1 |
dl |
1.2 |
/* |
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* Written by Doug Lea with assistance from members of JCP JSR-166 |
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* Expert Group and released to the public domain. Use, modify, and |
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* redistribute this code in any way without acknowledgement. |
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*/ |
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7 |
tim |
1.1 |
package java.util.concurrent; |
8 |
dl |
1.8 |
import java.util.concurrent.locks.*; |
9 |
tim |
1.1 |
import java.util.*; |
10 |
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11 |
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/** |
12 |
dl |
1.18 |
* A {@linkplain BlockingQueue blocking queue} in which each |
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* <tt>put</tt> must wait for a <tt>take</tt>, and vice versa. A |
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* synchronous queue does not have any internal capacity - in |
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* particular it does not have a capacity of one. You cannot |
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* <tt>peek</tt> at a synchronous queue because an element is only |
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* present when you try to take it; you cannot add an element (using |
18 |
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* any method) unless another thread is trying to remove it; you |
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* cannot iterate as there is nothing to iterate. The <em>head</em> |
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* of the queue is the element that the first queued thread is trying |
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* to add to the queue; if there are no queued threads then no element |
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* is being added and the head is <tt>null</tt>. For purposes of |
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* other <tt>Collection</tt> methods (for example <tt>contains</tt>), |
24 |
dl |
1.19 |
* a <tt>SynchronousQueue</tt> acts as an empty collection. This |
25 |
dl |
1.18 |
* queue does not permit <tt>null</tt> elements. |
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* |
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* <p>Synchronous queues are similar to rendezvous channels used in |
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* CSP and Ada. They are well suited for handoff designs, in which an |
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* object running in one thread must synch up with an object running |
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* in another thread in order to hand it some information, event, or |
31 |
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* task. |
32 |
dl |
1.19 |
* <p>This class implements all of the <em>optional</em> methods |
33 |
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* of the {@link Collection} and {@link Iterator} interfaces. |
34 |
dl |
1.6 |
* @since 1.5 |
35 |
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* @author Doug Lea |
36 |
dl |
1.23 |
* @param <E> the base class of all elements held in this collection |
37 |
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*/ |
38 |
dl |
1.2 |
public class SynchronousQueue<E> extends AbstractQueue<E> |
39 |
tim |
1.1 |
implements BlockingQueue<E>, java.io.Serializable { |
40 |
dl |
1.15 |
private static final long serialVersionUID = -3223113410248163686L; |
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tim |
1.1 |
|
42 |
dl |
1.2 |
/* |
43 |
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This implementation divides actions into two cases for puts: |
44 |
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|
45 |
tim |
1.10 |
* An arriving putter that does not already have a waiting taker |
46 |
dl |
1.2 |
creates a node holding item, and then waits for a taker to take it. |
47 |
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* An arriving putter that does already have a waiting taker fills |
48 |
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the slot node created by the taker, and notifies it to continue. |
49 |
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|
50 |
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And symmetrically, two for takes: |
51 |
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|
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* An arriving taker that does not already have a waiting putter |
