jdk/src/share/classes/java/lang/management/ThreadInfo.java

/*
 * Copyright 2003-2006 Sun Microsystems, Inc.  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.  Sun designates this
 * particular file as subject to the "Classpath" exception as provided
 * by Sun in the LICENSE file that accompanied this code.
 *
 * 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 Sun Microsystems, Inc., 4150 Network Circle, Santa Clara,
 * CA 95054 USA or visit www.sun.com if you need additional information or
 * have any questions.
 */

package java.lang.management;

import javax.management.openmbean.CompositeData;
import sun.management.ThreadInfoCompositeData;
import static java.lang.Thread.State.*;

/**
 * Thread information. <tt>ThreadInfo</tt> contains the information
 * about a thread including:
 * <h4>General thread information</h4>
 * <ul>
 *   <li>Thread ID.</li>
 *   <li>Name of the thread.</li>
 * </ul>
 *
 * <h4>Execution information</h4>
 * <ul>
 *   <li>Thread state.</li>
 *   <li>The object upon which the thread is blocked due to:
 *       <ul>
 *       <li>waiting to enter a synchronization block/method, or</li>
 *       <li>waiting to be notified in a {@link Object#wait Object.wait} method,
 *           or</li>
 *       <li>parking due to a {@link java.util.concurrent.locks.LockSupport#park
 *           LockSupport.park} call.</li>
 *       </ul>
 *   </li>
 *   <li>The ID of the thread that owns the object
 *       that the thread is blocked.</li>
 *   <li>Stack trace of the thread.</li>
 *   <li>List of object monitors locked by the thread.</li>
 *   <li>List of <a href="LockInfo.html#OwnableSynchronizer">
 *       ownable synchronizers</a> locked by the thread.</li>
 * </ul>
 *
 * <h4><a name="SyncStats">Synchronization Statistics</a></h4>
 * <ul>
 *   <li>The number of times that the thread has blocked for
 *       synchronization or waited for notification.</li>
 *   <li>The accumulated elapsed time that the thread has blocked
 *       for synchronization or waited for notification
 *       since {@link ThreadMXBean#setThreadContentionMonitoringEnabled
 *       thread contention monitoring}
 *       was enabled. Some Java virtual machine implementation
 *       may not support this.  The
 *       {@link ThreadMXBean#isThreadContentionMonitoringSupported()}
 *       method can be used to determine if a Java virtual machine
 *       supports this.</li>
 * </ul>
 *
 * <p>This thread information class is designed for use in monitoring of
 * the system, not for synchronization control.
 *
 * <h4>MXBean Mapping</h4>
 * <tt>ThreadInfo</tt> is mapped to a {@link CompositeData CompositeData}
 * with attributes as specified in
 * the {@link #from from} method.
 *
 * @see ThreadMXBean#getThreadInfo
 * @see ThreadMXBean#dumpAllThreads
 *
 * @author  Mandy Chung
 * @since   1.5
 */

public class ThreadInfo {
    private String       threadName;
    private long         threadId;
    private long         blockedTime;
    private long         blockedCount;
    private long         waitedTime;
    private long         waitedCount;
    private LockInfo     lock;
    private String       lockName;
    private long         lockOwnerId;
    private String       lockOwnerName;
    private boolean      inNative;
    private boolean      suspended;
    private Thread.State threadState;
    private StackTraceElement[] stackTrace;
    private MonitorInfo[]       lockedMonitors;
    private LockInfo[]          lockedSynchronizers;

    private static MonitorInfo[] EMPTY_MONITORS = new MonitorInfo[0];
    private static LockInfo[] EMPTY_SYNCS = new LockInfo[0];

    /**
     * Constructor of ThreadInfo created by the JVM
     *
     * @param t             Thread
     * @param state         Thread state
     * @param lockObj       Object on which the thread is blocked
     * @param lockOwner     the thread holding the lock
     * @param blockedCount  Number of times blocked to enter a lock
     * @param blockedTime   Approx time blocked to enter a lock
     * @param waitedCount   Number of times waited on a lock
     * @param waitedTime    Approx time waited on a lock
     * @param stackTrace    Thread stack trace
     */
    private ThreadInfo(Thread t, int state, Object lockObj, Thread lockOwner,
                       long blockedCount, long blockedTime,
                       long waitedCount, long waitedTime,
                       StackTraceElement[] stackTrace) {
        initialize(t, state, lockObj, lockOwner,
                   blockedCount, blockedTime,
                   waitedCount, waitedTime, stackTrace,
                   EMPTY_MONITORS, EMPTY_SYNCS);
    }

