1 |
dl |
1.2 |
/* |
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* Written by Doug Lea with assistance from members of JCP JSR-166 |
3 |
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* Expert Group and released to the public domain. Use, modify, and |
4 |
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* redistribute this code in any way without acknowledgement. |
5 |
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*/ |
6 |
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7 |
tim |
1.1 |
package java.util.concurrent; |
8 |
dl |
1.2 |
import java.util.concurrent.atomic.*; |
9 |
dl |
1.7 |
import java.util.concurrent.locks.*; |
10 |
tim |
1.1 |
import java.util.*; |
11 |
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12 |
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/** |
13 |
dholmes |
1.14 |
* An optionally-bounded {@linkplain BlockingQueue blocking queue} based on |
14 |
dholmes |
1.8 |
* linked nodes. |
15 |
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* This queue orders elements FIFO (first-in-first-out). |
16 |
tim |
1.12 |
* The <em>head</em> of the queue is that element that has been on the |
17 |
dholmes |
1.8 |
* queue the longest time. |
18 |
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* The <em>tail</em> of the queue is that element that has been on the |
19 |
dl |
1.20 |
* queue the shortest time. New elements |
20 |
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* are inserted at the tail of the queue, and the queue retrieval |
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* operations obtain elements at the head of the queue. |
22 |
dholmes |
1.8 |
* Linked queues typically have higher throughput than array-based queues but |
23 |
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* less predictable performance in most concurrent applications. |
24 |
tim |
1.12 |
* |
25 |
dl |
1.3 |
* <p> The optional capacity bound constructor argument serves as a |
26 |
dholmes |
1.8 |
* way to prevent excessive queue expansion. The capacity, if unspecified, |
27 |
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* is equal to {@link Integer#MAX_VALUE}. Linked nodes are |
28 |
dl |
1.3 |
* dynamically created upon each insertion unless this would bring the |
29 |
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* queue above capacity. |
30 |
dholmes |
1.8 |
* |
31 |
dl |
1.21 |
* <p>This class implements all of the <em>optional</em> methods |
32 |
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* of the {@link Collection} and {@link Iterator} interfaces. |
33 |
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* |
34 |
dl |
1.6 |
* @since 1.5 |
35 |
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* @author Doug Lea |
36 |
tim |
1.12 |
* |
37 |
tim |
1.1 |
**/ |
38 |
dl |
1.2 |
public class LinkedBlockingQueue<E> extends AbstractQueue<E> |
39 |
tim |
1.1 |
implements BlockingQueue<E>, java.io.Serializable { |
40 |
dl |
1.18 |
private static final long serialVersionUID = -6903933977591709194L; |
41 |
tim |
1.1 |
|
42 |
dl |
1.2 |
/* |
43 |
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* A variant of the "two lock queue" algorithm. The putLock gates |
44 |
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* entry to put (and offer), and has an associated condition for |
45 |
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* waiting puts. Similarly for the takeLock. The "count" field |
46 |
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* that they both rely on is maintained as an atomic to avoid |
47 |
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* needing to get both locks in most cases. Also, to minimize need |
48 |
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* for puts to get takeLock and vice-versa, cascading notifies are |
49 |
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* used. When a put notices that it has enabled at least one take, |
