1 /*

     2  * Copyright (c) 2018, Oracle and/or its affiliates. All rights reserved.

     3  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.

     4  *

     5  * This code is free software; you can redistribute it and/or modify it

     6  * under the terms of the GNU General Public License version 2 only, as

     7  * published by the Free Software Foundation.

     8  *

     9  * This code is distributed in the hope that it will be useful, but WITHOUT

    10  * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or

    11  * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License

    12  * version 2 for more details (a copy is included in the LICENSE file that

    13  * accompanied this code).

    14  *

    15  * You should have received a copy of the GNU General Public License version

    16  * 2 along with this work; if not, write to the Free Software Foundation,

    17  * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.

    18  *

    19  * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA

    20  * or visit www.oracle.com if you need additional information or have any

    21  * questions.

    22  *

    23  */

    24 

    25 package sun.jvm.hotspot.gc.z;

    26 

    27 import sun.jvm.hotspot.debugger.Address;

    28 import sun.jvm.hotspot.runtime.VM;

    29 import sun.jvm.hotspot.runtime.VMObject;

    30 import sun.jvm.hotspot.types.AddressField;

    31 import sun.jvm.hotspot.types.CIntegerField;

    32 import sun.jvm.hotspot.types.Type;

    33 import sun.jvm.hotspot.types.TypeDataBase;

    34 

    35 public class ZForwardingTable extends VMObject {

    36     private static AddressField tableField;

    37     private static CIntegerField sizeField;

    38 

    39     static {

    40         VM.registerVMInitializedObserver((o, d) -> initialize(VM.getVM().getTypeDataBase()));

    41     }

    42 

    43     static private synchronized void initialize(TypeDataBase db) {

    44         Type type = db.lookupType("ZForwardingTable");

    45 

    46         tableField = type.getAddressField("_table");

    47         sizeField = type.getCIntegerField("_size");

    48     }

    49 

    50     public ZForwardingTable(Address addr) {

    51         super(addr);

    52     }

    53 

    54     Address table() {

    55         return tableField.getAddress(addr);

    56     }

    57 

    58     long size() {

    59         return sizeField.getJLong(addr);

    60     }

    61 

    62     ZForwardingTableEntry at(ZForwardingTableCursor cursor) {

    63         return new ZForwardingTableEntry(table().getAddressAt(cursor._value * VM.getVM().getBytesPerLong()));

    64     }

    65 

    66     ZForwardingTableEntry first(long from_index, ZForwardingTableCursor cursor) {

    67         long mask = size() - 1;

    68         long hash = ZHash.uint32_to_uint32(from_index);

    69         cursor._value = hash & mask;

    70         return at(cursor);

    71     }

    72 

    73     ZForwardingTableEntry next(ZForwardingTableCursor cursor) {

    74         long mask = size() - 1;

    75         cursor._value = (cursor._value + 1) & mask;

    76         return at(cursor);

    77     }

    78 

    79     ZForwardingTableEntry find(long from_index, ZForwardingTableCursor cursor) {

    80         // Reading entries in the table races with the atomic cas done for

    81         // insertion into the table. This is safe because each entry is at

    82         // most updated once (from -1 to something else).

    83         ZForwardingTableEntry entry = first(from_index, cursor);

    84         while (!entry.is_empty()) {

    85             if (entry.from_index() == from_index) {

    86                 // Match found, return matching entry

    87                 return entry;

    88             }

    89 

    90             entry = next(cursor);

    91         }

    92 

    93         // Match not found, return empty entry

    94         return entry;

    95     }

    96 

    97     ZForwardingTableEntry find(long from_index) {

    98         ZForwardingTableCursor dummy = new ZForwardingTableCursor();

    99         return find(from_index, dummy);

   100     }

   101 

   102     void dump() {

   103         long s = size();

   104         long count = 0;

   105         System.out.println("Dumping ZForwardingTable[" + s + "]:");

   106         ZForwardingTableCursor cursor = new ZForwardingTableCursor();

   107         for (long i = 0; i < s; i++) {

   108             cursor._value = i;

   109             ZForwardingTableEntry entry = at(cursor);

   110             if (!entry.is_empty()) {

   111                 long hash = ZHash.uint32_to_uint32(entry.from_index());

   112                 System.out.println(i + " " + count + " " + entry + " hash: " + hash + " masked_hash: " + (hash & (s - 1)));

   113                 count++;

   114             }

   115         }

   116     }

   117 }