    /**
     * Constructor of ThreadInfo created by the JVM
     * for {@link ThreadMXBean#getThreadInfo(long[],boolean,boolean)}
     * and {@link ThreadMXBean#dumpAllThreads}
     *
     * @param t             Thread
     * @param state         Thread state
     * @param lockObj       Object on which the thread is blocked
     * @param lockOwner     the thread holding the lock
     * @param blockedCount  Number of times blocked to enter a lock
     * @param blockedTime   Approx time blocked to enter a lock
     * @param waitedCount   Number of times waited on a lock
     * @param waitedTime    Approx time waited on a lock
     * @param stackTrace    Thread stack trace
     * @param lockedMonitors List of locked monitors
     * @param lockedSynchronizers List of locked synchronizers
     */
    private ThreadInfo(Thread t, int state, Object lockObj, Thread lockOwner,
                       long blockedCount, long blockedTime,
                       long waitedCount, long waitedTime,
                       StackTraceElement[] stackTrace,
                       Object[] monitors,
                       int[] stackDepths,
                       Object[] synchronizers) {
        int numMonitors = (monitors == null ? 0 : monitors.length);
        MonitorInfo[] lockedMonitors;
        if (numMonitors == 0) {
            lockedMonitors = EMPTY_MONITORS;
        } else {
            lockedMonitors = new MonitorInfo[numMonitors];
            for (int i = 0; i < numMonitors; i++) {
                Object lock = monitors[i];
                String className = lock.getClass().getName();
                int identityHashCode = System.identityHashCode(lock);
                int depth = stackDepths[i];
                StackTraceElement ste = (depth >= 0 ? stackTrace[depth]
                                                    : null);
                lockedMonitors[i] = new MonitorInfo(className,
                                                    identityHashCode,
                                                    depth,
                                                    ste);
            }
        }

        int numSyncs = (synchronizers == null ? 0 : synchronizers.length);
        LockInfo[] lockedSynchronizers;
        if (numSyncs == 0) {
            lockedSynchronizers = EMPTY_SYNCS;
        } else {
            lockedSynchronizers = new LockInfo[numSyncs];
            for (int i = 0; i < numSyncs; i++) {
                Object lock = synchronizers[i];
                String className = lock.getClass().getName();
                int identityHashCode = System.identityHashCode(lock);
                lockedSynchronizers[i] = new LockInfo(className,
                                                      identityHashCode);
            }
        }

        initialize(t, state, lockObj, lockOwner,
                   blockedCount, blockedTime,
                   waitedCount, waitedTime, stackTrace,
                   lockedMonitors, lockedSynchronizers);
    }

    /**
     * Initialize ThreadInfo object
     *
     * @param t             Thread
     * @param state         Thread state
     * @param lockObj       Object on which the thread is blocked
     * @param lockOwner     the thread holding the lock
     * @param blockedCount  Number of times blocked to enter a lock
     * @param blockedTime   Approx time blocked to enter a lock
     * @param waitedCount   Number of times waited on a lock
     * @param waitedTime    Approx time waited on a lock
     * @param stackTrace    Thread stack trace
     * @param lockedMonitors List of locked monitors
     * @param lockedSynchronizers List of locked synchronizers
     */
    private void initialize(Thread t, int state, Object lockObj, Thread lockOwner,
                            long blockedCount, long blockedTime,
                            long waitedCount, long waitedTime,
                            StackTraceElement[] stackTrace,
                            MonitorInfo[] lockedMonitors,
                            LockInfo[] lockedSynchronizers) {
        this.threadId = t.getId();
        this.threadName = t.getName();
        this.threadState =
            sun.management.ManagementFactory.toThreadState(state);
        this.suspended =
            sun.management.ManagementFactory.isThreadSuspended(state);
        this.inNative =
            sun.management.ManagementFactory.isThreadRunningNative(state);
        this.blockedCount = blockedCount;
        this.blockedTime = blockedTime;
        this.waitedCount = waitedCount;
        this.waitedTime = waitedTime;