50 |
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* it signals taker. That taker in turn signals others if more |
51 |
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* items have been entered since the signal. And symmetrically for |
52 |
tim |
1.12 |
* takes signalling puts. Operations such as remove(Object) and |
53 |
dl |
1.2 |
* iterators acquire both locks. |
54 |
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*/ |
55 |
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56 |
dl |
1.6 |
/** |
57 |
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* Linked list node class |
58 |
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*/ |
59 |
dl |
1.2 |
static class Node<E> { |
60 |
dl |
1.6 |
/** The item, volatile to ensure barrier separating write and read */ |
61 |
dl |
1.2 |
volatile E item; |
62 |
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Node<E> next; |
63 |
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Node(E x) { item = x; } |
64 |
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} |
65 |
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|
66 |
dl |
1.6 |
/** The capacity bound, or Integer.MAX_VALUE if none */ |
67 |
dl |
1.2 |
private final int capacity; |
68 |
dl |
1.6 |
|
69 |
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/** Current number of elements */ |
70 |
dl |
1.19 |
private final AtomicInteger count = new AtomicInteger(0); |
71 |
dl |
1.2 |
|
72 |
dl |
1.6 |
/** Head of linked list */ |
73 |
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private transient Node<E> head; |
74 |
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|
75 |
dholmes |
1.8 |
/** Tail of linked list */ |
76 |
dl |
1.6 |
private transient Node<E> last; |
77 |
dl |
1.2 |
|
78 |
dl |
1.6 |
/** Lock held by take, poll, etc */ |
79 |
dl |
1.5 |
private final ReentrantLock takeLock = new ReentrantLock(); |
80 |
dl |
1.6 |
|
81 |
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/** Wait queue for waiting takes */ |
82 |
dl |
1.5 |
private final Condition notEmpty = takeLock.newCondition(); |
83 |
dl |
1.2 |
|
84 |
dl |
1.6 |
/** Lock held by put, offer, etc */ |
85 |
dl |
1.5 |
private final ReentrantLock putLock = new ReentrantLock(); |
86 |
dl |
1.6 |
|
87 |
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/** Wait queue for waiting puts */ |
88 |
dl |
1.5 |
private final Condition notFull = putLock.newCondition(); |
89 |
dl |
1.2 |
|
90 |
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/** |
91 |
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* Signal a waiting take. Called only from put/offer (which do not |
92 |
dl |
1.4 |
* otherwise ordinarily lock takeLock.) |
93 |
dl |
1.2 |
*/ |
94 |
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private void signalNotEmpty() { |
95 |
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takeLock.lock(); |
96 |
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try { |
97 |
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notEmpty.signal(); |
98 |
tim |
1.17 |
} finally { |
99 |
dl |
1.2 |
takeLock.unlock(); |
100 |
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} |
101 |
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} |
102 |
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103 |
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/** |
104 |
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* Signal a waiting put. Called only from take/poll. |
105 |
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*/ |
106 |
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private void signalNotFull() { |
107 |
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putLock.lock(); |
108 |
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try { |
109 |
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notFull.signal(); |
110 |
tim |
1.17 |
} finally { |
111 |
dl |