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creates an empty slot node, and then waits for a putter to fill it. |
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* An arriving taker that does already have a waiting putter takes |
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item from the node created by the putter, and notifies it to continue. |
56 |
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57 |
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This requires keeping two simple queues: waitingPuts and waitingTakes. |
58 |
tim |
1.10 |
|
59 |
dl |
1.2 |
When a put or take waiting for the actions of its counterpart |
60 |
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aborts due to interruption or timeout, it marks the node |
61 |
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it created as "CANCELLED", which causes its counterpart to retry |
62 |
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the entire put or take sequence. |
63 |
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*/ |
64 |
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|
65 |
tim |
1.10 |
/** |
66 |
dl |
1.2 |
* Special marker used in queue nodes to indicate that |
67 |
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* the thread waiting for a change in the node has timed out |
68 |
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* or been interrupted. |
69 |
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**/ |
70 |
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private static final Object CANCELLED = new Object(); |
71 |
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72 |
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/* |
73 |
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* Note that all fields are transient final, so there is |
74 |
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* no explicit serialization code. |
75 |
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*/ |
76 |
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77 |
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private transient final WaitQueue waitingPuts = new WaitQueue(); |
78 |
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private transient final WaitQueue waitingTakes = new WaitQueue(); |
79 |
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private transient final ReentrantLock qlock = new ReentrantLock(); |
80 |
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81 |
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/** |
82 |
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* Nodes each maintain an item and handle waits and signals for |
83 |
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* getting and setting it. The class opportunistically extends |
84 |
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* ReentrantLock to save an extra object allocation per |
85 |
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* rendezvous. |
86 |
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*/ |
87 |
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private static class Node extends ReentrantLock { |
88 |
dl |
1.6 |
/** Condition to wait on for other party; lazily constructed */ |
89 |
dl |
1.22 |
ReentrantLock.ConditionObject done; |
90 |
dl |
1.6 |
/** The item being transferred */ |
91 |
dl |
1.2 |
Object item; |
92 |
dl |
1.6 |
/** Next node in wait queue */ |
93 |
dl |
1.2 |
Node next; |
94 |
dl |
1.6 |
|
95 |
dl |
1.2 |
Node(Object x) { item = x; } |
96 |
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97 |
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/** |
98 |
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* Fill in the slot created by the taker and signal taker to |
99 |
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* continue. |
100 |
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*/ |
101 |
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boolean set(Object x) { |
102 |
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this.lock(); |
103 |
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try { |
104 |
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if (item != CANCELLED) { |
105 |
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item = x; |
106 |
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if (done != null) |
107 |
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done.signal(); |
108 |
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return true; |
109 |
tim |
1.14 |
} else // taker has cancelled |
110 |
dl |
1.2 |
return false; |
111 |
tim |
1.14 |
} finally { |
112 |
dl |
1.2 |