        if (lockObj == null) {
            this.lock = null;
            this.lockName = null;
        } else {
            this.lock = new LockInfo(lockObj);
            this.lockName =
                lock.getClassName() + '@' +
                    Integer.toHexString(lock.getIdentityHashCode());
        }
        if (lockOwner == null) {
            this.lockOwnerId = -1;
            this.lockOwnerName = null;
        } else {
            this.lockOwnerId = lockOwner.getId();
            this.lockOwnerName = lockOwner.getName();
        }
        if (stackTrace == null) {
            this.stackTrace = NO_STACK_TRACE;
        } else {
            this.stackTrace = stackTrace;
        }
        this.lockedMonitors = lockedMonitors;
        this.lockedSynchronizers = lockedSynchronizers;
    }

    /*
     * Constructs a <tt>ThreadInfo</tt> object from a
     * {@link CompositeData CompositeData}.
     */
    private ThreadInfo(CompositeData cd) {
        ThreadInfoCompositeData ticd = ThreadInfoCompositeData.getInstance(cd);

        threadId = ticd.threadId();
        threadName = ticd.threadName();
        blockedTime = ticd.blockedTime();
        blockedCount = ticd.blockedCount();
        waitedTime = ticd.waitedTime();
        waitedCount = ticd.waitedCount();
        lockName = ticd.lockName();
        lockOwnerId = ticd.lockOwnerId();
        lockOwnerName = ticd.lockOwnerName();
        threadState = ticd.threadState();
        suspended = ticd.suspended();
        inNative = ticd.inNative();
        stackTrace = ticd.stackTrace();

        // 6.0 attributes
        if (ticd.isCurrentVersion()) {
            lock = ticd.lockInfo();
            lockedMonitors = ticd.lockedMonitors();
            lockedSynchronizers = ticd.lockedSynchronizers();
        } else {
            // lockInfo is a new attribute added in 1.6 ThreadInfo
            // If cd is a 5.0 version, construct the LockInfo object
            //  from the lockName value.
            if (lockName != null) {
                String result[] = lockName.split("@");
                if (result.length == 2) {
                    int identityHashCode = Integer.parseInt(result[1], 16);
                    lock = new LockInfo(result[0], identityHashCode);
                } else {
                    assert result.length == 2;
                    lock = null;
                }
            } else {
                lock = null;
            }
            lockedMonitors = EMPTY_MONITORS;
            lockedSynchronizers = EMPTY_SYNCS;
        }
    }

    /**
     * Returns the ID of the thread associated with this <tt>ThreadInfo</tt>.
     *
     * @return the ID of the associated thread.
     */
    public long getThreadId() {
        return threadId;
    }

    /**
     * Returns the name of the thread associated with this <tt>ThreadInfo</tt>.
     *
     * @return the name of the associated thread.
     */
    public String getThreadName() {
        return threadName;
    }

    /**
     * Returns the state of the thread associated with this <tt>ThreadInfo</tt>.
     *
     * @return <tt>Thread.State</tt> of the associated thread.
     */
    public Thread.State getThreadState() {
         return threadState;
    }

    /**
     * Returns the approximate accumulated elapsed time (in milliseconds)
     * that the thread associated with this <tt>ThreadInfo</tt>
     * has blocked to enter or reenter a monitor
     * since thread contention monitoring is enabled.
     * I.e. the total accumulated time the thread has been in the
     * {@link java.lang.Thread.State#BLOCKED BLOCKED} state since thread
     * contention monitoring was last enabled.
     * This method returns <tt>-1</tt> if thread contention monitoring
     * is disabled.
     *
     * <p>The Java virtual machine may measure the time with a high
     * resolution timer.  This statistic is reset when
     * the thread contention monitoring is reenabled.
     *
     * @return the approximate accumulated elapsed time in milliseconds
     * that a thread entered the <tt>BLOCKED</tt> state;
     * <tt>-1</tt> if thread contention monitoring is disabled.
     *
     * @throws java.lang.UnsupportedOperationException if the Java
     * virtual machine does not support this operation.
     *
     * @see ThreadMXBean#isThreadContentionMonitoringSupported
     * @see ThreadMXBean#setThreadContentionMonitoringEnabled
     */
    public long getBlockedTime() {
        return blockedTime;
    }