1.2 |
putLock.unlock(); |
112 |
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} |
113 |
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} |
114 |
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115 |
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/** |
116 |
dholmes |
1.8 |
* Create a node and link it at end of queue |
117 |
dl |
1.6 |
* @param x the item |
118 |
dl |
1.2 |
*/ |
119 |
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private void insert(E x) { |
120 |
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last = last.next = new Node<E>(x); |
121 |
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} |
122 |
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123 |
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/** |
124 |
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* Remove a node from head of queue, |
125 |
dl |
1.6 |
* @return the node |
126 |
dl |
1.2 |
*/ |
127 |
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private E extract() { |
128 |
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Node<E> first = head.next; |
129 |
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head = first; |
130 |
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E x = (E)first.item; |
131 |
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first.item = null; |
132 |
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return x; |
133 |
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} |
134 |
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135 |
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/** |
136 |
tim |
1.12 |
* Lock to prevent both puts and takes. |
137 |
dl |
1.2 |
*/ |
138 |
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private void fullyLock() { |
139 |
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putLock.lock(); |
140 |
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takeLock.lock(); |
141 |
tim |
1.1 |
} |
142 |
dl |
1.2 |
|
143 |
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/** |
144 |
tim |
1.12 |
* Unlock to allow both puts and takes. |
145 |
dl |
1.2 |
*/ |
146 |
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private void fullyUnlock() { |
147 |
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takeLock.unlock(); |
148 |
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putLock.unlock(); |
149 |
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} |
150 |
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151 |
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152 |
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/** |
153 |
dholmes |
1.13 |
* Creates a <tt>LinkedBlockingQueue</tt> with a capacity of |
154 |
dholmes |
1.8 |
* {@link Integer#MAX_VALUE}. |
155 |
dl |
1.2 |
*/ |
156 |
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public LinkedBlockingQueue() { |
157 |
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this(Integer.MAX_VALUE); |
158 |
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} |
159 |
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160 |
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/** |
161 |
tim |
1.16 |
* Creates a <tt>LinkedBlockingQueue</tt> with the given (fixed) capacity. |
162 |
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* |
163 |
dholmes |
1.8 |
* @param capacity the capacity of this queue. |
164 |
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* @throws IllegalArgumentException if <tt>capacity</tt> is not greater |
165 |
tim |
1.16 |
* than zero. |
166 |
dl |
1.2 |
*/ |
167 |
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public LinkedBlockingQueue(int capacity) { |
168 |
dholmes |
1.8 |
if (capacity <= 0) throw new IllegalArgumentException(); |
169 |
dl |
1.2 |
this.capacity = capacity; |
170 |
dl |
1.6 |
last = head = new Node<E>(null); |
171 |
dl |
1.2 |
} |
172 |
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173 |