this.unlock(); |
113 |
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} |
114 |
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} |
115 |
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116 |
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/** |
117 |
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* Remove item from slot created by putter and signal putter |
118 |
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* to continue. |
119 |
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*/ |
120 |
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Object get() { |
121 |
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this.lock(); |
122 |
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try { |
123 |
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Object x = item; |
124 |
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if (x != CANCELLED) { |
125 |
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item = null; |
126 |
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next = null; |
127 |
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if (done != null) |
128 |
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done.signal(); |
129 |
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return x; |
130 |
tim |
1.14 |
} else |
131 |
dl |
1.2 |
return null; |
132 |
tim |
1.14 |
} finally { |
133 |
dl |
1.2 |
this.unlock(); |
134 |
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} |
135 |
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} |
136 |
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137 |
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/** |
138 |
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* Wait for a taker to take item placed by putter, or time out. |
139 |
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*/ |
140 |
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boolean waitForTake(boolean timed, long nanos) throws InterruptedException { |
141 |
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this.lock(); |
142 |
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try { |
143 |
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for (;;) { |
144 |
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if (item == null) |
145 |
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return true; |
146 |
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if (timed) { |
147 |
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if (nanos <= 0) { |
148 |
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item = CANCELLED; |
149 |
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return false; |
150 |
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} |
151 |
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} |
152 |
dl |
1.9 |
if (done == null) |
153 |
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done = this.newCondition(); |
154 |
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if (timed) |
155 |
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nanos = done.awaitNanos(nanos); |
156 |
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else |
157 |
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done.await(); |
158 |
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} |
159 |
tim |
1.14 |
} catch (InterruptedException ie) { |
160 |
dl |
1.9 |
// If taken, return normally but set interrupt status |
161 |
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if (item == null) { |
162 |
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Thread.currentThread().interrupt(); |
163 |
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return true; |
164 |
tim |
1.14 |
} else { |
165 |
dl |
1.9 |
item = CANCELLED; |
166 |
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done.signal(); // propagate signal |
167 |
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throw ie; |
168 |
dl |
1.2 |
} |
169 |
tim |
1.14 |
} finally { |
170 |
dl |
1.2 |
this.unlock(); |
171 |
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} |
172 |
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} |
173 |
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174 |
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/** |
175 |
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* Wait for a putter to put item placed by taker, or time out. |
176 |
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*/ |
177 |
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Object waitForPut(boolean timed, long nanos) throws InterruptedException { |
178 |
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this.lock(); |
179 |
