1 |
dl |
1.2 |
/* |
2 |
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* Written by Doug Lea with assistance from members of JCP JSR-166 |
3 |
dl |
1.33 |
* Expert Group and released to the public domain, as explained at |
4 |
jsr166 |
1.58 |
* http://creativecommons.org/publicdomain/zero/1.0/ |
5 |
dl |
1.2 |
*/ |
6 |
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|
7 |
tim |
1.1 |
package java.util.concurrent; |
8 |
jsr166 |
1.51 |
|
9 |
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import java.util.concurrent.atomic.AtomicInteger; |
10 |
|
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import java.util.concurrent.locks.Condition; |
11 |
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import java.util.concurrent.locks.ReentrantLock; |
12 |
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import java.util.AbstractQueue; |
13 |
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import java.util.Collection; |
14 |
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import java.util.Iterator; |
15 |
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import java.util.NoSuchElementException; |
16 |
tim |
1.1 |
|
17 |
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/** |
18 |
dholmes |
1.14 |
* An optionally-bounded {@linkplain BlockingQueue blocking queue} based on |
19 |
dholmes |
1.8 |
* linked nodes. |
20 |
|
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* This queue orders elements FIFO (first-in-first-out). |
21 |
tim |
1.12 |
* The <em>head</em> of the queue is that element that has been on the |
22 |
dholmes |
1.8 |
* queue the longest time. |
23 |
|
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* The <em>tail</em> of the queue is that element that has been on the |
24 |
dl |
1.20 |
* queue the shortest time. New elements |
25 |
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* are inserted at the tail of the queue, and the queue retrieval |
26 |
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* operations obtain elements at the head of the queue. |
27 |
dholmes |
1.8 |
* Linked queues typically have higher throughput than array-based queues but |
28 |
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* less predictable performance in most concurrent applications. |
29 |
tim |
1.12 |
* |
30 |
dl |
1.3 |
* <p> The optional capacity bound constructor argument serves as a |
31 |
dholmes |
1.8 |
* way to prevent excessive queue expansion. The capacity, if unspecified, |
32 |
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* is equal to {@link Integer#MAX_VALUE}. Linked nodes are |
33 |
dl |
1.3 |
* dynamically created upon each insertion unless this would bring the |
34 |
|
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* queue above capacity. |
35 |
dholmes |
1.8 |
* |
36 |
dl |
1.36 |
* <p>This class and its iterator implement all of the |
37 |
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* <em>optional</em> methods of the {@link Collection} and {@link |
38 |
dl |
1.38 |
* Iterator} interfaces. |
39 |
dl |
1.21 |
* |
40 |
dl |
1.34 |
* <p>This class is a member of the |
41 |
jsr166 |
1.48 |
* <a href="{@docRoot}/../technotes/guides/collections/index.html"> |
42 |
dl |
1.34 |
* Java Collections Framework</a>. |
43 |
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* |
44 |
dl |
1.6 |
* @since 1.5 |
45 |
|
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* @author Doug Lea |
46 |
dl |
1.27 |
* @param <E> the type of elements held in this collection |
47 |
tim |
1.12 |
* |
48 |
jsr166 |
1.40 |
*/ |
49 |
dl |
1.2 |
public class LinkedBlockingQueue<E> extends AbstractQueue<E> |
50 |
tim |
1.1 |
implements BlockingQueue<E>, java.io.Serializable { |
51 |
dl |
1.18 |
private static final long serialVersionUID = -6903933977591709194L; |
52 |
tim |
1.1 |
|
53 |
dl |
1.2 |
/* |
54 |
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* A variant of the "two lock queue" algorithm. The putLock gates |
55 |
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* entry to put (and offer), and has an associated condition for |
56 |
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* waiting puts. Similarly for the takeLock. The "count" field |
57 |
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* that they both rely on is maintained as an atomic to avoid |
58 |
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* needing to get both locks in most cases. Also, to minimize need |
59 |
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* for puts to get takeLock and vice-versa, cascading notifies are |
60 |
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* used. When a put notices that it has enabled at least one take, |
61 |
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* it signals taker. That taker in turn signals others if more |
62 |
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* items have been entered since the signal. And symmetrically for |
63 |
tim |
1.12 |
* takes signalling puts. Operations such as remove(Object) and |
64 |
dl |
1.2 |
* iterators acquire both locks. |
65 |
jsr166 |
1.51 |
* |
66 |
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* Visibility between writers and readers is provided as follows: |
67 |
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* |
68 |