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/** |
174 |
dholmes |
1.13 |
* Creates a <tt>LinkedBlockingQueue</tt> with a capacity of |
175 |
dholmes |
1.14 |
* {@link Integer#MAX_VALUE}, initially containing the elements of the |
176 |
tim |
1.12 |
* given collection, |
177 |
dholmes |
1.8 |
* added in traversal order of the collection's iterator. |
178 |
dholmes |
1.9 |
* @param c the collection of elements to initially contain |
179 |
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* @throws NullPointerException if <tt>c</tt> or any element within it |
180 |
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* is <tt>null</tt> |
181 |
dl |
1.2 |
*/ |
182 |
dholmes |
1.10 |
public LinkedBlockingQueue(Collection<? extends E> c) { |
183 |
dl |
1.2 |
this(Integer.MAX_VALUE); |
184 |
tim |
1.12 |
for (Iterator<? extends E> it = c.iterator(); it.hasNext();) |
185 |
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add(it.next()); |
186 |
dl |
1.2 |
} |
187 |
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188 |
dholmes |
1.9 |
|
189 |
dholmes |
1.8 |
// this doc comment is overridden to remove the reference to collections |
190 |
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// greater in size than Integer.MAX_VALUE |
191 |
tim |
1.12 |
/** |
192 |
dl |
1.20 |
* Returns the number of elements in this queue. |
193 |
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* |
194 |
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* @return the number of elements in this queue. |
195 |
dholmes |
1.8 |
*/ |
196 |
dl |
1.2 |
public int size() { |
197 |
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return count.get(); |
198 |
tim |
1.1 |
} |
199 |
dl |
1.2 |
|
200 |
dholmes |
1.8 |
// this doc comment is a modified copy of the inherited doc comment, |
201 |
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// without the reference to unlimited queues. |
202 |
tim |
1.12 |
/** |
203 |
dholmes |
1.13 |
* Returns the number of elements that this queue can ideally (in |
204 |
dholmes |
1.8 |
* the absence of memory or resource constraints) accept without |
205 |
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* blocking. This is always equal to the initial capacity of this queue |
206 |
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* less the current <tt>size</tt> of this queue. |
207 |
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* <p>Note that you <em>cannot</em> always tell if |
208 |
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* an attempt to <tt>add</tt> an element will succeed by |
209 |
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* inspecting <tt>remainingCapacity</tt> because it may be the |
210 |
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* case that a waiting consumer is ready to <tt>take</tt> an |
211 |
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* element out of an otherwise full queue. |
212 |
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*/ |
213 |
dl |
1.2 |
public int remainingCapacity() { |
214 |
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return capacity - count.get(); |
215 |
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} |
216 |
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|
217 |
dholmes |
1.22 |
/** |
218 |
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* Adds the specified element to the tail of this queue, waiting if |
219 |
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* necessary for space to become available. |
220 |
dl |
1.23 |
* @param o the element to add |
221 |
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* @throws InterruptedException if interrupted while waiting. |
222 |
dholmes |
1.22 |
* @throws NullPointerException if the specified element is <tt>null</tt>. |
223 |
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*/ |
224 |
dholmes |
1.14 |