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try { |
180 |
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for (;;) { |
181 |
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Object x = item; |
182 |
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if (x != null) { |
183 |
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item = null; |
184 |
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next = null; |
185 |
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return x; |
186 |
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} |
187 |
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if (timed) { |
188 |
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if (nanos <= 0) { |
189 |
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item = CANCELLED; |
190 |
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return null; |
191 |
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} |
192 |
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} |
193 |
dl |
1.9 |
if (done == null) |
194 |
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done = this.newCondition(); |
195 |
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if (timed) |
196 |
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nanos = done.awaitNanos(nanos); |
197 |
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else |
198 |
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done.await(); |
199 |
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} |
200 |
tim |
1.14 |
} catch (InterruptedException ie) { |
201 |
dl |
1.9 |
Object y = item; |
202 |
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if (y != null) { |
203 |
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item = null; |
204 |
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next = null; |
205 |
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Thread.currentThread().interrupt(); |
206 |
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return y; |
207 |
tim |
1.14 |
} else { |
208 |
dl |
1.9 |
item = CANCELLED; |
209 |
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done.signal(); // propagate signal |
210 |
|
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throw ie; |
211 |
dl |
1.2 |
} |
212 |
tim |
1.14 |
} finally { |
213 |
dl |
1.2 |
this.unlock(); |
214 |
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} |
215 |
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} |
216 |
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} |
217 |
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218 |
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/** |
219 |
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* Simple FIFO queue class to hold waiting puts/takes. |
220 |
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**/ |
221 |
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private static class WaitQueue<E> { |
222 |
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Node head; |
223 |
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Node last; |
224 |
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|
225 |
tim |
1.10 |
Node enq(Object x) { |
226 |
dl |
1.2 |
Node p = new Node(x); |
227 |
tim |
1.10 |
if (last == null) |
228 |
dl |
1.2 |
last = head = p; |
229 |
tim |
1.10 |
else |
230 |
dl |
1.2 |
last = last.next = p; |
231 |
|
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return p; |
232 |
|
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} |
233 |
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|
234 |
|
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Node deq() { |
235 |
|
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Node p = head; |
236 |
tim |
1.10 |
if (p != null && (head = p.next) == null) |
237 |
dl |
1.2 |
last = null; |
238 |
|
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return p; |
239 |
|
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} |
240 |
|
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} |
241 |
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242 |
|
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/** |
243 |
|
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* Main put algorithm, used by put, timed offer |
244 |
tim |
1.10 |
*/ |
245 |
dl |
1.2 |
private boolean doPut(E x, boolean timed, long nanos) throws InterruptedException { |
246 |
dl |
1.6 |
if (x == null) throw new NullPointerException(); |
247 |
tim |
1.10 |
for (;;) { |
248 |
dl |
1.2 |
Node node; |
249 |
|
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boolean mustWait; |
250 |
tim |
1.10 |
|
251 |
dl |
1.2 |
qlock.lockInterruptibly(); |
252 |
|
