Update how Memory Request Server works.

src/main/java/org/apache/datasketches/memory/DefaultMemoryRequestServer.java

@@ -27,39 +27,121 @@
  * manage continuous requests for larger or smaller memory.
  * This capability is only available for writable, non-file-memory-mapping resources.
  *
+ * <p>The operation of this implementation is controlled by three conditions:</p>
+ * <ul>
+ * <li><b><i>origOffHeap:</i></b> If <i>true</i>, the originally allocated WritableMemory is off-heap.</li>
+ *
+ * <li><b><i>oneArena:</i></b> If <i>true</i>, all subsequent off-heap allocations will use the same Arena
+ * obtained from the original off-heap WritableMemory. Otherwise, subsequent off-heap allocations will
+ * use a new confined Arena created by this implementation.</li>
+ *
+ * <li><b><i>offHeap:</i></b> If <i>true</i>, all subsequent allocations will be off-heap.
+ * If the originally allocated WritableMemory is on-heap, this variable is ignored.</li>
+ * </ul>
+ *
+ * <p>These three variables work together as follows:</p>
+ *
+ * <ul>
+ * <li>If the original WritableMemory is on-heap, all subsequent allocations will also be on-heap.</li>
+ *
+ * <li>If <i>origOffHeap</i> = <i>true</i>, <i>oneArena</i> = <i>true</i>, and <i>offHeap</i> = <i>true</i>,
+ * all subsequent allocations will also be off-heap and associated with the original Arena.
+ * It is the responsibility of the user to close the original Arena using a Try-With-Resource block, or directly.</li>
+ *
+ * <li>If the original WritableMemory is off-heap, <i>oneArena</i> is true, and <i>offHeap</i> is false,
+ * all subsequent allocations will be on-heap.
+ * It is the responsibility of the user to close the original Arena using a Try-With-Resource block, or directly.</li>
+ *
+ * <li>If the original WritableMemory is off-heap, <i>oneArena</i> is false, and <i>offHeap</i> is true,
+ * all subsequent allocations will also be off-heap and associated with a new confined Arena assigned by this implementation.
+ * It is the responsibility of the user to close the original Arena using a Try-With-Resource block, or directly,
+ * and close the last returned new WritableMemory directly.</li>
+ * </ul>
+ *
+ * <p>In summary:</p>
+ *
+ * <table> <caption><b>Configuration Options</b></caption>
+ * <tr><th>Original Off-Heap</th> <th>OneArena</th> <th>OffHeap</th> <th>Subsequent Allocations</th></tr>
+ * <tr><td>false</td>             <td>N/A</td>      <td>N/A</td>     <td>All on-heap</td></tr>
+ * <tr><td>true</td>              <td>N/A</td>     <td>false</td>    <td>All on-heap</td></tr>
+ * <tr><td>true</td>              <td>true</td>     <td>true</td>    <td>All off-heap in original Arena</td></tr>
+ * <tr><td>true</td>              <td>false</td>    <td>true</td>    <td>All off-heap in separate Arenas</td></tr>
+ * </table>
+ *
  * @author Lee Rhodes
  */
+@SuppressWarnings("resource") //can't use TWRs here
 public final class DefaultMemoryRequestServer implements MemoryRequestServer {
+  private final long alignmentBytes;
+  private final ByteOrder byteOrder;
+  private final boolean oneArena;
+  private final boolean offHeap;
 
   /**
    * Default constructor.
    */
-  public DefaultMemoryRequestServer() { }
+  public DefaultMemoryRequestServer() {
+    alignmentBytes = 8;
+    byteOrder = ByteOrder.nativeOrder();
+    oneArena = false;
+    offHeap = false;
+  }
 
