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diff --git a/libjava/classpath/external/jsr166/java/util/concurrent/locks/AbstractQueuedSynchronizer.java b/libjava/classpath/external/jsr166/java/util/concurrent/locks/AbstractQueuedSynchronizer.java new file mode 100644 index 000000000..647f4fcbc --- /dev/null +++ b/libjava/classpath/external/jsr166/java/util/concurrent/locks/AbstractQueuedSynchronizer.java @@ -0,0 +1,2159 @@ +/* + * Written by Doug Lea with assistance from members of JCP JSR-166 + * Expert Group and released to the public domain, as explained at + * http://creativecommons.org/licenses/publicdomain + */ + +package java.util.concurrent.locks; +import java.util.*; +import java.util.concurrent.*; +import java.util.concurrent.atomic.*; +import sun.misc.Unsafe; + +/** + * Provides a framework for implementing blocking locks and related + * synchronizers (semaphores, events, etc) that rely on + * first-in-first-out (FIFO) wait queues. This class is designed to + * be a useful basis for most kinds of synchronizers that rely on a + * single atomic <tt>int</tt> value to represent state. Subclasses + * must define the protected methods that change this state, and which + * define what that state means in terms of this object being acquired + * or released. Given these, the other methods in this class carry + * out all queuing and blocking mechanics. Subclasses can maintain + * other state fields, but only the atomically updated <tt>int</tt> + * value manipulated using methods {@link #getState}, {@link + * #setState} and {@link #compareAndSetState} is tracked with respect + * to synchronization. + * + * <p>Subclasses should be defined as non-public internal helper + * classes that are used to implement the synchronization properties + * of their enclosing class. Class + * <tt>AbstractQueuedSynchronizer</tt> does not implement any + * synchronization interface. Instead it defines methods such as + * {@link #acquireInterruptibly} that can be invoked as + * appropriate by concrete locks and related synchronizers to + * implement their public methods. + * + * <p>This class supports either or both a default <em>exclusive</em> + * mode and a <em>shared</em> mode. When acquired in exclusive mode, + * attempted acquires by other threads cannot succeed. Shared mode + * acquires by multiple threads may (but need not) succeed. This class + * does not "understand" these differences except in the + * mechanical sense that when a shared mode acquire succeeds, the next + * waiting thread (if one exists) must also determine whether it can + * acquire as well. Threads waiting in the different modes share the + * same FIFO queue. Usually, implementation subclasses support only + * one of these modes, but both can come into play for example in a + * {@link ReadWriteLock}. Subclasses that support only exclusive or + * only shared modes need not define the methods supporting the unused mode. + * + * <p>This class defines a nested {@link ConditionObject} class that + * can be used as a {@link Condition} implementation by subclasses + * supporting exclusive mode for which method {@link + * #isHeldExclusively} reports whether synchronization is exclusively + * held with respect to the current thread, method {@link #release} + * invoked with the current {@link #getState} value fully releases + * this object, and {@link #acquire}, given this saved state value, + * eventually restores this object to its previous acquired state. No + * <tt>AbstractQueuedSynchronizer</tt> method otherwise creates such a + * condition, so if this constraint cannot be met, do not use it. The + * behavior of {@link ConditionObject} depends of course on the + * semantics of its synchronizer implementation. + * + * <p>This class provides inspection, instrumentation, and monitoring + * methods for the internal queue, as well as similar methods for + * condition objects. These can be exported as desired into classes + * using an <tt>AbstractQueuedSynchronizer</tt> for their + * synchronization mechanics. + * + * <p>Serialization of this class stores only the underlying atomic + * integer maintaining state, so deserialized objects have empty + * thread queues. Typical subclasses requiring serializability will + * define a <tt>readObject</tt> method that restores this to a known + * initial state upon deserialization. + * + * <h3>Usage</h3> + * + * <p>To use this class as the basis of a synchronizer, redefine the + * following methods, as applicable, by inspecting and/or modifying + * the synchronization state using {@link #getState}, {@link + * #setState} and/or {@link #compareAndSetState}: + * + * <ul> + * <li> {@link #tryAcquire} + * <li> {@link #tryRelease} + * <li> {@link #tryAcquireShared} + * <li> {@link #tryReleaseShared} + * <li> {@link #isHeldExclusively} + *</ul> + * + * Each of these methods by default throws {@link + * UnsupportedOperationException}. Implementations of these methods + * must be internally thread-safe, and should in general be short and + * not block. Defining these methods is the <em>only</em> supported + * means of using this class. All other methods are declared + * <tt>final</tt> because they cannot be independently varied. + * + * <p>You may also find the inherited methods from {@link + * AbstractOwnableSynchronizer} useful to keep track of the thread + * owning an exclusive synchronizer. You are encouraged to use them + * -- this enables monitoring and diagnostic tools to assist users in + * determining which threads hold locks. + * + * <p>Even though this class is based on an internal FIFO queue, it + * does not automatically enforce FIFO acquisition policies. The core + * of exclusive synchronization takes the form: + * + * <pre> + * Acquire: + * while (!tryAcquire(arg)) { + * <em>enqueue thread if it is not already queued</em>; + * <em>possibly block current thread</em>; + * } + * + * Release: + * if (tryRelease(arg)) + * <em>unblock the first queued thread</em>; + * </pre> + * + * (Shared mode is similar but may involve cascading signals.) + * + * <p>Because checks in acquire are invoked before enqueuing, a newly + * acquiring thread may <em>barge</em> ahead of others that are + * blocked and queued. However, you can, if desired, define + * <tt>tryAcquire</tt> and/or <tt>tryAcquireShared</tt> to disable + * barging by internally invoking one or more of the inspection + * methods. In particular, a strict FIFO lock can define + * <tt>tryAcquire</tt> to immediately return <tt>false</tt> if {@link + * #getFirstQueuedThread} does not return the current thread. A + * normally preferable non-strict fair version can immediately return + * <tt>false</tt> only if {@link #hasQueuedThreads} returns + * <tt>true</tt> and <tt>getFirstQueuedThread</tt> is not the current + * thread; or equivalently, that <tt>getFirstQueuedThread</tt> is both + * non-null and not the current thread. Further variations are + * possible. + * + * <p>Throughput and scalability are generally highest for the + * default barging (also known as <em>greedy</em>, + * <em>renouncement</em>, and <em>convoy-avoidance</em>) strategy. + * While this is not guaranteed to be fair or starvation-free, earlier + * queued threads are allowed to recontend before later queued + * threads, and each recontention has an unbiased chance to succeed + * against incoming threads. Also, while acquires do not + * "spin" in the usual sense, they may perform multiple + * invocations of <tt>tryAcquire</tt> interspersed with other + * computations before blocking. This gives most of the benefits of + * spins when exclusive synchronization is only briefly held, without + * most of the liabilities when it isn't. If so desired, you can + * augment this by preceding calls to acquire methods with + * "fast-path" checks, possibly prechecking {@link #hasContended} + * and/or {@link #hasQueuedThreads} to only do so if the synchronizer + * is likely not to be contended. + * + * <p>This class provides an efficient and scalable basis for + * synchronization in part by specializing its range of use to + * synchronizers that can rely on <tt>int</tt> state, acquire, and + * release parameters, and an internal FIFO wait queue. When this does + * not suffice, you can build synchronizers from a lower level using + * {@link java.util.concurrent.atomic atomic} classes, your own custom + * {@link java.util.Queue} classes, and {@link LockSupport} blocking + * support. + * + * <h3>Usage Examples</h3> + * + * <p>Here is a non-reentrant mutual exclusion lock class that uses + * the value zero to represent the unlocked state, and one to + * represent the locked state. While a non-reentrant lock + * does not strictly require recording of the current owner + * thread, this class does so anyway to make usage easier to monitor. + * It also supports conditions and exposes + * one of the instrumentation methods: + * + * <pre> + * class Mutex implements Lock, java.io.Serializable { + * + * // Our internal helper class + * private static class Sync extends AbstractQueuedSynchronizer { + * // Report whether in locked state + * protected boolean isHeldExclusively() { + * return getState() == 1; + * } + * + * // Acquire the lock if state is zero + * public boolean tryAcquire(int acquires) { + * assert acquires == 1; // Otherwise unused + * if (compareAndSetState(0, 1)) { + * setExclusiveOwnerThread(Thread.currentThread()); + * return true; + * } + * return false; + * } + * + * // Release the lock by setting state to zero + * protected boolean tryRelease(int releases) { + * assert releases == 1; // Otherwise unused + * if (getState() == 0) throw new IllegalMonitorStateException(); + * setExclusiveOwnerThread(null); + * setState(0); + * return true; + * } + * + * // Provide a Condition + * Condition newCondition() { return new ConditionObject(); } + * + * // Deserialize properly + * private void readObject(ObjectInputStream s) + * throws IOException, ClassNotFoundException { + * s.defaultReadObject(); + * setState(0); // reset to unlocked state + * } + * } + * + * // The sync object does all the hard work. We just forward to it. + * private final Sync sync = new Sync(); + * + * public void lock() { sync.acquire(1); } + * public boolean tryLock() { return sync.tryAcquire(1); } + * public void unlock() { sync.release(1); } + * public Condition newCondition() { return sync.newCondition(); } + * public boolean isLocked() { return sync.isHeldExclusively(); } + * public boolean hasQueuedThreads() { return sync.hasQueuedThreads(); } + * public void lockInterruptibly() throws InterruptedException { + * sync.acquireInterruptibly(1); + * } + * public boolean tryLock(long timeout, TimeUnit unit) + * throws InterruptedException { + * return sync.tryAcquireNanos(1, unit.toNanos(timeout)); + * } + * } + * </pre> + * + * <p>Here is a latch class that is like a {@link CountDownLatch} + * except that it only requires a single <tt>signal</tt> to + * fire. Because a latch is non-exclusive, it uses the <tt>shared</tt> + * acquire and release methods. + * + * <pre> + * class BooleanLatch { + * + * private static class Sync extends AbstractQueuedSynchronizer { + * boolean isSignalled() { return getState() != 0; } + * + * protected int tryAcquireShared(int ignore) { + * return isSignalled()? 1 : -1; + * } + * + * protected boolean tryReleaseShared(int ignore) { + * setState(1); + * return true; + * } + * } + * + * private final Sync sync = new Sync(); + * public boolean isSignalled() { return sync.isSignalled(); } + * public void signal() { sync.releaseShared(1); } + * public void await() throws InterruptedException { + * sync.acquireSharedInterruptibly(1); + * } + * } + * </pre> + * + * @since 1.5 + * @author Doug Lea + */ +public abstract class AbstractQueuedSynchronizer + extends AbstractOwnableSynchronizer + implements java.io.Serializable { + + private static final long serialVersionUID = 7373984972572414691L; + + /** + * Creates a new <tt>AbstractQueuedSynchronizer</tt> instance + * with initial synchronization state of zero. + */ + protected AbstractQueuedSynchronizer() { } + + /** + * Wait queue node class. + * + * <p>The wait queue is a variant of a "CLH" (Craig, Landin, and + * Hagersten) lock queue. CLH locks are normally used for + * spinlocks. We instead use them for blocking synchronizers, but + * use the same basic tactic of holding some of the control + * information about a thread in the predecessor of its node. A + * "status" field in each node keeps track of whether a thread + * should block. A node is signalled when its predecessor + * releases. Each node of the queue otherwise serves as a + * specific-notification-style monitor holding a single waiting + * thread. The status field does NOT control whether threads are + * granted locks etc though. A thread may try to acquire if it is + * first in the queue. But being first does not guarantee success; + * it only gives the right to contend. So the currently released + * contender thread may need to rewait. + * + * <p>To enqueue into a CLH lock, you atomically splice it in as new + * tail. To dequeue, you just set the head field. + * <pre> + * +------+ prev +-----+ +-----+ + * head | | <---- | | <---- | | tail + * +------+ +-----+ +-----+ + * </pre> + * + * <p>Insertion into a CLH queue requires only a single atomic + * operation on "tail", so there is a simple atomic point of + * demarcation from unqueued to queued. Similarly, dequeing + * involves only updating the "head". However, it takes a bit + * more work for nodes to determine who their successors are, + * in part to deal with possible cancellation due to timeouts + * and interrupts. + * + * <p>The "prev" links (not used in original CLH locks), are mainly + * needed to handle cancellation. If a node is cancelled, its + * successor is (normally) relinked to a non-cancelled + * predecessor. For explanation of similar mechanics in the case + * of spin locks, see the papers by Scott and Scherer at + * http://www.cs.rochester.edu/u/scott/synchronization/ + * + * <p>We also use "next" links to implement blocking mechanics. + * The thread id for each node is kept in its own node, so a + * predecessor signals the next node to wake up by traversing + * next link to determine which thread it is. Determination of + * successor must avoid races with newly queued nodes to set + * the "next" fields of their predecessors. This is solved + * when necessary by checking backwards from the atomically + * updated "tail" when a node's successor appears to be null. + * (Or, said differently, the next-links are an optimization + * so that we don't usually need a backward scan.) + * + * <p>Cancellation introduces some conservatism to the basic + * algorithms. Since we must poll for cancellation of other + * nodes, we can miss noticing whether a cancelled node is + * ahead or behind us. This is dealt with by always unparking + * successors upon cancellation, allowing them to stabilize on + * a new predecessor. + * + * <p>CLH queues need a dummy header node to get started. But + * we don't create them on construction, because it would be wasted + * effort if there is never contention. Instead, the node + * is constructed and head and tail pointers are set upon first + * contention. + * + * <p>Threads waiting on Conditions use the same nodes, but + * use an additional link. Conditions only need to link nodes + * in simple (non-concurrent) linked queues because they are + * only accessed when exclusively held. Upon await, a node is + * inserted into a condition queue. Upon signal, the node is + * transferred to the main queue. A special value of status + * field is used to mark which queue a node is on. + * + * <p>Thanks go to Dave Dice, Mark Moir, Victor Luchangco, Bill + * Scherer and Michael Scott, along with members of JSR-166 + * expert group, for helpful ideas, discussions, and critiques + * on the design of this class. + */ + static final class Node { + /** waitStatus value to indicate thread has cancelled */ + static final int CANCELLED = 1; + /** waitStatus value to indicate successor's thread needs unparking */ + static final int SIGNAL = -1; + /** waitStatus value to indicate thread is waiting on condition */ + static final int CONDITION = -2; + /** Marker to indicate a node is waiting in shared mode */ + static final Node SHARED = new Node(); + /** Marker to indicate a node is waiting in exclusive mode */ + static final Node EXCLUSIVE = null; + + /** + * Status field, taking on only the values: + * SIGNAL: The successor of this node is (or will soon be) + * blocked (via park), so the current node must + * unpark its successor when it releases or + * cancels. To avoid races, acquire methods must + * first indicate they need a signal, + * then retry the atomic acquire, and then, + * on failure, block. + * CANCELLED: This node is cancelled due to timeout or interrupt. + * Nodes never leave this state. In particular, + * a thread with cancelled node never again blocks. + * CONDITION: This node is currently on a condition queue. + * It will not be used as a sync queue node until + * transferred. (Use of this value here + * has nothing to do with the other uses + * of the field, but simplifies mechanics.) + * 0: None of the above + * + * The values are arranged numerically to simplify use. + * Non-negative values mean that a node doesn't need to + * signal. So, most code doesn't need to check for particular + * values, just for sign. + * + * The field is initialized to 0 for normal sync nodes, and + * CONDITION for condition nodes. It is modified only using + * CAS. + */ + volatile int waitStatus; + + /** + * Link to predecessor node that current node/thread relies on + * for checking waitStatus. Assigned during enqueing, and nulled + * out (for sake of GC) only upon dequeuing. Also, upon + * cancellation of a predecessor, we short-circuit while + * finding a