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try { |
253 |
|
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node = waitingTakes.deq(); |
254 |
|
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if ( (mustWait = (node == null)) ) |
255 |
|
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node = waitingPuts.enq(x); |
256 |
tim |
1.14 |
} finally { |
257 |
dl |
1.2 |
qlock.unlock(); |
258 |
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} |
259 |
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|
260 |
|
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if (mustWait) |
261 |
|
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return node.waitForTake(timed, nanos); |
262 |
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|
263 |
|
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else if (node.set(x)) |
264 |
|
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return true; |
265 |
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|
266 |
|
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// else taker cancelled, so retry |
267 |
|
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} |
268 |
tim |
1.1 |
} |
269 |
dl |
1.2 |
|
270 |
|
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/** |
271 |
|
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* Main take algorithm, used by take, timed poll |
272 |
tim |
1.10 |
*/ |
273 |
dl |
1.2 |
private E doTake(boolean timed, long nanos) throws InterruptedException { |
274 |
|
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for (;;) { |
275 |
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Node node; |
276 |
|
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boolean mustWait; |
277 |
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|
278 |
|
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qlock.lockInterruptibly(); |
279 |
|
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try { |
280 |
|
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node = waitingPuts.deq(); |
281 |
|
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if ( (mustWait = (node == null)) ) |
282 |
|
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node = waitingTakes.enq(null); |
283 |
tim |
1.14 |
} finally { |
284 |
dl |
1.2 |
qlock.unlock(); |
285 |
|
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} |
286 |
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|
287 |
dl |
1.9 |
if (mustWait) |
288 |
dl |
1.2 |
return (E)node.waitForPut(timed, nanos); |
289 |
|
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|
290 |
|
|
else { |
291 |
|
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E x = (E)node.get(); |
292 |
|
|
if (x != null) |
293 |
|
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return x; |
294 |
|
|
// else cancelled, so retry |
295 |
|
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} |
296 |
|
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} |
297 |
tim |
1.1 |
} |
298 |
dl |
1.2 |
|
299 |
dholmes |
1.11 |
/** |
300 |
tim |
1.13 |
* Creates a <tt>SynchronousQueue</tt>. |
301 |
dholmes |
1.11 |
*/ |
302 |
dl |
1.2 |
public SynchronousQueue() {} |
303 |
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|
304 |
|
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|
305 |
dholmes |
1.11 |
/** |
306 |
|
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* Adds the specified element to this queue, waiting if necessary for |
307 |
|
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* another thread to receive it. |
308 |
dl |
1.18 |
* @param o the element to add |
309 |
|
|
* @throws InterruptedException if interrupted while waiting. |
310 |
|
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* @throws NullPointerException if the specified element is <tt>null</tt>. |
311 |
dholmes |
1.11 |
*/ |
312 |
|
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public void put(E o) throws InterruptedException { |
313 |
|
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doPut(o, false, 0); |
314 |
tim |
1.1 |
} |
315 |
|
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|
316 |
dholmes |
1.11 |
/** |
317 |
dl |
1.20 |
* Inserts the specified element into this queue, waiting if necessary |
318 |
dl |
1.18 |
* up to the specified wait time for another thread to receive it. |
319 |
|
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* @param o the element to add |
320 |
|
|
* @param timeout how long to wait before giving up, in units of |
321 |
|
|
* <tt>unit</tt> |
322 |
|
|
* @param unit a <tt>TimeUnit</tt> determining how to interpret the |
323 |
|
|
* <tt>timeout</tt> parameter |
324 |
dholmes |
1.11 |