public void put(E o) throws InterruptedException { |
225 |
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if (o == null) throw new NullPointerException(); |
226 |
dl |
1.2 |
// Note: convention in all put/take/etc is to preset |
227 |
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// local var holding count negative to indicate failure unless set. |
228 |
tim |
1.12 |
int c = -1; |
229 |
dl |
1.2 |
putLock.lockInterruptibly(); |
230 |
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try { |
231 |
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/* |
232 |
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* Note that count is used in wait guard even though it is |
233 |
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* not protected by lock. This works because count can |
234 |
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* only decrease at this point (all other puts are shut |
235 |
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* out by lock), and we (or some other waiting put) are |
236 |
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* signalled if it ever changes from |
237 |
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* capacity. Similarly for all other uses of count in |
238 |
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* other wait guards. |
239 |
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*/ |
240 |
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try { |
241 |
tim |
1.12 |
while (count.get() == capacity) |
242 |
dl |
1.2 |
notFull.await(); |
243 |
tim |
1.17 |
} catch (InterruptedException ie) { |
244 |
dl |
1.2 |
notFull.signal(); // propagate to a non-interrupted thread |
245 |
|
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throw ie; |
246 |
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} |
247 |
dholmes |
1.14 |
insert(o); |
248 |
dl |
1.2 |
c = count.getAndIncrement(); |
249 |
dl |
1.6 |
if (c + 1 < capacity) |
250 |
dl |
1.2 |
notFull.signal(); |
251 |
tim |
1.17 |
} finally { |
252 |
dl |
1.2 |
putLock.unlock(); |
253 |
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} |
254 |
tim |
1.12 |
if (c == 0) |
255 |
dl |
1.2 |
signalNotEmpty(); |
256 |
tim |
1.1 |
} |
257 |
dl |
1.2 |
|
258 |
dholmes |
1.22 |
/** |
259 |
|
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* Inserts the specified element at the tail of this queue, waiting if |
260 |
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* necessary up to the specified wait time for space to become available. |
261 |
dl |
1.23 |
* @param o the element to add |
262 |
|
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* @param timeout how long to wait before giving up, in units of |
263 |
|
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* <tt>unit</tt> |
264 |
|
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* @param unit a <tt>TimeUnit</tt> determining how to interpret the |
265 |
|
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* <tt>timeout</tt> parameter |
266 |
|
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* @return <tt>true</tt> if successful, or <tt>false</tt> if |
267 |
|
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* the specified waiting time elapses before space is available. |
268 |
|
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* @throws InterruptedException if interrupted while waiting. |
269 |
dholmes |
1.22 |
* @throws NullPointerException if the specified element is <tt>null</tt>. |
270 |
|
|
*/ |
271 |
dholmes |
1.14 |
public boolean offer(E o, long timeout, TimeUnit unit) |
272 |
dholmes |
1.8 |
throws InterruptedException { |
273 |
tim |
1.12 |
|
274 |
dholmes |
1.14 |
if (o == null) throw new NullPointerException(); |
275 |
dl |
1.2 |
long nanos = unit.toNanos(timeout); |
276 |
|
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int c = -1; |
277 |
dholmes |
1.8 |
putLock.lockInterruptibly(); |
278 |
dl |
1.2 |
try { |
279 |
|