non-cancelled one, which will always exist + * because the head node is never cancelled: A node becomes + * head only as a result of successful acquire. A + * cancelled thread never succeeds in acquiring, and a thread only + * cancels itself, not any other node. + */ + volatile Node prev; + + /** + * Link to the successor node that the current node/thread + * unparks upon release. Assigned once during enqueuing, and + * nulled out (for sake of GC) when no longer needed. Upon + * cancellation, we cannot adjust this field, but can notice + * status and bypass the node if cancelled. The enq operation + * does not assign next field of a predecessor until after + * attachment, so seeing a null next field does not + * necessarily mean that node is at end of queue. However, if + * a next field appears to be null, we can scan prev's from + * the tail to double-check. + */ + volatile Node next; + + /** + * The thread that enqueued this node. Initialized on + * construction and nulled out after use. + */ + volatile Thread thread; + + /** + * Link to next node waiting on condition, or the special + * value SHARED. Because condition queues are accessed only + * when holding in exclusive mode, we just need a simple + * linked queue to hold nodes while they are waiting on + * conditions. They are then transferred to the queue to + * re-acquire. And because conditions can only be exclusive, + * we save a field by using special value to indicate shared + * mode. + */ + Node nextWaiter; + + /** + * Returns true if node is waiting in shared mode + */ + final boolean isShared() { + return nextWaiter == SHARED; + } + + /** + * Returns previous node, or throws NullPointerException if + * null. Use when predecessor cannot be null. + * @return the predecessor of this node + */ + final Node predecessor() throws NullPointerException { + Node p = prev; + if (p == null) + throw new NullPointerException(); + else + return p; + } + + Node() { // Used to establish initial head or SHARED marker + } + + Node(Thread thread, Node mode) { // Used by addWaiter + this.nextWaiter = mode; + this.thread = thread; + } + + Node(Thread thread, int waitStatus) { // Used by Condition + this.waitStatus = waitStatus; + this.thread = thread; + } + } + + /** + * Head of the wait queue, lazily initialized. Except for + * initialization, it is modified only via method setHead. Note: + * If head exists, its waitStatus is guaranteed not to be + * CANCELLED. + */ + private transient volatile Node head; + + /** + * Tail of the wait queue, lazily initialized. Modified only via + * method enq to add new wait node. + */ + private transient volatile Node tail; + + /** + * The synchronization state. + */ + private volatile int state; + + /** + * Returns the current value of synchronization state. + * This operation has memory semantics of a <tt>volatile</tt> read. + * @return current state value + */ + protected final int getState() { + return state; + } + + /** + * Sets the value of synchronization state. + * This operation has memory semantics of a <tt>volatile</tt> write. + * @param newState the new state value + */ + protected final void setState(int newState) { + state = newState; + } + + /** + * Atomically sets synchronization state to the given updated + * value if the current state value equals the expected value. + * This operation has memory semantics of a <tt>volatile</tt> read + * and write. + * + * @param expect the expected value + * @param update the new value + * @return true if successful. False return indicates that the actual + * value was not equal to the expected value. + */ + protected final boolean compareAndSetState(int expect, int update) { + // See below for intrinsics setup to support this + return unsafe.compareAndSwapInt(this, stateOffset, expect, update); + } + + // Queuing utilities + + /** + * The number of nanoseconds for which it is faster to spin + * rather than to use timed park. A rough estimate suffices + * to improve responsiveness with very short timeouts. + */ + static final long spinForTimeoutThreshold = 1000L; + + /** + * Inserts node into queue, initializing if necessary. See picture above. + * @param node the node to insert + * @return node's predecessor + */ + private Node enq(final Node node) { + for (;;) { + Node t = tail; + if (t == null) { // Must initialize + Node h = new Node(); // Dummy header + h.next = node; + node.prev = h; + if (compareAndSetHead(h)) { + tail = node; + return h; + } + } + else { + node.prev = t; + if (compareAndSetTail(t, node)) { + t.next = node; + return t; + } + } + } + } + + /** + * Creates and enqueues node for given thread and mode. + * + * @param current the thread + * @param mode Node.EXCLUSIVE for exclusive, Node.SHARED for shared + * @return the new node + */ + private Node addWaiter(Node mode) { + Node node = new Node(Thread.currentThread(), mode); + // Try the fast path of enq; backup to full enq on failure + Node pred = tail; + if (pred != null) { + node.prev = pred; + if (compareAndSetTail(pred, node)) { + pred.next = node; + return node; + } + } + enq(node); + return node; + } + + /** + * Sets head of queue to be node, thus dequeuing. Called only by + * acquire methods. Also nulls out unused fields for sake of GC + * and to suppress unnecessary signals and traversals. + * + * @param node the node + */ + private void setHead(Node node) { + head = node; + node.thread = null; + node.prev = null; + } + + /** + * Wakes up node's successor, if one exists. + * + * @param node the node + */ + private void unparkSuccessor(Node node) { + /* + * Try to clear status in anticipation of signalling. It is + * OK if this fails or if status is changed by waiting thread. + */ + compareAndSetWaitStatus(node, Node.SIGNAL, 0); + + /* + * Thread to unpark is held in successor, which is normally + * just the next node. But if cancelled or apparently null, + * traverse backwards from tail to find the actual + * non-cancelled successor. + */ + Node s = node.next; + if (s == null || s.waitStatus > 0) { + s = null; + for (Node t = tail; t != null && t != node; t = t.prev) + if (t.waitStatus <= 0) + s = t; + } + if (s != null) + LockSupport.unpark(s.thread); + } + + /** + * Sets head of queue, and checks if successor may be waiting + * in shared mode, if so propagating if propagate > 0. + * + * @param pred the node holding waitStatus for node + * @param node the node + * @param propagate the return value from a tryAcquireShared + */ + private void setHeadAndPropagate(Node node, int propagate) { + setHead(node); + if (propagate > 0 && node.waitStatus != 0) { + /* + * Don't bother fully figuring out successor. If it + * looks null, call unparkSuccessor anyway to be safe. + */ + Node s = node.next; + if (s == null || s.isShared()) + unparkSuccessor(node); + } + } + + // Utilities for various versions of acquire + + /** + * Cancels an ongoing attempt to acquire. + * + * @param node the node + */ + private void cancelAcquire(Node node) { + if (node != null) { // Ignore if node doesn't exist + node.thread = null; + // Can use unconditional write instead of CAS here + node.waitStatus = Node.CANCELLED; + unparkSuccessor(node); + } + } + + /** + * Checks and updates status for a node that failed to acquire. + * Returns true if thread should block. This is the main signal + * control in all acquire loops. Requires that pred == node.prev + * + * @param pred node's predecessor holding status + * @param node the node + * @return {@code true} if thread should block + */ + private static boolean shouldParkAfterFailedAcquire(Node pred, Node node) { + int s = pred.waitStatus; + if (s < 0) + /* + * This node has already set status asking a release + * to signal it, so it can safely park + */ + return true; + if (s > 0) + /* + * Predecessor was cancelled. Move up to its predecessor + * and indicate retry. + */ + node.prev = pred.prev; + else + /* + * Indicate that we need a signal, but don't park yet. Caller + * will need to retry to make sure it cannot acquire before + * parking. + */ + compareAndSetWaitStatus(pred, 0, Node.SIGNAL); + return false; + } + + /** + * Convenience method to interrupt current thread. + */ + private static void selfInterrupt() { + Thread.currentThread().interrupt(); + } + + /** + * Convenience method to park and then check if interrupted + * + * @return {@code true} if interrupted + */ + private final boolean parkAndCheckInterrupt() { + LockSupport.park(this); + return Thread.interrupted(); + } + + /* + * Various flavors of acquire, varying in exclusive/shared and + * control modes. Each is mostly the same, but annoyingly + * different. Only a little bit of factoring is possible due to + * interactions of exception mechanics (including ensuring that we + * cancel if tryAcquire throws exception) and other control, at + * least not without hurting performance too much. + */ + + /** + * Acquires in exclusive uninterruptible mode for thread already in + * queue. Used