Mercurial > hg > Members > kono > jpf-core

annotate src/main/gov/nasa/jpf/jvm/bytecode/RETURN.java @ 24:6774e2e08d37

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the fix I would have liked to avoid - apparently hotspot internally does nested locking during class init, which can lead to deadlocks such as described in http://ternarysearch.blogspot.ru/2013/07/static-initialization-deadlock.html. Actually, it's not a regular deadlock since core dumps still list the threads as runnable, althouth it doesn't seem to be a livelock either. In any case, it can be simulated by nested locking and clinit execution, and it is such a serious defect that we want to be able to catch it. The general mechanism is to replace the disparate (but properly ordered) direct clinit calls of the generic ClassInfo.initializeClass() with a single sythetic method that includes all required locking (bottom up), clinit calls / class status change (top down), and unlocking (top down). We also need to add a synthetic insn to defer changing the class status of classes that don't have clinits(), or otherwise the correct lock/unlock order will not amount to anything if the hierarchy is entered through one of the clinit-absent classes. Now we get proper deadlocks if there are concurrent cyclic dependencies during class resolution. However, this can be such a state exploder that we certainly don't want this as the default behavior, especially since it probably is hotspot specific. Nested class init locking is therefore controlled by jvm.nested_init and respective jvm.nested_init.include/exclude options. Added a NestedInitTest to demonstrate use. Thanks to Lilia Abdulina for bringing this long forgotten issue up In the wake of nested locks, there were a number of cases to fix that implicitly relied on absent clinits because clients were not properly checking for re-execution (most notably java.util.Exchanger). This mostly came in through MJIEnv.newObject/ElementInfo. We might turn ClinitRequired into a handled exception at some point, to catch such cases during compilation. Added a UnknownJPFClass exception (in analogy to ClinitRequired), to make clients aware of failed class load attempts/reasons. fixed Exchanger peer, which was not giving up the lock when timing out. This is an example of a lockfree wait op that can time out. Basically, ThreadInfo.isWaiting() needs to be complemented by a isWaitingOrTimedOut(), and ElementInfo.notifies0() has to be aware of it fixed NPE when setting report.probe_interval in tests, which was missing that it had to create a stat object
author Peter Mehlitz <Peter.C.Mehlitz@nasa.gov>
date Tue, 21 Apr 2015 00:34:15 -0700
parents 61d41facf527
children 8aded593a50f
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1 /*
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2 * Copyright (C) 2014, United States Government, as represented by the
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3 * Administrator of the National Aeronautics and Space Administration.
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4 * All rights reserved.
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5 *
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6 * The Java Pathfinder core (jpf-core) platform is licensed under the
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7 * Apache License, Version 2.0 (the "License"); you may not use this file except
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8 * in compliance with the License. You may obtain a copy of the License at
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9 *
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10 * http://www.apache.org/licenses/LICENSE-2.0.
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11 *
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12 * Unless required by applicable law or agreed to in writing, software
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13 * distributed under the License is distributed on an "AS IS" BASIS,
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14 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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15 * See the License for the specific language governing permissions and
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16 * limitations under the License.
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17 */
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18 package gov.nasa.jpf.jvm.bytecode;
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19
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20 import gov.nasa.jpf.vm.ClassInfo;
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21 import gov.nasa.jpf.vm.ElementInfo;
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22 import gov.nasa.jpf.vm.Instruction;
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23 import gov.nasa.jpf.vm.StackFrame;
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24 import gov.nasa.jpf.vm.ThreadInfo;
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25
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27 /**
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28 * Return void from method
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29 * ... [empty]
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30 */
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31 public class RETURN extends JVMReturnInstruction {
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32
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33 @Override
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34 public Instruction execute (ThreadInfo ti) {
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35
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36 if (mi.isInit()) { // Check to see if this method is a constructor.
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37 int objref = ti.getThis();
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38 ElementInfo ei = ti.getElementInfo(objref); // Get the object.
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39
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40 if (!ei.isConstructed()) { // Don't bother doing the following work if the object is already constructed.
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41
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42 ClassInfo ei_ci = ei.getClassInfo(); // Get the object's class.
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43 ClassInfo mi_ci = mi.getClassInfo(); // Get the method's class.
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44
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45 if (ei_ci == mi_ci) { // If the object's class and the method's class are equal, then the thread is returning from the object's constructor.
