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From hinde...@apache.org
Subject svn commit: r798469 [19/28] - in /harmony/enhanced/classlib/branches/java6: ./ depends/build/platform/ depends/files/ depends/jars/ depends/manifests/icu4j_4.0/ depends/manifests/icu4j_4.2.1/ depends/manifests/icu4j_4.2.1/META-INF/ make/ modules/access...
Date Tue, 28 Jul 2009 09:30:48 GMT
Modified: harmony/enhanced/classlib/branches/java6/modules/concurrent/src/main/java/java/util/concurrent/locks/ReentrantLock.java
URL: http://svn.apache.org/viewvc/harmony/enhanced/classlib/branches/java6/modules/concurrent/src/main/java/java/util/concurrent/locks/ReentrantLock.java?rev=798469&r1=798468&r2=798469&view=diff
==============================================================================
--- harmony/enhanced/classlib/branches/java6/modules/concurrent/src/main/java/java/util/concurrent/locks/ReentrantLock.java
(original)
+++ harmony/enhanced/classlib/branches/java6/modules/concurrent/src/main/java/java/util/concurrent/locks/ReentrantLock.java
Tue Jul 28 09:30:33 2009
@@ -12,19 +12,19 @@
 /**
  * A reentrant mutual exclusion {@link Lock} with the same basic
  * behavior and semantics as the implicit monitor lock accessed using
- * <tt>synchronized</tt> methods and statements, but with extended
+ * {@code synchronized} methods and statements, but with extended
  * capabilities.
  *
- * <p> A <tt>ReentrantLock</tt> is <em>owned</em> by the thread
last
+ * <p>A {@code ReentrantLock} is <em>owned</em> by the thread last
  * successfully locking, but not yet unlocking it. A thread invoking
- * <tt>lock</tt> will return, successfully acquiring the lock, when
+ * {@code lock} will return, successfully acquiring the lock, when
  * the lock is not owned by another thread. The method will return
  * immediately if the current thread already owns the lock. This can
  * be checked using methods {@link #isHeldByCurrentThread}, and {@link
- * #getHoldCount}.  
+ * #getHoldCount}.
  *
- * <p> The constructor for this class accepts an optional
- * <em>fairness</em> parameter.  When set <tt>true</tt>, under
+ * <p>The constructor for this class accepts an optional
+ * <em>fairness</em> parameter.  When set {@code true}, under
  * contention, locks favor granting access to the longest-waiting
  * thread.  Otherwise this lock does not guarantee any particular
  * access order.  Programs using fair locks accessed by many threads
@@ -36,9 +36,12 @@
  * fair lock may obtain it multiple times in succession while other
  * active threads are not progressing and not currently holding the
  * lock.
+ * Also note that the untimed {@link #tryLock() tryLock} method does not
+ * honor the fairness setting. It will succeed if the lock
+ * is available even if other threads are waiting.
  *
- * <p> It is recommended practice to <em>always</em> immediately
- * follow a call to <tt>lock</tt> with a <tt>try</tt> block, most
+ * <p>It is recommended practice to <em>always</em> immediately
+ * follow a call to {@code lock} with a {@code try} block, most
  * typically in a before/after construction such as:
  *
  * <pre>
@@ -46,7 +49,7 @@
  *   private final ReentrantLock lock = new ReentrantLock();
  *   // ...
  *
- *   public void m() { 
+ *   public void m() {
  *     lock.lock();  // block until condition holds
  *     try {
  *       // ... method body
@@ -58,21 +61,21 @@
  * </pre>
  *
  * <p>In addition to implementing the {@link Lock} interface, this
- * class defines methods <tt>isLocked</tt> and
- * <tt>getLockQueueLength</tt>, as well as some associated
- * <tt>protected</tt> access methods that may be useful for
+ * class defines methods {@code isLocked} and
+ * {@code getLockQueueLength}, as well as some associated
+ * {@code protected} access methods that may be useful for
  * instrumentation and monitoring.
  *
- * <p> Serialization of this class behaves in the same way as built-in
+ * <p>Serialization of this class behaves in the same way as built-in
  * locks: a deserialized lock is in the unlocked state, regardless of
  * its state when serialized.
  *
- * <p> This lock supports a maximum of 2147483648 recursive locks by
- * the same thread. 
+ * <p>This lock supports a maximum of 2147483647 recursive locks by
+ * the same thread. Attempts to exceed this limit result in
+ * {@link Error} throws from locking methods.
  *
  * @since 1.5
  * @author Doug Lea
- * 
  */
 public class ReentrantLock implements Lock, java.io.Serializable {
     private static final long serialVersionUID = 7373984872572414699L;
@@ -84,32 +87,34 @@
      * into fair and nonfair versions below. Uses AQS state to
      * represent the number of holds on the lock.
      */
-    static abstract class Sync  extends AbstractQueuedSynchronizer {
-        /** Current owner thread */
-        transient Thread owner;
+    static abstract class Sync extends AbstractQueuedSynchronizer {
+        private static final long serialVersionUID = -5179523762034025860L;
 