by condition wait methods as well as acquire. + * + * @param node the node + * @param arg the acquire argument + * @return {@code true} if interrupted while waiting + */ + final boolean acquireQueued(final Node node, int arg) { + try { + boolean interrupted = false; + for (;;) { + final Node p = node.predecessor(); + if (p == head && tryAcquire(arg)) { + setHead(node); + p.next = null; // help GC + return interrupted; + } + if (shouldParkAfterFailedAcquire(p, node) && + parkAndCheckInterrupt()) + interrupted = true; + } + } catch (RuntimeException ex) { + cancelAcquire(node); + throw ex; + } + } + + /** + * Acquires in exclusive interruptible mode. + * @param arg the acquire argument + */ + private void doAcquireInterruptibly(int arg) + throws InterruptedException { + final Node node = addWaiter(Node.EXCLUSIVE); + try { + for (;;) { + final Node p = node.predecessor(); + if (p == head && tryAcquire(arg)) { + setHead(node); + p.next = null; // help GC + return; + } + if (shouldParkAfterFailedAcquire(p, node) && + parkAndCheckInterrupt()) + break; + } + } catch (RuntimeException ex) { + cancelAcquire(node); + throw ex; + } + // Arrive here only if interrupted + cancelAcquire(node); + throw new InterruptedException(); + } + + /** + * Acquires in exclusive timed mode. + * + * @param arg the acquire argument + * @param nanosTimeout max wait time + * @return {@code true} if acquired + */ + private boolean doAcquireNanos(int arg, long nanosTimeout) + throws InterruptedException { + long lastTime = System.nanoTime(); + final Node node = addWaiter(Node.EXCLUSIVE); + try { + for (;;) { + final Node p = node.predecessor(); + if (p == head && tryAcquire(arg)) { + setHead(node); + p.next = null; // help GC + return true; + } + if (nanosTimeout <= 0) { + cancelAcquire(node); + return false; + } + if (nanosTimeout > spinForTimeoutThreshold && + shouldParkAfterFailedAcquire(p, node)) + LockSupport.parkNanos(this, nanosTimeout); + long now = System.nanoTime(); + nanosTimeout -= now - lastTime; + lastTime = now; + if (Thread.interrupted()) + break; + } + } catch (RuntimeException ex) { + cancelAcquire(node); + throw ex; + } + // Arrive here only if interrupted + cancelAcquire(node); + throw new InterruptedException(); + } + + /** + * Acquires in shared uninterruptible mode. + * @param arg the acquire argument + */ + private void doAcquireShared(int arg) { + final Node node = addWaiter(Node.SHARED); + try { + boolean interrupted = false; + for (;;) { + final Node p = node.predecessor(); + if (p == head) { + int r = tryAcquireShared(arg); + if (r >= 0) { + setHeadAndPropagate(node, r); + p.next = null; // help GC + if (interrupted) + selfInterrupt(); + return; + } + } + if (shouldParkAfterFailedAcquire(p, node) && + parkAndCheckInterrupt()) + interrupted = true; + } + } catch (RuntimeException ex) { + cancelAcquire(node); + throw ex; + } + } + + /** + * Acquires in shared interruptible mode. + * @param arg the acquire argument + */ + private void doAcquireSharedInterruptibly(int arg) + throws InterruptedException { + final Node node = addWaiter(Node.SHARED); + try { + for (;;) { + final Node p = node.predecessor(); + if (p == head) { + int r = tryAcquireShared(arg); + if (r >= 0) { + setHeadAndPropagate(node, r); + p.next = null; // help GC + return; + } + } + if (shouldParkAfterFailedAcquire(p, node) && + parkAndCheckInterrupt()) + break; + } + } catch (RuntimeException ex) { + cancelAcquire(node); + throw ex; + } + // Arrive here only if interrupted + cancelAcquire(node); + throw new InterruptedException(); + } + + /** + * Acquires in shared timed mode. + * + * @param arg the acquire argument + * @param nanosTimeout max wait time + * @return {@code true} if acquired + */ + private boolean doAcquireSharedNanos(int arg, long nanosTimeout) + throws InterruptedException { + + long lastTime = System.nanoTime(); + final Node node = addWaiter(Node.SHARED); + try { + for (;;) { + final Node p = node.predecessor(); + if (p == head) { + int r = tryAcquireShared(arg); + if (r >= 0) { + setHeadAndPropagate(node, r); + p.next = null; // help GC + return true; + } + } + if (nanosTimeout <= 0) { + cancelAcquire(node); + return false; + } + if (nanosTimeout > spinForTimeoutThreshold && + shouldParkAfterFailedAcquire(p, node)) + LockSupport.parkNanos(this, nanosTimeout); + long now = System.nanoTime(); + nanosTimeout -= now - lastTime; + lastTime = now; + if (Thread.interrupted()) + break; + } + } catch (RuntimeException ex) { + cancelAcquire(node); + throw ex; + } + // Arrive here only if interrupted + cancelAcquire(node); + throw new InterruptedException(); + } + + // Main exported methods + + /** + * Attempts to acquire in exclusive mode. This method should query + * if the state of the object permits it to be acquired in the + * exclusive mode, and if so to acquire it. + * + * <p>This method is always invoked by the thread performing + * acquire. If this method reports failure, the acquire method + * may queue the thread, if it is not already queued, until it is + * signalled by a release from some other thread. This can be used + * to implement method {@link Lock#tryLock()}. + * + * <p>The default + * implementation throws {@link UnsupportedOperationException}. + * + * @param arg the acquire argument. This value is always the one + * passed to an acquire method, or is the value saved on entry + * to a condition wait. The value is otherwise uninterpreted + * and can represent anything you like. + * @return {@code true} if successful. Upon success, this object has + * been acquired. + * @throws IllegalMonitorStateException if acquiring would place this + * synchronizer in an illegal state. This exception must be + * thrown in a consistent fashion for synchronization to work + * correctly. + * @throws UnsupportedOperationException if exclusive mode is not supported + */ + protected boolean tryAcquire(int arg) { + throw new UnsupportedOperationException(); + } + + /** + * Attempts to set the state to reflect a release in exclusive + * mode. + * + * <p>This method is always invoked by the thread performing release. + * + * <p>The default implementation throws + * {@link UnsupportedOperationException}. + * + * @param arg the release argument. This value is always the one + * passed to a release method, or the current state value upon + * entry to a condition wait. The value is otherwise + * uninterpreted and can represent anything you like. + * @return {@code true} if this object is now in a fully released + * state, so that any waiting threads may attempt to acquire; + * and {@code false} otherwise. + * @throws IllegalMonitorStateException if releasing would place this + * synchronizer in an illegal state. This exception must be + * thrown in a consistent fashion for synchronization to work + * correctly. + * @throws UnsupportedOperationException if exclusive mode is not supported + */ + protected boolean tryRelease(int arg) { + throw new UnsupportedOperationException(); + } + + /** + * Attempts to acquire in shared mode. This method should query if + * the state of the object permits it to be acquired in the shared + * mode, and if so to acquire it. + * + * <p>This method is always invoked by the thread performing + * acquire. If this method reports failure, the acquire method + * may queue the thread, if it is not already queued, until it is + * signalled by a release from some other thread. + * + * <p>The default implementation throws {@link + * UnsupportedOperationException}. + * + * @param arg the acquire argument. This value is always the one + * passed to an acquire method, or is the value saved on entry + * to a condition wait. The value is otherwise uninterpreted + * and can represent anything you like. + * @return a negative value on failure; zero if acquisition in shared + * mode succeeded but no subsequent shared-mode acquire can + * succeed; and a positive value if acquisition in shared + * mode succeeded and subsequent shared-mode acquires might + * also succeed, in which case a subsequent waiting thread + * must check availability. (Support for three different + * return values enables this method to be used in contexts + * where acquires only sometimes act exclusively.) Upon + * success, this object has been acquired. + * @throws IllegalMonitorStateException if acquiring would place this + * synchronizer in an illegal state. This exception must be + * thrown in a consistent fashion for synchronization to work + * correctly. + * @throws UnsupportedOperationException if shared mode is not supported + */ + protected int tryAcquireShared(int arg) { + throw new UnsupportedOperationException(); + } + + /** + * Attempts to set the state to reflect a release in shared mode. + * + * <p>This method is always invoked by the thread performing release. + * + * <p>The default implementation throws + * {@link UnsupportedOperationException}. + * + * @param arg the release argument. This value is