    /**
     * Returns the total number of times that
     * the thread associated with this <tt>ThreadInfo</tt>
     * blocked to enter or reenter a monitor.
     * I.e. the number of times a thread has been in the
     * {@link java.lang.Thread.State#BLOCKED BLOCKED} state.
     *
     * @return the total number of times that the thread
     * entered the <tt>BLOCKED</tt> state.
     */
    public long getBlockedCount() {
        return blockedCount;
    }

    /**
     * Returns the approximate accumulated elapsed time (in milliseconds)
     * that the thread associated with this <tt>ThreadInfo</tt>
     * has waited for notification
     * since thread contention monitoring is enabled.
     * I.e. the total accumulated time the thread has been in the
     * {@link java.lang.Thread.State#WAITING WAITING}
     * or {@link java.lang.Thread.State#TIMED_WAITING TIMED_WAITING} state
     * since thread contention monitoring is enabled.
     * This method returns <tt>-1</tt> if thread contention monitoring
     * is disabled.
     *
     * <p>The Java virtual machine may measure the time with a high
     * resolution timer.  This statistic is reset when
     * the thread contention monitoring is reenabled.
     *
     * @return the approximate accumulated elapsed time in milliseconds
     * that a thread has been in the <tt>WAITING</tt> or
     * <tt>TIMED_WAITING</tt> state;
     * <tt>-1</tt> if thread contention monitoring is disabled.
     *
     * @throws java.lang.UnsupportedOperationException if the Java
     * virtual machine does not support this operation.
     *
     * @see ThreadMXBean#isThreadContentionMonitoringSupported
     * @see ThreadMXBean#setThreadContentionMonitoringEnabled
     */
    public long getWaitedTime() {
        return waitedTime;
    }

    /**
     * Returns the total number of times that
     * the thread associated with this <tt>ThreadInfo</tt>
     * waited for notification.
     * I.e. the number of times that a thread has been
     * in the {@link java.lang.Thread.State#WAITING WAITING}
     * or {@link java.lang.Thread.State#TIMED_WAITING TIMED_WAITING} state.
     *
     * @return the total number of times that the thread
     * was in the <tt>WAITING</tt> or <tt>TIMED_WAITING</tt> state.
     */
    public long getWaitedCount() {
        return waitedCount;
    }

    /**
     * Returns the <tt>LockInfo</tt> of an object for which
     * the thread associated with this <tt>ThreadInfo</tt>
     * is blocked waiting.
     * A thread can be blocked waiting for one of the following:
     * <ul>
     * <li>an object monitor to be acquired for entering or reentering
     *     a synchronization block/method.
     *     <br>The thread is in the {@link java.lang.Thread.State#BLOCKED BLOCKED}
     *     state waiting to enter the <tt>synchronized</tt> statement
     *     or method.
     *     <p></li>
     * <li>an object monitor to be notified by another thread.
     *     <br>The thread is in the {@link java.lang.Thread.State#WAITING WAITING}
     *     or {@link java.lang.Thread.State#TIMED_WAITING TIMED_WAITING} state
     *     due to a call to the {@link Object#wait Object.wait} method.
     *     <p></li>
     * <li>a synchronization object responsible for the thread parking.
     *     <br>The thread is in the {@link java.lang.Thread.State#WAITING WAITING}
     *     or {@link java.lang.Thread.State#TIMED_WAITING TIMED_WAITING} state
     *     due to a call to the
     *     {@link java.util.concurrent.locks.LockSupport#park(Object)
     *     LockSupport.park} method.  The synchronization object
     *     is the object returned from
     *     {@link java.util.concurrent.locks.LockSupport#getBlocker
     *     LockSupport.getBlocker} method. Typically it is an
     *     <a href="LockInfo.html#OwnableSynchronizer"> ownable synchronizer</a>
     *     or a {@link java.util.concurrent.locks.Condition Condition}.</li>
     * </ul>
     *
     * <p>This method returns <tt>null</tt> if the thread is not in any of
     * the above conditions.
     *
     * @return <tt>LockInfo</tt> of an object for which the thread
     *         is blocked waiting if any; <tt>null</tt> otherwise.
     * @since 1.6
     */
    public LockInfo getLockInfo() {
        return lock;
    }

