Github user kiszk commented on a diff in the pull request:
https://github.com/apache/spark/pull/19222#discussion_r172037938
--- Diff:
common/unsafe/src/main/java/org/apache/spark/unsafe/memory/OnHeapMemoryBlock.java
---
@@ -0,0 +1,142 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements. See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License. You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.apache.spark.unsafe.memory;
+
+import org.apache.spark.unsafe.Platform;
+
+/**
+ * A consecutive block of memory with a long array on Java heap.
+ */
+public final class OnHeapMemoryBlock extends MemoryBlock {
+
+ private final long[] array;
+
+ public OnHeapMemoryBlock(long[] obj, long offset, long size) {
+ super(obj, offset, size);
+ this.array = obj;
+ assert(offset - Platform.LONG_ARRAY_OFFSET + size <= obj.length * 8L) :
--- End diff --
Thank you for your explanation. Now, we focus on the path 3. I understand
what you pointed out. How the following code should work?
```
val mb = new OnHeapMemoryBlock(new long[16]), Platform.LONG_ARRAY_OFFSET,
8);
val mb1 = mb.subBlock(0, 96);
```
According to the name `subBlock()`, I understand that you would like to
ensure `sub block's size <= super block's size` (`not (96 <= 8)`)` logically.
I would like to allow us to the above code since the array actually
reserved enough space (`96 <= 128`). This is because I have already seen such a
code when we would use `MemoryBlock` for `
I. Add additional method `block()` (or different name) with this assertion.
Keep `subBlock()` with a new assert that you proposed.
2. Use another name `block()` (or different name) instead of `subBlock()`
with this assertion.
WDYT? cc: @cloud-fan
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