always the one + * passed to a release method, or the current state value upon + * entry to a condition wait. The value is otherwise + * uninterpreted and can represent anything you like. + * @return {@code true} if this release of shared mode may permit a + * waiting acquire (shared or exclusive) to succeed; and + * {@code false} otherwise + * @throws IllegalMonitorStateException if releasing would place this + * synchronizer in an illegal state. This exception must be + * thrown in a consistent fashion for synchronization to work + * correctly. + * @throws UnsupportedOperationException if shared mode is not supported + */ + protected boolean tryReleaseShared(int arg) { + throw new UnsupportedOperationException(); + } + + /** + * Returns {@code true} if synchronization is held exclusively with + * respect to the current (calling) thread. This method is invoked + * upon each call to a non-waiting {@link ConditionObject} method. + * (Waiting methods instead invoke {@link #release}.) + * + * <p>The default implementation throws {@link + * UnsupportedOperationException}. This method is invoked + * internally only within {@link ConditionObject} methods, so need + * not be defined if conditions are not used. + * + * @return {@code true} if synchronization is held exclusively; + * {@code false} otherwise + * @throws UnsupportedOperationException if conditions are not supported + */ + protected boolean isHeldExclusively() { + throw new UnsupportedOperationException(); + } + + /** + * Acquires in exclusive mode, ignoring interrupts. Implemented + * by invoking at least once {@link #tryAcquire}, + * returning on success. Otherwise the thread is queued, possibly + * repeatedly blocking and unblocking, invoking {@link + * #tryAcquire} until success. This method can be used + * to implement method {@link Lock#lock}. + * + * @param arg the acquire argument. This value is conveyed to + * {@link #tryAcquire} but is otherwise uninterpreted and + * can represent anything you like. + */ + public final void acquire(int arg) { + if (!tryAcquire(arg) && + acquireQueued(addWaiter(Node.EXCLUSIVE), arg)) + selfInterrupt(); + } + + /** + * Acquires in exclusive mode, aborting if interrupted. + * Implemented by first checking interrupt status, then invoking + * at least once {@link #tryAcquire}, returning on + * success. Otherwise the thread is queued, possibly repeatedly + * blocking and unblocking, invoking {@link #tryAcquire} + * until success or the thread is interrupted. This method can be + * used to implement method {@link Lock#lockInterruptibly}. + * + * @param arg the acquire argument. This value is conveyed to + * {@link #tryAcquire} but is otherwise uninterpreted and + * can represent anything you like. + * @throws InterruptedException if the current thread is interrupted + */ + public final void acquireInterruptibly(int arg) throws InterruptedException { + if (Thread.interrupted()) + throw new InterruptedException(); + if (!tryAcquire(arg)) + doAcquireInterruptibly(arg); + } + + /** + * Attempts to acquire in exclusive mode, aborting if interrupted, + * and failing if the given timeout elapses. Implemented by first + * checking interrupt status, then invoking at least once {@link + * #tryAcquire}, returning on success. Otherwise, the thread is + * queued, possibly repeatedly blocking and unblocking, invoking + * {@link #tryAcquire} until success or the thread is interrupted + * or the timeout elapses. This method can be used to implement + * method {@link Lock#tryLock(long, TimeUnit)}. + * + * @param arg the acquire argument. This value is conveyed to + * {@link #tryAcquire} but is otherwise uninterpreted and + * can represent anything you like. + * @param nanosTimeout the maximum number of nanoseconds to wait + * @return {@code true} if acquired; {@code false} if timed out + * @throws InterruptedException if the current thread is interrupted + */ + public final boolean tryAcquireNanos(int arg, long nanosTimeout) throws InterruptedException { + if (Thread.interrupted()) + throw new InterruptedException(); + return tryAcquire(arg) || + doAcquireNanos(arg, nanosTimeout); + } + + /** + * Releases in exclusive mode. Implemented by unblocking one or + * more threads if {@link #tryRelease} returns true. + * This method can be used to implement method {@link Lock#unlock}. + * + * @param arg the release argument. This value is conveyed to + * {@link #tryRelease} but is otherwise uninterpreted and + * can represent anything you like. + * @return the value returned from {@link #tryRelease} + */ + public final boolean release(int arg) { + if (tryRelease(arg)) { + Node h = head; + if (h != null && h.waitStatus != 0) + unparkSuccessor(h); + return true; + } + return false; + } + + /** + * Acquires in shared mode, ignoring interrupts. Implemented by + * first invoking at least once {@link #tryAcquireShared}, + * returning on success. Otherwise the thread is queued, possibly + * repeatedly blocking and unblocking, invoking {@link + * #tryAcquireShared} until success. + * + * @param arg the acquire argument. This value is conveyed to + * {@link #tryAcquireShared} but is otherwise uninterpreted + * and can represent anything you like. + */ + public final void acquireShared(int arg) { + if (tryAcquireShared(arg) < 0) + doAcquireShared(arg); + } + + /** + * Acquires in shared mode, aborting if interrupted. Implemented + * by first checking interrupt status, then invoking at least once + * {@link #tryAcquireShared}, returning on success. Otherwise the + * thread is queued, possibly repeatedly blocking and unblocking, + * invoking {@link #tryAcquireShared} until success or the thread + * is interrupted. + * @param arg the acquire argument. + * This value is conveyed to {@link #tryAcquireShared} but is + * otherwise uninterpreted and can represent anything + * you like. + * @throws InterruptedException if the current thread is interrupted + */ + public final void acquireSharedInterruptibly(int arg) throws InterruptedException { + if (Thread.interrupted()) + throw new InterruptedException(); + if (tryAcquireShared(arg) < 0) + doAcquireSharedInterruptibly(arg); + } + + /** + * Attempts to acquire in shared mode, aborting if interrupted, and + * failing if the given timeout elapses. Implemented by first + * checking interrupt status, then invoking at least once {@link + * #tryAcquireShared}, returning on success. Otherwise, the + * thread is queued, possibly repeatedly blocking and unblocking, + * invoking {@link #tryAcquireShared} until success or the thread + * is interrupted or the timeout elapses. + * + * @param arg the acquire argument. This value is conveyed to + * {@link #tryAcquireShared} but is otherwise uninterpreted + * and can represent anything you like. + * @param nanosTimeout the maximum number of nanoseconds to wait + * @return {@code true} if acquired; {@code false} if timed out + * @throws InterruptedException if the current thread is interrupted + */ + public final boolean tryAcquireSharedNanos(int arg, long nanosTimeout) throws InterruptedException { + if (Thread.interrupted()) + throw new InterruptedException(); + return tryAcquireShared(arg) >= 0 || + doAcquireSharedNanos(arg, nanosTimeout); + } + + /** + * Releases in shared mode. Implemented by unblocking one or more + * threads if {@link #tryReleaseShared} returns true. + * + * @param arg the release argument. This value is conveyed to + * {@link #tryReleaseShared} but is otherwise uninterpreted + * and can represent anything you like. + * @return the value returned from {@link #tryReleaseShared} + */ + public final boolean releaseShared(int arg) { + if (tryReleaseShared(arg)) { + Node h = head; + if (h != null && h.waitStatus != 0) + unparkSuccessor(h); + return true; + } + return false; + } + + // Queue inspection methods + + /** + * Queries whether any threads are waiting to acquire. Note that + * because cancellations due to interrupts and timeouts may occur + * at any time, a {@code true} return does not guarantee that any + * other thread will ever acquire. + * + * <p>In this implementation, this operation returns in + * constant time. + * + * @return {@code true} if there may be other threads waiting to acquire + */ + public final boolean hasQueuedThreads() { + return head != tail; + } + + /** + * Queries whether any threads have ever contended to acquire this + * synchronizer; that is if an acquire method has ever blocked. + * + * <p>In this implementation, this operation returns in + * constant time. + * + * @return {@code true} if there has ever been contention + */ + public final boolean hasContended() { + return head != null; + } + + /** + * Returns the first (longest-waiting) thread in the queue, or + * {@code null} if no threads are currently queued. + * + * <p>In this implementation, this operation normally returns in + * constant time, but may iterate upon contention if other threads are + * concurrently modifying