* @return <tt>true</tt> if successful, or <tt>false</tt> if |
325 |
|
|
* the specified waiting time elapses before a taker appears. |
326 |
dl |
1.18 |
* @throws InterruptedException if interrupted while waiting. |
327 |
|
|
* @throws NullPointerException if the specified element is <tt>null</tt>. |
328 |
dholmes |
1.11 |
*/ |
329 |
dl |
1.18 |
public boolean offer(E o, long timeout, TimeUnit unit) throws InterruptedException { |
330 |
|
|
return doPut(o, true, unit.toNanos(timeout)); |
331 |
tim |
1.1 |
} |
332 |
|
|
|
333 |
dl |
1.2 |
|
334 |
dholmes |
1.11 |
/** |
335 |
|
|
* Retrieves and removes the head of this queue, waiting if necessary |
336 |
|
|
* for another thread to insert it. |
337 |
|
|
* @return the head of this queue |
338 |
|
|
*/ |
339 |
dl |
1.2 |
public E take() throws InterruptedException { |
340 |
|
|
return doTake(false, 0); |
341 |
tim |
1.1 |
} |
342 |
dl |
1.2 |
|
343 |
dholmes |
1.11 |
/** |
344 |
|
|
* Retrieves and removes the head of this queue, waiting |
345 |
|
|
* if necessary up to the specified wait time, for another thread |
346 |
|
|
* to insert it. |
347 |
dl |
1.18 |
* @param timeout how long to wait before giving up, in units of |
348 |
|
|
* <tt>unit</tt> |
349 |
|
|
* @param unit a <tt>TimeUnit</tt> determining how to interpret the |
350 |
|
|
* <tt>timeout</tt> parameter |
351 |
|
|
* @return the head of this queue, or <tt>null</tt> if the |
352 |
|
|
* specified waiting time elapses before an element is present. |
353 |
|
|
* @throws InterruptedException if interrupted while waiting. |
354 |
dholmes |
1.11 |
*/ |
355 |
dl |
1.2 |
public E poll(long timeout, TimeUnit unit) throws InterruptedException { |
356 |
|
|
return doTake(true, unit.toNanos(timeout)); |
357 |
tim |
1.1 |
} |
358 |
dl |
1.2 |
|
359 |
|
|
// Untimed nonblocking versions |
360 |
|
|
|
361 |
dl |
1.18 |
/** |
362 |
dl |
1.20 |
* Inserts the specified element into this queue, if another thread is |
363 |
dl |
1.18 |
* waiting to receive it. |
364 |
|
|
* |
365 |
|
|
* @param o the element to add. |
366 |
|
|
* @return <tt>true</tt> if it was possible to add the element to |
367 |
|
|
* this queue, else <tt>false</tt> |
368 |
|
|
* @throws NullPointerException if the specified element is <tt>null</tt> |
369 |
|
|
*/ |
370 |
dholmes |
1.11 |
public boolean offer(E o) { |
371 |
|
|
if (o == null) throw new NullPointerException(); |
372 |
tim |
1.10 |
|
373 |
|
|
for (;;) { |
374 |
dl |
1.2 |
qlock.lock(); |
375 |
|
|
Node node; |
376 |
|
|
try { |
377 |
|
|
node = waitingTakes.deq(); |
378 |
tim |
1.14 |
} finally { |
379 |
dl |
1.2 |
qlock.unlock(); |
380 |
|
|
} |
381 |
|
|
if (node == null) |
382 |
|
|
return false; |
383 |
tim |
1.10 |
|
384 |
dholmes |
1.11 |
else if (node.set(o)) |
385 |
dl |
1.2 |
return true; |
386 |
|
|
// else retry |
387 |
|
|
} |
388 |
tim |
1.1 |
} |
389 |
dl |
1.2 |
|
390 |
dl |
1.18 |
/** |
391 |
|
|
* Retrieves and removes the head of this queue, if another thread |
392 |
|
|
* is currently making an element available. |
393 |
|
|
* |
394 |
|
|
* @return the head of this queue, or <tt>null</tt> if no |
395 |
|
|
* element is available. |
396 |
|
|
*/ |
397 |
dl |
1.2 |
public E poll() { |
398 |
|
|
for (;;) { |
399 |
|
|
Node node; |
400 |
|
|
qlock.lock(); |
401 |
|
|
try { |
402 |
|
|
node = waitingPuts.deq(); |
403 |
tim |
1.14 |
} finally { |
404 |
dl |
1.2 |
qlock.unlock(); |
405 |
|
|
} |
406 |
|
|
if (node == null) |
407 |
|
|
return null; |
408 |
|
|
|
409 |
|
|
else { |
410 |
|
|
Object x = node.get(); |
411 |
|
|
if (x != null) |
412 |
|
|
return (E)x; |
413 |
|
|
// else retry |
414 |
|
|
} |
415 |
|
|
} |
416 |
tim |
1.1 |
} |
417 |
dl |
1.2 |
|
418 |
dl |
1.5 |
/** |
419 |
dholmes |
1.11 |
* Always returns <tt>true</tt>. |
420 |
|
|
* A <tt>SynchronousQueue</tt> has no internal capacity. |
421 |
|
|
* @return <tt>true</tt> |
422 |
dl |
1.5 |
*/ |
423 |
|
|
public boolean isEmpty() { |
424 |
|
|
return true; |
425 |
|
|
} |
426 |
|
|
|
427 |
|
|
/** |
428 |
dholmes |
1.11 |
* Always returns zero. |
429 |
|
|
* A <tt>SynchronousQueue</tt> has no internal capacity. |
430 |
dl |
1.5 |
* @return zero. |
431 |
|
|
*/ |
432 |
|
|
public int size() { |
433 |
|
|
return 0; |
434 |
tim |
1.1 |
} |
435 |
dl |
1.2 |
|
436 |
dl |
1.5 |
/** |
437 |
dholmes |
1.11 |
* Always returns zero. |
438 |
|
|
* A <tt>SynchronousQueue</tt> has no internal capacity. |
439 |
dl |
1.5 |
* @return zero. |
440 |
|
|
*/ |
441 |
|
|
public int remainingCapacity() { |
442 |
|
|
return 0; |
443 |
|
|
} |
444 |
|
|
|
445 |
|
|
/** |
446 |
dholmes |
1.11 |
* Does nothing. |
447 |
|
|
* A <tt>SynchronousQueue</tt> has no internal capacity. |
448 |
|
|
*/ |
449 |
