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dl |
1.1 |
/* |
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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, as explained at |
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* http://creativecommons.org/licenses/publicdomain |
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*/ |
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package jsr166y; |
8 |
jsr166 |
1.26 |
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9 |
dl |
1.1 |
import java.util.concurrent.*; |
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jsr166 |
1.26 |
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11 |
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import java.util.AbstractQueue; |
12 |
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import java.util.Collection; |
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import java.util.Iterator; |
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import java.util.NoSuchElementException; |
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import java.util.concurrent.locks.LockSupport; |
16 |
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import java.util.concurrent.atomic.AtomicReference; |
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dl |
1.1 |
|
18 |
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/** |
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* An unbounded {@linkplain TransferQueue} based on linked nodes. |
20 |
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* This queue orders elements FIFO (first-in-first-out) with respect |
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* to any given producer. The <em>head</em> of the queue is that |
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* element that has been on the queue the longest time for some |
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* producer. The <em>tail</em> of the queue is that element that has |
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* been on the queue the shortest time for some producer. |
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* |
26 |
jsr166 |
1.11 |
* <p>Beware that, unlike in most collections, the {@code size} |
27 |
dl |
1.1 |
* method is <em>NOT</em> a constant-time operation. Because of the |
28 |
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* asynchronous nature of these queues, determining the current number |
29 |
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* of elements requires a traversal of the elements. |
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* |
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* <p>This class and its iterator implement all of the |
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* <em>optional</em> methods of the {@link Collection} and {@link |
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* Iterator} interfaces. |
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* |
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* <p>Memory consistency effects: As with other concurrent |
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* collections, actions in a thread prior to placing an object into a |
37 |
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* {@code LinkedTransferQueue} |
38 |
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* <a href="package-summary.html#MemoryVisibility"><i>happen-before</i></a> |
39 |
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* actions subsequent to the access or removal of that element from |
40 |
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* the {@code LinkedTransferQueue} in another thread. |
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* |
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* <p>This class is a member of the |
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* <a href="{@docRoot}/../technotes/guides/collections/index.html"> |
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* Java Collections Framework</a>. |
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* |
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dl |
1.3 |
* @since 1.7 |
47 |
dl |
1.1 |
* @author Doug Lea |
48 |
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* @param <E> the type of elements held in this collection |
49 |
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*/ |
50 |
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public class LinkedTransferQueue<E> extends AbstractQueue<E> |
51 |
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implements TransferQueue<E>, java.io.Serializable { |
52 |
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private static final long serialVersionUID = -3223113410248163686L; |
53 |
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54 |
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/* |
55 |
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* This class extends the approach used in FIFO-mode |
56 |
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* SynchronousQueues. See the internal documentation, as well as |
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* the PPoPP 2006 paper "Scalable Synchronous Queues" by Scherer, |
58 |
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* Lea & Scott |
59 |
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* (http://www.cs.rice.edu/~wns1/papers/2006-PPoPP-SQ.pdf) |
60 |
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* |
61 |
dl |
1.9 |