the queue. + * + * @return the first (longest-waiting) thread in the queue, or + * {@code null} if no threads are currently queued + */ + public final Thread getFirstQueuedThread() { + // handle only fast path, else relay + return (head == tail)? null : fullGetFirstQueuedThread(); + } + + /** + * Version of getFirstQueuedThread called when fastpath fails + */ + private Thread fullGetFirstQueuedThread() { + /* + * The first node is normally h.next. Try to get its + * thread field, ensuring consistent reads: If thread + * field is nulled out or s.prev is no longer head, then + * some other thread(s) concurrently performed setHead in + * between some of our reads. We try this twice before + * resorting to traversal. + */ + Node h, s; + Thread st; + if (((h = head) != null && (s = h.next) != null && + s.prev == head && (st = s.thread) != null) || + ((h = head) != null && (s = h.next) != null && + s.prev == head && (st = s.thread) != null)) + return st; + + /* + * Head's next field might not have been set yet, or may have + * been unset after setHead. So we must check to see if tail + * is actually first node. If not, we continue on, safely + * traversing from tail back to head to find first, + * guaranteeing termination. + */ + + Node t = tail; + Thread firstThread = null; + while (t != null && t != head) { + Thread tt = t.thread; + if (tt != null) + firstThread = tt; + t = t.prev; + } + return firstThread; + } + + /** + * Returns true if the given thread is currently queued. + * + * <p>This implementation traverses the queue to determine + * presence of the given thread. + * + * @param thread the thread + * @return {@code true} if the given thread is on the queue + * @throws NullPointerException if the thread is null + */ + public final boolean isQueued(Thread thread) { + if (thread == null) + throw new NullPointerException(); + for (Node p = tail; p != null; p = p.prev) + if (p.thread == thread) + return true; + return false; + } + + /** + * Return {@code true} if the apparent first queued thread, if one + * exists, is not waiting in exclusive mode. Used only as a heuristic + * in ReentrantReadWriteLock. + */ + final boolean apparentlyFirstQueuedIsExclusive() { + Node h, s; + return ((h = head) != null && (s = h.next) != null && + s.nextWaiter != Node.SHARED); + } + + /** + * Return {@code true} if the queue is empty or if the given thread + * is at the head of the queue. This is reliable only if + * <tt>current</tt> is actually Thread.currentThread() of caller. + */ + final boolean isFirst(Thread current) { + Node h, s; + return ((h = head) == null || + ((s = h.next) != null && s.thread == current) || + fullIsFirst(current)); + } + + final boolean fullIsFirst(Thread current) { + // same idea as fullGetFirstQueuedThread + Node h, s; + Thread firstThread = null; + if (((h = head) != null && (s = h.next) != null && + s.prev == head && (firstThread = s.thread) != null)) + return firstThread == current; + Node t = tail; + while (t != null && t != head) { + Thread tt = t.thread; + if (tt != null) + firstThread = tt; + t = t.prev; + } + return firstThread == current || firstThread == null; + } + + + // Instrumentation and monitoring methods + + /** + * Returns an estimate of the number of threads waiting to + * acquire. 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 system state, not for synchronization + * control. + * + * @return the estimated number of threads waiting to acquire + */ + public final int getQueueLength() { + int n = 0; + for (Node p = tail; p != null; p = p.prev) { + if (p.thread != null) + ++n; + } + return n; + } + + /** + * Returns a collection containing threads that may be waiting to + * acquire. 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 + */ + public final Collection<Thread> getQueuedThreads() { + ArrayList<Thread> list = new ArrayList<Thread>(); + for (Node p = tail; p != null; p = p.prev) { + Thread t = p.thread; + if (t != null) + list.add(t); + } + return list; + } + + /** + * Returns a collection containing threads that may be waiting to + * acquire in exclusive mode. This has the same properties + * as {@link #getQueuedThreads} except that it only returns + * those threads waiting due to an exclusive acquire. + * + * @return the collection of threads + */ + public final Collection<Thread> getExclusiveQueuedThreads() { + ArrayList<Thread> list = new ArrayList<Thread>(); + for (Node p = tail; p != null; p = p.prev) { + if (!p.isShared()) { + Thread t = p.thread; + if (t != null) + list.add(t); + } + } + return list; + } + + /** + * Returns a collection containing threads that may be waiting to + * acquire in shared mode. This has the same properties + * as {@link #getQueuedThreads} except that it only returns + * those threads waiting due to a shared acquire. + * + * @return the collection of threads + */ + public final Collection<Thread> getSharedQueuedThreads() { + ArrayList<Thread> list = new ArrayList<Thread>(); + for (Node p = tail; p != null; p = p.prev) { + if (p.isShared()) { + Thread t = p.thread; + if (t != null) + list.add(t); + } + } + return list; + } + + /** + * Returns a string identifying this synchronizer, as well as its state. + * The state, in brackets, includes the String {@code "State ="} + * followed by the current value of {@link #getState}, and either + * {@code "nonempty"} or {@code "empty"} depending on whether the + * queue is empty. + * + * @return a string identifying this synchronizer, as well as its state + */ + public String toString() { + int s = getState(); + String q = hasQueuedThreads()? "non" : ""; + return super.toString() + + "[State = " + s + ", " + q + "empty queue]"; + } + + + // Internal support methods for Conditions + + /** + * Returns true if a node, always one that was initially placed on + * a condition queue, is now waiting to reacquire on sync queue. + * @param node the node + * @return true if is reacquiring + */ + final boolean isOnSyncQueue(Node node) { + if (node.waitStatus == Node.CONDITION || node.prev == null) + return false; + if (node.next != null) // If has successor, it must be on queue + return true; + /* + * node.prev can be non-null, but not yet on queue because + * the CAS to place it on queue can fail. So we have to + * traverse from tail to make sure it actually made it. It + * will always be near the tail in calls to this method, and + * unless the CAS failed (which is unlikely), it will be + * there, so we hardly ever traverse much. + */ + return findNodeFromTail(node); + } + + /** + * Returns true if node is on sync queue by searching backwards from tail. + * Called only when needed by isOnSyncQueue. + * @return true if present + */ + private boolean findNodeFromTail(Node node) { + Node t = tail; + for (;;) { + if (t == node) + return true; + if (t == null) + return false; + t = t.prev; + } + } + + /** + * Transfers a node from a condition queue onto sync queue. + * Returns true if successful. + * @param node the node + * @return true if successfully transferred (else the node was + * cancelled before signal). + */ + final boolean transferForSignal(Node node) { + /* + * If cannot change waitStatus, the node has been cancelled. + */ + if (!compareAndSetWaitStatus(node, Node.CONDITION, 0)) + return false; + + /* + * Splice onto queue and try to set waitStatus of predecessor to + * indicate that thread is (probably) waiting. If cancelled or + * attempt to set waitStatus fails, wake up to resync (in which + * case the waitStatus can be transiently and harmlessly wrong). + */ + Node p = enq(node); + int c = p.waitStatus; + if (c > 0 || !compareAndSetWaitStatus(p, c, Node.SIGNAL)) + LockSupport.unpark(node.thread); + return true; + } + + /** + * Transfers node, if necessary, to sync queue after a cancelled + * wait. Returns true if thread was cancelled before being + * signalled. + * @param current the waiting thread + * @param node its node + * @return true if cancelled before the node was signalled. + */ + final boolean transferAfterCancelledWait(Node node) { + if (compareAndSetWaitStatus(node, Node.CONDITION, 0)) { + enq(node); + return true; + } + /* + * If we lost out to a signal(), then we can't proceed + * until it finishes its enq(). Cancelling during an + * incomplete transfer is both rare and transient, so just + * spin. + */ + while (!isOnSyncQueue(node)) + Thread.yield(); + return false; + } + + /** + * Invokes release with current state value; returns saved state. + * Cancels node and throws exception on failure. + * @param node the condition node for this wait + * @return previous sync state + */ + final int fullyRelease(Node node) { + try { + int savedState = getState(); + if (release(savedState)) + return savedState; + } catch (RuntimeException ex) { + node.waitStatus = Node.CANCELLED; + throw ex; + } + // reach here if release fails + node.waitStatus = Node.CANCELLED; + throw new IllegalMonitorStateException(); + } + + // Instrumentation methods for conditions + + /** + * Queries whether the given ConditionObject + * uses this synchronizer as its lock. + * + * @param condition the condition + * @return <tt>true</tt> if owned + * @throws NullPointerException if the condition is null + */ + public final boolean owns(ConditionObject condition) { + if (condition == null) + throw new NullPointerException(); + return condition.isOwnedBy(this); + } + + /** + * Queries whether any threads are waiting on the given condition + * associated with this synchronizer. 