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src/java.base/share/classes/java/lang/ref/FinalizerList.java
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@@ -31,222 +31,17 @@
* Written by Doug Lea and Martin Buchholz with assistance from members of
* JCP JSR-166 Expert Group and released to the public domain, as explained
* at http://creativecommons.org/publicdomain/zero/1.0/
*/
-package java.util.concurrent;
-
-import java.util.AbstractCollection;
-import java.util.ArrayList;
-import java.util.Collection;
-import java.util.Deque;
-import java.util.Iterator;
-import java.util.NoSuchElementException;
-import java.util.Queue;
-import java.util.Spliterator;
-import java.util.Spliterators;
-import java.util.function.Consumer;
+package java.lang.ref;
/**
- * An unbounded concurrent {@linkplain Deque deque} based on linked nodes.
- * Concurrent insertion, removal, and access operations execute safely
- * across multiple threads.
- * A {@code ConcurrentLinkedDeque} is an appropriate choice when
- * many threads will share access to a common collection.
- * Like most other concurrent collection implementations, this class
- * does not permit the use of {@code null} elements.
- *
- * <p>Iterators and spliterators are
- * <a href="package-summary.html#Weakly"><i>weakly consistent</i></a>.
- *
- * <p>Beware that, unlike in most collections, the {@code size} method
- * is <em>NOT</em> a constant-time operation. Because of the
- * asynchronous nature of these deques, determining the current number
- * of elements requires a traversal of the elements, and so may report
- * inaccurate results if this collection is modified during traversal.
- * Additionally, the bulk operations {@code addAll},
- * {@code removeAll}, {@code retainAll}, {@code containsAll},
- * {@code equals}, and {@code toArray} are <em>not</em> guaranteed
- * to be performed atomically. For example, an iterator operating
- * concurrently with an {@code addAll} operation might view only some
- * of the added elements.
- *
- * <p>This class and its iterator implement all of the <em>optional</em>
- * methods of the {@link Deque} and {@link Iterator} interfaces.
- *
- * <p>Memory consistency effects: As with other concurrent collections,
- * actions in a thread prior to placing an object into a
- * {@code ConcurrentLinkedDeque}
- * <a href="package-summary.html#MemoryVisibility"><i>happen-before</i></a>
- * actions subsequent to the access or removal of that element from
- * the {@code ConcurrentLinkedDeque} in another thread.
- *
- * <p>This class is a member of the
- * <a href="{@docRoot}/../technotes/guides/collections/index.html">
- * Java Collections Framework</a>.
- *
- * @since 1.7
- * @author Doug Lea
- * @author Martin Buchholz
- * @param <E> the type of elements held in this collection
- */
-public class ConcurrentLinkedDeque<E>
- extends AbstractCollection<E>
- implements Deque<E>, java.io.Serializable {
-
- /*
- * This is an implementation of a concurrent lock-free deque
- * supporting interior removes but not interior insertions, as
- * required to support the entire Deque interface.
- *
- * We extend the techniques developed for ConcurrentLinkedQueue and
- * LinkedTransferQueue (see the internal docs for those classes).
- * Understanding the ConcurrentLinkedQueue implementation is a
- * prerequisite for understanding the implementation of this class.
- *
- * The data structure is a symmetrical doubly-linked "GC-robust"
- * linked list of nodes. We minimize the number of volatile writes
- * using two techniques: advancing multiple hops with a single CAS
- * and mixing volatile and non-volatile writes of the same memory
- * locations.
- *
- * A node contains the expected E ("item") and links to predecessor
- * ("prev") and successor ("next") nodes:
- *
- * class Node<E> { volatile Node<E> prev, next; volatile E item; }
- *
- * A node p is considered "live" if it contains a non-null item
- * (p.item != null). When an item is CASed to null, the item is
- * atomically logically deleted from the collection.
- *
- * At any time, there is precisely one "first" node with a null
- * prev reference that terminates any chain of prev references
- * starting at a live node. Similarly there is precisely one
- * "last" node terminating any chain of next references starting at
- * a live node. The "first" and "last" nodes may or may not be live.
- * The "first" and "last" nodes are always mutually reachable.
- *
- * A new element is added atomically by CASing the null prev or
- * next reference in the first or last node to a fresh node
- * containing the element. The element's node atomically becomes
- * "live" at that point.
- *
- * A node is considered "active" if it is a live node, or the
- * first or last node. Active nodes cannot be unlinked.
- *
- * A "self-link" is a next or prev reference that is the same node:
- * p.prev == p or p.next == p
- * Self-links are used in the node unlinking process. Active nodes
- * never have self-links.
- *
- * A node p is active if and only if:
- *
- * p.item != null ||
- * (p.prev == null && p.next != p) ||
- * (p.next == null && p.prev != p)
- *
- * The deque object has two node references, "head" and "tail".
- * The head and tail are only approximations to the first and last
- * nodes of the deque. The first node can always be found by
- * following prev pointers from head; likewise for tail. However,
- * it is permissible for head and tail to be referring to deleted
- * nodes that have been unlinked and so may not be reachable from
- * any live node.
- *
- * There are 3 stages of node deletion;
- * "logical deletion", "unlinking", and "gc-unlinking".
- *
- * 1. "logical deletion" by CASing item to null atomically removes
- * the element from the collection, and makes the containing node
- * eligible for unlinking.
- *
- * 2. "unlinking" makes a deleted node unreachable from active
- * nodes, and thus eventually reclaimable by GC. Unlinked nodes
- * may remain reachable indefinitely from an iterator.
- *
- * Physical node unlinking is merely an optimization (albeit a
- * critical one), and so can be performed at our convenience. At
- * any time, the set of live nodes maintained by prev and next
- * links are identical, that is, the live nodes found via next
- * links from the first node is equal to the elements found via
- * prev links from the last node. However, this is not true for
- * nodes that have already been logically deleted - such nodes may
- * be reachable in one direction only.
- *
- * 3. "gc-unlinking" takes unlinking further by making active
- * nodes unreachable from deleted nodes, making it easier for the
- * GC to reclaim future deleted nodes. This step makes the data
- * structure "gc-robust", as first described in detail by Boehm
- * (http://portal.acm.org/citation.cfm?doid=503272.503282).