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* Whenever an element is enqueued, the putLock is acquired and |
69 |
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* count updated. A subsequent reader guarantees visibility to the |
70 |
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* enqueued Node by either acquiring the putLock (via fullyLock) |
71 |
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* or by acquiring the takeLock, and then reading n = count.get(); |
72 |
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* this gives visibility to the first n items. |
73 |
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* |
74 |
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* To implement weakly consistent iterators, it appears we need to |
75 |
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* keep all Nodes GC-reachable from a predecessor dequeued Node. |
76 |
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* That would cause two problems: |
77 |
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* - allow a rogue Iterator to cause unbounded memory retention |
78 |
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* - cause cross-generational linking of old Nodes to new Nodes if |
79 |
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* a Node was tenured while live, which generational GCs have a |
80 |
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* hard time dealing with, causing repeated major collections. |
81 |
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* However, only non-deleted Nodes need to be reachable from |
82 |
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* dequeued Nodes, and reachability does not necessarily have to |
83 |
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* be of the kind understood by the GC. We use the trick of |
84 |
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* linking a Node that has just been dequeued to itself. Such a |
85 |
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* self-link implicitly means to advance to head.next. |
86 |
dl |
1.38 |
*/ |
87 |
dl |
1.2 |
|
88 |
dl |
1.6 |
/** |
89 |
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* Linked list node class |
90 |
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*/ |
91 |
dl |
1.2 |
static class Node<E> { |
92 |
jsr166 |
1.51 |
E item; |
93 |
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|
94 |
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/** |
95 |
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* One of: |
96 |
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* - the real successor Node |
97 |
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* - this Node, meaning the successor is head.next |
98 |
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* - null, meaning there is no successor (this is the last node) |
99 |
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*/ |
100 |
dl |
1.2 |
Node<E> next; |
101 |
jsr166 |
1.51 |
|
102 |
dl |
1.2 |
Node(E x) { item = x; } |
103 |
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} |
104 |
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|
105 |
dl |
1.6 |
/** The capacity bound, or Integer.MAX_VALUE if none */ |
106 |
dl |
1.2 |
private final int capacity; |
107 |
dl |
1.6 |
|
108 |
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/** Current number of elements */ |
109 |
jsr166 |
1.61 |
private final AtomicInteger count = new AtomicInteger(); |
110 |
dl |
1.2 |
|
111 |
jsr166 |
1.51 |
/** |
112 |
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* Head of linked list. |
113 |
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* Invariant: head.item == null |
114 |
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*/ |
115 |
dl |
1.6 |
private transient Node<E> head; |
116 |
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|
117 |
jsr166 |
1.51 |
/** |
118 |
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* Tail of linked list. |
119 |
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* Invariant: last.next == null |
120 |
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*/ |
121 |
dl |
1.6 |
private transient Node<E> last; |
122 |
dl |
1.2 |
|
123 |
dl |
1.6 |
/** Lock held by take, poll, etc */ |
124 |
dl |
1.5 |
private final ReentrantLock takeLock = new ReentrantLock(); |
125 |
dl |
1.6 |
|
126 |
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/** Wait queue for waiting takes */ |
127 |
dl |
1.32 |
private final Condition notEmpty = takeLock.newCondition(); |
128 |
dl |
1.2 |
|
129 |
dl |
1.6 |
/** Lock held by put, offer, etc */ |
130 |
dl |
1.5 |
private final ReentrantLock putLock = new ReentrantLock(); |
131 |
dl |
1.6 |
|
132 |
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/** Wait queue for waiting puts */ |
133 |
dl |
1.32 |
private final Condition notFull = putLock.newCondition(); |
134 |
dl |
1.2 |
|
135 |
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/** |
136 |
jsr166 |
1.40 |
* Signals a waiting take. Called only from put/offer (which do not |
137 |
dl |
1.4 |
* otherwise ordinarily lock takeLock.) |
138 |
dl |
1.2 |
*/ |
139 |
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private void signalNotEmpty() { |
140 |
dl |
1.31 |
final ReentrantLock takeLock = this.takeLock; |
141 |
dl |
1.2 |
takeLock.lock(); |
142 |
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try { |