         /**
-         * Perform {@link Lock#lock}. The main reason for subclassing
+         * Performs {@link Lock#lock}. The main reason for subclassing
          * is to allow fast path for nonfair version.
          */
         abstract void lock();
 
-        /** 
-         * Perform non-fair tryLock.  tryAcquire is
+        /**
+         * Performs non-fair tryLock.  tryAcquire is
          * implemented in subclasses, but both need nonfair
-         * try for trylock method
+         * try for trylock method.
          */
-        final boolean nonfairTryAcquire(int acquires) { 
+        final boolean nonfairTryAcquire(int acquires) {
             final Thread current = Thread.currentThread();
             int c = getState();
             if (c == 0) {
                 if (compareAndSetState(0, acquires)) {
-                    owner = current;
+                    setExclusiveOwnerThread(current);
                     return true;
                 }
             }
-            else if (current == owner) {
-                setState(c+acquires);
+            else if (current == getExclusiveOwnerThread()) {
+                int nextc = c + acquires;
+                if (nextc < 0) // overflow
+                    throw new Error("Maximum lock count exceeded");
+                setState(nextc);
                 return true;
             }
             return false;
@@ -117,19 +122,21 @@
 
         protected final boolean tryRelease(int releases) {
             int c = getState() - releases;
-            if (Thread.currentThread() != owner)
+            if (Thread.currentThread() != getExclusiveOwnerThread())
                 throw new IllegalMonitorStateException();
             boolean free = false;
             if (c == 0) {
                 free = true;
-                owner = null;
+                setExclusiveOwnerThread(null);
             }
             setState(c);
             return free;
         }
 
         protected final boolean isHeldExclusively() {
-            return getState() != 0 && owner == Thread.currentThread();
+            // While we must in general read state before owner,
+            // we don't need to do so to check if current thread is owner
+            return getExclusiveOwnerThread() == Thread.currentThread();
         }
 
         final ConditionObject newCondition() {
@@ -139,23 +146,19 @@
         // Methods relayed from outer class
 
         final Thread getOwner() {
-            int c = getState();
-            Thread o = owner;
-            return (c == 0)? null : o;
+            return getState() == 0 ? null : getExclusiveOwnerThread();
         }
-        
+
         final int getHoldCount() {
-            int c = getState();
-            Thread o = owner;
-            return (o == Thread.currentThread())? c : 0;
+            return isHeldExclusively() ? getState() : 0;
         }
-        
+
         final boolean isLocked() {
             return getState() != 0;
         }
 
         /**
-         * Reconstitute this lock instance from a stream
+         * Reconstitutes this lock instance from a stream.
          * @param s the stream
          */
         private void readObject(java.io.ObjectInputStream s)
@@ -169,18 +172,20 @@
      * Sync object for non-fair locks
      */
     final static class NonfairSync extends Sync {
+        private static final long serialVersionUID = 7316153563782823691L;
+
         /**
-         * Perform lock.  Try immediate barge, backing up to normal
+         * Performs lock.  Try immediate barge, backing up to normal
          * acquire on failure.
          */
         final void lock() {
             if (compareAndSetState(0, 1))
-                owner = Thread.currentThread();
+                setExclusiveOwnerThread(Thread.currentThread());
             else
                 acquire(1);
         }
 