    /**
     * Returns the {@link LockInfo#toString string representation}
     * of an object for which the thread associated with this
     * <tt>ThreadInfo</tt> is blocked waiting.
     * This method is equivalent to calling:
     * <blockquote>
     * <pre>
     * getLockInfo().toString()
     * </pre></blockquote>
     *
     * <p>This method will return <tt>null</tt> if this thread is not blocked
     * waiting for any object or if the object is not owned by any thread.
     *
     * @return the string representation of the object on which
     * the thread is blocked if any;
     * <tt>null</tt> otherwise.
     *
     * @see #getLockInfo
     */
    public String getLockName() {
        return lockName;
    }

    /**
     * Returns the ID of the thread which owns the object
     * for which the thread associated with this <tt>ThreadInfo</tt>
     * is blocked waiting.
     * This method will return <tt>-1</tt> if this thread is not blocked
     * waiting for any object or if the object is not owned by any thread.
     *
     * @return the thread ID of the owner thread of the object
     * this thread is blocked on;
     * <tt>-1</tt> if this thread is not blocked
     * or if the object lis not owned by any thread.
     *
     * @see #getLockInfo
     */
    public long getLockOwnerId() {
        return lockOwnerId;
    }

    /**
     * Returns the name of the thread which owns the object
     * for which the thread associated with this <tt>ThreadInfo</tt>
     * is blocked waiting.
     * This method will return <tt>null</tt> if this thread is not blocked
     * waiting for any object or if the object is not owned by any thread.
     *
     * @return the name of the thread that owns the object
     * this thread is blocked on;
     * <tt>null</tt> if this thread is not blocked
     * or if the object is not owned by any thread.
     *
     * @see #getLockInfo
     */
    public String getLockOwnerName() {
        return lockOwnerName;
    }

    /**
     * Returns the stack trace of the thread
     * associated with this <tt>ThreadInfo</tt>.
     * If no stack trace was requested for this thread info, this method
     * will return a zero-length array.
     * If the returned array is of non-zero length then the first element of
     * the array represents the top of the stack, which is the most recent
     * method invocation in the sequence.  The last element of the array
     * represents the bottom of the stack, which is the least recent method
     * invocation in the sequence.
     *
     * <p>Some Java virtual machines may, under some circumstances, omit one
     * or more stack frames from the stack trace.  In the extreme case,
     * a virtual machine that has no stack trace information concerning
     * the thread associated with this <tt>ThreadInfo</tt>
     * is permitted to return a zero-length array from this method.
     *
     * @return an array of <tt>StackTraceElement</tt> objects of the thread.
     */
    public StackTraceElement[] getStackTrace() {
        return stackTrace;
    }

    /**
     * Tests if the thread associated with this <tt>ThreadInfo</tt>
     * is suspended.  This method returns <tt>true</tt> if
     * {@link Thread#suspend} has been called.
     *
     * @return <tt>true</tt> if the thread is suspended;
     *         <tt>false</tt> otherwise.
     */
    public boolean isSuspended() {
         return suspended;
    }

    /**
     * Tests if the thread associated with this <tt>ThreadInfo</tt>
     * is executing native code via the Java Native Interface (JNI).
     * The JNI native code does not include
     * the virtual machine support code or the compiled native
     * code generated by the virtual machine.
     *
     * @return <tt>true</tt> if the thread is executing native code;
     *         <tt>false</tt> otherwise.
     */
    public boolean isInNative() {
         return inNative;
    }