- *
- * GC-unlinked nodes may remain reachable indefinitely from an
- * iterator, but unlike unlinked nodes, are never reachable from
- * head or tail.
- *
- * Making the data structure GC-robust will eliminate the risk of
- * unbounded memory retention with conservative GCs and is likely
- * to improve performance with generational GCs.
- *
- * When a node is dequeued at either end, e.g. via poll(), we would
- * like to break any references from the node to active nodes. We
- * develop further the use of self-links that was very effective in
- * other concurrent collection classes. The idea is to replace
- * prev and next pointers with special values that are interpreted
- * to mean off-the-list-at-one-end. These are approximations, but
- * good enough to preserve the properties we want in our
- * traversals, e.g. we guarantee that a traversal will never visit
- * the same element twice, but we don't guarantee whether a
- * traversal that runs out of elements will be able to see more
- * elements later after enqueues at that end. Doing gc-unlinking
- * safely is particularly tricky, since any node can be in use
- * indefinitely (for example by an iterator). We must ensure that
- * the nodes pointed at by head/tail never get gc-unlinked, since
- * head/tail are needed to get "back on track" by other nodes that
- * are gc-unlinked. gc-unlinking accounts for much of the
- * implementation complexity.
- *
- * Since neither unlinking nor gc-unlinking are necessary for
- * correctness, there are many implementation choices regarding
- * frequency (eagerness) of these operations. Since volatile
- * reads are likely to be much cheaper than CASes, saving CASes by
- * unlinking multiple adjacent nodes at a time may be a win.
- * gc-unlinking can be performed rarely and still be effective,
- * since it is most important that long chains of deleted nodes
- * are occasionally broken.
- *
- * The actual representation we use is that p.next == p means to
- * goto the first node (which in turn is reached by following prev
- * pointers from head), and p.next == null && p.prev == p means
- * that the iteration is at an end and that p is a (static final)
- * dummy node, NEXT_TERMINATOR, and not the last active node.
- * Finishing the iteration when encountering such a TERMINATOR is
- * good enough for read-only traversals, so such traversals can use
- * p.next == null as the termination condition. When we need to
- * find the last (active) node, for enqueueing a new node, we need
- * to check whether we have reached a TERMINATOR node; if so,
- * restart traversal from tail.
- *
- * The implementation is completely directionally symmetrical,
- * except that most public methods that iterate through the list
- * follow next pointers ("forward" direction).
- *
- * We believe (without full proof) that all single-element deque
- * operations (e.g., addFirst, peekLast, pollLast) are linearizable
- * (see Herlihy and Shavit's book). However, some combinations of
- * operations are known not to be linearizable. In particular,
- * when an addFirst(A) is racing with pollFirst() removing B, it is
- * possible for an observer iterating over the elements to observe
- * A B C and subsequently observe A C, even though no interior
- * removes are ever performed. Nevertheless, iterators behave
- * reasonably, providing the "weakly consistent" guarantees.
- *
- * Empirically, microbenchmarks suggest that this class adds about
- * 40% overhead relative to ConcurrentLinkedQueue, which feels as
- * good as we can hope for.
+ * A concurrent doubly-linked list of {@link java.lang.ref.Finalizer} nodes
+ * modeled by {@link java.util.concurrent.ConcurrentLinkedDeque}.
*/
-
- private static final long serialVersionUID = 876323262645176354L;
+final class FinalizerList {
/**
* A node from which the first node on list (that is, the unique node p
* with p.prev == null && p.next != p) can be reached in O(1) time.
* Invariants:
@@ -257,11 +52,11 @@
* - head is never gc-unlinked (but may be unlinked)
* Non-invariants:
* - head.item may or may not be null
* - head may not be reachable from the first or last node, or from tail
*/
- private transient volatile Node<E> head;
+ private volatile Finalizer head;
/**
* A node from which the last node on list (that is, the unique node p
* with p.next == null && p.prev != p) can be reached in O(1) time.
* Invariants:
@@ -271,142 +66,81 @@
* - tail is never gc-unlinked (but may be unlinked)
* Non-invariants:
* - tail.item may or may not be null
* - tail may not be reachable from the first or last node, or from head
*/
- private transient volatile Node<E> tail;
+ private volatile Finalizer tail;
- private static final Node<Object> PREV_TERMINATOR, NEXT_TERMINATOR;
-
- @SuppressWarnings("unchecked")
- Node<E> prevTerminator() {
- return (Node<E>) PREV_TERMINATOR;
- }
-
- @SuppressWarnings("unchecked")
- Node<E> nextTerminator() {
- return (Node<E>) NEXT_TERMINATOR;
- }
-
- static final class Node<E> {
- volatile Node<E> prev;
- volatile E item;
- volatile Node<E> next;
-
- Node() { // default constructor for NEXT_TERMINATOR, PREV_TERMINATOR
- }
+ private static final Finalizer PREV_TERMINATOR, NEXT_TERMINATOR;
/**
- * Constructs a new node. Uses relaxed write because item can
- * only be seen after publication via casNext or casPrev.
+ * Links newFinalizer as first or last element, depending on
+ * specified boolean flag.
*/
- Node(E item) {
- UNSAFE.putObject(this, itemOffset, item);
- }
-
- boolean casItem(E cmp, E val) {
- return UNSAFE.compareAndSwapObject(this, itemOffset, cmp, val);
- }
-
- void lazySetNext(Node<E> val) {
- UNSAFE.putOrderedObject(this, nextOffset, val);
- }
-
- boolean casNext(Node<E> cmp, Node<E> val) {
- return UNSAFE.compareAndSwapObject(this, nextOffset, cmp, val);
- }
-
- void lazySetPrev(Node<E> val) {
- UNSAFE.putOrderedObject(this, prevOffset, val);
- }
-
- boolean casPrev(Node<E> cmp, Node<E> val) {
- return UNSAFE.compareAndSwapObject(this, prevOffset, cmp, val);
- }
-
- // Unsafe mechanics
-
- private static final sun.misc.Unsafe UNSAFE;
- private static final long prevOffset;
- private static final long itemOffset;
- private static final long nextOffset;
-
- static {
- try {
- UNSAFE = sun.misc.Unsafe.getUnsafe();
- Class<?> k = Node.class;
- prevOffset = UNSAFE.objectFieldOffset
- (k.getDeclaredField("prev"));
- itemOffset = UNSAFE.objectFieldOffset
- (k.getDeclaredField("item"));
- nextOffset = UNSAFE.objectFieldOffset
- (k.getDeclaredField("next"));
- } catch (Exception e) {
- throw new Error(e);
- }
+ void link(Finalizer newFinalizer, boolean first) {
+ if (first) {
+ linkFirst(newFinalizer);
+ } else {
+ linkLast(newFinalizer);
}
}
/**
- * Links e as first element.