* The main extension is to provide different Wait modes for the |
62 |
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* main "xfer" method that puts or takes items. These don't |
63 |
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* impact the basic dual-queue logic, but instead control whether |
64 |
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* or how threads block upon insertion of request or data nodes |
65 |
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* into the dual queue. It also uses slightly different |
66 |
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* conventions for tracking whether nodes are off-list or |
67 |
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* cancelled. |
68 |
dl |
1.1 |
*/ |
69 |
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70 |
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// Wait modes for xfer method |
71 |
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static final int NOWAIT = 0; |
72 |
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static final int TIMEOUT = 1; |
73 |
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static final int WAIT = 2; |
74 |
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75 |
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/** The number of CPUs, for spin control */ |
76 |
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static final int NCPUS = Runtime.getRuntime().availableProcessors(); |
77 |
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78 |
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/** |
79 |
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* The number of times to spin before blocking in timed waits. |
80 |
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* The value is empirically derived -- it works well across a |
81 |
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* variety of processors and OSes. Empirically, the best value |
82 |
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* seems not to vary with number of CPUs (beyond 2) so is just |
83 |
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* a constant. |
84 |
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*/ |
85 |
jsr166 |
1.22 |
static final int maxTimedSpins = (NCPUS < 2) ? 0 : 32; |
86 |
dl |
1.1 |
|
87 |
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/** |
88 |
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* The number of times to spin before blocking in untimed waits. |
89 |
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* This is greater than timed value because untimed waits spin |
90 |
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* faster since they don't need to check times on each spin. |
91 |
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*/ |
92 |
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static final int maxUntimedSpins = maxTimedSpins * 16; |
93 |
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94 |
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/** |
95 |
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* The number of nanoseconds for which it is faster to spin |
96 |
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* rather than to use timed park. A rough estimate suffices. |
97 |
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*/ |
98 |
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static final long spinForTimeoutThreshold = 1000L; |
99 |
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|
100 |
jsr166 |
1.5 |
/** |
101 |
dl |
1.9 |
* Node class for LinkedTransferQueue. Opportunistically |
102 |
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* subclasses from AtomicReference to represent item. Uses Object, |
103 |
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* not E, to allow setting item to "this" after use, to avoid |
104 |
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* garbage retention. Similarly, setting the next field to this is |
105 |
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* used as sentinel that node is off list. |
106 |
dl |
1.1 |
*/ |
107 |
jsr166 |
1.25 |
static final class Node<E> extends AtomicReference<Object> { |
108 |
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volatile Node<E> next; |
109 |
dl |
1.1 |
volatile Thread waiter; // to control park/unpark |
110 |
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final boolean isData; |
111 |
jsr166 |
1.25 |
|
112 |
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Node(E item, boolean isData) { |
113 |
dl |
1.1 |
super(item); |
114 |
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this.isData = isData; |
115 |
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} |
116 |
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117 |
jsr166 |
1.32 |
// Unsafe mechanics |
118 |
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119 |
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private static final sun.misc.Unsafe UNSAFE = getUnsafe(); |
120 |
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private static final long nextOffset = |
121 |
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objectFieldOffset(UNSAFE, "next", Node.class); |
122 |
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123 |
jsr166 |
1.25 |
final boolean casNext(Node<E> cmp, Node<E> val) { |
124 |
jsr166 |
1.31 |
return UNSAFE.compareAndSwapObject(this, nextOffset, cmp, val); |
125 |
dl |
1.1 |
} |
126 |
dl |
1.15 |
|
127 |
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final void clearNext() { |
128 |