143 |
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notEmpty.signal(); |
144 |
tim |
1.17 |
} finally { |
145 |
dl |
1.2 |
takeLock.unlock(); |
146 |
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} |
147 |
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} |
148 |
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|
149 |
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/** |
150 |
jsr166 |
1.40 |
* Signals a waiting put. Called only from take/poll. |
151 |
dl |
1.2 |
*/ |
152 |
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private void signalNotFull() { |
153 |
dl |
1.31 |
final ReentrantLock putLock = this.putLock; |
154 |
dl |
1.2 |
putLock.lock(); |
155 |
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try { |
156 |
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notFull.signal(); |
157 |
tim |
1.17 |
} finally { |
158 |
dl |
1.2 |
putLock.unlock(); |
159 |
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} |
160 |
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} |
161 |
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|
162 |
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/** |
163 |
dl |
1.54 |
* Links node at end of queue. |
164 |
jsr166 |
1.51 |
* |
165 |
dl |
1.54 |
* @param node the node |
166 |
dl |
1.2 |
*/ |
167 |
dl |
1.54 |
private void enqueue(Node<E> node) { |
168 |
jsr166 |
1.51 |
// assert putLock.isHeldByCurrentThread(); |
169 |
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// assert last.next == null; |
170 |
dl |
1.54 |
last = last.next = node; |
171 |
dl |
1.2 |
} |
172 |
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|
173 |
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/** |
174 |
jsr166 |
1.51 |
* Removes a node from head of queue. |
175 |
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* |
176 |
dl |
1.6 |
* @return the node |
177 |
dl |
1.2 |
*/ |
178 |
jsr166 |
1.51 |
private E dequeue() { |
179 |
|
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// assert takeLock.isHeldByCurrentThread(); |
180 |
|
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// assert head.item == null; |
181 |
dl |
1.50 |
Node<E> h = head; |
182 |
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Node<E> first = h.next; |
183 |
jsr166 |
1.51 |
h.next = h; // help GC |
184 |
dl |
1.2 |
head = first; |
185 |
dl |
1.28 |
E x = first.item; |
186 |
dl |
1.2 |
first.item = null; |
187 |
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return x; |
188 |
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} |
189 |
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|
190 |
|
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/** |
191 |
tim |
1.12 |
* Lock to prevent both puts and takes. |
192 |
dl |
1.2 |
*/ |
193 |
jsr166 |
1.51 |
void fullyLock() { |
194 |
dl |
1.2 |
putLock.lock(); |
195 |
|
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takeLock.lock(); |
196 |
tim |
1.1 |
} |
197 |
dl |
1.2 |
|
198 |
|
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/** |
199 |
tim |
1.12 |
* Unlock to allow both puts and takes. |
200 |
dl |
1.2 |
*/ |
201 |
jsr166 |
1.51 |
void fullyUnlock() { |
202 |
dl |
1.2 |
takeLock.unlock(); |
203 |
|
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putLock.unlock(); |
204 |
|
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} |
205 |
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|
206 |
jsr166 |
1.51 |
// /** |
207 |
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// * Tells whether both locks are held by current thread. |
208 |
|
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// */ |
209 |
|
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// boolean isFullyLocked() { |
210 |
|
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// return (putLock.isHeldByCurrentThread() && |
211 |
|
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// takeLock.isHeldByCurrentThread()); |
212 |
|
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// } |
213 |
dl |
1.2 |
|
214 |
|
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/** |
215 |
jsr166 |
1.51 |
* Creates a {@code LinkedBlockingQueue} with a capacity of |
216 |
dholmes |
1.8 |
* {@link Integer#MAX_VALUE}. |
217 |
dl |
1.2 |
*/ |
218 |
|
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public LinkedBlockingQueue() { |
219 |
|
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this(Integer.MAX_VALUE); |
220 |
|
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} |
221 |
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|
222 |
|
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/** |
223 |
jsr166 |
1.51 |
* Creates a {@code LinkedBlockingQueue} with the given (fixed) capacity. |
224 |
tim |
1.16 |
* |
225 |
jsr166 |
1.43 |
* @param capacity the capacity of this queue |
226 |
jsr166 |
1.51 |
* @throws IllegalArgumentException if {@code capacity} is not greater |
227 |
jsr166 |
1.43 |
* than zero |
228 |
dl |
1.2 |
*/ |
229 |
|
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public LinkedBlockingQueue(int capacity) { |
230 |
dholmes |
1.8 |
if (capacity <= 0) throw new IllegalArgumentException(); |
231 |
dl |
1.2 |
this.capacity = capacity; |
232 |
dl |
1.6 |
last = head = new Node<E>(null); |
233 |
dl |
1.2 |
} |
234 |
|
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|
235 |
|