+ * Links newFinalizer as first element.
*/
- private void linkFirst(E e) {
- checkNotNull(e);
- final Node<E> newNode = new Node<E>(e);
+ private void linkFirst(Finalizer newFinalizer) {
restartFromHead:
for (;;)
- for (Node<E> h = head, p = h, q;;) {
+ for (Finalizer h = head, p = h, q;;) {
if ((q = p.prev) != null &&
(q = (p = q).prev) != null)
// Check for head updates every other hop.
// If p == q, we are sure to follow head instead.
p = (h != (h = head)) ? h : q;
else if (p.next == p) // PREV_TERMINATOR
continue restartFromHead;
else {
// p is first node
- newNode.lazySetNext(p); // CAS piggyback
- if (p.casPrev(null, newNode)) {
+ newFinalizer.lazySetNext(p); // CAS piggyback
+ if (p.casPrev(null, newFinalizer)) {
// Successful CAS is the linearization point
// for e to become an element of this deque,
// and for newNode to become "live".
if (p != h) // hop two nodes at a time
- casHead(h, newNode); // Failure is OK.
+ casHead(h, newFinalizer); // Failure is OK.
return;
}
// Lost CAS race to another thread; re-read prev
}
}
}
/**
- * Links e as last element.
+ * Links newNode as last element.
*/
- private void linkLast(E e) {
- checkNotNull(e);
- final Node<E> newNode = new Node<E>(e);
+ private void linkLast(Finalizer newFinalizer) {
restartFromTail:
for (;;)
- for (Node<E> t = tail, p = t, q;;) {
+ for (Finalizer t = tail, p = t, q;;) {
if ((q = p.next) != null &&
(q = (p = q).next) != null)
// Check for tail updates every other hop.
// If p == q, we are sure to follow tail instead.
p = (t != (t = tail)) ? t : q;
else if (p.prev == p) // NEXT_TERMINATOR
continue restartFromTail;
else {
// p is last node
- newNode.lazySetPrev(p); // CAS piggyback
- if (p.casNext(null, newNode)) {
+ newFinalizer.lazySetPrev(p); // CAS piggyback
+ if (p.casNext(null, newFinalizer)) {
// Successful CAS is the linearization point
// for e to become an element of this deque,
// and for newNode to become "live".
if (p != t) // hop two nodes at a time
- casTail(t, newNode); // Failure is OK.
+ casTail(t, newFinalizer); // Failure is OK.
return;
}
// Lost CAS race to another thread; re-read next
}
}
@@ -415,18 +149,18 @@
private static final int HOPS = 2;
/**
* Unlinks non-null node x.
*/
- void unlink(Node<E> x) {
+ void unlink(Finalizer x) {
// assert x != null;
// assert x.item == null;
// assert x != PREV_TERMINATOR;
// assert x != NEXT_TERMINATOR;
- final Node<E> prev = x.prev;
- final Node<E> next = x.next;
+ final Finalizer prev = x.prev;
+ final Finalizer next = x.next;
if (prev == null) {
unlinkFirst(x, next);
} else if (next == null) {
unlinkLast(x, prev);
} else {
@@ -447,22 +181,22 @@
// leaving active nodes unreachable from x, by rechecking
// that the status of predecessor and successor are
// unchanged and ensuring that x is not reachable from
// tail/head, before setting x's prev/next links to their
// logical approximate replacements, self/TERMINATOR.
- Node<E> activePred, activeSucc;
+ Finalizer activePred, activeSucc;
boolean isFirst, isLast;
int hops = 1;
// Find active predecessor
- for (Node<E> p = prev; ; ++hops) {
- if (p.item != null) {
+ for (Finalizer p = prev; ; ++hops) {
+ if (p.isAlive()) {
activePred = p;
isFirst = false;
break;
}
- Node<E> q = p.prev;
+ Finalizer q = p.prev;
if (q == null) {
if (p.next == p)
return;
activePred = p;
isFirst = true;
@@ -473,17 +207,17 @@
else
p = q;
}
// Find active successor
- for (Node<E> p = next; ; ++hops) {
- if (p.item != null) {
+ for (Finalizer p = next; ; ++hops) {
+ if (p.isAlive()) {
activeSucc = p;
isLast = false;
break;
}
- Node<E> q = p.next;
+ Finalizer q = p.next;
if (q == null) {
if (p.prev == p)
return;
activeSucc = p;
isLast = true;
@@ -510,44 +244,44 @@
if ((isFirst | isLast) &&
// Recheck expected state of predecessor and successor
(activePred.next == activeSucc) &&
(activeSucc.prev == activePred) &&
- (isFirst ? activePred.prev == null : activePred.item != null) &&
- (isLast ? activeSucc.next == null : activeSucc.item != null)) {
+ (isFirst ? activePred.prev == null : activePred.isAlive()) &&
+ (isLast ? activeSucc.next == null : activeSucc.isAlive())) {
updateHead(); // Ensure x is not reachable from head
updateTail(); // Ensure x is not reachable from tail
// Finally, actually gc-unlink
- x.lazySetPrev(isFirst ? prevTerminator() : x);
- x.lazySetNext(isLast ? nextTerminator() : x);
+ x.lazySetPrev(isFirst ? PREV_TERMINATOR : x);
+ x.lazySetNext(isLast ? NEXT_TERMINATOR : x);
}
}
}
/**
* Unlinks non-null first node.