|
|
public void clear() {} |
450 |
|
|
|
451 |
|
|
/** |
452 |
|
|
* Always returns <tt>false</tt>. |
453 |
|
|
* A <tt>SynchronousQueue</tt> has no internal capacity. |
454 |
dl |
1.18 |
* @param o the element |
455 |
dholmes |
1.11 |
* @return <tt>false</tt> |
456 |
|
|
*/ |
457 |
|
|
public boolean contains(Object o) { |
458 |
|
|
return false; |
459 |
|
|
} |
460 |
|
|
|
461 |
|
|
/** |
462 |
dl |
1.18 |
* Always returns <tt>false</tt>. |
463 |
|
|
* A <tt>SynchronousQueue</tt> has no internal capacity. |
464 |
|
|
* |
465 |
|
|
* @param o the element to remove |
466 |
|
|
* @return <tt>false</tt> |
467 |
|
|
*/ |
468 |
|
|
public boolean remove(Object o) { |
469 |
|
|
return false; |
470 |
|
|
} |
471 |
|
|
|
472 |
|
|
/** |
473 |
dl |
1.16 |
* Returns <tt>false</tt> unless given collection is empty. |
474 |
dholmes |
1.11 |
* A <tt>SynchronousQueue</tt> has no internal capacity. |
475 |
dl |
1.18 |
* @param c the collection |
476 |
dl |
1.16 |
* @return <tt>false</tt> unless given collection is empty |
477 |
dholmes |
1.11 |
*/ |
478 |
dl |
1.12 |
public boolean containsAll(Collection<?> c) { |
479 |
dl |
1.16 |
return c.isEmpty(); |
480 |
dholmes |
1.11 |
} |
481 |
|
|
|
482 |
|
|
/** |
483 |
|
|
* Always returns <tt>false</tt>. |
484 |
|
|
* A <tt>SynchronousQueue</tt> has no internal capacity. |
485 |
dl |
1.18 |
* @param c the collection |
486 |
dholmes |
1.11 |
* @return <tt>false</tt> |
487 |
|
|
*/ |
488 |
dl |
1.12 |
public boolean removeAll(Collection<?> c) { |
489 |
dholmes |
1.11 |
return false; |
490 |
|
|
} |
491 |
|
|
|
492 |
|
|
/** |
493 |
|
|
* Always returns <tt>false</tt>. |
494 |
|
|
* A <tt>SynchronousQueue</tt> has no internal capacity. |
495 |
dl |
1.18 |
* @param c the collection |
496 |
dholmes |
1.11 |
* @return <tt>false</tt> |
497 |
|
|
*/ |
498 |
dl |
1.12 |
public boolean retainAll(Collection<?> c) { |
499 |
dholmes |
1.11 |
return false; |
500 |
|
|
} |
501 |
|
|
|
502 |
|
|
/** |
503 |
|
|
* Always returns <tt>null</tt>. |
504 |
|
|
* A <tt>SynchronousQueue</tt> does not return elements |
505 |
dl |
1.5 |
* unless actively waited on. |
506 |
dholmes |
1.11 |
* @return <tt>null</tt> |
507 |
dl |
1.5 |
*/ |
508 |
|
|
public E peek() { |
509 |
|
|
return null; |
510 |
|
|
} |
511 |
|
|
|
512 |
|
|
|
513 |
|
|
static class EmptyIterator<E> implements Iterator<E> { |
514 |
dl |
1.2 |
public boolean hasNext() { |
515 |
|
|
return false; |
516 |
|
|
} |
517 |
|
|
public E next() { |
518 |
|
|
throw new NoSuchElementException(); |
519 |
|
|
} |
520 |
|
|
public void remove() { |
521 |
dl |
1.17 |
throw new IllegalStateException(); |
522 |
dl |
1.2 |
} |
523 |
tim |
1.1 |
} |
524 |
dl |
1.2 |
|
525 |
dl |
1.5 |
/** |
526 |
dl |
1.18 |
* Returns an empty iterator in which <tt>hasNext</tt> always returns |
527 |
tim |
1.13 |
* <tt>false</tt>. |
528 |
|
|
* |
529 |
dholmes |
1.11 |
* @return an empty iterator |
530 |
dl |
1.5 |
*/ |
531 |
dl |
1.2 |
public Iterator<E> iterator() { |
532 |
dl |
1.5 |
return new EmptyIterator<E>(); |
533 |
tim |
1.1 |
} |
534 |
|
|
|
535 |
dl |
1.2 |
|
536 |
dl |
1.5 |
/** |
537 |
dholmes |
1.11 |
* Returns a zero-length array. |
538 |
|
|
* @return a zero-length array |
539 |
dl |
1.5 |
*/ |
540 |
dl |
1.3 |
public Object[] toArray() { |
541 |
tim |
1.10 |
return (E[]) new Object[0]; |
542 |
tim |
1.1 |
} |
543 |
|
|
|
544 |
dholmes |
1.11 |
/** |
545 |
|
|
* Sets the zeroeth element of the specified array to <tt>null</tt> |
546 |
|
|
* (if the array has non-zero length) and returns it. |
547 |
|
|
* @return the specified array |
548 |
|
|
*/ |
549 |
dl |
1.2 |
public <T> T[] toArray(T[] a) { |
550 |
|
|
if (a.length > 0) |
551 |
|
|
a[0] = null; |
552 |
|
|
return a; |
553 |
|
|
} |
554 |
dl |
1.21 |
|
555 |
|
|
|
556 |
|
|
public int drainTo(Collection<? super E> c) { |
557 |
|
|
if (c == null) |
558 |
|
|
throw new NullPointerException(); |
559 |
|
|
if (c == this) |
560 |
|
|
throw new IllegalArgumentException(); |
561 |
|
|
int n = 0; |
562 |
|
|
E e; |
563 |
|
|
while ( (e = poll()) != null) { |
564 |
|
|
c.add(e); |
565 |
|
|
++n; |
566 |
|
|
} |
567 |
|
|
return n; |
568 |
|
|
} |
569 |
|
|
|
570 |
|
|
public int drainTo(Collection<? super E> c, int maxElements) { |
571 |
|
|
if (c == null) |
572 |
|
|
throw new NullPointerException(); |
573 |
|
|
if (c == this) |
574 |
|
|
throw new IllegalArgumentException(); |
575 |
|
|
int n = 0; |
576 |
|
|
E e; |
577 |
|
|
while (n < maxElements && (e = poll()) != null) { |
578 |
|
|
c.add(e); |
579 |
|
|
++n; |
580 |
|
|
} |
581 |
|
|
return n; |
582 |
|
|
} |
583 |
tim |
1.1 |
} |
584 |
dholmes |
1.11 |
|
585 |
|
|
|
586 |
|
|
|
587 |
|
|
|
588 |
|
|
|