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/** |
236 |
jsr166 |
1.51 |
* Creates a {@code LinkedBlockingQueue} with a capacity of |
237 |
dholmes |
1.14 |
* {@link Integer#MAX_VALUE}, initially containing the elements of the |
238 |
tim |
1.12 |
* given collection, |
239 |
dholmes |
1.8 |
* added in traversal order of the collection's iterator. |
240 |
jsr166 |
1.43 |
* |
241 |
dholmes |
1.9 |
* @param c the collection of elements to initially contain |
242 |
jsr166 |
1.43 |
* @throws NullPointerException if the specified collection or any |
243 |
|
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* of its elements are null |
244 |
dl |
1.2 |
*/ |
245 |
dholmes |
1.10 |
public LinkedBlockingQueue(Collection<? extends E> c) { |
246 |
dl |
1.2 |
this(Integer.MAX_VALUE); |
247 |
jsr166 |
1.51 |
final ReentrantLock putLock = this.putLock; |
248 |
|
|
putLock.lock(); // Never contended, but necessary for visibility |
249 |
|
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try { |
250 |
|
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int n = 0; |
251 |
|
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for (E e : c) { |
252 |
|
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if (e == null) |
253 |
|
|
throw new NullPointerException(); |
254 |
|
|
if (n == capacity) |
255 |
|
|
throw new IllegalStateException("Queue full"); |
256 |
dl |
1.54 |
enqueue(new Node<E>(e)); |
257 |
jsr166 |
1.51 |
++n; |
258 |
|
|
} |
259 |
|
|
count.set(n); |
260 |
|
|
} finally { |
261 |
|
|
putLock.unlock(); |
262 |
|
|
} |
263 |
dl |
1.2 |
} |
264 |
|
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|
265 |
dholmes |
1.9 |
|
266 |
dholmes |
1.8 |
// this doc comment is overridden to remove the reference to collections |
267 |
|
|
// greater in size than Integer.MAX_VALUE |
268 |
tim |
1.12 |
/** |
269 |
dl |
1.20 |
* Returns the number of elements in this queue. |
270 |
|
|
* |
271 |
jsr166 |
1.43 |
* @return the number of elements in this queue |
272 |
dholmes |
1.8 |
*/ |
273 |
dl |
1.2 |
public int size() { |
274 |
|
|
return count.get(); |
275 |
tim |
1.1 |
} |
276 |
dl |
1.2 |
|
277 |
dholmes |
1.8 |
// this doc comment is a modified copy of the inherited doc comment, |
278 |
|
|
// without the reference to unlimited queues. |
279 |
tim |
1.12 |
/** |
280 |
jsr166 |
1.41 |
* Returns the number of additional elements that this queue can ideally |
281 |
|
|
* (in the absence of memory or resource constraints) accept without |
282 |
dholmes |
1.8 |
* blocking. This is always equal to the initial capacity of this queue |
283 |
jsr166 |
1.51 |
* less the current {@code size} of this queue. |
284 |
jsr166 |
1.41 |
* |
285 |
|
|
* <p>Note that you <em>cannot</em> always tell if an attempt to insert |
286 |
jsr166 |
1.51 |
* an element will succeed by inspecting {@code remainingCapacity} |
287 |
jsr166 |
1.41 |
* because it may be the case that another thread is about to |
288 |
jsr166 |
1.43 |
* insert or remove an element. |
289 |
dholmes |
1.8 |
*/ |
290 |
dl |
1.2 |
public int remainingCapacity() { |
291 |
|
|
return capacity - count.get(); |
292 |
|
|
} |
293 |
|
|
|
294 |
dholmes |
1.22 |
/** |
295 |
jsr166 |
1.44 |
* Inserts the specified element at the tail of this queue, waiting if |
296 |
dholmes |
1.22 |
* necessary for space to become available. |
297 |
jsr166 |
1.43 |
* |
298 |
|
|
* @throws InterruptedException {@inheritDoc} |
299 |
|
|
* @throws NullPointerException {@inheritDoc} |
300 |
dholmes |
1.22 |
*/ |
301 |
jsr166 |
1.42 |
public void put(E e) throws InterruptedException { |
302 |
|
|
if (e == null) throw new NullPointerException(); |
303 |
jsr166 |
1.51 |
// Note: convention in all put/take/etc is to preset local var |
304 |
|
|
// holding count negative to indicate failure unless set. |
305 |
tim |
1.12 |
int c = -1; |
306 |
jsr166 |
1.60 |
Node<E> node = new Node<E>(e); |
307 |
dl |
1.31 |
final ReentrantLock putLock = this.putLock; |
308 |
|
|
final AtomicInteger count = this.count; |
309 |
dl |
1.2 |
putLock.lockInterruptibly(); |
310 |
|
|
try { |
311 |
|
|
/* |
312 |
|
|
* Note that count is used in wait guard even though it is |
313 |
|
|
* not protected by lock. This works because count can |
314 |
|
|
* only decrease at this point (all other puts are shut |
315 |
|
|
* out by lock), and we (or some other waiting put) are |
316 |
jsr166 |
1.51 |
* signalled if it ever changes from capacity. Similarly |
317 |
|
|
* for all other uses of count in other wait guards. |
318 |
dl |
1.2 |
*/ |
319 |
jsr166 |
1.51 |
while (count.get() == capacity) { |
320 |
|
|
notFull.await(); |
321 |
dl |
1.2 |
} |
322 |
dl |
1.54 |
enqueue(node); |
323 |
dl |
1.2 |
c = count.getAndIncrement(); |
324 |
dl |
1.6 |
if (c + 1 < capacity) |
325 |
dl |
1.2 |
notFull.signal(); |
326 |
tim |
1.17 |
} finally { |
327 |
dl |
1.2 |
putLock.unlock(); |
328 |
|
|
} |
329 |
tim |
1.12 |
if (c == 0) |
330 |
dl |
1.2 |
signalNotEmpty(); |
331 |
tim |
1.1 |
} |
332 |
dl |
1.2 |
|
333 |
dholmes |
1.22 |
/** |
334 |
|
|
* Inserts the specified element at the tail of this queue, waiting if |
335 |
|
|
* necessary up to the specified wait time for space to become available. |
336 |
jsr166 |
1.43 |
* |
337 |
jsr166 |
1.51 |
* @return {@code true} if successful, or {@code false} if |
338 |
jsr166 |
1.43 |
* the specified waiting time elapses before space is available. |
339 |
|
|