jsr166 |
1.31 |
UNSAFE.putOrderedObject(this, nextOffset, this); |
129 |
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} |
130 |
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131 |
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/** |
132 |
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* Returns a sun.misc.Unsafe. Suitable for use in a 3rd party package. |
133 |
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* Replace with a simple call to Unsafe.getUnsafe when integrating |
134 |
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* into a jdk. |
135 |
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* |
136 |
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* @return a sun.misc.Unsafe |
137 |
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*/ |
138 |
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private static sun.misc.Unsafe getUnsafe() { |
139 |
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try { |
140 |
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return sun.misc.Unsafe.getUnsafe(); |
141 |
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} catch (SecurityException se) { |
142 |
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try { |
143 |
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return java.security.AccessController.doPrivileged |
144 |
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(new java.security |
145 |
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.PrivilegedExceptionAction<sun.misc.Unsafe>() { |
146 |
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public sun.misc.Unsafe run() throws Exception { |
147 |
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java.lang.reflect.Field f = sun.misc |
148 |
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.Unsafe.class.getDeclaredField("theUnsafe"); |
149 |
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f.setAccessible(true); |
150 |
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return (sun.misc.Unsafe) f.get(null); |
151 |
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}}); |
152 |
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} catch (java.security.PrivilegedActionException e) { |
153 |
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throw new RuntimeException("Could not initialize intrinsics", |
154 |
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e.getCause()); |
155 |
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} |
156 |
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} |
157 |
dl |
1.15 |
} |
158 |
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|
159 |
jsr166 |
1.24 |
private static final long serialVersionUID = -3375979862319811754L; |
160 |
dl |
1.1 |
} |
161 |
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162 |
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/** |
163 |
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* Padded version of AtomicReference used for head, tail and |
164 |
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* cleanMe, to alleviate contention across threads CASing one vs |
165 |
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* the other. |
166 |
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*/ |
167 |
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static final class PaddedAtomicReference<T> extends AtomicReference<T> { |
168 |
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// enough padding for 64bytes with 4byte refs |
169 |
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Object p0, p1, p2, p3, p4, p5, p6, p7, p8, p9, pa, pb, pc, pd, pe; |
170 |
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PaddedAtomicReference(T r) { super(r); } |
171 |
jsr166 |
1.24 |
private static final long serialVersionUID = 8170090609809740854L; |
172 |
dl |
1.1 |
} |
173 |
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174 |
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|
175 |
dl |
1.7 |
/** head of the queue */ |
176 |
jsr166 |
1.25 |
private transient final PaddedAtomicReference<Node<E>> head; |
177 |
jsr166 |
1.23 |
|
178 |
dl |
1.7 |
/** tail of the queue */ |
179 |
jsr166 |
1.25 |
private transient final PaddedAtomicReference<Node<E>> tail; |
180 |
dl |
1.1 |
|
181 |
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/** |
182 |
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* Reference to a cancelled node that might not yet have been |
183 |
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* unlinked from queue because it was the last inserted node |
184 |
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* when it cancelled. |
185 |
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*/ |
186 |
jsr166 |
1.25 |
private transient final PaddedAtomicReference<Node<E>> cleanMe; |
187 |
dl |
1.1 |
|
188 |
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/** |
189 |
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* Tries to cas nh as new head; if successful, unlink |
190 |
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* old head's next node to avoid garbage retention. |
191 |
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*/ |
192 |
jsr166 |
1.25 |
private boolean advanceHead(Node<E> h, Node<E> nh) { |
193 |
dl |
1.1 |
if (h == head.get() && head.compareAndSet(h, nh)) { |
194 |
dl |
1.15 |
h.clearNext(); // forget old next |
195 |
dl |
1.1 |
return true; |
196 |
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} |
197 |
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return false; |
198 |