*/
- private void unlinkFirst(Node<E> first, Node<E> next) {
+ private void unlinkFirst(Finalizer first, Finalizer next) {
// assert first != null;
// assert next != null;
// assert first.item == null;
- for (Node<E> o = null, p = next, q;;) {
- if (p.item != null || (q = p.next) == null) {
+ for (Finalizer o = null, p = next, q;;) {
+ if (p.isAlive() || (q = p.next) == null) {
if (o != null && p.prev != p && first.casNext(next, p)) {
skipDeletedPredecessors(p);
if (first.prev == null &&
- (p.next == null || p.item != null) &&
+ (p.next == null || p.isAlive()) &&
p.prev == first) {
updateHead(); // Ensure o is not reachable from head
updateTail(); // Ensure o is not reachable from tail
// Finally, actually gc-unlink
o.lazySetNext(o);
- o.lazySetPrev(prevTerminator());
+ o.lazySetPrev(PREV_TERMINATOR);
}
}
return;
}
else if (p == q)
@@ -560,28 +294,28 @@
}
/**
* Unlinks non-null last node.
*/
- private void unlinkLast(Node<E> last, Node<E> prev) {
+ private void unlinkLast(Finalizer last, Finalizer prev) {
// assert last != null;
// assert prev != null;
// assert last.item == null;
- for (Node<E> o = null, p = prev, q;;) {
- if (p.item != null || (q = p.prev) == null) {
+ for (Finalizer o = null, p = prev, q;;) {
+ if (p.isAlive() || (q = p.prev) == null) {
if (o != null && p.next != p && last.casPrev(prev, p)) {
skipDeletedSuccessors(p);
if (last.next == null &&
- (p.prev == null || p.item != null) &&
+ (p.prev == null || p.isAlive()) &&
p.next == last) {
updateHead(); // Ensure o is not reachable from head
updateTail(); // Ensure o is not reachable from tail
// Finally, actually gc-unlink
o.lazySetPrev(o);
- o.lazySetNext(nextTerminator());
+ o.lazySetNext(NEXT_TERMINATOR);
}
}
return;
}
else if (p == q)
@@ -597,16 +331,16 @@
* Guarantees that any node which was unlinked before a call to
* this method will be unreachable from head after it returns.
* Does not guarantee to eliminate slack, only that head will
* point to a node that was active while this method was running.
*/
- private final void updateHead() {
+ private void updateHead() {
// Either head already points to an active node, or we keep
// trying to cas it to the first node until it does.
- Node<E> h, p, q;
+ Finalizer h, p, q;
restartFromHead:
- while ((h = head).item == null && (p = h.prev) != null) {
+ while ((h = head).isDeleted() && (p = h.prev) != null) {
for (;;) {
if ((q = p.prev) == null ||
(q = (p = q).prev) == null) {
// It is possible that p is PREV_TERMINATOR,
// but if so, the CAS is guaranteed to fail.
@@ -627,16 +361,16 @@
* Guarantees that any node which was unlinked before a call to
* this method will be unreachable from tail after it returns.
* Does not guarantee to eliminate slack, only that tail will
* point to a node that was active while this method was running.
*/
- private final void updateTail() {
+ private void updateTail() {
// Either tail already points to an active node, or we keep
// trying to cas it to the last node until it does.
- Node<E> t, p, q;
+ Finalizer t, p, q;
restartFromTail:
- while ((t = tail).item == null && (p = t.next) != null) {
+ while ((t = tail).isDeleted() && (p = t.next) != null) {
for (;;) {
if ((q = p.next) == null ||
(q = (p = q).next) == null) {
// It is possible that p is NEXT_TERMINATOR,
// but if so, the CAS is guaranteed to fail.
@@ -651,23 +385,23 @@
p = q;
}
}
}
- private void skipDeletedPredecessors(Node<E> x) {
+ private void skipDeletedPredecessors(Finalizer x) {
whileActive:
do {
- Node<E> prev = x.prev;
+ Finalizer prev = x.prev;
// assert prev != null;
// assert x != NEXT_TERMINATOR;
// assert x != PREV_TERMINATOR;
- Node<E> p = prev;
+ Finalizer p = prev;
findActive:
for (;;) {
- if (p.item != null)
+ if (p.isAlive())
break findActive;
- Node<E> q = p.prev;
+ Finalizer q = p.prev;
if (q == null) {
if (p.next == p)
continue whileActive;
break findActive;
}
@@ -679,26 +413,26 @@
// found active CAS target
if (prev == p || x.casPrev(prev, p))
return;
- } while (x.item != null || x.next == null);
+ } while (x.isAlive() || x.next == null);
}
- private void skipDeletedSuccessors(Node<E> x) {
+ private void skipDeletedSuccessors(Finalizer x) {
whileActive:
do {
- Node<E> next = x.next;
+ Finalizer next = x.next;
// assert next != null;
// assert x != NEXT_TERMINATOR;
// assert x != PREV_TERMINATOR;
- Node<E> p = next;
+ Finalizer p = next;
findActive:
for (;;) {
- if (p.item != null)
+ if (p.isAlive())
break findActive;
- Node<E> q = p.next;
+ Finalizer q = p.next;
if (q == null) {
if (p.prev == p)
continue whileActive;
break findActive;
}
@@ -710,44 +444,44 @@
// found active CAS target
if (next == p || x.casNext(next, p))
return;
- } while (x.item != null || x.prev == null);
+ } while (x.isAlive() || x.prev == null);
}
/**
* Returns the successor of p, or the first node if p.next has been
* linked to self, which will only be true if traversing with a
* stale pointer that is now off the list.
*/
- final Node<E> succ(Node<E> p) {
+ Finalizer succ(Finalizer p) {
// TODO: should we skip deleted nodes here?
- Node<E> q = p.next;
+ Finalizer q = p.next;
return (p == q) ? first() : q;
}
/**
* Returns the predecessor of p, or the last node if p.prev has been
* linked to self, which will only be true if traversing with a
* stale pointer that is now off the list.
*/
- final Node<E> pred(Node<E> p) {
- Node<E> q = p.prev;
+ Finalizer pred(Finalizer p) {
+ Finalizer q = p.prev;
return (p == q) ? last() : q;
}
/**
* Returns the first node, the unique node p for which:
* p.prev == null && p.next != p
* The returned node may or may not be logically deleted.