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for (;;) { |
280 |
|
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if (count.get() < capacity) { |
281 |
dholmes |
1.14 |
insert(o); |
282 |
dl |
1.2 |
c = count.getAndIncrement(); |
283 |
dl |
1.6 |
if (c + 1 < capacity) |
284 |
dl |
1.2 |
notFull.signal(); |
285 |
|
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break; |
286 |
|
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} |
287 |
|
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if (nanos <= 0) |
288 |
|
|
return false; |
289 |
|
|
try { |
290 |
|
|
nanos = notFull.awaitNanos(nanos); |
291 |
tim |
1.17 |
} catch (InterruptedException ie) { |
292 |
dl |
1.2 |
notFull.signal(); // propagate to a non-interrupted thread |
293 |
|
|
throw ie; |
294 |
|
|
} |
295 |
|
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} |
296 |
tim |
1.17 |
} finally { |
297 |
dl |
1.2 |
putLock.unlock(); |
298 |
|
|
} |
299 |
tim |
1.12 |
if (c == 0) |
300 |
dl |
1.2 |
signalNotEmpty(); |
301 |
|
|
return true; |
302 |
tim |
1.1 |
} |
303 |
dl |
1.2 |
|
304 |
dl |
1.23 |
/** |
305 |
|
|
* Inserts the specified element at the tail of this queue if possible, |
306 |
|
|
* returning immediately if this queue is full. |
307 |
|
|
* |
308 |
|
|
* @param o the element to add. |
309 |
|
|
* @return <tt>true</tt> if it was possible to add the element to |
310 |
|
|
* this queue, else <tt>false</tt> |
311 |
|
|
* @throws NullPointerException if the specified element is <tt>null</tt> |
312 |
|
|
*/ |
313 |
dholmes |
1.14 |
public boolean offer(E o) { |
314 |
|
|
if (o == null) throw new NullPointerException(); |
315 |
dl |
1.2 |
if (count.get() == capacity) |
316 |
|
|
return false; |
317 |
tim |
1.12 |
int c = -1; |
318 |
dholmes |
1.8 |
putLock.lock(); |
319 |
dl |
1.2 |
try { |
320 |
|
|
if (count.get() < capacity) { |
321 |
dholmes |
1.14 |
insert(o); |
322 |
dl |
1.2 |
c = count.getAndIncrement(); |
323 |
dl |
1.6 |
if (c + 1 < capacity) |
324 |
dl |
1.2 |
notFull.signal(); |
325 |
|
|
} |
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 |
|
|
return c >= 0; |
332 |
tim |
1.1 |
} |
333 |
dl |
1.2 |
|
334 |
|
|
|
335 |
|
|
public E take() throws InterruptedException { |
336 |
|
|
E x; |
337 |
|
|
int c = -1; |
338 |
|
|
takeLock.lockInterruptibly(); |
339 |
|
|
try { |
340 |
|
|
try { |
341 |
tim |
1.12 |
while (count.get() == 0) |
342 |
dl |
1.2 |
notEmpty.await(); |
343 |
tim |
1.17 |
} catch (InterruptedException ie) { |
344 |
dl |
1.2 |
notEmpty.signal(); // propagate to a non-interrupted thread |
345 |
|
|
throw ie; |
346 |
|
|
} |
347 |
|
|
|
348 |
|
|
x = extract(); |
349 |
|
|
c = count.getAndDecrement(); |
350 |
|
|
if (c > 1) |
351 |
|
|
notEmpty.signal(); |
352 |
tim |
1.17 |
} finally { |
353 |
dl |
1.2 |
takeLock.unlock(); |
354 |
|
|
} |
355 |
tim |
1.12 |
if (c == capacity) |
356 |
dl |
1.2 |
signalNotFull(); |
357 |
|
|
return x; |
358 |
|
|
} |
359 |
|
|
|
360 |
|
|
public E poll(long timeout, TimeUnit unit) throws InterruptedException { |
361 |
|
|
E x = null; |
362 |
|
|
int c = -1; |
363 |
dholmes |
1.8 |
long nanos = unit.toNanos(timeout); |
364 |
dl |
1.2 |
takeLock.lockInterruptibly(); |
365 |
|
|
try { |
366 |
|
|
for (;;) { |
367 |
|
|
if (count.get() > 0) { |
368 |
|
|
x = extract(); |
369 |
|
|
c = count.getAndDecrement(); |
370 |
|
|
if (c > 1) |
371 |
|
|
notEmpty.signal(); |
372 |
|
|
break; |
373 |
|
|
} |
374 |
|
|
if (nanos <= 0) |
375 |
|
|
return null; |
376 |
|
|
try { |
377 |
|
|
nanos = notEmpty.awaitNanos(nanos); |
378 |
tim |
1.17 |
} catch (InterruptedException ie) { |
379 |
dl |
1.2 |
notEmpty.signal(); // propagate to a non-interrupted thread |
380 |
|
|
throw ie; |
381 |
|
|
} |
382 |
|
|
} |
383 |
tim |
1.17 |
} finally { |
384 |
dl |
1.2 |
takeLock.unlock(); |
385 |
|
|
} |
386 |
tim |
1.12 |
if (c == capacity) |
387 |
dl |
1.2 |
signalNotFull(); |
388 |
|
|
return x; |
389 |
|
|
} |
390 |