-        protected final boolean tryAcquire(int acquires) { 
+        protected final boolean tryAcquire(int acquires) {
             return nonfairTryAcquire(acquires);
         }
     }
@@ -188,28 +193,32 @@
     /**
      * Sync object for fair locks
      */
-    final static class FairSync  extends Sync {
-        final void lock() { 
-            acquire(1); 
+    final static class FairSync extends Sync {
+        private static final long serialVersionUID = -3000897897090466540L;
+
+        final void lock() {
+            acquire(1);
         }
 
         /**
          * Fair version of tryAcquire.  Don't grant access unless
          * recursive call or no waiters or is first.
          */
-        protected final boolean tryAcquire(int acquires) { 
+        protected final boolean tryAcquire(int acquires) {
             final Thread current = Thread.currentThread();
             int c = getState();
             if (c == 0) {
-                Thread first = getFirstQueuedThread();
-                if ((first == null || first == current) && 
+                if (!hasQueuedPredecessors() &&
                     compareAndSetState(0, acquires)) {
-                    owner = current;
+                    setExclusiveOwnerThread(current);
                     return true;
                 }
             }
-            else if (current == owner) {
-                setState(c+acquires);
+            else if (current == getExclusiveOwnerThread()) {
+                int nextc = c + acquires;
+                if (nextc < 0)
+                    throw new Error("Maximum lock count exceeded");
+                setState(nextc);
                 return true;
             }
             return false;
@@ -217,89 +226,88 @@
     }
 
     /**
-     * Creates an instance of <tt>ReentrantLock</tt>.
-     * This is equivalent to using <tt>ReentrantLock(false)</tt>.
+     * Creates an instance of {@code ReentrantLock}.
+     * This is equivalent to using {@code ReentrantLock(false)}.
      */
-    public ReentrantLock() { 
+    public ReentrantLock() {
         sync = new NonfairSync();
     }
 
     /**
-     * Creates an instance of <tt>ReentrantLock</tt> with the
+     * Creates an instance of {@code ReentrantLock} with the
      * given fairness policy.
-     * @param fair true if this lock will be fair; else false
+     *
+     * @param fair {@code true} if this lock should use a fair ordering policy
      */
-    public ReentrantLock(boolean fair) { 
+    public ReentrantLock(boolean fair) {
         sync = (fair)? new FairSync() : new NonfairSync();
     }
 
     /**
-     * Acquires the lock. 
+     * Acquires the lock.
      *
-     * <p>Acquires the lock if it is not held by another thread and returns 
+     * <p>Acquires the lock if it is not held by another thread and returns
      * immediately, setting the lock hold count to one.
      *
-     * <p>If the current thread
-     * already holds the lock then the hold count is incremented by one and
-     * the method returns immediately.
+     * <p>If the current thread already holds the lock then the hold
+     * count is incremented by one and the method returns immediately.
      *
      * <p>If the lock is held by another thread then the
-     * current thread becomes disabled for thread scheduling 
+     * current thread becomes disabled for thread scheduling
      * purposes and lies dormant until the lock has been acquired,
-     * at which time the lock hold count is set to one. 
+     * at which time the lock hold count is set to one.
      */
     public void lock() {
         sync.lock();
     }
 