* Guarantees that head is set to the returned node.
*/
- Node<E> first() {
+ Finalizer first() {
restartFromHead:
for (;;)
- for (Node<E> h = head, p = h, q;;) {
+ for (Finalizer h = head, p = h, q;;) {
if ((q = p.prev) != null &&
(q = (p = q).prev) != null)
// Check for head updates every other hop.
// If p == q, we are sure to follow head instead.
p = (h != (h = head)) ? h : q;
@@ -765,14 +499,14 @@
* Returns the last node, the unique node p for which:
* p.next == null && p.prev != p
* The returned node may or may not be logically deleted.
* Guarantees that tail is set to the returned node.
*/
- Node<E> last() {
+ Finalizer last() {
restartFromTail:
for (;;)
- for (Node<E> t = tail, p = t, q;;) {
+ for (Finalizer t = tail, p = t, q;;) {
if ((q = p.next) != null &&
(q = (p = q).next) != null)
// Check for tail updates every other hop.
// If p == q, we are sure to follow tail instead.
p = (t != (t = tail)) ? t : q;
@@ -784,803 +518,42 @@
else
continue restartFromTail;
}
}
- // Minor convenience utilities
-
- /**
- * Throws NullPointerException if argument is null.
- *
- * @param v the element
- */
- private static void checkNotNull(Object v) {
- if (v == null)
- throw new NullPointerException();
- }
-
- /**
- * Returns element unless it is null, in which case throws
- * NoSuchElementException.
- *
- * @param v the element
- * @return the element
- */
- private E screenNullResult(E v) {
- if (v == null)
- throw new NoSuchElementException();
- return v;
- }
-
- /**
- * Creates an array list and fills it with elements of this list.
- * Used by toArray.
- *
- * @return the array list
- */
- private ArrayList<E> toArrayList() {
- ArrayList<E> list = new ArrayList<E>();
- for (Node<E> p = first(); p != null; p = succ(p)) {
- E item = p.item;
- if (item != null)
- list.add(item);
- }
- return list;
- }
-
- /**
- * Constructs an empty deque.
- */
- public ConcurrentLinkedDeque() {
- head = tail = new Node<E>(null);
- }
-
/**
- * Constructs a deque initially containing the elements of
- * the given collection, added in traversal order of the
- * collection's iterator.
- *
- * @param c the collection of elements to initially contain
- * @throws NullPointerException if the specified collection or any
- * of its elements are null
+ * Constructs an empty list.
*/
- public ConcurrentLinkedDeque(Collection<? extends E> c) {
- // Copy c into a private chain of Nodes
- Node<E> h = null, t = null;
- for (E e : c) {
- checkNotNull(e);
- Node<E> newNode = new Node<E>(e);
- if (h == null)
- h = t = newNode;
- else {
- t.lazySetNext(newNode);
- newNode.lazySetPrev(t);
- t = newNode;
- }
- }
- initHeadTail(h, t);
- }
-
- /**
- * Initializes head and tail, ensuring invariants hold.
- */
- private void initHeadTail(Node<E> h, Node<E> t) {
- if (h == t) {
- if (h == null)
- h = t = new Node<E>(null);
- else {
- // Avoid edge case of a single Node with non-null item.
- Node<E> newNode = new Node<E>(null);
- t.lazySetNext(newNode);
- newNode.lazySetPrev(t);
- t = newNode;
- }
- }
- head = h;
- tail = t;
- }
-
- /**
- * Inserts the specified element at the front of this deque.
- * As the deque is unbounded, this method will never throw
- * {@link IllegalStateException}.
- *
- * @throws NullPointerException if the specified element is null
- */
- public void addFirst(E e) {
- linkFirst(e);
- }
-
- /**
- * Inserts the specified element at the end of this deque.
- * As the deque is unbounded, this method will never throw
- * {@link IllegalStateException}.
- *
- * <p>This method is equivalent to {@link #add}.
- *
- * @throws NullPointerException if the specified element is null
- */
- public void addLast(E e) {
- linkLast(e);
- }
-
- /**
- * Inserts the specified element at the front of this deque.
- * As the deque is unbounded, this method will never return {@code false}.
- *
- * @return {@code true} (as specified by {@link Deque#offerFirst})
- * @throws NullPointerException if the specified element is null
- */
- public boolean offerFirst(E e) {
- linkFirst(e);
- return true;
- }
-
- /**
- * Inserts the specified element at the end of this deque.
- * As the deque is unbounded, this method will never return {@code false}.
- *
- * <p>This method is equivalent to {@link #add}.
- *
- * @return {@code true} (as specified by {@link Deque#offerLast})
- * @throws NullPointerException if the specified element is null
- */
- public boolean offerLast(E e) {
- linkLast(e);
- return true;
- }
-
- public E peekFirst() {
- for (Node<E> p = first(); p != null; p = succ(p)) {
- E item = p.item;
- if (item != null)
- return item;
- }
- return null;
- }
-
- public E peekLast() {
- for (Node<E> p = last(); p != null; p = pred(p)) {
- E item = p.item;
- if (item != null)
- return item;
- }
- return null;
- }
-
- /**
- * @throws NoSuchElementException {@inheritDoc}
- */
- public E getFirst() {
- return screenNullResult(peekFirst());
- }
-
- /**
- * @throws NoSuchElementException {@inheritDoc}
- */
- public E getLast() {
- return screenNullResult(peekLast());
- }
-
- public E pollFirst() {
- for (Node<E> p = first(); p != null; p = succ(p)) {
- E item = p.item;
- if (item != null && p.casItem(item, null)) {
- unlink(p);
- return item;
- }
- }
- return null;
- }
-
- public E pollLast() {
- for (Node<E> p = last(); p != null; p = pred(p)) {
- E item = p.item;
- if (item != null && p.casItem(item, null)) {
- unlink(p);
- return item;
- }
- }
- return null;
- }
-
- /**
- * @throws NoSuchElementException {@inheritDoc}
- */
- public E removeFirst() {
- return screenNullResult(pollFirst());
- }
-
- /**
- * @throws NoSuchElementException {@inheritDoc}
- */
- public E removeLast() {
- return screenNullResult(pollLast());
- }
-
- // *** Queue and stack methods ***
-
- /**
- * Inserts the specified element at the tail of this deque.