    /**
     * Returns a string representation of this thread info.
     * The format of this string depends on the implementation.
     * The returned string will typically include
     * the {@linkplain #getThreadName thread name},
     * the {@linkplain #getThreadId thread ID},
     * its {@linkplain #getThreadState state},
     * and a {@linkplain #getStackTrace stack trace} if any.
     *
     * @return a string representation of this thread info.
     */
    public String toString() {
        StringBuilder sb = new StringBuilder("\"" + getThreadName() + "\"" +
                                             " Id=" + getThreadId() + " " +
                                             getThreadState());
        if (getLockName() != null) {
            sb.append(" on " + getLockName());
        }
        if (getLockOwnerName() != null) {
            sb.append(" owned by \"" + getLockOwnerName() +
                      "\" Id=" + getLockOwnerId());
        }
        if (isSuspended()) {
            sb.append(" (suspended)");
        }
        if (isInNative()) {
            sb.append(" (in native)");
        }
        sb.append('\n');
        int i = 0;
        for (; i < stackTrace.length && i < MAX_FRAMES; i++) {
            StackTraceElement ste = stackTrace[i];
            sb.append("\tat " + ste.toString());
            sb.append('\n');
            if (i == 0 && getLockInfo() != null) {
                Thread.State ts = getThreadState();
                switch (ts) {
                    case BLOCKED:
                        sb.append("\t-  blocked on " + getLockInfo());
                        sb.append('\n');
                        break;
                    case WAITING:
                        sb.append("\t-  waiting on " + getLockInfo());
                        sb.append('\n');
                        break;
                    case TIMED_WAITING:
                        sb.append("\t-  waiting on " + getLockInfo());
                        sb.append('\n');
                        break;
                    default:
                }
            }

            for (MonitorInfo mi : lockedMonitors) {
                if (mi.getLockedStackDepth() == i) {
                    sb.append("\t-  locked " + mi);
                    sb.append('\n');
                }
            }
       }
       if (i < stackTrace.length) {
           sb.append("\t...");
           sb.append('\n');
       }

       LockInfo[] locks = getLockedSynchronizers();
       if (locks.length > 0) {
           sb.append("\n\tNumber of locked synchronizers = " + locks.length);
           sb.append('\n');
           for (LockInfo li : locks) {
               sb.append("\t- " + li);
               sb.append('\n');
           }
       }
       sb.append('\n');
       return sb.toString();
    }
    private static final int MAX_FRAMES = 8;