* @throws InterruptedException {@inheritDoc} |
340 |
|
|
* @throws NullPointerException {@inheritDoc} |
341 |
dholmes |
1.22 |
*/ |
342 |
jsr166 |
1.42 |
public boolean offer(E e, long timeout, TimeUnit unit) |
343 |
dholmes |
1.8 |
throws InterruptedException { |
344 |
tim |
1.12 |
|
345 |
jsr166 |
1.42 |
if (e == null) throw new NullPointerException(); |
346 |
dl |
1.2 |
long nanos = unit.toNanos(timeout); |
347 |
|
|
int c = -1; |
348 |
dl |
1.31 |
final ReentrantLock putLock = this.putLock; |
349 |
|
|
final AtomicInteger count = this.count; |
350 |
dholmes |
1.8 |
putLock.lockInterruptibly(); |
351 |
dl |
1.2 |
try { |
352 |
jsr166 |
1.51 |
while (count.get() == capacity) { |
353 |
dl |
1.2 |
if (nanos <= 0) |
354 |
|
|
return false; |
355 |
jsr166 |
1.51 |
nanos = notFull.awaitNanos(nanos); |
356 |
dl |
1.2 |
} |
357 |
dl |
1.54 |
enqueue(new Node<E>(e)); |
358 |
jsr166 |
1.51 |
c = count.getAndIncrement(); |
359 |
|
|
if (c + 1 < capacity) |
360 |
|
|
notFull.signal(); |
361 |
tim |
1.17 |
} finally { |
362 |
dl |
1.2 |
putLock.unlock(); |
363 |
|
|
} |
364 |
tim |
1.12 |
if (c == 0) |
365 |
dl |
1.2 |
signalNotEmpty(); |
366 |
|
|
return true; |
367 |
tim |
1.1 |
} |
368 |
dl |
1.2 |
|
369 |
dl |
1.23 |
/** |
370 |
jsr166 |
1.44 |
* Inserts the specified element at the tail of this queue if it is |
371 |
|
|
* possible to do so immediately without exceeding the queue's capacity, |
372 |
jsr166 |
1.51 |
* returning {@code true} upon success and {@code false} if this queue |
373 |
jsr166 |
1.44 |
* is full. |
374 |
|
|
* When using a capacity-restricted queue, this method is generally |
375 |
|
|
* preferable to method {@link BlockingQueue#add add}, which can fail to |
376 |
|
|
* insert an element only by throwing an exception. |
377 |
dl |
1.23 |
* |
378 |
jsr166 |
1.43 |
* @throws NullPointerException if the specified element is null |
379 |
dl |
1.23 |
*/ |
380 |
jsr166 |
1.42 |
public boolean offer(E e) { |
381 |
|
|
if (e == null) throw new NullPointerException(); |
382 |
dl |
1.31 |
final AtomicInteger count = this.count; |
383 |
dl |
1.2 |
if (count.get() == capacity) |
384 |
|
|
return false; |
385 |
tim |
1.12 |
int c = -1; |
386 |
jsr166 |
1.60 |
Node<E> node = new Node<E>(e); |
387 |
dl |
1.31 |
final ReentrantLock putLock = this.putLock; |
388 |
dholmes |
1.8 |
putLock.lock(); |
389 |
dl |
1.2 |
try { |
390 |
|
|
if (count.get() < capacity) { |
391 |
dl |
1.54 |
enqueue(node); |
392 |
dl |
1.2 |
c = count.getAndIncrement(); |
393 |
dl |
1.6 |
if (c + 1 < capacity) |
394 |
dl |
1.2 |
notFull.signal(); |
395 |
|
|
} |
396 |
tim |
1.17 |
} finally { |
397 |
dl |
1.2 |
putLock.unlock(); |
398 |
|
|
} |
399 |
tim |
1.12 |
if (c == 0) |
400 |
dl |
1.2 |
signalNotEmpty(); |
401 |
|
|
return c >= 0; |
402 |
tim |
1.1 |
} |
403 |
dl |
1.2 |
|
404 |
|
|
|
405 |
|
|
public E take() throws InterruptedException { |
406 |
|
|
E x; |
407 |
|
|
int c = -1; |
408 |
dl |
1.31 |
final AtomicInteger count = this.count; |
409 |
|
|
final ReentrantLock takeLock = this.takeLock; |
410 |
dl |
1.2 |
takeLock.lockInterruptibly(); |
411 |
|
|
try { |
412 |
jsr166 |
1.51 |
while (count.get() == 0) { |
413 |
|
|
notEmpty.await(); |
414 |
dl |
1.2 |
} |
415 |
jsr166 |
1.51 |
x = dequeue(); |
416 |
dl |
1.2 |
c = count.getAndDecrement(); |
417 |
|
|
if (c > 1) |
418 |
|
|
notEmpty.signal(); |
419 |
tim |
1.17 |
} finally { |
420 |
dl |
1.2 |
takeLock.unlock(); |
421 |
|
|
} |
422 |
tim |
1.12 |
if (c == capacity) |
423 |
dl |
1.2 |
signalNotFull(); |
424 |
|
|
return x; |
425 |
|
|
} |
426 |
|
|
|
427 |
|
|
public E poll(long timeout, TimeUnit unit) throws InterruptedException { |
428 |
|
|
E x = null; |
429 |
|
|
int c = -1; |
430 |
dholmes |
1.8 |
long nanos = unit.toNanos(timeout); |
431 |
dl |
1.31 |
final AtomicInteger count = this.count; |
432 |
|
|
final ReentrantLock takeLock = this.takeLock; |
433 |
dl |
1.2 |
takeLock.lockInterruptibly(); |
434 |
|
|
try { |
435 |
jsr166 |
1.51 |
while (count.get() == 0) { |
436 |
dl |
1.2 |
if (nanos <= 0) |
437 |
|
|
return null; |
438 |
jsr166 |
1.51 |
nanos = notEmpty.awaitNanos(nanos); |
439 |
dl |
1.2 |
} |
440 |
jsr166 |
1.51 |
x = dequeue(); |
441 |
|
|
c = count.getAndDecrement(); |
442 |
|
|
if (c > 1) |
443 |
|
|
notEmpty.signal(); |
444 |
tim |
1.17 |
} finally { |
445 |
dl |
1.2 |
takeLock.unlock(); |
446 |
|
|
} |
447 |
tim |
1.12 |
if (c == capacity) |
448 |
dl |
1.2 |
signalNotFull(); |
449 |
|
|
return x; |
450 |
|
|
} |
451 |
|
|
|
452 |
|
|
public E poll() { |
453 |
dl |
1.31 |
final AtomicInteger count = this.count; |
454 |
dl |
1.2 |
if (count.get() == 0) |
455 |
|
|
return null; |
456 |
|
|
E x = null; |
457 |
tim |
1.12 |
int c = -1; |
458 |
dl |
1.31 |
final ReentrantLock takeLock = this.takeLock; |
459 |
dl |
1.30 |
takeLock.lock(); |
460 |
dl |
1.2 |
try { |
461 |
|
|
if (count.get() > 0) { |
462 |
jsr166 |
1.51 |
x = dequeue(); |
463 |
dl |
1.2 |
c = count.getAndDecrement(); |
464 |
|
|
if (c > 1) |
465 |
|
|
notEmpty.signal(); |
466 |
|
|
} |
467 |
tim |
1.17 |
} finally { |
468 |
dl |
1.2 |
takeLock.unlock(); |
469 |
|
|
} |
470 |
tim |
1.12 |
if (c == capacity) |
471 |
dl |
1.2 |
signalNotFull(); |
472 |
|
|
return x; |
473 |
tim |
1.1 |
} |
474 |
dl |
1.2 |
|
475 |
|
|
public E peek() { |
476 |
|
|
if (count.get() == 0) |
477 |
|
|
return null; |
478 |
dl |
1.31 |
final ReentrantLock takeLock = this.takeLock; |