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} |
199 |
jsr166 |
1.5 |
|
200 |
dl |
1.1 |
/** |
201 |
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* Puts or takes an item. Used for most queue operations (except |
202 |
dl |
1.9 |
* poll() and tryTransfer()). See the similar code in |
203 |
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* SynchronousQueue for detailed explanation. |
204 |
jsr166 |
1.17 |
* |
205 |
jsr166 |
1.4 |
* @param e the item or if null, signifies that this is a take |
206 |
dl |
1.1 |
* @param mode the wait mode: NOWAIT, TIMEOUT, WAIT |
207 |
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* @param nanos timeout in nanosecs, used only if mode is TIMEOUT |
208 |
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* @return an item, or null on failure |
209 |
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*/ |
210 |
jsr166 |
1.25 |
private E xfer(E e, int mode, long nanos) { |
211 |
dl |
1.1 |
boolean isData = (e != null); |
212 |
jsr166 |
1.25 |
Node<E> s = null; |
213 |
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final PaddedAtomicReference<Node<E>> head = this.head; |
214 |
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final PaddedAtomicReference<Node<E>> tail = this.tail; |
215 |
dl |
1.1 |
|
216 |
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for (;;) { |
217 |
jsr166 |
1.25 |
Node<E> t = tail.get(); |
218 |
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Node<E> h = head.get(); |
219 |
dl |
1.1 |
|
220 |
|
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if (t != null && (t == h || t.isData == isData)) { |
221 |
|
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if (s == null) |
222 |
jsr166 |
1.25 |
s = new Node<E>(e, isData); |
223 |
|
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Node<E> last = t.next; |
224 |
dl |
1.1 |
if (last != null) { |
225 |
|
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if (t == tail.get()) |
226 |
|
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tail.compareAndSet(t, last); |
227 |
|
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} |
228 |
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else if (t.casNext(null, s)) { |
229 |
|
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tail.compareAndSet(t, s); |
230 |
|
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return awaitFulfill(t, s, e, mode, nanos); |
231 |
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} |
232 |
|
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} |
233 |
jsr166 |
1.5 |
|
234 |
dl |
1.1 |
else if (h != null) { |
235 |
jsr166 |
1.25 |
Node<E> first = h.next; |
236 |
jsr166 |
1.5 |
if (t == tail.get() && first != null && |
237 |
dl |
1.1 |
advanceHead(h, first)) { |
238 |
|
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Object x = first.get(); |
239 |
|
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if (x != first && first.compareAndSet(x, e)) { |
240 |
|
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LockSupport.unpark(first.waiter); |
241 |
jsr166 |
1.25 |
return isData ? e : (E) x; |
242 |
dl |
1.1 |
} |
243 |
|
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} |
244 |
|
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} |
245 |
|
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} |
246 |
|
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} |
247 |
|
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|
248 |
|
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|
249 |
|
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/** |
250 |
|
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* Version of xfer for poll() and tryTransfer, which |
251 |
jsr166 |
1.17 |
* simplifies control paths both here and in xfer. |
252 |
dl |
1.1 |
*/ |
253 |
jsr166 |
1.25 |
private E fulfill(E e) { |
254 |
dl |
1.1 |
boolean isData = (e != null); |
255 |
jsr166 |
1.25 |
final PaddedAtomicReference<Node<E>> head = this.head; |
256 |
|
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final PaddedAtomicReference<Node<E>> tail = this.tail; |
257 |
dl |
1.1 |
|
258 |
|
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for (;;) { |
259 |
jsr166 |
1.25 |
Node<E> t = tail.get(); |
260 |
|
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Node<E> h = head.get(); |
261 |
dl |
1.1 |
|
262 |
|
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if (t != null && (t == h || t.isData == isData)) { |
263 |
jsr166 |
1.25 |
Node<E> last = t.next; |
264 |
dl |
1.1 |
if (t == tail.get()) { |
265 |
|
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if (last != null) |
266 |
|
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tail.compareAndSet(t, last); |
267 |
|
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else |
268 |
|
|
return null; |
269 |
|
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} |
270 |
|
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} |
271 |
|
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else if (h != null) { |
272 |
jsr166 |
1.25 |
Node<E> first = h.next; |
273 |
jsr166 |
1.5 |
if (t == tail.get() && |
274 |
dl |
1.1 |
first != null && |
275 |
|
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advanceHead(h, first)) { |
276 |
|
|
Object x = first.get(); |
277 |
|
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if (x != first && first.compareAndSet(x, e)) { |
278 |
|
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LockSupport.unpark(first.waiter); |
279 |
jsr166 |
1.25 |
return isData ? e : (E) x; |
280 |
dl |
1.1 |
} |
281 |
