Remove usage of Unsafe.setMemory

Author: JoshRosen

unsafe/src/main/java/org/apache/spark/unsafe/map/BytesToBytesMap.java

@@ -429,7 +429,7 @@ public void putNewKey(
   private void allocate(int capacity) {
     capacity = Math.max((int) Math.min(Integer.MAX_VALUE, nextPowerOf2(capacity)), 64);
     longArray = new LongArray(memoryManager.allocate(capacity * 8 * 2));
-    bitset = new BitSet(memoryManager.allocate(capacity / 8).zero());
+    bitset = new BitSet(MemoryBlock.fromLongArray(new long[capacity / 64]));
 
     this.growthThreshold = (int) (capacity * loadFactor);
     this.mask = capacity - 1;
@@ -447,7 +447,7 @@ public void free() {
       longArray = null;
     }
     if (bitset != null) {
-      memoryManager.free(bitset.memoryBlock());
+      // The bitset's heap memory isn't managed by a memory manager, so no need to free it here.
       bitset = null;
     }
     Iterator<MemoryBlock> dataPagesIterator = dataPages.iterator();
@@ -535,7 +535,6 @@ private void growAndRehash() {
 
     // Deallocate the old data structures.
     memoryManager.free(oldLongArray.memoryBlock());
-    memoryManager.free(oldBitSet.memoryBlock());
     if (enablePerfMetrics) {
       timeSpentResizingNs += System.nanoTime() - resizeStartTime;
     }

unsafe/src/main/java/org/apache/spark/unsafe/memory/MemoryBlock.java

@@ -46,14 +46,6 @@ public long size() {
     return length;
   }
 
-  /**
-   * Clear the contents of this memory block.  Returns `this` to facilitate chaining.
-   */
-  public MemoryBlock zero() {
-    PlatformDependent.UNSAFE.setMemory(obj, offset, length, (byte) 0);
-    return this;
-  }
-
   /**
    * Creates a memory block pointing to the memory used by the long array.
    */

unsafe/src/test/java/org/apache/spark/unsafe/bitset/BitSetSuite.java

@@ -27,7 +27,7 @@ public class BitSetSuite {
 
   private static BitSet createBitSet(int capacity) {
     assert capacity % 64 == 0;
-    return new BitSet(MemoryBlock.fromLongArray(new long[capacity / 64]).zero());
+    return new BitSet(MemoryBlock.fromLongArray(new long[capacity / 64]));
   }
 
   @Test