1 /*
   2  * Copyright (c) 2014, 2014, 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 package jdk.vm.ci.hotspot;
  24 
  25 import java.util.Collection;
  26 import java.util.HashSet;
  27 import java.util.Set;
  28 import java.util.concurrent.ConcurrentLinkedQueue;
  29 
  30 import jdk.vm.ci.meta.JavaConstant;
  31 import jdk.vm.ci.meta.SpeculationLog;
  32 
  33 public class HotSpotSpeculationLog implements SpeculationLog {
  34 
  35     /** Written by the C++ code that performs deoptimization. */
  36     private volatile Object lastFailed;
  37 
  38     /** All speculations that have been a deoptimization reason. */
  39     private Set<SpeculationReason> failedSpeculations;
  40 
  41     /** Strong references to all reasons embedded in the current nmethod. */
  42     private volatile Collection<SpeculationReason> speculations;
  43 
  44     @Override
  45     public synchronized void collectFailedSpeculations() {
  46         if (lastFailed != null) {
  47             if (failedSpeculations == null) {
  48                 failedSpeculations = new HashSet<>(2);
  49             }
  50             failedSpeculations.add((SpeculationReason) lastFailed);
  51             lastFailed = null;
  52             speculations = null;
  53         }
  54     }
  55 
  56     @Override
  57     public boolean maySpeculate(SpeculationReason reason) {
  58         if (failedSpeculations != null && failedSpeculations.contains(reason)) {
  59             return false;
  60         }
  61         return true;
  62     }
  63 
  64     @Override
  65     public JavaConstant speculate(SpeculationReason reason) {
  66         assert maySpeculate(reason);
  67 
  68         /*
  69          * Objects referenced from nmethods are weak references. We need a strong reference to the
  70          * reason objects that are embedded in nmethods, so we add them to the speculations
  71          * collection.
  72          */
  73         if (speculations == null) {
  74             synchronized (this) {
  75                 if (speculations == null) {
  76                     speculations = new ConcurrentLinkedQueue<>();
  77                 }
  78             }
  79         }
  80         speculations.add(reason);
  81 
  82         return HotSpotObjectConstantImpl.forObject(reason);
  83     }
  84 
  85     @Override
  86     public synchronized boolean hasSpeculations() {
  87         return speculations != null && !speculations.isEmpty();
  88     }
  89 }