479 |
dholmes |
1.8 |
takeLock.lock(); |
480 |
dl |
1.2 |
try { |
481 |
|
|
Node<E> first = head.next; |
482 |
|
|
if (first == null) |
483 |
|
|
return null; |
484 |
|
|
else |
485 |
|
|
return first.item; |
486 |
tim |
1.17 |
} finally { |
487 |
dl |
1.2 |
takeLock.unlock(); |
488 |
|
|
} |
489 |
tim |
1.1 |
} |
490 |
|
|
|
491 |
dl |
1.35 |
/** |
492 |
jsr166 |
1.51 |
* Unlinks interior Node p with predecessor trail. |
493 |
|
|
*/ |
494 |
|
|
void unlink(Node<E> p, Node<E> trail) { |
495 |
|
|
// assert isFullyLocked(); |
496 |
|
|
// p.next is not changed, to allow iterators that are |
497 |
|
|
// traversing p to maintain their weak-consistency guarantee. |
498 |
|
|
p.item = null; |
499 |
|
|
trail.next = p.next; |
500 |
|
|
if (last == p) |
501 |
|
|
last = trail; |
502 |
|
|
if (count.getAndDecrement() == capacity) |
503 |
|
|
notFull.signal(); |
504 |
|
|
} |
505 |
|
|
|
506 |
|
|
/** |
507 |
jsr166 |
1.44 |
* Removes a single instance of the specified element from this queue, |
508 |
jsr166 |
1.51 |
* if it is present. More formally, removes an element {@code e} such |
509 |
|
|
* that {@code o.equals(e)}, if this queue contains one or more such |
510 |
jsr166 |
1.44 |
* elements. |
511 |
jsr166 |
1.51 |
* Returns {@code true} if this queue contained the specified element |
512 |
jsr166 |
1.44 |
* (or equivalently, if this queue changed as a result of the call). |
513 |
|
|
* |
514 |
|
|
* @param o element to be removed from this queue, if present |
515 |
jsr166 |
1.51 |
* @return {@code true} if this queue changed as a result of the call |
516 |
dl |
1.35 |
*/ |
517 |
dholmes |
1.9 |
public boolean remove(Object o) { |
518 |
|
|
if (o == null) return false; |
519 |
dl |
1.2 |
fullyLock(); |
520 |
|
|
try { |
521 |
jsr166 |
1.51 |
for (Node<E> trail = head, p = trail.next; |
522 |
|
|
p != null; |
523 |
|
|
trail = p, p = p.next) { |
524 |
dholmes |
1.9 |
if (o.equals(p.item)) { |
525 |
jsr166 |
1.51 |
unlink(p, trail); |
526 |
|
|
return true; |
527 |
dl |
1.2 |
} |
528 |
|
|
} |
529 |
jsr166 |
1.51 |
return false; |
530 |
tim |
1.17 |
} finally { |
531 |
dl |
1.2 |
fullyUnlock(); |
532 |
|
|
} |
533 |
tim |
1.1 |
} |
534 |
dl |
1.2 |
|
535 |
jsr166 |
1.43 |
/** |
536 |
jsr166 |
1.56 |
* Returns {@code true} if this queue contains the specified element. |
537 |
|
|
* More formally, returns {@code true} if and only if this queue contains |
538 |
|
|
* at least one element {@code e} such that {@code o.equals(e)}. |
539 |
|
|
* |
540 |
|
|
* @param o object to be checked for containment in this queue |
541 |
|
|
* @return {@code true} if this queue contains the specified element |
542 |
|
|
*/ |
543 |
|
|
public boolean contains(Object o) { |
544 |
|
|
if (o == null) return false; |
545 |
|
|
fullyLock(); |
546 |
|
|
try { |
547 |
|
|
for (Node<E> p = head.next; p != null; p = p.next) |
548 |
|
|
if (o.equals(p.item)) |
549 |
|
|
return true; |
550 |
|
|
return false; |
551 |
|
|
} finally { |
552 |
|
|
fullyUnlock(); |
553 |
|
|
} |
554 |
|
|
} |
555 |
|
|
|
556 |
|
|
/** |
557 |
jsr166 |
1.43 |
* Returns an array containing all of the elements in this queue, in |
558 |
|
|
* proper sequence. |
559 |
|
|
* |
560 |
|
|
* <p>The returned array will be "safe" in that no references to it are |
561 |
|
|
* maintained by this queue. (In other words, this method must allocate |
562 |
|
|
* a new array). The caller is thus free to modify the returned array. |
563 |
jsr166 |
1.45 |
* |
564 |
jsr166 |
1.43 |
* <p>This method acts as bridge between array-based and collection-based |
565 |
|
|
* APIs. |
566 |
|
|
* |
567 |
|
|
* @return an array containing all of the elements in this queue |
568 |
|
|
*/ |
569 |
dl |
1.2 |
public Object[] toArray() { |
570 |
|
|
fullyLock(); |
571 |
|
|
try { |
572 |
|
|
int size = count.get(); |
573 |
tim |
1.12 |
Object[] a = new Object[size]; |
574 |
dl |
1.2 |
int k = 0; |
575 |
tim |
1.12 |
for (Node<E> p = head.next; p != null; p = p.next) |
576 |
dl |
1.2 |
a[k++] = p.item; |
577 |
|
|
return a; |
578 |
tim |
1.17 |
} finally { |
579 |
dl |
1.2 |
fullyUnlock(); |
580 |
|
|
} |
581 |
tim |
1.1 |
} |
582 |
dl |
1.2 |
|
583 |
jsr166 |
1.43 |
/** |
584 |
|
|
* Returns an array containing all of the elements in this queue, in |
585 |
|
|
* proper sequence; the runtime type of the returned array is that of |
586 |
|
|
* the specified array. If the queue fits in the specified array, it |
587 |
|
|
* is returned therein. Otherwise, a new array is allocated with the |
588 |
|
|
* runtime type of the specified array and the size of this queue. |
589 |
|
|
* |
590 |
|
|
* <p>If this queue fits in the specified array with room to spare |
591 |
|
|
* (i.e., the array has more elements than this queue), the element in |
592 |
|
|
* the array immediately following the end of the queue is set to |
593 |
jsr166 |
1.51 |
* {@code null}. |
594 |
jsr166 |
1.43 |
* |
595 |
|
|
* <p>Like the {@link #toArray()} method, this method acts as bridge between |
596 |
|
|
* array-based and collection-based APIs. Further, this method allows |
597 |
|
|
* precise control over the runtime type of the output array, and may, |
598 |
|
|
* under certain circumstances, be used to save allocation costs. |
599 |
|
|
* |
600 |
jsr166 |
1.51 |
* <p>Suppose {@code x} is a queue known to contain only strings. |
601 |
jsr166 |
1.43 |