    /**
     * Returns a <tt>ThreadInfo</tt> object represented by the
     * given <tt>CompositeData</tt>.
     * The given <tt>CompositeData</tt> must contain the following attributes
     * unless otherwise specified below:
     * <blockquote>
     * <table border>
     * <tr>
     *   <th align=left>Attribute Name</th>
     *   <th align=left>Type</th>
     * </tr>
     * <tr>
     *   <td>threadId</td>
     *   <td><tt>java.lang.Long</tt></td>
     * </tr>
     * <tr>
     *   <td>threadName</td>
     *   <td><tt>java.lang.String</tt></td>
     * </tr>
     * <tr>
     *   <td>threadState</td>
     *   <td><tt>java.lang.String</tt></td>
     * </tr>
     * <tr>
     *   <td>suspended</td>
     *   <td><tt>java.lang.Boolean</tt></td>
     * </tr>
     * <tr>
     *   <td>inNative</td>
     *   <td><tt>java.lang.Boolean</tt></td>
     * </tr>
     * <tr>
     *   <td>blockedCount</td>
     *   <td><tt>java.lang.Long</tt></td>
     * </tr>
     * <tr>
     *   <td>blockedTime</td>
     *   <td><tt>java.lang.Long</tt></td>
     * </tr>
     * <tr>
     *   <td>waitedCount</td>
     *   <td><tt>java.lang.Long</tt></td>
     * </tr>
     * <tr>
     *   <td>waitedTime</td>
     *   <td><tt>java.lang.Long</tt></td>
     * </tr>
     * <tr>
     *   <td>lockInfo</td>
     *   <td><tt>javax.management.openmbean.CompositeData</tt>
     *       - the mapped type for {@link LockInfo} as specified in the
     *       <a href="../../../javax/management/MXBean.html#mapping-rules">
     *       type mapping rules</a> of
     *       {@linkplain javax.management.MXBean MXBeans}.
     *       <p>
     *       If <tt>cd</tt> does not contain this attribute,
     *       the <tt>LockInfo</tt> object will be constructed from
     *       the value of the <tt>lockName</tt> attribute. </td>
     * </tr>
     * <tr>
     *   <td>lockName</td>
     *   <td><tt>java.lang.String</tt></td>
     * </tr>
     * <tr>
     *   <td>lockOwnerId</td>
     *   <td><tt>java.lang.Long</tt></td>
     * </tr>
     * <tr>
     *   <td>lockOwnerName</td>
     *   <td><tt>java.lang.String</tt></td>
     * </tr>
     * <tr>
     *   <td><a name="StackTrace">stackTrace</a></td>
     *   <td><tt>javax.management.openmbean.CompositeData[]</tt>
     *       <p>
     *       Each element is a <tt>CompositeData</tt> representing
     *       StackTraceElement containing the following attributes:
     *       <blockquote>
     *       <table cellspacing=1 cellpadding=0>
     *       <tr>
     *         <th align=left>Attribute Name</th>
     *         <th align=left>Type</th>
     *       </tr>
     *       <tr>
     *         <td>className</td>
     *         <td><tt>java.lang.String</tt></td>
     *       </tr>
     *       <tr>
     *         <td>methodName</td>
     *         <td><tt>java.lang.String</tt></td>
     *       </tr>
     *       <tr>
     *         <td>fileName</td>
     *         <td><tt>java.lang.String</tt></td>
     *       </tr>
     *       <tr>
     *         <td>lineNumber</td>
     *         <td><tt>java.lang.Integer</tt></td>
     *       </tr>
     *       <tr>
     *         <td>nativeMethod</td>
     *         <td><tt>java.lang.Boolean</tt></td>
     *       </tr>
     *       </table>
     *       </blockquote>
     *   </td>
     * </tr>
     * <tr>
     *   <td>lockedMonitors</td>
     *   <td><tt>javax.management.openmbean.CompositeData[]</tt>
     *       whose element type is the mapped type for
     *       {@link MonitorInfo} as specified in the
     *       {@link MonitorInfo#from Monitor.from} method.
     *       <p>
     *       If <tt>cd</tt> does not contain this attribute,
     *       this attribute will be set to an empty array. </td>
     * </tr>
     * <tr>
     *   <td>lockedSynchronizers</td>
     *   <td><tt>javax.management.openmbean.CompositeData[]</tt>
     *       whose element type is the mapped type for
     *       {@link LockInfo} as specified in the
     *       <a href="../../../javax/management/MXBean.html#mapping-rules">
     *       type mapping rules</a> of
     *       {@linkplain javax.management.MXBean MXBeans}.
     *       <p>
     *       If <tt>cd</tt> does not contain this attribute,
     *       this attribute will be set to an empty array. </td>
     * </tr>
     * </table>
     * </blockquote>
     *
     * @param cd <tt>CompositeData</tt> representing a <tt>ThreadInfo</tt>
     *
     * @throws IllegalArgumentException if <tt>cd</tt> does not
     *   represent a <tt>ThreadInfo</tt> with the attributes described
     *   above.
     *
     * @return a <tt>ThreadInfo</tt> object represented
     *         by <tt>cd</tt> if <tt>cd</tt> is not <tt>null</tt>;
     *         <tt>null</tt> otherwise.
     */
    public static ThreadInfo from(CompositeData cd) {
        if (cd == null) {
            return null;
        }

        if (cd instanceof ThreadInfoCompositeData) {
            return ((ThreadInfoCompositeData) cd).getThreadInfo();
        } else {
            return new ThreadInfo(cd);
        }
    }

    /**
     * Returns an array of {@link MonitorInfo} objects, each of which
     * represents an object monitor currently locked by the thread
     * associated with this <tt>ThreadInfo</tt>.
     * If no locked monitor was requested for this thread info or
     * no monitor is locked by the thread, this method
     * will return a zero-length array.
     *
     * @return an array of <tt>MonitorInfo</tt> objects representing
     *         the object monitors locked by the thread.
     *
     * @since 1.6
     */
    public MonitorInfo[] getLockedMonitors() {
        return lockedMonitors;
    }

    /**
     * Returns an array of {@link LockInfo} objects, each of which
     * represents an <a href="LockInfo.html#OwnableSynchronizer">ownable
     * synchronizer</a> currently locked by the thread associated with
     * this <tt>ThreadInfo</tt>.  If no locked synchronizer was
     * requested for this thread info or no synchronizer is locked by
     * the thread, this method will return a zero-length array.
     *
     * @return an array of <tt>LockInfo</tt> objects representing
     *         the ownable synchronizers locked by the thread.
     *
     * @since 1.6
     */
    public LockInfo[] getLockedSynchronizers() {
       // represents an <a href="LockInfo.html#OwnableSynchronizer">
        return lockedSynchronizers;
    }

    private static final StackTraceElement[] NO_STACK_TRACE =
        new StackTraceElement[0];
}