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46 ei = ei.getModifiableInstance();
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47 ei.setConstructed();
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48 }
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49 }
24
6774e2e08d37 the fix I would have liked to avoid - apparently hotspot internally does nested locking during class init, which can lead to deadlocks such as described in http://ternarysearch.blogspot.ru/2013/07/static-initialization-deadlock.html. Actually, it's not a regular deadlock since core dumps still list the threads as runnable, althouth it doesn't seem to be a livelock either. In any case, it can be simulated by nested locking and clinit execution, and it is such a serious defect that we want to be able to catch it. The general mechanism is to replace the disparate (but properly ordered) direct clinit calls of the generic ClassInfo.initializeClass() with a single sythetic method that includes all required locking (bottom up), clinit calls / class status change (top down), and unlocking (top down). We also need to add a synthetic insn to defer changing the class status of classes that don't have clinits(), or otherwise the correct lock/unlock order will not amount to anything if the hierarchy is entered through one of the clinit-absent classes. Now we get proper deadlocks if there are concurrent cyclic dependencies during class resolution. However, this can be such a state exploder that we certainly don't want this as the default behavior, especially since it probably is hotspot specific. Nested class init locking is therefore controlled by jvm.nested_init and respective jvm.nested_init.include/exclude options. Added a NestedInitTest to demonstrate use. Thanks to Lilia Abdulina for bringing this long forgotten issue up
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50
6774e2e08d37 the fix I would have liked to avoid - apparently hotspot internally does nested locking during class init, which can lead to deadlocks such as described in http://ternarysearch.blogspot.ru/2013/07/static-initialization-deadlock.html. Actually, it's not a regular deadlock since core dumps still list the threads as runnable, althouth it doesn't seem to be a livelock either. In any case, it can be simulated by nested locking and clinit execution, and it is such a serious defect that we want to be able to catch it. The general mechanism is to replace the disparate (but properly ordered) direct clinit calls of the generic ClassInfo.initializeClass() with a single sythetic method that includes all required locking (bottom up), clinit calls / class status change (top down), and unlocking (top down). We also need to add a synthetic insn to defer changing the class status of classes that don't have clinits(), or otherwise the correct lock/unlock order will not amount to anything if the hierarchy is entered through one of the clinit-absent classes. Now we get proper deadlocks if there are concurrent cyclic dependencies during class resolution. However, this can be such a state exploder that we certainly don't want this as the default behavior, especially since it probably is hotspot specific. Nested class init locking is therefore controlled by jvm.nested_init and respective jvm.nested_init.include/exclude options. Added a NestedInitTest to demonstrate use. Thanks to Lilia Abdulina for bringing this long forgotten issue up
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51 } else if (mi.isClinit()) {
6774e2e08d37 the fix I would have liked to avoid - apparently hotspot internally does nested locking during class init, which can lead to deadlocks such as described in http://ternarysearch.blogspot.ru/2013/07/static-initialization-deadlock.html. Actually, it's not a regular deadlock since core dumps still list the threads as runnable, althouth it doesn't seem to be a livelock either. In any case, it can be simulated by nested locking and clinit execution, and it is such a serious defect that we want to be able to catch it. The general mechanism is to replace the disparate (but properly ordered) direct clinit calls of the generic ClassInfo.initializeClass() with a single sythetic method that includes all required locking (bottom up), clinit calls / class status change (top down), and unlocking (top down). We also need to add a synthetic insn to defer changing the class status of classes that don't have clinits(), or otherwise the correct lock/unlock order will not amount to anything if the hierarchy is entered through one of the clinit-absent classes. Now we get proper deadlocks if there are concurrent cyclic dependencies during class resolution. However, this can be such a state exploder that we certainly don't want this as the default behavior, especially since it probably is hotspot specific. Nested class init locking is therefore controlled by jvm.nested_init and respective jvm.nested_init.include/exclude options. Added a NestedInitTest to demonstrate use. Thanks to Lilia Abdulina for bringing this long forgotten issue up
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52 mi.getClassInfo().setInitialized();
0
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53 }
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55 return super.execute(ti);
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56 }
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57
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58 @Override
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59 public int getReturnTypeSize() {
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60 return 0;
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61 }
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62
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63 @Override
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64 protected Object getReturnedOperandAttr (StackFrame frame) {
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65 return null;
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66 }
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67
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68
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69 @Override
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70 public Object getReturnAttr (ThreadInfo ti){
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71 return null; // no return value
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72 }
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73
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74 @Override
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75 protected void getAndSaveReturnValue (StackFrame frame) {
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76 // we don't have any
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77 }
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78
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79 @Override
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80 protected void pushReturnValue (StackFrame frame) {
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81 // nothing to do
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82 }
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83
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84 @Override
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85 public Object getReturnValue(ThreadInfo ti) {
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86 //return Void.class; // Hmm, not sure if this is right, but we have to distinguish from ARETURN <null>
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87 return null;
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88 }
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90 @Override
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91 public String toString() {
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92 return "return " + mi.getFullName();
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93 }
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94
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95 @Override
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96 public int getByteCode () {
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97 return 0xB1;
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98 }
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99
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100 @Override
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101 public void accept(JVMInstructionVisitor insVisitor) {
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102 insVisitor.visit(this);
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103 }
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104 }