     /**
-     * Acquires the lock unless the current thread is 
-     * {@link Thread#interrupt interrupted}.
+     * Acquires the lock unless the current thread is
+     * {@linkplain Thread#interrupt interrupted}.
      *
-     * <p>Acquires the lock if it is not held by another thread and returns 
+     * <p>Acquires the lock if it is not held by another thread and returns
      * immediately, setting the lock hold count to one.
      *
-     * <p>If the current thread already holds this lock then the hold count 
+     * <p>If the current thread already holds this lock then the hold count
      * is incremented by one and the method returns immediately.
      *
      * <p>If the lock is held by another thread then the
-     * current thread becomes disabled for thread scheduling 
+     * current thread becomes disabled for thread scheduling
      * purposes and lies dormant until one of two things happens:
      *
      * <ul>
      *
      * <li>The lock is acquired by the current thread; or
      *
-     * <li>Some other thread {@link Thread#interrupt interrupts} the current
-     * thread.
+     * <li>Some other thread {@linkplain Thread#interrupt interrupts} the
+     * current thread.
      *
      * </ul>
      *
-     * <p>If the lock is acquired by the current thread then the lock hold 
+     * <p>If the lock is acquired by the current thread then the lock hold
      * count is set to one.
      *
      * <p>If the current thread:
      *
      * <ul>
      *
-     * <li>has its interrupted status set on entry to this method; or 
+     * <li>has its interrupted status set on entry to this method; or
      *
-     * <li>is {@link Thread#interrupt interrupted} while acquiring 
+     * <li>is {@linkplain Thread#interrupt interrupted} while acquiring
      * the lock,
      *
      * </ul>
      *
-     * then {@link InterruptedException} is thrown and the current thread's 
-     * interrupted status is cleared. 
+     * then {@link InterruptedException} is thrown and the current thread's
+     * interrupted status is cleared.
      *
-     * <p>In this implementation, as this method is an explicit interruption 
-     * point, preference is 
-     * given to responding to the interrupt over normal or reentrant 
-     * acquisition of the lock.
+     * <p>In this implementation, as this method is an explicit
+     * interruption point, preference is given to responding to the
+     * interrupt over normal or reentrant acquisition of the lock.
      *
      * @throws InterruptedException if the current thread is interrupted
      */
-    public void lockInterruptibly() throws InterruptedException { 
+    public void lockInterruptibly() throws InterruptedException {
         sync.acquireInterruptibly(1);
     }
 
@@ -308,43 +316,42 @@
      * of invocation.
      *
      * <p>Acquires the lock if it is not held by another thread and
-     * returns immediately with the value <tt>true</tt>, setting the
+     * returns immediately with the value {@code true}, setting the
      * lock hold count to one. Even when this lock has been set to use a
-     * fair ordering policy, a call to <tt>tryLock()</tt> <em>will</em>
+     * fair ordering policy, a call to {@code tryLock()} <em>will</em>
      * immediately acquire the lock if it is available, whether or not
-     * other threads are currently waiting for the lock. 
-     * This &quot;barging&quot; behavior can be useful in certain 
+     * other threads are currently waiting for the lock.
+     * This &quot;barging&quot; behavior can be useful in certain
      * circumstances, even though it breaks fairness. If you want to honor
-     * the fairness setting for this lock, then use 
+     * the fairness setting for this lock, then use
      * {@link #tryLock(long, TimeUnit) tryLock(0, TimeUnit.SECONDS) }
      * which is almost equivalent (it also detects interruption).
      *
-     * <p> If the current thread
-     * already holds this lock then the hold count is incremented by one and
-     * the method returns <tt>true</tt>.
+     * <p> If the current thread already holds this lock then the hold
+     * count is incremented by one and the method returns {@code true}.
      *
-     * <p>If the lock is held by another thread then this method will return 
-     * immediately with the value <tt>false</tt>.  
+     * <p>If the lock is held by another thread then this method will return
+     * immediately with the value {@code false}.
      *
-     * @return <tt>true</tt> if the lock was free and was acquired by the
-     * current thread, or the lock was already held by the current thread; and
-     * <tt>false</tt> otherwise.
+     * @return {@code true} if the lock was free and was acquired by the
+     *         current thread, or the lock was already held by the current
+     *         thread; and {@code false} otherwise
      */
     public boolean tryLock() {
         return sync.nonfairTryAcquire(1);
     }
 
     /**
-     * Acquires the lock if it is not held by another thread within the given 
-     * waiting time and the current thread has not been 
-     * {@link Thread#interrupt interrupted}.
+     * Acquires the lock if it is not held by another thread within the given
+     * waiting time and the current thread has not been
+     * {@linkplain Thread#interrupt interrupted}.
      *
-     * <p>Acquires the lock if it is not held by another thread and returns 
-     * immediately with the value <tt>true</tt>, setting the lock hold count