- * As the deque is unbounded, this method will never return {@code false}.
- *
- * @return {@code true} (as specified by {@link Queue#offer})
- * @throws NullPointerException if the specified element is null
- */
- public boolean offer(E e) {
- return offerLast(e);
- }
-
- /**
- * Inserts the specified element at the tail of this deque.
- * As the deque is unbounded, this method will never throw
- * {@link IllegalStateException} or return {@code false}.
- *
- * @return {@code true} (as specified by {@link Collection#add})
- * @throws NullPointerException if the specified element is null
- */
- public boolean add(E e) {
- return offerLast(e);
- }
-
- public E poll() { return pollFirst(); }
- public E peek() { return peekFirst(); }
-
- /**
- * @throws NoSuchElementException {@inheritDoc}
- */
- public E remove() { return removeFirst(); }
-
- /**
- * @throws NoSuchElementException {@inheritDoc}
- */
- public E pop() { return removeFirst(); }
-
- /**
- * @throws NoSuchElementException {@inheritDoc}
- */
- public E element() { return getFirst(); }
-
- /**
- * @throws NullPointerException {@inheritDoc}
- */
- public void push(E e) { addFirst(e); }
-
- /**
- * Removes the first element {@code e} such that
- * {@code o.equals(e)}, if such an element exists in this deque.
- * If the deque does not contain the element, it is unchanged.
- *
- * @param o element to be removed from this deque, if present
- * @return {@code true} if the deque contained the specified element
- * @throws NullPointerException if the specified element is null
- */
- public boolean removeFirstOccurrence(Object o) {
- checkNotNull(o);
- for (Node<E> p = first(); p != null; p = succ(p)) {
- E item = p.item;
- if (item != null && o.equals(item) && p.casItem(item, null)) {
- unlink(p);
- return true;
- }
- }
- return false;
+ FinalizerList() {
+ head = tail = new Finalizer();
}
- /**
- * Removes the last element {@code e} such that
- * {@code o.equals(e)}, if such an element exists in this deque.
- * If the deque does not contain the element, it is unchanged.
- *
- * @param o element to be removed from this deque, if present
- * @return {@code true} if the deque contained the specified element
- * @throws NullPointerException if the specified element is null
- */
- public boolean removeLastOccurrence(Object o) {
- checkNotNull(o);
- for (Node<E> p = last(); p != null; p = pred(p)) {
- E item = p.item;
- if (item != null && o.equals(item) && p.casItem(item, null)) {
- unlink(p);
- return true;
- }
- }
- return false;
- }
-
- /**
- * Returns {@code true} if this deque contains at least one
- * element {@code e} such that {@code o.equals(e)}.
- *
- * @param o element whose presence in this deque is to be tested
- * @return {@code true} if this deque contains the specified element
- */
- public boolean contains(Object o) {
- if (o == null) return false;
- for (Node<E> p = first(); p != null; p = succ(p)) {
- E item = p.item;
- if (item != null && o.equals(item))
- return true;
- }
- return false;
- }
-
- /**
- * Returns {@code true} if this collection contains no elements.
- *
- * @return {@code true} if this collection contains no elements
- */
- public boolean isEmpty() {
- return peekFirst() == null;
- }
-
- /**
- * Returns the number of elements in this deque. If this deque
- * contains more than {@code Integer.MAX_VALUE} elements, it
- * returns {@code Integer.MAX_VALUE}.
- *
- * <p>Beware that, unlike in most collections, this method is
- * <em>NOT</em> a constant-time operation. Because of the
- * asynchronous nature of these deques, determining the current
- * number of elements requires traversing them all to count them.
- * Additionally, it is possible for the size to change during
- * execution of this method, in which case the returned result
- * will be inaccurate. Thus, this method is typically not very
- * useful in concurrent applications.
- *
- * @return the number of elements in this deque
- */
- public int size() {
- int count = 0;
- for (Node<E> p = first(); p != null; p = succ(p))
- if (p.item != null)
- // Collection.size() spec says to max out
- if (++count == Integer.MAX_VALUE)
- break;
- return count;
- }
-
- /**
- * Removes the first element {@code e} such that
- * {@code o.equals(e)}, if such an element exists in this deque.
- * If the deque does not contain the element, it is unchanged.
- *
- * @param o element to be removed from this deque, if present
- * @return {@code true} if the deque contained the specified element
- * @throws NullPointerException if the specified element is null
- */
- public boolean remove(Object o) {
- return removeFirstOccurrence(o);
- }
-
- /**
- * Appends all of the elements in the specified collection to the end of
- * this deque, in the order that they are returned by the specified
- * collection's iterator. Attempts to {@code addAll} of a deque to
- * itself result in {@code IllegalArgumentException}.
- *
- * @param c the elements to be inserted into this deque
- * @return {@code true} if this deque changed as a result of the call
- * @throws NullPointerException if the specified collection or any
- * of its elements are null
- * @throws IllegalArgumentException if the collection is this deque
- */
- public boolean addAll(Collection<? extends E> c) {
- if (c == this)
- // As historically specified in AbstractQueue#addAll
- throw new IllegalArgumentException();
-
- // Copy c into a private chain of Nodes
- Node<E> beginningOfTheEnd = null, last = null;
- for (E e : c) {
- checkNotNull(e);
- Node<E> newNode = new Node<E>(e);
- if (beginningOfTheEnd == null)
- beginningOfTheEnd = last = newNode;
- else {
- last.lazySetNext(newNode);
- newNode.lazySetPrev(last);
- last = newNode;
- }
- }
- if (beginningOfTheEnd == null)
- return false;
-
- // Atomically append the chain at the tail of this collection
- restartFromTail:
- for (;;)
- for (Node<E> t = tail, p = t, q;;) {
- if ((q = p.next) != null &&
- (q = (p = q).next) != null)
- // Check for tail updates every other hop.
- // If p == q, we are sure to follow tail instead.