* The following code can be used to dump the queue into a newly |
602 |
jsr166 |
1.51 |
* allocated array of {@code String}: |
603 |
jsr166 |
1.43 |
* |
604 |
jsr166 |
1.62 |
* <pre> {@code String[] y = x.toArray(new String[0]);}</pre> |
605 |
jsr166 |
1.43 |
* |
606 |
jsr166 |
1.51 |
* Note that {@code toArray(new Object[0])} is identical in function to |
607 |
|
|
* {@code toArray()}. |
608 |
jsr166 |
1.43 |
* |
609 |
|
|
* @param a the array into which the elements of the queue are to |
610 |
|
|
* be stored, if it is big enough; otherwise, a new array of the |
611 |
|
|
* same runtime type is allocated for this purpose |
612 |
|
|
* @return an array containing all of the elements in this queue |
613 |
|
|
* @throws ArrayStoreException if the runtime type of the specified array |
614 |
|
|
* is not a supertype of the runtime type of every element in |
615 |
|
|
* this queue |
616 |
|
|
* @throws NullPointerException if the specified array is null |
617 |
|
|
*/ |
618 |
jsr166 |
1.51 |
@SuppressWarnings("unchecked") |
619 |
dl |
1.2 |
public <T> T[] toArray(T[] a) { |
620 |
|
|
fullyLock(); |
621 |
|
|
try { |
622 |
|
|
int size = count.get(); |
623 |
|
|
if (a.length < size) |
624 |
dl |
1.4 |
a = (T[])java.lang.reflect.Array.newInstance |
625 |
|
|
(a.getClass().getComponentType(), size); |
626 |
tim |
1.12 |
|
627 |
dl |
1.2 |
int k = 0; |
628 |
jsr166 |
1.51 |
for (Node<E> p = head.next; p != null; p = p.next) |
629 |
dl |
1.2 |
a[k++] = (T)p.item; |
630 |
jsr166 |
1.47 |
if (a.length > k) |
631 |
|
|
a[k] = null; |
632 |
dl |
1.2 |
return a; |
633 |
tim |
1.17 |
} finally { |
634 |
dl |
1.2 |
fullyUnlock(); |
635 |
|
|
} |
636 |
tim |
1.1 |
} |
637 |
dl |
1.2 |
|
638 |
|
|
public String toString() { |
639 |
|
|
fullyLock(); |
640 |
|
|
try { |
641 |
jsr166 |
1.55 |
Node<E> p = head.next; |
642 |
|
|
if (p == null) |
643 |
|
|
return "[]"; |
644 |
|
|
|
645 |
|
|
StringBuilder sb = new StringBuilder(); |
646 |
|
|
sb.append('['); |
647 |
|
|
for (;;) { |
648 |
|
|
E e = p.item; |
649 |
|
|
sb.append(e == this ? "(this Collection)" : e); |
650 |
|
|
p = p.next; |
651 |
|
|
if (p == null) |
652 |
|
|
return sb.append(']').toString(); |
653 |
|
|
sb.append(',').append(' '); |
654 |
|
|
} |
655 |
tim |
1.17 |
} finally { |
656 |
dl |
1.2 |
fullyUnlock(); |
657 |
|
|
} |
658 |
tim |
1.1 |
} |
659 |
dl |
1.2 |
|
660 |
dl |
1.35 |
/** |
661 |
|
|
* Atomically removes all of the elements from this queue. |
662 |
|
|
* The queue will be empty after this call returns. |
663 |
|
|
*/ |
664 |
dl |
1.24 |
public void clear() { |
665 |
|
|
fullyLock(); |
666 |
|
|
try { |
667 |
jsr166 |
1.51 |
for (Node<E> p, h = head; (p = h.next) != null; h = p) { |
668 |
|
|
h.next = h; |
669 |
|
|
p.item = null; |
670 |
|
|
} |
671 |
|
|
head = last; |
672 |
|
|
// assert head.item == null && head.next == null; |
673 |
dl |
1.24 |
if (count.getAndSet(0) == capacity) |
674 |
jsr166 |
1.51 |
notFull.signal(); |
675 |
dl |
1.24 |
} finally { |
676 |
|
|
fullyUnlock(); |
677 |
|
|
} |
678 |
|
|
} |
679 |
|
|
|
680 |
jsr166 |
1.43 |
/** |
681 |
|
|
* @throws UnsupportedOperationException {@inheritDoc} |
682 |
|
|
* @throws ClassCastException {@inheritDoc} |
683 |
|
|
* @throws NullPointerException {@inheritDoc} |
684 |
|
|
* @throws IllegalArgumentException {@inheritDoc} |
685 |
|
|
*/ |
686 |
dl |
1.24 |
public int drainTo(Collection<? super E> c) { |
687 |
jsr166 |
1.51 |
return drainTo(c, Integer.MAX_VALUE); |
688 |
dl |
1.24 |
} |
689 |
jsr166 |
1.40 |
|
690 |
jsr166 |
1.43 |
/** |
691 |
|
|
* @throws UnsupportedOperationException {@inheritDoc} |
692 |
|
|
* @throws ClassCastException {@inheritDoc} |
693 |
|
|
* @throws NullPointerException {@inheritDoc} |
694 |
|
|
* @throws IllegalArgumentException {@inheritDoc} |
695 |
|
|
*/ |
696 |
dl |
1.24 |
public int drainTo(Collection<? super E> c, int maxElements) { |
697 |
|
|
if (c == null) |
698 |
|
|
throw new NullPointerException(); |
699 |
|
|
if (c == this) |
700 |
|
|
throw new IllegalArgumentException(); |
701 |
jsr166 |
1.63 |
if (maxElements <= 0) |
702 |
|
|
return 0; |
703 |
jsr166 |
1.51 |
boolean signalNotFull = false; |
704 |
|
|
final ReentrantLock takeLock = this.takeLock; |
705 |
|
|
takeLock.lock(); |
706 |
dl |
1.24 |
try { |
707 |
jsr166 |
1.51 |
int n = Math.min(maxElements, count.get()); |
708 |
|
|
// count.get provides visibility to first n Nodes |
709 |
|
|
Node<E> h = head; |
710 |
|
|
int i = 0; |
711 |
|
|
try { |
712 |
|
|
while (i < n) { |
713 |
|
|
Node<E> p = h.next; |
714 |
|
|
c.add(p.item); |
715 |
|
|
p.item = null; |
716 |
|
|
h.next = h; |
717 |
|
|
h = p; |
718 |
|
|
++i; |
719 |
|
|
} |
720 |
|
|
return n; |
721 |
|
|
} finally { |
722 |
|
|
// Restore invariants even if c.add() threw |
723 |
|
|
if (i > 0) { |
724 |
|
|
// assert h.item == null; |
725 |
|
|
head = h; |
726 |
|
|
signalNotFull = (count.getAndAdd(-i) == capacity); |
727 |
|
|
} |
728 |
dl |
1.24 |
} |
729 |
|
|
} finally { |
730 |
jsr166 |
1.51 |
takeLock.unlock(); |
731 |
|
|
if (signalNotFull) |
732 |
|
|
signalNotFull(); |
733 |
dl |
1.24 |
} |
734 |
|
|
} |
735 |
|
|
|
736 |
dholmes |
1.14 |
/** |
737 |
|
|
* Returns an iterator over the elements in this queue in proper sequence. |
738 |
jsr166 |
1.57 |
* The elements will be returned in order from first (head) to last (tail). |
739 |
|
|
* |
740 |
|
|
* <p>The returned iterator is a "weakly consistent" iterator that |
