the current {@code BlobByteBuffer}
      */
     public BlobByteBuffer duplicate() {
-        return new BlobByteBuffer(this.capacity, this.shift, this.mask, this.spine, this.position);
+        return new BlobByteBuffer(this.capacity, this.shift, this.mask, this.spine, this.position, this.channel, false);
     }
 
     /**
@@ -107,7 +114,7 @@ public static BlobByteBuffer mmapBlob(FileChannel channel, int singleBufferCapac
             spine[i] = buffer;
         }
 
-        return new BlobByteBuffer(size, shift, mask, spine);
+        return new BlobByteBuffer(size, shift, mask, spine, channel, true);
     }
 
     /**
@@ -239,4 +246,19 @@ private long bigEndian(long index, long boundary) {
         }
         return result;
     }
+
+    public void destroy() throws IOException {
+        // NOTE: invoking this will clean up the entire buffer and truncate the backing file, so it should invoked with
+        //       care- I'm thinking maybe safe to invoke on BlobByteBuffers over delta-target files since those are
+        //       per {type,shard} so if a destroy operation is called presumably it isn't being used moving fwd.
+        //       The BlobByteBuffer over the original snapshot file may be getting referenced for a while so maybe best
+        //       to defer to GC to clean that up based on reference count.
+        if (original) {
+            for (int i = 0; i < spine.length; i++) {
+                ByteBuffer buf = spine[i];
+                ((DirectBuffer) buf).cleaner().clean();
+            }
+            channel.truncate(0);
+        }
+    }
 }

hollow/src/main/java/com/netflix/hollow/core/memory/encoding/EncodedLongBuffer.java

@@ -223,4 +223,9 @@ public void set(long index, long value) {
     public long get(long index) {
         return this.bufferView.getLong(this.bufferView.position() + (index * 8));
     }
+
+    public void destroy() throws IOException {
+        System.out.println("SNAP: WARNING - shouldn't be getting invoked");
+        // since we operate on a bufferView here, we should't mutate the underlying buffer
+    }
 }

hollow/src/main/java/com/netflix/hollow/core/read/engine/list/HollowListTypeDataElements.java

@@ -109,7 +109,7 @@ public void applyDelta(HollowListTypeDataElements fromData, HollowListTypeDataEl
         new HollowListDeltaApplicator(fromData, deltaData, this).applyDelta();
     }
 
-    public void destroy() {
+    public void destroy() throws IOException {
         FixedLengthDataFactory.destroy(listPointerData, memoryRecycler);
         FixedLengthDataFactory.destroy(elementData, memoryRecycler);
     }

hollow/src/main/java/com/netflix/hollow/core/read/engine/map/HollowMapTypeDataElements.java

@@ -121,7 +121,7 @@ public void applyDelta(HollowMapTypeDataElements fromData, HollowMapTypeDataElem
         new HollowMapDeltaApplicator(fromData, deltaData, this).applyDelta();
     }
 
-    public void destroy() {
+    public void destroy() throws IOException {
         FixedLengthDataFactory.destroy(mapPointerAndSizeData, memoryRecycler);
         FixedLengthDataFactory.destroy(entryData, memoryRecycler);
     }

hollow/src/main/java/com/netflix/hollow/core/read/engine/object/HollowObjectDeltaApplicator.java

@@ -143,7 +143,7 @@ File provisionTargetFile(long numBytes, String fileName) throws IOException {
         RandomAccessFile raf = new RandomAccessFile(targetFile, "rw");
         raf.setLength(numBytes);
         raf.close();
-        System.out.println("SNAP: Provisioned targetFile (one per type per shard) of size " + numBytes + " bytes: " + targetFile.getPath());
+        System.out.println("SNAP: Provisioned targetFile (one per shard per type) of size " + numBytes + " bytes: " + targetFile.getPath());
         return targetFile;
     }
 

hollow/src/main/java/com/netflix/hollow/core/read/engine/object/HollowObjectTypeDataElements.java

@@ -98,7 +98,7 @@ void readFromInput(HollowBlobInput in, boolean isDelta, HollowObjectSchema unfil
         readVarLengthData(in, unfilteredSchema);
     }
 
-    private void removeExcludedFieldsFromFixedLengthData() {
+    private void removeExcludedFieldsFromFixedLengthData() throws IOException {
         if(bitsPerField.length < bitsPerUnfilteredField.length) {
             if (!memoryMode.equals(MemoryMode.ON_HEAP)) {
                 LOG.warning("Type filter is not supported in Shared Memory mode");
@@ -217,7 +217,7 @@ void applyDelta(HollowObjectTypeDataElements fromData, HollowObjectTypeDataEleme
 
     }
 
-    public void destroy() {
+    public void destroy() throws IOException {
         FixedLengthDataFactory.destroy(fixedLengthData, memoryRecycler);
         for(int i=0;i<varLengthData.length;i++) {
             if(varLengthData[i] != null)

hollow/src/main/java/com/netflix/hollow/core/read/engine/set/HollowSetTypeDataElements.java

@@ -117,7 +117,7 @@ public void applyDelta(HollowSetTypeDataElements fromData, HollowSetTypeDataElem
         new HollowSetDeltaApplicator(fromData, deltaData, this).applyDelta();
     }
 
-    public void destroy() {
+    public void destroy() throws IOException {
         FixedLengthDataFactory.destroy(setPointerAndSizeData, memoryRecycler);
         FixedLengthDataFactory.destroy(elementData, memoryRecycler);
     }