|
|
|
391 |
|
|
public E poll() { |
392 |
|
|
if (count.get() == 0) |
393 |
|
|
return null; |
394 |
|
|
E x = null; |
395 |
tim |
1.12 |
int c = -1; |
396 |
dl |
1.2 |
takeLock.tryLock(); |
397 |
|
|
try { |
398 |
|
|
if (count.get() > 0) { |
399 |
|
|
x = extract(); |
400 |
|
|
c = count.getAndDecrement(); |
401 |
|
|
if (c > 1) |
402 |
|
|
notEmpty.signal(); |
403 |
|
|
} |
404 |
tim |
1.17 |
} finally { |
405 |
dl |
1.2 |
takeLock.unlock(); |
406 |
|
|
} |
407 |
tim |
1.12 |
if (c == capacity) |
408 |
dl |
1.2 |
signalNotFull(); |
409 |
|
|
return x; |
410 |
tim |
1.1 |
} |
411 |
dl |
1.2 |
|
412 |
|
|
|
413 |
|
|
public E peek() { |
414 |
|
|
if (count.get() == 0) |
415 |
|
|
return null; |
416 |
dholmes |
1.8 |
takeLock.lock(); |
417 |
dl |
1.2 |
try { |
418 |
|
|
Node<E> first = head.next; |
419 |
|
|
if (first == null) |
420 |
|
|
return null; |
421 |
|
|
else |
422 |
|
|
return first.item; |
423 |
tim |
1.17 |
} finally { |
424 |
dl |
1.2 |
takeLock.unlock(); |
425 |
|
|
} |
426 |
tim |
1.1 |
} |
427 |
|
|
|
428 |
dholmes |
1.9 |
public boolean remove(Object o) { |
429 |
|
|
if (o == null) return false; |
430 |
dl |
1.2 |
boolean removed = false; |
431 |
|
|
fullyLock(); |
432 |
|
|
try { |
433 |
|
|
Node<E> trail = head; |
434 |
|
|
Node<E> p = head.next; |
435 |
|
|
while (p != null) { |
436 |
dholmes |
1.9 |
if (o.equals(p.item)) { |
437 |
dl |
1.2 |
removed = true; |
438 |
|
|
break; |
439 |
|
|
} |
440 |
|
|
trail = p; |
441 |
|
|
p = p.next; |
442 |
|
|
} |
443 |
|
|
if (removed) { |
444 |
|
|
p.item = null; |
445 |
|
|
trail.next = p.next; |
446 |
|
|
if (count.getAndDecrement() == capacity) |
447 |
|
|
notFull.signalAll(); |
448 |
|
|
} |
449 |
tim |
1.17 |
} finally { |
450 |
dl |
1.2 |
fullyUnlock(); |
451 |
|
|
} |
452 |
|
|
return removed; |
453 |
tim |
1.1 |
} |
454 |
dl |
1.2 |
|
455 |
|
|
public Object[] toArray() { |
456 |
|
|
fullyLock(); |
457 |
|
|
try { |
458 |
|
|
int size = count.get(); |
459 |
tim |
1.12 |
Object[] a = new Object[size]; |
460 |
dl |
1.2 |
int k = 0; |
461 |
tim |
1.12 |
for (Node<E> p = head.next; p != null; p = p.next) |
462 |
dl |
1.2 |
a[k++] = p.item; |
463 |
|
|
return a; |
464 |
tim |
1.17 |
} finally { |
465 |
dl |
1.2 |
fullyUnlock(); |
466 |
|
|
} |
467 |
tim |
1.1 |
} |
468 |
dl |
1.2 |
|
469 |
|
|
public <T> T[] toArray(T[] a) { |
470 |
|
|
fullyLock(); |
471 |
|
|
try { |
472 |
|
|
int size = count.get(); |
473 |
|
|
if (a.length < size) |
474 |
dl |
1.4 |
a = (T[])java.lang.reflect.Array.newInstance |
475 |
|
|
(a.getClass().getComponentType(), size); |
476 |
tim |
1.12 |
|
477 |
dl |
1.2 |
int k = 0; |
478 |
tim |
1.12 |
for (Node p = head.next; p != null; p = p.next) |
479 |
dl |
1.2 |
a[k++] = (T)p.item; |
480 |
|
|
return a; |
481 |
tim |
1.17 |
} finally { |
482 |
dl |
1.2 |
fullyUnlock(); |
483 |
|
|
} |
484 |
tim |
1.1 |
} |
485 |
dl |
1.2 |
|
486 |
|
|
public String toString() { |
487 |
|
|
fullyLock(); |
488 |
|
|
try { |
489 |
|
|
return super.toString(); |
490 |
tim |
1.17 |
} finally { |
491 |
dl |
1.2 |
fullyUnlock(); |
492 |
|
|
} |
493 |
tim |
1.1 |
} |
494 |
dl |
1.2 |
|
495 |
dholmes |
1.14 |
/** |
496 |
|
|
* Returns an iterator over the elements in this queue in proper sequence. |
497 |
dl |
1.15 |
* The returned <tt>Iterator</tt> is a "weakly consistent" iterator that |
498 |
|
|
* will never throw {@link java.util.ConcurrentModificationException}, |
499 |
|
|
* and guarantees to traverse elements as they existed upon |
500 |
|
|
* construction of the iterator, and may (but is not guaranteed to) |
501 |
|
|
* reflect any modifications subsequent to construction. |
502 |
dholmes |
1.14 |
* |
503 |
|
|
* @return an iterator over the elements in this queue in proper sequence. |
504 |
|
|
*/ |
505 |
dl |
1.2 |
public Iterator<E> iterator() { |
506 |
|
|
return new Itr(); |
507 |
tim |
1.1 |
} |
508 |
dl |
1.2 |
|
509 |
|
|
private class Itr implements Iterator<E> { |