-  @Override
-  public WritableMemory request(
-      final long newCapacityBytes,
+  /**
+   * Optional constructor 1.
+   * @param oneArena if true, the original arena will be used for all requested allocations.
+   * @param offHeap if true, new allocations will be off-heap.
+   */
+  public DefaultMemoryRequestServer(
+      final boolean oneArena,
+      final boolean offHeap) {
+    this.alignmentBytes = 8;
+    this.byteOrder = ByteOrder.nativeOrder();
+    this.oneArena = oneArena;
+    this.offHeap = offHeap;
+  }
+
+  /**
+   * Optional constructor 2.
+   * @param alignmentBytes requested segment alignment for all allocations. Typically 1, 2, 4 or 8.
+   * @param byteOrder the given <i>ByteOrder</i>.  It must be non-null.
+   * @param oneArena if true, the same arena will be used for all requested allocations.
+   * @param offHeap if true, new allocations will be off-heap.
+   */
+  public DefaultMemoryRequestServer(
       final long alignmentBytes,
       final ByteOrder byteOrder,
-      final Arena arena) {
-    final WritableMemory newWmem;
+      final boolean oneArena,
+      final boolean offHeap) {
+    this.alignmentBytes = alignmentBytes;
+    this.byteOrder = byteOrder;
+    this.oneArena = oneArena;
+    this.offHeap = offHeap;
+  }
 
-    if (arena != null) {
-      newWmem = WritableMemory.allocateDirect(newCapacityBytes, alignmentBytes, byteOrder, this, arena);
-    }
-    else { //On-heap
+  @Override
+  public WritableMemory request(
+      final WritableMemory oldWmem,
+      final long newCapacityBytes) {
+
+    //On-heap
+    if (oldWmem.getArena() == null || !offHeap) {
       if (newCapacityBytes > Integer.MAX_VALUE) {
         throw new IllegalArgumentException("Requested capacity exceeds Integer.MAX_VALUE.");
       }
-      newWmem = WritableMemory.allocate((int)newCapacityBytes, byteOrder, this);
+      return WritableMemory.allocate((int)newCapacityBytes, byteOrder, this);
     }
 
-    return newWmem;
+    //Acquire Arena
+    final Arena arena = (oneArena) ? oldWmem.getArena() : Arena.ofConfined();
+    return WritableMemory.allocateDirect(newCapacityBytes, alignmentBytes, byteOrder, this, arena);
   }
 
   @Override
-  public void requestClose(final Arena arena) {
-    if (arena.scope().isAlive()) { arena.close(); }
+  public void requestClose(final WritableMemory wmemToClose) {
+    final Arena arena = wmemToClose.getArena();
+    if (oneArena || arena == null || !arena.scope().isAlive()) { return; } //can't close
+    arena.close();
   }
 
 }

src/main/java/org/apache/datasketches/memory/Memory.java

@@ -222,7 +222,7 @@ static Memory wrap(
       int lengthBytes,
       ByteOrder byteOrder) {
     final MemorySegment slice = MemorySegment.ofArray(array).asSlice(offsetBytes, lengthBytes).asReadOnly();
-    return WritableMemoryImpl.wrapSegmentAsArray(slice, byteOrder, null);
+    return WritableMemoryImpl.wrapSegment(slice, byteOrder);
   }
 
   //intentionally removed wrap(boolean[])
@@ -234,7 +234,7 @@ static Memory wrap(
    */
   static Memory wrap(char[] array) {
     final MemorySegment seg = MemorySegment.ofArray(array).asReadOnly();
-    return WritableMemoryImpl.wrapSegmentAsArray(seg, ByteOrder.nativeOrder(), null);
+    return WritableMemoryImpl.wrapSegment(seg, ByteOrder.nativeOrder());
   }
 
   /**
@@ -244,7 +244,7 @@ static Memory wrap(char[] array) {
    */
   static Memory wrap(short[] array) {
     final MemorySegment seg = MemorySegment.ofArray(array).asReadOnly();
-    return WritableMemoryImpl.wrapSegmentAsArray(seg, ByteOrder.nativeOrder(), null);
+    return WritableMemoryImpl.wrapSegment(seg, ByteOrder.nativeOrder());
   }
 