- p = (t != (t = tail)) ? t : q;
- else if (p.prev == p) // NEXT_TERMINATOR
- continue restartFromTail;
- else {
- // p is last node
- beginningOfTheEnd.lazySetPrev(p); // CAS piggyback
- if (p.casNext(null, beginningOfTheEnd)) {
- // Successful CAS is the linearization point
- // for all elements to be added to this deque.
- if (!casTail(t, last)) {
- // Try a little harder to update tail,
- // since we may be adding many elements.
- t = tail;
- if (last.next == null)
- casTail(t, last);
- }
- return true;
- }
- // Lost CAS race to another thread; re-read next
- }
- }
- }
-
- /**
- * Removes all of the elements from this deque.
- */
- public void clear() {
- while (pollFirst() != null)
- ;
- }
-
- /**
- * Returns an array containing all of the elements in this deque, in
- * proper sequence (from first to last element).
- *
- * <p>The returned array will be "safe" in that no references to it are
- * maintained by this deque. (In other words, this method must allocate
- * a new array). The caller is thus free to modify the returned array.
- *
- * <p>This method acts as bridge between array-based and collection-based
- * APIs.
- *
- * @return an array containing all of the elements in this deque
- */
- public Object[] toArray() {
- return toArrayList().toArray();
- }
-
- /**
- * Returns an array containing all of the elements in this deque,
- * in proper sequence (from first to last element); the runtime
- * type of the returned array is that of the specified array. If
- * the deque fits in the specified array, it is returned therein.
- * Otherwise, a new array is allocated with the runtime type of
- * the specified array and the size of this deque.
- *
- * <p>If this deque fits in the specified array with room to spare
- * (i.e., the array has more elements than this deque), the element in
- * the array immediately following the end of the deque is set to
- * {@code null}.
- *
- * <p>Like the {@link #toArray()} method, this method acts as
- * bridge between array-based and collection-based APIs. Further,
- * this method allows precise control over the runtime type of the
- * output array, and may, under certain circumstances, be used to
- * save allocation costs.
- *
- * <p>Suppose {@code x} is a deque known to contain only strings.
- * The following code can be used to dump the deque into a newly
- * allocated array of {@code String}:
- *
- * <pre> {@code String[] y = x.toArray(new String[0]);}</pre>
- *
- * Note that {@code toArray(new Object[0])} is identical in function to
- * {@code toArray()}.
- *
- * @param a the array into which the elements of the deque are to
- * be stored, if it is big enough; otherwise, a new array of the
- * same runtime type is allocated for this purpose
- * @return an array containing all of the elements in this deque
- * @throws ArrayStoreException if the runtime type of the specified array
- * is not a supertype of the runtime type of every element in
- * this deque
- * @throws NullPointerException if the specified array is null
- */
- public <T> T[] toArray(T[] a) {
- return toArrayList().toArray(a);
- }
-
- /**
- * Returns an iterator over the elements in this deque in proper sequence.
- * The elements will be returned in order from first (head) to last (tail).
- *
- * <p>The returned iterator is
- * <a href="package-summary.html#Weakly"><i>weakly consistent</i></a>.
- *
- * @return an iterator over the elements in this deque in proper sequence
- */
- public Iterator<E> iterator() {
- return new Itr();
- }
-
- /**
- * Returns an iterator over the elements in this deque in reverse
- * sequential order. The elements will be returned in order from
- * last (tail) to first (head).
- *
- * <p>The returned iterator is
- * <a href="package-summary.html#Weakly"><i>weakly consistent</i></a>.
- *
- * @return an iterator over the elements in this deque in reverse order
- */
- public Iterator<E> descendingIterator() {
- return new DescendingItr();
- }
-
- private abstract class AbstractItr implements Iterator<E> {
- /**
- * Next node to return item for.
- */
- private Node<E> nextNode;
-
- /**
- * nextItem holds on to item fields because once we claim
- * that an element exists in hasNext(), we must return it in
- * the following next() call even if it was in the process of
- * being removed when hasNext() was called.
- */
- private E nextItem;
-
- /**
- * Node returned by most recent call to next. Needed by remove.
- * Reset to null if this element is deleted by a call to remove.
- */
- private Node<E> lastRet;
-
- abstract Node<E> startNode();
- abstract Node<E> nextNode(Node<E> p);
-
- AbstractItr() {
- advance();
- }
-
- /**
- * Sets nextNode and nextItem to next valid node, or to null
- * if no such.
- */
- private void advance() {
- lastRet = nextNode;
-
- Node<E> p = (nextNode == null) ? startNode() : nextNode(nextNode);
- for (;; p = nextNode(p)) {
- if (p == null) {
- // p might be active end or TERMINATOR node; both are OK
- nextNode = null;
- nextItem = null;
- break;
- }
- E item = p.item;
- if (item != null) {
- nextNode = p;
- nextItem = item;
- break;
- }
- }
- }
-
- public boolean hasNext() {
- return nextItem != null;
- }
-
- public E next() {
- E item = nextItem;
- if (item == null) throw new NoSuchElementException();
- advance();
- return item;
- }
-
- public void remove() {
- Node<E> l = lastRet;
- if (l == null) throw new IllegalStateException();
- l.item = null;
- unlink(l);
- lastRet = null;
- }
- }
-
- /** Forward iterator */
- private class Itr extends AbstractItr {
- Node<E> startNode() { return first(); }
- Node<E> nextNode(Node<E> p) { return succ(p); }
- }
-
- /** Descending iterator */
- private class DescendingItr extends AbstractItr {
- Node<E> startNode() { return last(); }
- Node<E> nextNode(Node<E> p) { return pred(p); }