+     * <p>Acquires the lock if it is not held by another thread and returns
+     * immediately with the value {@code true}, setting the lock hold count
      * to one. If this lock has been set to use a fair ordering policy then
      * an available lock <em>will not</em> be acquired if any other threads
      * are waiting for the lock. This is in contrast to the {@link #tryLock()}
-     * method. If you want a timed <tt>tryLock</tt> that does permit barging
on
+     * method. If you want a timed {@code tryLock} that does permit barging on
      * a fair lock then combine the timed and un-timed forms together:
      *
      * <pre>if (lock.tryLock() || lock.tryLock(timeout, unit) ) { ... }
@@ -352,60 +359,56 @@
      *
      * <p>If the current thread
      * already holds this lock then the hold count is incremented by one and
-     * the method returns <tt>true</tt>.
+     * the method returns {@code true}.
      *
      * <p>If the lock is held by another thread then the
-     * current thread becomes disabled for thread scheduling 
+     * current thread becomes disabled for thread scheduling
      * purposes and lies dormant until one of three things happens:
      *
      * <ul>
      *
      * <li>The lock is acquired by the current thread; or
      *
-     * <li>Some other thread {@link Thread#interrupt interrupts} the current
-     * thread; or
+     * <li>Some other thread {@linkplain Thread#interrupt interrupts}
+     * the current thread; or
      *
      * <li>The specified waiting time elapses
      *
      * </ul>
      *
-     * <p>If the lock is acquired then the value <tt>true</tt> is returned
and
+     * <p>If the lock is acquired then the value {@code true} is returned and
      * the lock hold count is set to one.
      *
      * <p>If the current thread:
      *
      * <ul>
      *
-     * <li>has its interrupted status set on entry to this method; or 
+     * <li>has its interrupted status set on entry to this method; or
      *
-     * <li>is {@link Thread#interrupt interrupted} while acquiring
-     * the lock,
+     * <li>is {@linkplain Thread#interrupt interrupted} while
+     * acquiring the lock,
      *
      * </ul>
-     * then {@link InterruptedException} is thrown and the current thread's 
-     * interrupted status is cleared. 
+     * then {@link InterruptedException} is thrown and the current thread's
+     * interrupted status is cleared.
      *
-     * <p>If the specified waiting time elapses then the value <tt>false</tt>
-     * is returned.
-     * If the time is 
-     * less than or equal to zero, the method will not wait at all.
-     *
-     * <p>In this implementation, as this method is an explicit interruption 
-     * point, preference is 
-     * given to responding to the interrupt over normal or reentrant 
-     * acquisition of the lock, and over reporting the elapse of the waiting
-     * time.
+     * <p>If the specified waiting time elapses then the value {@code false}
+     * is returned.  If the time is less than or equal to zero, the method
+     * will not wait at all.
+     *
+     * <p>In this implementation, as this method is an explicit
+     * interruption point, preference is given to responding to the
+     * interrupt over normal or reentrant acquisition of the lock, and
+     * over reporting the elapse of the waiting time.
      *
      * @param timeout the time to wait for the lock
      * @param unit the time unit of the timeout argument
-     *
-     * @return <tt>true</tt> if the lock was free and was acquired by the
-     * current thread, or the lock was already held by the current thread; and
-     * <tt>false</tt> if the waiting time elapsed before the lock could be 
-     * acquired.
-     *
+     * @return {@code true} if the lock was free and was acquired by the
+     *         current thread, or the lock was already held by the current
+     *         thread; and {@code false} if the waiting time elapsed before
+     *         the lock could be acquired
      * @throws InterruptedException if the current thread is interrupted
-     * @throws NullPointerException if unit is null
+     * @throws NullPointerException if the time unit is null
      *
      */
     public boolean tryLock(long timeout, TimeUnit unit) throws InterruptedException {
@@ -413,22 +416,22 @@
     }
 