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 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 exclusive synchronization + * is not held + * @throws IllegalArgumentException if the given condition is + * not associated with this synchronizer + * @throws NullPointerException if the condition is null + */ + public final boolean hasWaiters(ConditionObject condition) { + if (!owns(condition)) + throw new IllegalArgumentException("Not owner"); + return condition.hasWaiters(); + } + + /** + * Returns an estimate of the number of threads waiting on the + * given condition associated with this synchronizer. Note that + * because timeouts and interrupts may occur at any time, the + * estimate 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 exclusive synchronization + * is not held + * @throws IllegalArgumentException if the given condition is + * not associated with this synchronizer + * @throws NullPointerException if the condition is null + */ + public final int getWaitQueueLength(ConditionObject condition) { + if (!owns(condition)) + throw new IllegalArgumentException("Not owner"); + return condition.getWaitQueueLength(); + } + + /** + * Returns a collection containing those threads that may be + * waiting on the given condition associated with this + * synchronizer. 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. + * + * @param condition the condition + * @return the collection of threads + * @throws IllegalMonitorStateException if exclusive synchronization + * is not held + * @throws IllegalArgumentException if the given condition is + * not associated with this synchronizer + * @throws NullPointerException if the condition is null + */ + public final Collection<Thread> getWaitingThreads(ConditionObject condition) { + if (!owns(condition)) + throw new IllegalArgumentException("Not owner"); + return condition.getWaitingThreads(); + } + + /** + * Condition implementation for a {@link + * AbstractQueuedSynchronizer} serving as the basis of a {@link + * Lock} implementation. + * + * <p>Method documentation for this class describes mechanics, + * not behavioral specifications from the point of view of Lock + * and Condition users. Exported versions of this class will in + * general need to be accompanied by documentation describing + * condition semantics that rely on those of the associated + * <tt>AbstractQueuedSynchronizer</tt>. + * + * <p>This class is Serializable, but all fields are transient, + * so deserialized conditions have no waiters. + */ + public class ConditionObject implements Condition, java.io.Serializable { + private static final long serialVersionUID = 1173984872572414699L; + /** First node of condition queue. */ + private transient Node firstWaiter; + /** Last node of condition queue. */ + private transient Node lastWaiter; + + /** + * Creates a new <tt>ConditionObject</tt> instance. + */ + public ConditionObject() { } + + // Internal methods + + /** + * Adds a new waiter to wait queue. + * @return its new wait node + */ + private Node addConditionWaiter() { + Node node = new Node(Thread.currentThread(), Node.CONDITION); + Node t = lastWaiter; + if (t == null) + firstWaiter = node; + else + t.nextWaiter = node; + lastWaiter = node; + return node; + } + + /** + * Removes and transfers nodes until hit non-cancelled one or + * null. Split out from signal in part to encourage compilers + * to inline the case of no waiters. + * @param first (non-null) the first node on condition queue + */ + private void doSignal(Node first) { + do { + if ( (firstWaiter = first.nextWaiter) == null) + lastWaiter = null; + first.nextWaiter = null; + } while (!transferForSignal(first) && + (first = firstWaiter) != null); + } + + /** + * Removes and transfers all nodes. + * @param first (non-null) the first node on condition queue + */ + private void doSignalAll(Node first) { + lastWaiter = firstWaiter = null; + do { + Node next = first.nextWaiter; + first.nextWaiter = null; + transferForSignal(first); + first = next; + } while (first != null); + } + + /** + * Returns true if given node is on this condition queue. + * Call only when holding lock. + */ + private boolean isOnConditionQueue(Node node) { + return node.next != null || node == lastWaiter; + } + + /** + * Unlinks a cancelled waiter node from condition queue. This + * is called when cancellation occurred during condition wait, + * not lock wait, and is called only after lock has been + * re-acquired by a cancelled waiter and the node is not known + * to already have been dequeued. It is needed to avoid + * garbage retention in the absence of signals. So even though + * it may require a full traversal, it comes into play only + * when timeouts or cancellations occur in the absence of + * signals. + */ + private void unlinkCancelledWaiter(Node node) { + Node t = firstWaiter; + Node trail = null; + while (t != null) { + if (t == node) { + Node next = t.nextWaiter; + if (trail == null) + firstWaiter = next; + else + trail.nextWaiter = next; + if (lastWaiter == node) + lastWaiter = trail; + break; + } + trail = t; + t = t.nextWaiter; + } + } + + // public methods + + /** + * Moves the longest-waiting thread, if one exists, from the + * wait queue for this condition to the wait queue for the + * owning lock. + * + * @throws IllegalMonitorStateException if {@link #isHeldExclusively} + * returns {@code false} + */ + public final void signal() { + if (!isHeldExclusively()) + throw new IllegalMonitorStateException(); + Node first = firstWaiter; + if (first != null) + doSignal(first); + } + + /** + * Moves all threads from the wait queue for this condition to + * the wait queue for the owning lock. + * + * @throws IllegalMonitorStateException if {@link #isHeldExclusively} + * returns {@code false} + */ + public final void signalAll() { + if (!isHeldExclusively()) + throw new IllegalMonitorStateException(); + Node first = firstWaiter; + if (first != null) + doSignalAll(first); + } + + /** + * Implements uninterruptible condition wait. + * <ol> + * <li> Save lock state returned by {@link #getState} + * <li> Invoke {@link #release} with + * saved state as argument, throwing + * IllegalMonitorStateException if it fails. + * <li> Block until signalled + * <li> Reacquire by invoking specialized version of + * {@link #acquire} with saved state as argument. + * </ol> + */ + public final void awaitUninterruptibly() { + Node node = addConditionWaiter(); + int savedState = fullyRelease(node); + boolean interrupted = false; + while (!isOnSyncQueue(node)) { + LockSupport.park(this); + if (Thread.interrupted()) + interrupted = true; + } + if (acquireQueued(node, savedState) || interrupted) + selfInterrupt(); + } + + /* + * For interruptible waits, we need to track whether to throw + * InterruptedException, if interrupted while blocked on + * condition, versus reinterrupt current thread, if + * interrupted while blocked waiting to re-acquire. + */ + + /** Mode meaning to reinterrupt on exit from wait */ + private static final int REINTERRUPT = 1; + /** Mode meaning to throw InterruptedException on exit from wait */ + private static final int THROW_IE = -1; + + /** + * Checks for interrupt, returning THROW_IE if interrupted + * before signalled, REINTERRUPT if after signalled, or + * 0 if not interrupted. + */ + private int checkInterruptWhileWaiting(Node node) { + return (Thread.interrupted()) ? + ((transferAfterCancelledWait(node))? THROW_IE : REINTERRUPT) : + 0; + } + + /** + * Throws InterruptedException, reinterrupts current thread, or + * does nothing, depending on mode. + */ + private void reportInterruptAfterWait(int interruptMode) + throws InterruptedException { + if (interruptMode == THROW_IE) + throw new InterruptedException(); + else if (interruptMode == REINTERRUPT) + selfInterrupt(); + } + + /** + * Implements interruptible condition wait. + * <ol> + * <li> If current thread is interrupted, throw InterruptedException + * <li> Save lock state returned by {@link #getState} + * <li> Invoke {@link #release} with + * saved state as argument, throwing + * IllegalMonitorStateException if it fails. + * <li> Block until signalled or interrupted + * <li> Reacquire by invoking specialized version of + * {@link #acquire} with saved state as argument. + * <li> If interrupted while blocked in step 4, throw exception + * </ol> + */ + public final void await() throws InterruptedException { + if (Thread.interrupted()) + throw