510 |
tim |
1.12 |
/* |
511 |
dl |
1.4 |
* Basic weak-consistent iterator. At all times hold the next |
512 |
|
|
* item to hand out so that if hasNext() reports true, we will |
513 |
|
|
* still have it to return even if lost race with a take etc. |
514 |
|
|
*/ |
515 |
dl |
1.2 |
Node<E> current; |
516 |
|
|
Node<E> lastRet; |
517 |
dl |
1.4 |
E currentElement; |
518 |
tim |
1.12 |
|
519 |
dl |
1.2 |
Itr() { |
520 |
|
|
fullyLock(); |
521 |
|
|
try { |
522 |
|
|
current = head.next; |
523 |
dl |
1.4 |
if (current != null) |
524 |
|
|
currentElement = current.item; |
525 |
tim |
1.17 |
} finally { |
526 |
dl |
1.2 |
fullyUnlock(); |
527 |
|
|
} |
528 |
|
|
} |
529 |
tim |
1.12 |
|
530 |
|
|
public boolean hasNext() { |
531 |
dl |
1.2 |
return current != null; |
532 |
|
|
} |
533 |
|
|
|
534 |
tim |
1.12 |
public E next() { |
535 |
dl |
1.2 |
fullyLock(); |
536 |
|
|
try { |
537 |
|
|
if (current == null) |
538 |
|
|
throw new NoSuchElementException(); |
539 |
dl |
1.4 |
E x = currentElement; |
540 |
dl |
1.2 |
lastRet = current; |
541 |
|
|
current = current.next; |
542 |
dl |
1.4 |
if (current != null) |
543 |
|
|
currentElement = current.item; |
544 |
dl |
1.2 |
return x; |
545 |
tim |
1.17 |
} finally { |
546 |
dl |
1.2 |
fullyUnlock(); |
547 |
|
|
} |
548 |
tim |
1.12 |
|
549 |
dl |
1.2 |
} |
550 |
|
|
|
551 |
tim |
1.12 |
public void remove() { |
552 |
dl |
1.2 |
if (lastRet == null) |
553 |
tim |
1.12 |
throw new IllegalStateException(); |
554 |
dl |
1.2 |
fullyLock(); |
555 |
|
|
try { |
556 |
|
|
Node<E> node = lastRet; |
557 |
|
|
lastRet = null; |
558 |
|
|
Node<E> trail = head; |
559 |
|
|
Node<E> p = head.next; |
560 |
|
|
while (p != null && p != node) { |
561 |
|
|
trail = p; |
562 |
|
|
p = p.next; |
563 |
|
|
} |
564 |
|
|
if (p == node) { |
565 |
|
|
p.item = null; |
566 |
|
|
trail.next = p.next; |
567 |
|
|
int c = count.getAndDecrement(); |
568 |
|
|
if (c == capacity) |
569 |
|
|
notFull.signalAll(); |
570 |
|
|
} |
571 |
tim |
1.17 |
} finally { |
572 |
dl |
1.2 |
fullyUnlock(); |
573 |
|
|
} |
574 |
|
|
} |
575 |
tim |
1.1 |
} |
576 |
dl |
1.2 |
|
577 |
|
|
/** |
578 |
|
|
* Save the state to a stream (that is, serialize it). |
579 |
|
|
* |
580 |
|
|
* @serialData The capacity is emitted (int), followed by all of |
581 |
|
|
* its elements (each an <tt>Object</tt>) in the proper order, |
582 |
|
|
* followed by a null |
583 |
dl |
1.6 |
* @param s the stream |
584 |
dl |
1.2 |
*/ |
585 |
|
|
private void writeObject(java.io.ObjectOutputStream s) |
586 |
|
|
throws java.io.IOException { |
587 |
|
|
|
588 |
tim |
1.12 |
fullyLock(); |
589 |
dl |
1.2 |
try { |
590 |
|
|
// Write out any hidden stuff, plus capacity |
591 |
|
|
s.defaultWriteObject(); |
592 |
|
|
|
593 |
|
|
// Write out all elements in the proper order. |
594 |
tim |
1.12 |
for (Node<E> p = head.next; p != null; p = p.next) |
595 |
dl |
1.2 |
s.writeObject(p.item); |
596 |
|
|
|
597 |
|
|
// Use trailing null as sentinel |
598 |
|
|
s.writeObject(null); |
599 |
tim |
1.17 |
} finally { |
600 |
dl |
1.2 |
fullyUnlock(); |
601 |
|
|
} |
602 |
tim |
1.1 |
} |
603 |
|
|
|
604 |
dl |
1.2 |
/** |
605 |
dholmes |
1.8 |
* Reconstitute this queue instance from a stream (that is, |
606 |
dl |
1.2 |
* deserialize it). |
607 |
dl |
1.6 |
* @param s the stream |
608 |
dl |
1.2 |
*/ |
609 |
|
|
private void readObject(java.io.ObjectInputStream s) |
610 |
|
|
throws java.io.IOException, ClassNotFoundException { |
611 |
tim |
1.12 |
// Read in capacity, and any hidden stuff |
612 |
|
|
s.defaultReadObject(); |
613 |
dl |
1.2 |
|
614 |
dl |
1.19 |
count.set(0); |
615 |
|
|
last = head = new Node<E>(null); |
616 |
|
|
|
617 |
dl |
1.6 |
// Read in all elements and place in queue |
618 |
dl |
1.2 |
for (;;) { |
619 |
|
|
E item = (E)s.readObject(); |
620 |
|
|
if (item == null) |
621 |
|
|
break; |
622 |
|
|
add(item); |
623 |
|
|
} |
624 |
tim |
1.1 |
} |
625 |
|
|
} |