src/java.base/share/classes/jdk/internal/util/ArraysSupport.java

rev 54801 : [mq]: 8223593-Refactor-code-for-reallocating-storage

*** 1,7 ****
  /*
!  * Copyright (c) 2015, 2017, Oracle and/or its affiliates. All rights reserved.
   * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
   *
   * This code is free software; you can redistribute it and/or modify it
   * under the terms of the GNU General Public License version 2 only, as
   * published by the Free Software Foundation.  Oracle designates this
--- 1,7 ----
  /*
!  * Copyright (c) 2015, 2019, Oracle and/or its affiliates. All rights reserved.
   * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
   *
   * This code is free software; you can redistribute it and/or modify it
   * under the terms of the GNU General Public License version 2 only, as
   * published by the Free Software Foundation.  Oracle designates this
*** 26,36 ****
  
  import jdk.internal.HotSpotIntrinsicCandidate;
  import jdk.internal.misc.Unsafe;
  
  /**
!  * Utility methods to find a mismatch between two primitive arrays.
   *
   * <p>Array equality and lexicographical comparison can be built on top of
   * array mismatch functionality.
   *
   * <p>The mismatch method implementation, {@link #vectorizedMismatch}, leverages
--- 26,38 ----
  
  import jdk.internal.HotSpotIntrinsicCandidate;
  import jdk.internal.misc.Unsafe;
  
  /**
!  * Utility methods to work with arrays.  This includes a set of methods
!  * to find a mismatch between two primitive arrays.  Also included is
!  * a method to calculate the new size of an array to be reallocated 
   *
   * <p>Array equality and lexicographical comparison can be built on top of
   * array mismatch functionality.
   *
   * <p>The mismatch method implementation, {@link #vectorizedMismatch}, leverages
*** 569,574 ****
--- 571,621 ----
              }
          }
  
          return -1;
      }
+ 
+     /**
+      * The maximum size of array to allocate (unless necessary).
+      * Some VMs reserve some header words in an array.
+      * Attempts to allocate larger arrays may result in
+      * OutOfMemoryError: Requested array size exceeds VM limit
+      */
+     public static final int MAX_ARRAY_SIZE = Integer.MAX_VALUE - 8;
+ 
+     /**
+      * Calculates new size of an array to be reallocated.
+      *
+      * The result will be at least {@code X = oldCapacity + growAtLeastBy}.
+      * The result can be greater (normally, up to
+      * {@code oldCapacity + preferredGrowBy}).
+      * This function will not return values greater than
+      * {@link #MAX_ARRAY_SIZE} unless the minimum required size
+      * {@code X} is greater.
+      *
+      * @param oldCapacity       current size of the array (must be non negative)
+      * @param growAtLeastBy     minimum required growth of the array size (must
+                                 be positive)
+      * @param preferredGrowBy   preferred growth of the array size
+      * @return the new size of the array
+      * @throws OutOfMemoryError if increasing {@code oldCapacity) by
+      *                          {@code growAtLeastBy} overflows.
+      */
+     public static int newCapacity(int oldCapacity,
+                                   int growAtLeastBy,
+                                   int preferredGrowBy) {
+         // assert oldCapacity >= 0
+         // assert growAtLeastBy > 0
+ 
+         int newCapacity = oldCapacity + Math.max(growAtLeastBy, preferredGrowBy);
+         return (newCapacity - MAX_ARRAY_SIZE > 0)
+                 ? hugeCapacity(oldCapacity + growAtLeastBy) : newCapacity;
+     }
+ 
+     private static int hugeCapacity(int minCapacity) {
+         if (minCapacity < 0) { // overflow
+             throw new OutOfMemoryError("Required array size too large");
+         }
+         return (minCapacity > MAX_ARRAY_SIZE)
+                 ? Integer.MAX_VALUE : MAX_ARRAY_SIZE;
+     }
  }