     /**
-     * Attempts to release this lock.  
+     * Attempts to release this lock.
+     *
+     * <p>If the current thread is the holder of this lock then the hold
+     * count is decremented.  If the hold count is now zero then the lock
+     * is released.  If the current thread is not the holder of this
+     * lock then {@link IllegalMonitorStateException} is thrown.
      *
-     * <p>If the current thread is the
-     * holder of this lock then the hold count is decremented. If the
-     * hold count is now zero then the lock is released.  If the
-     * current thread is not the holder of this lock then {@link
-     * IllegalMonitorStateException} is thrown.
      * @throws IllegalMonitorStateException if the current thread does not
-     * hold this lock.
+     *         hold this lock
      */
     public void unlock() {
         sync.release(1);
     }
 
     /**
-     * Returns a {@link Condition} instance for use with this 
+     * Returns a {@link Condition} instance for use with this
      * {@link Lock} instance.
      *
      * <p>The returned {@link Condition} instance supports the same
@@ -440,28 +443,28 @@
      * <ul>
      *
      * <li>If this lock is not held when any of the {@link Condition}
-     * {@link Condition#await() waiting} or {@link Condition#signal
-     * signalling} methods are called, then an {@link
+     * {@linkplain Condition#await() waiting} or {@linkplain
+     * Condition#signal signalling} methods are called, then an {@link
      * IllegalMonitorStateException} is thrown.
      *
-     * <li>When the condition {@link Condition#await() waiting}
+     * <li>When the condition {@linkplain Condition#await() waiting}
      * methods are called the lock is released and, before they
      * return, the lock is reacquired and the lock hold count restored
      * to what it was when the method was called.
      *
-     * <li>If a thread is {@link Thread#interrupt interrupted} while
-     * waiting then the wait will terminate, an {@link
+     * <li>If a thread is {@linkplain Thread#interrupt interrupted}
+     * while waiting then the wait will terminate, an {@link
      * InterruptedException} will be thrown, and the thread's
      * interrupted status will be cleared.
      *
-     * <li> Waiting threads are signalled in FIFO order
+     * <li> Waiting threads are signalled in FIFO order.
      *
      * <li>The ordering of lock reacquisition for threads returning
      * from waiting methods is the same as for threads initially
      * acquiring the lock, which is in the default case not specified,
      * but for <em>fair</em> locks favors those threads that have been
      * waiting the longest.
-     * 
+     *
      * </ul>
      *
      * @return the Condition object
@@ -473,7 +476,7 @@
     /**
      * Queries the number of holds on this lock by the current thread.
      *
-     * <p>A thread has a hold on a lock for each lock action that is not 
+     * <p>A thread has a hold on a lock for each lock action that is not
      * matched by an unlock action.
      *
      * <p>The hold count information is typically only used for testing and
@@ -484,8 +487,8 @@
      * <pre>
      * class X {
      *   ReentrantLock lock = new ReentrantLock();
-     *   // ...     
-     *   public void m() { 
+     *   // ...
+     *   public void m() {
      *     assert lock.getHoldCount() == 0;
      *     lock.lock();
      *     try {
@@ -498,7 +501,7 @@
      * </pre>
      *
      * @return the number of holds on this lock by the current thread,
-     * or zero if this lock is not held by the current thread.
+     *         or zero if this lock is not held by the current thread
      */
     public int getHoldCount() {
         return sync.getHoldCount();
@@ -517,7 +520,7 @@
      *   ReentrantLock lock = new ReentrantLock();
      *   // ...
      *
-     *   public void m() { 
+     *   public void m() {
      *       assert lock.isHeldByCurrentThread();
      *       // ... method body
      *   }
@@ -532,7 +535,7 @@
      *   ReentrantLock lock = new ReentrantLock();
      *   // ...
      *
-     *   public void m() { 
+     *   public void m() {
      *       assert !lock.isHeldByCurrentThread();
      *       lock.lock();
      *       try {
@@ -543,8 +546,9 @@
      *   }
      * }
      * </pre>
-     * @return <tt>true</tt> if current thread holds this lock and 
-     * <tt>false</tt> otherwise.
+     *
+     * @return {@code true} if current thread holds this lock and
+     *         {@code false} otherwise
      */
     public boolean isHeldByCurrentThread() {
         return sync.isHeldExclusively();
@@ -552,47 +556,53 @@
 