- }
-
- /** A customized variant of Spliterators.IteratorSpliterator */
- static final class CLDSpliterator<E> implements Spliterator<E> {
- static final int MAX_BATCH = 1 << 25; // max batch array size;
- final ConcurrentLinkedDeque<E> queue;
- Node<E> current; // current node; null until initialized
- int batch; // batch size for splits
- boolean exhausted; // true when no more nodes
- CLDSpliterator(ConcurrentLinkedDeque<E> queue) {
- this.queue = queue;
- }
-
- public Spliterator<E> trySplit() {
- Node<E> p;
- final ConcurrentLinkedDeque<E> q = this.queue;
- int b = batch;
- int n = (b <= 0) ? 1 : (b >= MAX_BATCH) ? MAX_BATCH : b + 1;
- if (!exhausted &&
- ((p = current) != null || (p = q.first()) != null)) {
- if (p.item == null && p == (p = p.next))
- current = p = q.first();
- if (p != null && p.next != null) {
- Object[] a = new Object[n];
- int i = 0;
- do {
- if ((a[i] = p.item) != null)
- ++i;
- if (p == (p = p.next))
- p = q.first();
- } while (p != null && i < n);
- if ((current = p) == null)
- exhausted = true;
- if (i > 0) {
- batch = i;
- return Spliterators.spliterator
- (a, 0, i, Spliterator.ORDERED | Spliterator.NONNULL |
- Spliterator.CONCURRENT);
- }
- }
- }
- return null;
- }
-
- public void forEachRemaining(Consumer<? super E> action) {
- Node<E> p;
- if (action == null) throw new NullPointerException();
- final ConcurrentLinkedDeque<E> q = this.queue;
- if (!exhausted &&
- ((p = current) != null || (p = q.first()) != null)) {
- exhausted = true;
- do {
- E e = p.item;
- if (p == (p = p.next))
- p = q.first();
- if (e != null)
- action.accept(e);
- } while (p != null);
- }
- }
-
- public boolean tryAdvance(Consumer<? super E> action) {
- Node<E> p;
- if (action == null) throw new NullPointerException();
- final ConcurrentLinkedDeque<E> q = this.queue;
- if (!exhausted &&
- ((p = current) != null || (p = q.first()) != null)) {
- E e;
- do {
- e = p.item;
- if (p == (p = p.next))
- p = q.first();
- } while (e == null && p != null);
- if ((current = p) == null)
- exhausted = true;
- if (e != null) {
- action.accept(e);
- return true;
- }
- }
- return false;
- }
-
- public long estimateSize() { return Long.MAX_VALUE; }
-
- public int characteristics() {
- return Spliterator.ORDERED | Spliterator.NONNULL |
- Spliterator.CONCURRENT;
- }
- }
-
- /**
- * Returns a {@link Spliterator} over the elements in this deque.
- *
- * <p>The returned spliterator is
- * <a href="package-summary.html#Weakly"><i>weakly consistent</i></a>.
- *
- * <p>The {@code Spliterator} reports {@link Spliterator#CONCURRENT},
- * {@link Spliterator#ORDERED}, and {@link Spliterator#NONNULL}.
- *
- * @implNote
- * The {@code Spliterator} implements {@code trySplit} to permit limited
- * parallelism.
- *
- * @return a {@code Spliterator} over the elements in this deque
- * @since 1.8
- */
- public Spliterator<E> spliterator() {
- return new CLDSpliterator<E>(this);
- }
-
- /**
- * Saves this deque to a stream (that is, serializes it).
- *
- * @param s the stream
- * @throws java.io.IOException if an I/O error occurs
- * @serialData All of the elements (each an {@code E}) in
- * the proper order, followed by a null
- */
- private void writeObject(java.io.ObjectOutputStream s)
- throws java.io.IOException {
-
- // Write out any hidden stuff
- s.defaultWriteObject();
-
- // Write out all elements in the proper order.
- for (Node<E> p = first(); p != null; p = succ(p)) {
- E item = p.item;
- if (item != null)
- s.writeObject(item);
- }
-
- // Use trailing null as sentinel
- s.writeObject(null);
- }
-
- /**
- * Reconstitutes this deque from a stream (that is, deserializes it).
- * @param s the stream
- * @throws ClassNotFoundException if the class of a serialized object
- * could not be found
- * @throws java.io.IOException if an I/O error occurs
- */
- private void readObject(java.io.ObjectInputStream s)
- throws java.io.IOException, ClassNotFoundException {
- s.defaultReadObject();
-
- // Read in elements until trailing null sentinel found
- Node<E> h = null, t = null;
- Object item;
- while ((item = s.readObject()) != null) {
- @SuppressWarnings("unchecked")
- Node<E> newNode = new Node<E>((E) item);
- if (h == null)
- h = t = newNode;
- else {
- t.lazySetNext(newNode);
- newNode.lazySetPrev(t);
- t = newNode;
- }
- }
- initHeadTail(h, t);
- }
+ // Unsafe mechanics
- private boolean casHead(Node<E> cmp, Node<E> val) {
- return UNSAFE.compareAndSwapObject(this, headOffset, cmp, val);
+ private boolean casHead(Finalizer cmp, Finalizer val) {
+ return UNSAFE.compareAndSwapObject(this, HEAD, cmp, val);
}
- private boolean casTail(Node<E> cmp, Node<E> val) {
- return UNSAFE.compareAndSwapObject(this, tailOffset, cmp, val);
+ private boolean casTail(Finalizer cmp, Finalizer val) {
+ return UNSAFE.compareAndSwapObject(this, TAIL, cmp, val);
}
- // Unsafe mechanics
-
private static final sun.misc.Unsafe UNSAFE;
- private static final long headOffset;
- private static final long tailOffset;
+ private static final long HEAD;
+ private static final long TAIL;
static {
- PREV_TERMINATOR = new Node<Object>();
+ PREV_TERMINATOR = new Finalizer();
PREV_TERMINATOR.next = PREV_TERMINATOR;
- NEXT_TERMINATOR = new Node<Object>();
+ NEXT_TERMINATOR = new Finalizer();
NEXT_TERMINATOR.prev = NEXT_TERMINATOR;
try {
UNSAFE = sun.misc.Unsafe.getUnsafe();
- Class<?> k = ConcurrentLinkedDeque.class;
- headOffset = UNSAFE.objectFieldOffset
- (k.getDeclaredField("head"));
- tailOffset = UNSAFE.objectFieldOffset
- (k.getDeclaredField("tail"));
+ Class<?> flc = FinalizerList.class;
+ HEAD = UNSAFE.objectFieldOffset
+ (flc.getDeclaredField("head"));
+ TAIL = UNSAFE.objectFieldOffset
+ (flc.getDeclaredField("tail"));
} catch (Exception e) {
throw new Error(e);
}
}
}
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