new InterruptedException(); + Node node = addConditionWaiter(); + int savedState = fullyRelease(node); + int interruptMode = 0; + while (!isOnSyncQueue(node)) { + LockSupport.park(this); + if ((interruptMode = checkInterruptWhileWaiting(node)) != 0) + break; + } + if (acquireQueued(node, savedState) && interruptMode != THROW_IE) + interruptMode = REINTERRUPT; + if (isOnConditionQueue(node)) + unlinkCancelledWaiter(node); + if (interruptMode != 0) + reportInterruptAfterWait(interruptMode); + } + + /** + * Implements timed condition wait. + * <ol> + * <li> If current thread is interrupted, throw InterruptedException + * <li> Save lock state returned by {@link #getState} + * <li> Invoke {@link #release} with + * saved state as argument, throwing + * IllegalMonitorStateException if it fails. + * <li> Block until signalled, interrupted, or timed out + * <li> Reacquire by invoking specialized version of + * {@link #acquire} with saved state as argument. + * <li> If interrupted while blocked in step 4, throw InterruptedException + * </ol> + */ + public final long awaitNanos(long nanosTimeout) throws InterruptedException { + if (Thread.interrupted()) + throw new InterruptedException(); + Node node = addConditionWaiter(); + int savedState = fullyRelease(node); + long lastTime = System.nanoTime(); + int interruptMode = 0; + while (!isOnSyncQueue(node)) { + if (nanosTimeout <= 0L) { + transferAfterCancelledWait(node); + break; + } + LockSupport.parkNanos(this, nanosTimeout); + if ((interruptMode = checkInterruptWhileWaiting(node)) != 0) + break; + + long now = System.nanoTime(); + nanosTimeout -= now - lastTime; + lastTime = now; + } + if (acquireQueued(node, savedState) && interruptMode != THROW_IE) + interruptMode = REINTERRUPT; + if (isOnConditionQueue(node)) + unlinkCancelledWaiter(node); + if (interruptMode != 0) + reportInterruptAfterWait(interruptMode); + return nanosTimeout - (System.nanoTime() - lastTime); + } + + /** + * Implements absolute timed condition wait. + * <ol> + * <li> If current thread is interrupted, throw InterruptedException + * <li> Save lock state returned by {@link #getState} + * <li> Invoke {@link #release} with + * saved state as argument, throwing + * IllegalMonitorStateException if it fails. + * <li> Block until signalled, interrupted, or timed out + * <li> Reacquire by invoking specialized version of + * {@link #acquire} with saved state as argument. + * <li> If interrupted while blocked in step 4, throw InterruptedException + * <li> If timed out while blocked in step 4, return false, else true + * </ol> + */ + public final boolean awaitUntil(Date deadline) throws InterruptedException { + if (deadline == null) + throw new NullPointerException(); + long abstime = deadline.getTime(); + if (Thread.interrupted()) + throw new InterruptedException(); + Node node = addConditionWaiter(); + int savedState = fullyRelease(node); + boolean timedout = false; + int interruptMode = 0; + while (!isOnSyncQueue(node)) { + if (System.currentTimeMillis() > abstime) { + timedout = transferAfterCancelledWait(node); + break; + } + LockSupport.parkUntil(this, abstime); + if ((interruptMode = checkInterruptWhileWaiting(node)) != 0) + break; + } + if (acquireQueued(node, savedState) && interruptMode != THROW_IE) + interruptMode = REINTERRUPT; + if (isOnConditionQueue(node)) + unlinkCancelledWaiter(node); + if (interruptMode != 0) + reportInterruptAfterWait(interruptMode); + return !timedout; + } + + /** + * Implements timed condition wait. + * <ol> + * <li> If current thread is interrupted, throw InterruptedException + * <li> Save lock state returned by {@link #getState} + * <li> Invoke {@link #release} with + * saved state as argument, throwing + * IllegalMonitorStateException if it fails. + * <li> Block until signalled, interrupted, or timed out + * <li> Reacquire by invoking specialized version of + * {@link #acquire} with saved state as argument. + * <li> If interrupted while blocked in step 4, throw InterruptedException + * <li> If timed out while blocked in step 4, return false, else true + * </ol> + */ + public final boolean await(long time, TimeUnit unit) throws InterruptedException { + if (unit == null) + throw new NullPointerException(); + long nanosTimeout = unit.toNanos(time); + if (Thread.interrupted()) + throw new InterruptedException(); + Node node = addConditionWaiter(); + int savedState = fullyRelease(node); + long lastTime = System.nanoTime(); + boolean timedout = false; + int interruptMode = 0; + while (!isOnSyncQueue(node)) { + if (nanosTimeout <= 0L) { + timedout = transferAfterCancelledWait(node); + break; + } + LockSupport.parkNanos(this, nanosTimeout); + if ((interruptMode = checkInterruptWhileWaiting(node)) != 0) + break; + long now = System.nanoTime(); + nanosTimeout -= now - lastTime; + lastTime = now; + } + if (acquireQueued(node, savedState) && interruptMode != THROW_IE) + interruptMode = REINTERRUPT; + if (isOnConditionQueue(node)) + unlinkCancelledWaiter(node); + if (interruptMode != 0) + reportInterruptAfterWait(interruptMode); + return !timedout; + } + + // support for instrumentation + + /** + * Returns true if this condition was created by the given + * synchronization object. + * + * @return {@code true} if owned + */ + final boolean isOwnedBy(AbstractQueuedSynchronizer sync) { + return sync == AbstractQueuedSynchronizer.this; + } + + /** + * Queries whether any threads are waiting on this condition. + * Implements {@link AbstractQueuedSynchronizer#hasWaiters}. + * + * @return {@code true} if there are any waiting threads + * @throws IllegalMonitorStateException if {@link #isHeldExclusively} + * returns {@code false} + */ + protected final boolean hasWaiters() { + if (!isHeldExclusively()) + throw new IllegalMonitorStateException(); + for (Node w = firstWaiter; w != null; w = w.nextWaiter) { + if (w.waitStatus == Node.CONDITION) + return true; + } + return false; + } + + /** + * Returns an estimate of the number of threads waiting on + * this condition. + * Implements {@link AbstractQueuedSynchronizer#getWaitQueueLength}. + * + * @return the estimated number of waiting threads + * @throws IllegalMonitorStateException if {@link #isHeldExclusively} + * returns {@code false} + */ + protected final int getWaitQueueLength() { + if (!isHeldExclusively()) + throw new IllegalMonitorStateException(); + int n = 0; + for (Node w = firstWaiter; w != null; w = w.nextWaiter) { + if (w.waitStatus == Node.CONDITION) + ++n; + } + return n; + } + + /** + * Returns a collection containing those threads that may be + * waiting on this Condition. + * Implements {@link AbstractQueuedSynchronizer#getWaitingThreads}. + * + * @return the collection of threads + * @throws IllegalMonitorStateException if {@link #isHeldExclusively} + * returns {@code false} + */ + protected final Collection<Thread> getWaitingThreads() { + if (!isHeldExclusively()) + throw new IllegalMonitorStateException(); + ArrayList<Thread> list = new ArrayList<Thread>(); + for (Node w = firstWaiter; w != null; w = w.nextWaiter) { + if (w.waitStatus == Node.CONDITION) { + Thread t = w.thread; + if (t != null) + list.add(t); + } + } + return list; + } + } + + /** + * Setup to support compareAndSet. We need to natively implement + * this here: For the sake of permitting future enhancements, we + * cannot explicitly subclass AtomicInteger, which would be + * efficient and useful otherwise. So, as the lesser of evils, we + * natively implement using hotspot intrinsics API. And while we + * are at it, we do the same for other CASable fields (which could + * otherwise be done with atomic field updaters). + */ + private static final Unsafe unsafe = Unsafe.getUnsafe(); + private static final long stateOffset; + private static final long headOffset; + private static final long tailOffset; + private static final long waitStatusOffset; + + static { + try { + stateOffset = unsafe.objectFieldOffset + (AbstractQueuedSynchronizer.class.getDeclaredField("state")); + headOffset = unsafe.objectFieldOffset + (AbstractQueuedSynchronizer.class.getDeclaredField("head")); + tailOffset = unsafe.objectFieldOffset + (AbstractQueuedSynchronizer.class.getDeclaredField("tail")); + waitStatusOffset = unsafe.objectFieldOffset + (Node.class.getDeclaredField("waitStatus")); + + } catch (Exception ex) { throw new Error(ex); } + } + + /** + * CAS head field. Used only by enq + */ + private final boolean compareAndSetHead(Node update) { + return unsafe.compareAndSwapObject(this, headOffset, null, update); + } + + /** + * CAS tail field. Used only by enq + */ + private final boolean compareAndSetTail(Node expect, Node update) { + return unsafe.compareAndSwapObject(this, tailOffset, expect, update); + } + + /** + * CAS waitStatus field of a node. + */ + private final static boolean compareAndSetWaitStatus(Node node, + int expect, + int update) { + return unsafe.compareAndSwapInt(node, waitStatusOffset, + expect, update); + } +} |