     /**
      * Queries if this lock is held by any thread. This method is
-     * designed for use in monitoring of the system state, 
+     * designed for use in monitoring of the system state,
      * not for synchronization control.
-     * @return <tt>true</tt> if any thread holds this lock and 
-     * <tt>false</tt> otherwise.
+     *
+     * @return {@code true} if any thread holds this lock and
+     *         {@code false} otherwise
      */
     public boolean isLocked() {
         return sync.isLocked();
     }
 
     /**
-     * Returns true if this lock has fairness set true.
-     * @return true if this lock has fairness set true.
+     * Returns {@code true} if this lock has fairness set true.
+     *
+     * @return {@code true} if this lock has fairness set true
      */
     public final boolean isFair() {
         return sync instanceof FairSync;
     }
 
     /**
-     * Returns the thread that currently owns the exclusive lock, or
-     * <tt>null</tt> if not owned. Note that the owner may be
-     * momentarily <tt>null</tt> even if there are threads trying to
-     * acquire the lock but have not yet done so.  This method is
-     * designed to facilitate construction of subclasses that provide
-     * more extensive lock monitoring facilities.
-     * @return the owner, or <tt>null</tt> if not owned.
+     * Returns the thread that currently owns this lock, or
+     * {@code null} if not owned. When this method is called by a
+     * thread that is not the owner, the return value reflects a
+     * best-effort approximation of current lock status. For example,
+     * the owner may be momentarily {@code null} even if there are
+     * threads trying to acquire the lock but have not yet done so.
+     * This method is designed to facilitate construction of
+     * subclasses that provide more extensive lock monitoring
+     * facilities.
+     *
+     * @return the owner, or {@code null} if not owned
      */
     protected Thread getOwner() {
         return sync.getOwner();
     }
 
     /**
-     * Queries whether any threads are waiting to acquire. Note that
-     * because cancellations may occur at any time, a <tt>true</tt>
+     * Queries whether any threads are waiting to acquire this lock. Note that
+     * because cancellations may occur at any time, a {@code true}
      * return does not guarantee that any other thread will ever
-     * acquire.  This method is designed primarily for use in
+     * acquire this lock.  This method is designed primarily for use in
      * monitoring of the system state.
      *
-     * @return true if there may be other threads waiting to acquire
-     * the lock.
+     * @return {@code true} if there may be other threads waiting to
+     *         acquire the lock
      */
-    public final boolean hasQueuedThreads() { 
+    public final boolean hasQueuedThreads() {
         return sync.hasQueuedThreads();
     }
 
@@ -600,26 +610,27 @@
     /**
      * Queries whether the given thread is waiting to acquire this
      * lock. Note that because cancellations may occur at any time, a
-     * <tt>true</tt> return does not guarantee that this thread
-     * will ever acquire.  This method is designed primarily for use
+     * {@code true} return does not guarantee that this thread
+     * will ever acquire this lock.  This method is designed primarily for use
      * in monitoring of the system state.
      *
      * @param thread the thread
-     * @return true if the given thread is queued waiting for this lock.
-     * @throws NullPointerException if thread is null
+     * @return {@code true} if the given thread is queued waiting for this lock
+     * @throws NullPointerException if the thread is null
      */
-    public final boolean hasQueuedThread(Thread thread) { 
+    public final boolean hasQueuedThread(Thread thread) {
         return sync.isQueued(thread);
     }
 
 
     /**
      * Returns an estimate of the number of threads waiting to
-     * acquire.  The value is only an estimate because the number of
+     * acquire this lock.  The value is only an estimate because the number of
      * threads may change dynamically while this method traverses
      * internal data structures.  This method is designed for use in
      * monitoring of the system state, not for synchronization
      * control.
+     *
      * @return the estimated number of threads waiting for this lock
      */
     public final int getQueueLength() {
@@ -628,12 +639,13 @@
 
