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comparison src/main/gov/nasa/jpf/jvm/bytecode/FINISHCLINIT.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
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23:db918c531e6d 24:6774e2e08d37
1 /*
2 * Copyright (C) 2015, United States Government, as represented by the
3 * Administrator of the National Aeronautics and Space Administration.
4 * All rights reserved.
5 *
6 * The Java Pathfinder core (jpf-core) platform is licensed under the
7 * Apache License, Version 2.0 (the "License"); you may not use this file except
8 * in compliance with the License. You may obtain a copy of the License at
9 *
10 * http://www.apache.org/licenses/LICENSE-2.0.
11 *
12 * Unless required by applicable law or agreed to in writing, software
13 * distributed under the License is distributed on an "AS IS" BASIS,
14 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
15 * See the License for the specific language governing permissions and
16 * limitations under the License.
17 */
18 package gov.nasa.jpf.jvm.bytecode;
19
20 import gov.nasa.jpf.vm.ClassInfo;
21 import gov.nasa.jpf.vm.Instruction;
22 import gov.nasa.jpf.vm.ThreadInfo;
23
24 /**
25 * artificial bytecode to defer class status changes of classes that don't have
26 * a <clinit>(), simulating native VM specific behavior that involves nested locking
27 * during class init
28 */
29 public class FINISHCLINIT extends Instruction {
30
31 protected ClassInfo ciInit;
32
33 public FINISHCLINIT (ClassInfo ci){
34 ciInit = ci;
35 }
36
37 @Override
38 public Instruction execute (ThreadInfo ti) {
39 ciInit.setInitialized();
40 return getNext(ti);
41 }
42
43 @Override
44 public boolean isExtendedInstruction() {
45 return true;
46 }
47
48 public static final int OPCODE = 262;
49
50 @Override
51 public int getByteCode () {
52 return OPCODE;
53 }
54 }