   /**
@@ -254,7 +254,7 @@ static Memory wrap(short[] array) {
    */
   static Memory wrap(int[] array) {
     final MemorySegment seg = MemorySegment.ofArray(array).asReadOnly();
-    return WritableMemoryImpl.wrapSegmentAsArray(seg, ByteOrder.nativeOrder(), null);
+    return WritableMemoryImpl.wrapSegment(seg, ByteOrder.nativeOrder());
   }
 
   /**
@@ -264,7 +264,7 @@ static Memory wrap(int[] array) {
    */
   static Memory wrap(long[] array) {
     final MemorySegment seg = MemorySegment.ofArray(array).asReadOnly();
-    return WritableMemoryImpl.wrapSegmentAsArray(seg, ByteOrder.nativeOrder(), null);
+    return WritableMemoryImpl.wrapSegment(seg, ByteOrder.nativeOrder());
   }
 
   /**
@@ -274,7 +274,7 @@ static Memory wrap(long[] array) {
    */
   static Memory wrap(float[] array) {
     final MemorySegment seg = MemorySegment.ofArray(array).asReadOnly();
-    return WritableMemoryImpl.wrapSegmentAsArray(seg, ByteOrder.nativeOrder(), null);
+    return WritableMemoryImpl.wrapSegment(seg, ByteOrder.nativeOrder());
   }
 
   /**
@@ -284,7 +284,7 @@ static Memory wrap(float[] array) {
    */
   static Memory wrap(double[] array) {
     final MemorySegment seg = MemorySegment.ofArray(array).asReadOnly();
-    return WritableMemoryImpl.wrapSegmentAsArray(seg, ByteOrder.nativeOrder(), null);
+    return WritableMemoryImpl.wrapSegment(seg, ByteOrder.nativeOrder());
   }
   //END OF CONSTRUCTOR-TYPE METHODS
 

src/main/java/org/apache/datasketches/memory/MemoryRequestServer.java

@@ -19,9 +19,6 @@
 
 package org.apache.datasketches.memory;
 
-import java.lang.foreign.Arena;
-import java.nio.ByteOrder;
-
 /**
  * The MemoryRequestServer is a callback interface to provide a means to request more or less memory
  * for heap and off-heap WritableMemory resources that are not file-memory-mapped backed resources.
@@ -33,26 +30,21 @@
 public interface MemoryRequestServer {
 
   /**
-   * Request new WritableMemory with the given newCapacityBytes.
+   * Request a new WritableMemory with the given newCapacityBytes.
+   * @param oldWmem the previous WritableMemory to be possibly closed and which provides an associated Arena
+   * that may be used for allocating the new WritableMemory.
+   * If the arena is null, the requested WritableMemory will be on-heap.
    * @param newCapacityBytes The capacity being requested.
-   * @param alignmentBytes requested segment alignment. Typically 1, 2, 4 or 8.
-   * @param byteOrder the given <i>ByteOrder</i>.  It must be non-null.
-   * @param arena the given arena to manage the new off-heap WritableMemory.
-   * If arena is null, the requested WritableMemory will be on-heap.
-   * Warning: This class is not thread-safe. Specifying an Arena that allows multiple threads is not recommended.
+   *
    * @return new WritableMemory with the requested capacity.
    */
-  WritableMemory request(
-      long newCapacityBytes,
-      long alignmentBytes,
-      ByteOrder byteOrder,
-      Arena arena);
+  WritableMemory request(WritableMemory oldWmem, long newCapacityBytes);
 
   /**
-   * Request to close the area managing all the related resources, if applicable.
-   * Be careful when you request to close the given Arena, you may be closing other resources as well.
-   * @param arena the given arena to use to close all its managed resources.
+   * Request to close the given WritableMemory.  If applicable, it will be closed by its associated Arena.
+   * Be careful. Closing the associated Arena may be closing other resources as well.
+   * @param wmemToClose the given WritableMemory to close.
    */
-  void requestClose( Arena arena);
+  void requestClose(WritableMemory wmemToClose);
 
 }