     /**
      * Returns a collection containing threads that may be waiting to
-     * acquire.  Because the actual set of threads may change
+     * acquire this lock.  Because the actual set of threads may change
      * dynamically while constructing this result, the returned
      * collection is only a best-effort estimate.  The elements of the
      * returned collection are in no particular order.  This method is
      * designed to facilitate construction of subclasses that provide
      * more extensive monitoring facilities.
+     *
      * @return the collection of threads
      */
     protected Collection<Thread> getQueuedThreads() {
@@ -643,18 +655,18 @@
     /**
      * Queries whether any threads are waiting on the given condition
      * associated with this lock. Note that because timeouts and
-     * interrupts may occur at any time, a <tt>true</tt> return does
-     * not guarantee that a future <tt>signal</tt> will awaken any
+     * interrupts may occur at any time, a {@code true} return does
+     * not guarantee that a future {@code signal} will awaken any
      * threads.  This method is designed primarily for use in
      * monitoring of the system state.
+     *
      * @param condition the condition
-     * @return <tt>true</tt> if there are any waiting threads.
-     * @throws IllegalMonitorStateException if this lock 
-     * is not held
+     * @return {@code true} if there are any waiting threads
+     * @throws IllegalMonitorStateException if this lock is not held
      * @throws IllegalArgumentException if the given condition is
-     * not associated with this lock
-     * @throws NullPointerException if condition null
-     */ 
+     *         not associated with this lock
+     * @throws NullPointerException if the condition is null
+     */
     public boolean hasWaiters(Condition condition) {
         if (condition == null)
             throw new NullPointerException();
@@ -670,14 +682,14 @@
      * serves only as an upper bound on the actual number of waiters.
      * This method is designed for use in monitoring of the system
      * state, not for synchronization control.
+     *
      * @param condition the condition
-     * @return the estimated number of waiting threads.
-     * @throws IllegalMonitorStateException if this lock 
-     * is not held
+     * @return the estimated number of waiting threads
+     * @throws IllegalMonitorStateException if this lock is not held
      * @throws IllegalArgumentException if the given condition is
-     * not associated with this lock
-     * @throws NullPointerException if condition null
-     */ 
+     *         not associated with this lock
+     * @throws NullPointerException if the condition is null
+     */
     public int getWaitQueueLength(Condition condition) {
         if (condition == null)
             throw new NullPointerException();
@@ -695,13 +707,13 @@
      * are in no particular order.  This method is designed to
      * facilitate construction of subclasses that provide more
      * extensive condition monitoring facilities.
+     *
      * @param condition the condition
      * @return the collection of threads
-     * @throws IllegalMonitorStateException if this lock 
-     * is not held
+     * @throws IllegalMonitorStateException if this lock is not held
      * @throws IllegalArgumentException if the given condition is
-     * not associated with this lock
-     * @throws NullPointerException if condition null
+     *         not associated with this lock
+     * @throws NullPointerException if the condition is null
      */
     protected Collection<Thread> getWaitingThreads(Condition condition) {
         if (condition == null)
@@ -712,16 +724,17 @@
     }
 
     /**
-     * Returns a string identifying this lock, as well as its lock
-     * state.  The state, in brackets, includes either the String
-     * &quot;Unlocked&quot; or the String &quot;Locked by&quot;
-     * followed by the {@link Thread#getName} of the owning thread.
-     * @return a string identifying this lock, as well as its lock state.
+     * Returns a string identifying this lock, as well as its lock state.
+     * The state, in brackets, includes either the String {@code "Unlocked"}
+     * or the String {@code "Locked by"} followed by the
+     * {@linkplain Thread#getName name} of the owning thread.
+     *
+     * @return a string identifying this lock, as well as its lock state
      */
     public String toString() {
-        Thread owner = sync.getOwner();
-        return super.toString() + ((owner == null) ?
+        Thread o = sync.getOwner();
+        return super.toString() + ((o == null) ?
                                    "[Unlocked]" :
-                                   "[Locked by thread " + owner.getName() + "]");
+                                   "[Locked by thread " + o.getName() + "]");
     }
 }



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