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/*
* Copyright (c) 2018, 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.
*
* This code is distributed in the hope that it will be useful, but WITHOUT
* ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
* FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
* version 2 for more details (a copy is included in the LICENSE file that
* accompanied this code).
*
* You should have received a copy of the GNU General Public License version
* 2 along with this work; if not, write to the Free Software Foundation,
* Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
*
* Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
* or visit www.oracle.com if you need additional information or have any
* questions.
*/
/*
* @test
* @bug 4087516
* @summary Incorrect locking leads to deadlock in monitorCacheMaybeExpand.
* @author Anand Palaniswamy
* @build MonitorCacheMaybeExpand_DeadLock
* @run main/othervm MonitorCacheMaybeExpand_DeadLock
*/
/**
* Background on the bug:
*
* The thread local monitor cache had a locking bug (till
* 1.2beta1) where two threads trying to expand the monitor cache
* at the same time would cause deadlock. The code paths that the
* two threads must be executing for this to happen is described
* in the bug report.
*
* Caveat and red-flag:
*
* Since deadlocks are very timing dependent, there is a good
* chance this test case will not catch the bug most of the time
* -- on your machine and setting, it is _possible_ that the two
* threads might not try a monitorCacheExpand at the same
* time. But in practice, on Solaris native threads, this program
* deadlocks the VM in about 2 seconds pretty consistently,
* whether MP or not.
*
* The rationale for running this test despite this rather large
* caveat is that at worst, it can do no harm.
*
* The idea:
*
* Is to create two monitor hungry threads.
*
* Originally Tom Rodriguez and I suspected that this weird state
* of two threads trying to expand monitor cache can happen only
* if:
*
* Thread 1: Is in the middle of a monitorCacheMaybeExpand.
* Thread 2: Runs GC and tries to freeClasses(). This causes
* sysFree() to be invoked, which in turn needs a
* mutex_lock -- and oops, we end up deadlocking
* with 1 on green_threads.
*
* Which is why this test tries to cause class GC at regular
* intervals.
*
* Turns out that the GC is not required. Two instances of the
* monitor hungry threads deadlock the VM pretty quick. :-) Infact
* the static initializer in the forName'd classes running
* alongside one of the hungry threads is sufficient to
* deadlock. Still keep the GC stuff just-in-case (and also
* because I wrote it :-).
*
*/
public class MonitorCacheMaybeExpand_DeadLock {
/**
* A monitor-hungry thread.
*/
static class LotsaMonitors extends Thread {
/** How many recursions? Could cause Java stack overflow. */
static final int MAX_DEPTH = 800;
/** What is our depth? */
int depth = 0;
/** Thread ID */
int tid;
/** So output will have thread number. */
public LotsaMonitors(int tid, int depth) {
super("LotsaMonitors #" + new Integer(tid).toString());
this.tid = tid;
this.depth = depth;
}
/** Start a recursion that grabs monitors. */
public void run() {
System.out.println(">>>Starting " + this.toString() + " ...");
Thread.currentThread().yield();
this.recurse();
System.out.println("<<<Finished " + this.toString());
}
/** Every call to this method grabs an extra monitor. */
synchronized void recurse() {
if (this.depth > 0) {
new LotsaMonitors(tid, depth-1).recurse();
}
}
}
/**
* The test.
*/
public static void main(String[] args) {
/* Start the two of these crazy threads. */
new LotsaMonitors(1, LotsaMonitors.MAX_DEPTH).start();
new LotsaMonitors(2, LotsaMonitors.MAX_DEPTH).start();
/* And sit there and GC for good measure. */
for (int i = 0; i < MAX_GC_ITERATIONS; i++) {
new LotsaMonitors(i+3, LotsaMonitors.MAX_DEPTH).start();
System.out.println(">>>Loading 10 classes and gc'ing ...");
Class[] classes = new Class[10];
fillClasses(classes);
classes = null;
System.gc();
Thread.currentThread().yield();
System.out.println("<<<Finished loading 10 classes and gc'ing");
}
}
/** How many times to GC? */
static final int MAX_GC_ITERATIONS = 10;
/** Load some classes into the array. */
static void fillClasses(Class[] classes) {
for (int i = 0; i < classes.length; i++) {
try {
classes[i] = Class.forName(classnames[i]);
} catch (ClassNotFoundException cnfe) {
cnfe.printStackTrace();
}
}
}
/** Some random classes to load. */
private static String[] classnames = {
"java.text.DecimalFormat",
"java.text.MessageFormat",
"java.util.GregorianCalendar",
"java.util.ResourceBundle",
"java.text.Collator",
"java.util.Date",
"java.io.Reader",
"java.io.Writer",
"java.lang.IllegalAccessException",
"java.lang.InstantiationException",
"java.lang.ClassNotFoundException",
"java.lang.CloneNotSupportedException",
"java.lang.InterruptedException",
"java.lang.NoSuchFieldException",
"java.lang.NoSuchMethodException",
"java.lang.RuntimeException",
"java.lang.ArithmeticException",
"java.lang.ArrayStoreException",
"java.lang.ClassCastException",
"java.lang.StringIndexOutOfBoundsException",
"java.lang.NegativeArraySizeException",
"java.lang.IllegalStateException",
"java.lang.IllegalArgumentException",
"java.lang.NumberFormatException",
"java.lang.IllegalThreadStateException",
"java.lang.IllegalMonitorStateException",
"java.lang.SecurityException",
"java.lang.ExceptionInInitializerError"
};
}
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