Read state concurrent access bugfix- atomicity in accessing fields of…

… shard holder
Netflix · Oct 7, 2023 · a739efc · a739efc
1 parent 547fcab
commit a739efc
Showing 1 changed file with 22 additions and 9 deletions.
diff --git a/...w/src/main/java/com/netflix/hollow/core/read/engine/object/HollowObjectTypeReadState.java b/...w/src/main/java/com/netflix/hollow/core/read/engine/object/HollowObjectTypeReadState.java
@@ -360,63 +360,76 @@ public int readOrdinal(int ordinal, int fieldIndex) {
     @Override
     public int readInt(int ordinal, int fieldIndex) {
         sampler.recordFieldAccess(fieldIndex);
-        HollowObjectTypeReadStateShard shard = shardsVolatile.shards[ordinal & shardsVolatile.shardNumberMask];
+        ShardsHolder shardsHolder = shardsVolatile; // this read can return a stale shardHolder with greater or lesser than current
+                                                    // num shards but maxOrdinal remains same across stale vs current. So given this
+                                                    // atomic assignment below operations on a stale shards holder will be legal
+                                                    // SNAP: Here: but which shard to map to should probably be re-computed right, if
+                                                    // the we got a stale shard here?
+        HollowObjectTypeReadStateShard shard = shardsHolder.shards[ordinal & shardsHolder.shardNumberMask];
         return shard.readInt(ordinal >> shard.shardOrdinalShift, fieldIndex);
     }
 
     @Override
     public float readFloat(int ordinal, int fieldIndex) {
         sampler.recordFieldAccess(fieldIndex);
-        HollowObjectTypeReadStateShard shard = shardsVolatile.shards[ordinal & shardsVolatile.shardNumberMask];
+        ShardsHolder shardsHolder = shardsVolatile;
+        HollowObjectTypeReadStateShard shard = shardsHolder.shards[ordinal & shardsHolder.shardNumberMask];
         return shard.readFloat(ordinal >> shard.shardOrdinalShift, fieldIndex);
     }
 
     @Override
     public double readDouble(int ordinal, int fieldIndex) {
         sampler.recordFieldAccess(fieldIndex);
-        HollowObjectTypeReadStateShard shard = shardsVolatile.shards[ordinal & shardsVolatile.shardNumberMask];
+        ShardsHolder shardsHolder = shardsVolatile;
+        HollowObjectTypeReadStateShard shard = shardsHolder.shards[ordinal & shardsHolder.shardNumberMask];
         return shard.readDouble(ordinal >> shard.shardOrdinalShift, fieldIndex);
     }
 
     @Override
     public long readLong(int ordinal, int fieldIndex) {
         sampler.recordFieldAccess(fieldIndex);
-        HollowObjectTypeReadStateShard shard = shardsVolatile.shards[ordinal & shardsVolatile.shardNumberMask];
+        ShardsHolder shardsHolder = shardsVolatile;
+        HollowObjectTypeReadStateShard shard = shardsHolder.shards[ordinal & shardsHolder.shardNumberMask];
         return shard.readLong(ordinal >> shard.shardOrdinalShift, fieldIndex);
     }
 
     @Override
     public Boolean readBoolean(int ordinal, int fieldIndex) {
         sampler.recordFieldAccess(fieldIndex);
-        HollowObjectTypeReadStateShard shard = shardsVolatile.shards[ordinal & shardsVolatile.shardNumberMask];
+        ShardsHolder shardsHolder = shardsVolatile;
+        HollowObjectTypeReadStateShard shard = shardsHolder.shards[ordinal & shardsHolder.shardNumberMask];
         return shard.readBoolean(ordinal >> shard.shardOrdinalShift, fieldIndex);
     }
 
     @Override
     public byte[] readBytes(int ordinal, int fieldIndex) {
         sampler.recordFieldAccess(fieldIndex);
-        HollowObjectTypeReadStateShard shard = shardsVolatile.shards[ordinal & shardsVolatile.shardNumberMask];
+        ShardsHolder shardsHolder = shardsVolatile;
+        HollowObjectTypeReadStateShard shard = shardsHolder.shards[ordinal & shardsHolder.shardNumberMask];
         return shard.readBytes(ordinal >> shard.shardOrdinalShift, fieldIndex);
     }
 
     @Override
     public String readString(int ordinal, int fieldIndex) {
         sampler.recordFieldAccess(fieldIndex);
-        HollowObjectTypeReadStateShard shard = shardsVolatile.shards[ordinal & shardsVolatile.shardNumberMask];
+        ShardsHolder shardsHolder = shardsVolatile;
+        HollowObjectTypeReadStateShard shard = shardsHolder.shards[ordinal & shardsHolder.shardNumberMask];
         return shard.readString(ordinal >> shard.shardOrdinalShift, fieldIndex);
     }
 
     @Override
     public boolean isStringFieldEqual(int ordinal, int fieldIndex, String testValue) {
         sampler.recordFieldAccess(fieldIndex);
-        HollowObjectTypeReadStateShard shard = shardsVolatile.shards[ordinal & shardsVolatile.shardNumberMask];
+        ShardsHolder shardsHolder = shardsVolatile;
+        HollowObjectTypeReadStateShard shard = shardsHolder.shards[ordinal & shardsHolder.shardNumberMask];
         return shard.isStringFieldEqual(ordinal >> shard.shardOrdinalShift, fieldIndex, testValue);
     }
 
     @Override
     public int findVarLengthFieldHashCode(int ordinal, int fieldIndex) {
         sampler.recordFieldAccess(fieldIndex);
-        HollowObjectTypeReadStateShard shard = shardsVolatile.shards[ordinal & shardsVolatile.shardNumberMask];
+        ShardsHolder shardsHolder = shardsVolatile;
+        HollowObjectTypeReadStateShard shard = shardsHolder.shards[ordinal & shardsHolder.shardNumberMask];
         return shard.findVarLengthFieldHashCode(ordinal >> shard.shardOrdinalShift, fieldIndex);
     }