741 |
jsr166 |
1.52 |
* will never throw {@link java.util.ConcurrentModificationException |
742 |
jsr166 |
1.57 |
* ConcurrentModificationException}, and guarantees to traverse |
743 |
|
|
* elements as they existed upon construction of the iterator, and |
744 |
|
|
* may (but is not guaranteed to) reflect any modifications |
745 |
|
|
* subsequent to construction. |
746 |
dholmes |
1.14 |
* |
747 |
jsr166 |
1.43 |
* @return an iterator over the elements in this queue in proper sequence |
748 |
dholmes |
1.14 |
*/ |
749 |
dl |
1.2 |
public Iterator<E> iterator() { |
750 |
jsr166 |
1.59 |
return new Itr(); |
751 |
tim |
1.1 |
} |
752 |
dl |
1.2 |
|
753 |
|
|
private class Itr implements Iterator<E> { |
754 |
tim |
1.12 |
/* |
755 |
jsr166 |
1.51 |
* Basic weakly-consistent iterator. At all times hold the next |
756 |
dl |
1.4 |
* item to hand out so that if hasNext() reports true, we will |
757 |
|
|
* still have it to return even if lost race with a take etc. |
758 |
|
|
*/ |
759 |
dl |
1.31 |
private Node<E> current; |
760 |
|
|
private Node<E> lastRet; |
761 |
|
|
private E currentElement; |
762 |
tim |
1.12 |
|
763 |
dl |
1.2 |
Itr() { |
764 |
jsr166 |
1.51 |
fullyLock(); |
765 |
dl |
1.2 |
try { |
766 |
|
|
current = head.next; |
767 |
dl |
1.4 |
if (current != null) |
768 |
|
|
currentElement = current.item; |
769 |
tim |
1.17 |
} finally { |
770 |
jsr166 |
1.51 |
fullyUnlock(); |
771 |
dl |
1.2 |
} |
772 |
|
|
} |
773 |
tim |
1.12 |
|
774 |
|
|
public boolean hasNext() { |
775 |
dl |
1.2 |
return current != null; |
776 |
|
|
} |
777 |
|
|
|
778 |
jsr166 |
1.51 |
/** |
779 |
jsr166 |
1.53 |
* Returns the next live successor of p, or null if no such. |
780 |
|
|
* |
781 |
|
|
* Unlike other traversal methods, iterators need to handle both: |
782 |
jsr166 |
1.51 |
* - dequeued nodes (p.next == p) |
783 |
jsr166 |
1.53 |
* - (possibly multiple) interior removed nodes (p.item == null) |
784 |
jsr166 |
1.51 |
*/ |
785 |
|
|
private Node<E> nextNode(Node<E> p) { |
786 |
jsr166 |
1.53 |
for (;;) { |
787 |
|
|
Node<E> s = p.next; |
788 |
|
|
if (s == p) |
789 |
|
|
return head.next; |
790 |
|
|
if (s == null || s.item != null) |
791 |
|
|
return s; |
792 |
|
|
p = s; |
793 |
|
|
} |
794 |
jsr166 |
1.51 |
} |
795 |
|
|
|
796 |
tim |
1.12 |
public E next() { |
797 |
jsr166 |
1.51 |
fullyLock(); |
798 |
dl |
1.2 |
try { |
799 |
|
|
if (current == null) |
800 |
|
|
throw new NoSuchElementException(); |
801 |
dl |
1.4 |
E x = currentElement; |
802 |
dl |
1.2 |
lastRet = current; |
803 |
jsr166 |
1.51 |
current = nextNode(current); |
804 |
|
|
currentElement = (current == null) ? null : current.item; |
805 |
dl |
1.2 |
return x; |
806 |
tim |
1.17 |
} finally { |
807 |
jsr166 |
1.51 |
fullyUnlock(); |
808 |
dl |
1.2 |
} |
809 |
|
|
} |
810 |
|
|
|
811 |
tim |
1.12 |
public void remove() { |
812 |
dl |
1.2 |
if (lastRet == null) |
813 |
tim |
1.12 |
throw new IllegalStateException(); |
814 |
jsr166 |
1.51 |
fullyLock(); |
815 |
dl |
1.2 |
try { |
816 |
|
|
Node<E> node = lastRet; |
817 |
|
|
lastRet = null; |
818 |
jsr166 |
1.51 |
for (Node<E> trail = head, p = trail.next; |
819 |
|
|
p != null; |
820 |
|
|
trail = p, p = p.next) { |
821 |
|
|
if (p == node) { |
822 |
|
|
unlink(p, trail); |
823 |
|
|
break; |
824 |
|
|
} |
825 |
dl |
1.2 |
} |
826 |
tim |
1.17 |
} finally { |
827 |
jsr166 |
1.51 |
fullyUnlock(); |
828 |
dl |
1.2 |
} |
829 |
|
|
} |
830 |
tim |
1.1 |
} |
831 |
dl |
1.2 |
|
832 |
|
|
/** |
833 |
|
|
* Save the state to a stream (that is, serialize it). |
834 |
|
|
* |
835 |
|
|
* @serialData The capacity is emitted (int), followed by all of |
836 |
jsr166 |
1.51 |
* its elements (each an {@code Object}) in the proper order, |
837 |
dl |
1.2 |
* followed by a null |
838 |
dl |
1.6 |
* @param s the stream |
839 |
dl |
1.2 |
*/ |
840 |
|
|
private void writeObject(java.io.ObjectOutputStream s) |
841 |
|
|
throws java.io.IOException { |
842 |
|
|
|
843 |
tim |
1.12 |
fullyLock(); |
844 |
dl |
1.2 |
try { |
845 |
|
|
// Write out any hidden stuff, plus capacity |
846 |
|
|
s.defaultWriteObject(); |
847 |
|
|
|
848 |
|
|
// Write out all elements in the proper order. |
849 |
tim |
1.12 |
for (Node<E> p = head.next; p != null; p = p.next) |
850 |
dl |
1.2 |
s.writeObject(p.item); |
851 |
|
|
|
852 |
|
|
// Use trailing null as sentinel |
853 |
|
|
s.writeObject(null); |
854 |
tim |
1.17 |
} finally { |
855 |
dl |
1.2 |
fullyUnlock(); |
856 |
|
|
} |
857 |
tim |
1.1 |
} |
858 |
|
|
|
859 |
dl |
1.2 |
/** |
860 |
dholmes |
1.8 |
* Reconstitute this queue instance from a stream (that is, |
861 |
dl |
1.2 |
* deserialize it). |
862 |
jsr166 |
1.51 |
* |
863 |
dl |
1.6 |
* @param s the stream |
864 |
dl |
1.2 |
*/ |
865 |
|
|
private void readObject(java.io.ObjectInputStream s) |
866 |
|
|
throws java.io.IOException, ClassNotFoundException { |
867 |
tim |
1.12 |
// Read in capacity, and any hidden stuff |
868 |
|
|
s.defaultReadObject(); |
869 |
dl |
1.2 |
|
870 |
dl |
1.19 |
count.set(0); |
871 |
|
|
last = head = new Node<E>(null); |
872 |
|
|
|
873 |
dl |
1.6 |
// Read in all elements and place in queue |
874 |
dl |
1.2 |
for (;;) { |
875 |
jsr166 |
1.51 |
@SuppressWarnings("unchecked") |
876 |
dl |
1.2 |
E item = (E)s.readObject(); |
877 |
|
|
if (item == null) |
878 |
|
|
break; |
879 |
|
|
add(item); |
880 |
|
|
} |
881 |
tim |
1.1 |
} |
882 |
|
|
} |