|
|
} |
282 |
|
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} |
283 |
|
|
} |
284 |
|
|
} |
285 |
|
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|
286 |
|
|
/** |
287 |
|
|
* Spins/blocks until node s is fulfilled or caller gives up, |
288 |
|
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* depending on wait mode. |
289 |
|
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* |
290 |
|
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* @param pred the predecessor of waiting node |
291 |
|
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* @param s the waiting node |
292 |
|
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* @param e the comparison value for checking match |
293 |
|
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* @param mode mode |
294 |
|
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* @param nanos timeout value |
295 |
|
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* @return matched item, or s if cancelled |
296 |
|
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*/ |
297 |
jsr166 |
1.25 |
private E awaitFulfill(Node<E> pred, Node<E> s, E e, |
298 |
|
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int mode, long nanos) { |
299 |
dl |
1.1 |
if (mode == NOWAIT) |
300 |
|
|
return null; |
301 |
|
|
|
302 |
jsr166 |
1.22 |
long lastTime = (mode == TIMEOUT) ? System.nanoTime() : 0; |
303 |
dl |
1.1 |
Thread w = Thread.currentThread(); |
304 |
|
|
int spins = -1; // set to desired spin count below |
305 |
|
|
for (;;) { |
306 |
|
|
if (w.isInterrupted()) |
307 |
|
|
s.compareAndSet(e, s); |
308 |
|
|
Object x = s.get(); |
309 |
|
|
if (x != e) { // Node was matched or cancelled |
310 |
|
|
advanceHead(pred, s); // unlink if head |
311 |
jsr166 |
1.17 |
if (x == s) { // was cancelled |
312 |
dl |
1.9 |
clean(pred, s); |
313 |
|
|
return null; |
314 |
|
|
} |
315 |
jsr166 |
1.5 |
else if (x != null) { |
316 |
dl |
1.1 |
s.set(s); // avoid garbage retention |
317 |
jsr166 |
1.25 |
return (E) x; |
318 |
dl |
1.1 |
} |
319 |
|
|
else |
320 |
|
|
return e; |
321 |
|
|
} |
322 |
|
|
if (mode == TIMEOUT) { |
323 |
|
|
long now = System.nanoTime(); |
324 |
|
|
nanos -= now - lastTime; |
325 |
|
|
lastTime = now; |
326 |
|
|
if (nanos <= 0) { |
327 |
|
|
s.compareAndSet(e, s); // try to cancel |
328 |
|
|
continue; |
329 |
|
|
} |
330 |
|
|
} |
331 |
|
|
if (spins < 0) { |
332 |
jsr166 |
1.25 |
Node<E> h = head.get(); // only spin if at head |
333 |
dl |
1.1 |
spins = ((h != null && h.next == s) ? |
334 |
jsr166 |
1.22 |
((mode == TIMEOUT) ? |
335 |
dl |
1.1 |
maxTimedSpins : maxUntimedSpins) : 0); |
336 |
|
|
} |
337 |
|
|
if (spins > 0) |
338 |
|
|
--spins; |
339 |
|
|
else if (s.waiter == null) |
340 |
|
|
s.waiter = w; |
341 |
|
|
else if (mode != TIMEOUT) { |
342 |
dl |
1.12 |
LockSupport.park(this); |
343 |
dl |
1.1 |
s.waiter = null; |
344 |
|
|
spins = -1; |
345 |
|
|
} |
346 |
|
|
else if (nanos > spinForTimeoutThreshold) { |
347 |
dl |
1.12 |
LockSupport.parkNanos(this, nanos); |
348 |
dl |
1.1 |
s.waiter = null; |
349 |
|
|
spins = -1; |
350 |
|
|
} |
351 |
|
|
} |
352 |
|
|
} |
353 |
|
|
|
354 |
|
|
/** |
355 |
jsr166 |
1.17 |
* Returns validated tail for use in cleaning methods. |
356 |
dl |
1.9 |
*/ |
357 |
jsr166 |
1.25 |
private Node<E> getValidatedTail() { |
358 |
dl |
1.9 |
for (;;) { |
359 |
jsr166 |
1.25 |
Node<E> h = head.get(); |
360 |
|
|
Node<E> first = h.next; |
361 |
dl |
1.9 |
if (first != null && first.next == first) { // help advance |
362 |
|
|
advanceHead(h, first); |
363 |
|
|
continue; |
364 |
|
|
} |
365 |
jsr166 |
1.25 |
Node<E> t = tail.get(); |
366 |
|
|
Node<E> last = t.next; |
367 |
dl |
1.9 |
if (t == tail.get()) { |
368 |
|
|
if (last != null) |
369 |
|
|
tail.compareAndSet(t, last); // help advance |
370 |
|
|
else |
371 |
|
|
return t; |
372 |
|
|
} |
373 |
|
|
} |
374 |
jsr166 |
1.10 |
} |
375 |
dl |
1.9 |
|
376 |
|
|
/** |
377 |
dl |
1.1 |
* Gets rid of cancelled node s with original predecessor pred. |
378 |
jsr166 |
1.17 |
* |
379 |
dl |
1.9 |
* @param pred predecessor of cancelled node |
380 |
|
|
* @param s the cancelled node |
381 |
dl |
1.1 |
*/ |
382 |
jsr166 |
1.25 |
private void clean(Node<E> pred, Node<E> s) { |
383 |
dl |
1.1 |
Thread w = s.waiter; |
384 |
|
|
if (w != null) { // Wake up thread |
385 |
|
|
s.waiter = null; |
386 |
|
|
if (w != Thread.currentThread()) |
387 |
|
|
LockSupport.unpark(w); |
388 |
|
|
} |
389 |
dl |
1.15 |
|
390 |
|
|
if (pred == null) |
391 |
|
|
return; |
392 |
|
|
|
393 |
dl |
1.9 |
/* |
394 |
|
|
* At any given time, exactly one node on list cannot be |
395 |
|
|
* deleted -- the last inserted node. To accommodate this, if |
396 |
|
|
* we cannot delete s, we save its predecessor as "cleanMe", |
397 |
|
|
* processing the previously saved version first. At least one |
398 |
|
|
* of node s or the node previously saved can always be |
399 |
|
|
* processed, so this always terminates. |
400 |
|
|
*/ |
401 |
|
|
while (pred.next == s) { |
402 |
jsr166 |
1.25 |
Node<E> oldpred = reclean(); // First, help get rid of cleanMe |
403 |
|
|
Node<E> t = getValidatedTail(); |
404 |
dl |
1.9 |
if (s != t) { // If not tail, try to unsplice |
405 |
jsr166 |
1.25 |
Node<E> sn = s.next; // s.next == s means s already off list |
406 |
jsr166 |
1.10 |
if (sn == s || pred.casNext(s, sn)) |
407 |
dl |
1.9 |
break; |
408 |
|
|
} |
409 |
|
|
else if (oldpred == pred || // Already saved |
410 |
|
|
(oldpred == null && cleanMe.compareAndSet(null, pred))) |
411 |
|
|
break; // Postpone cleaning |
412 |
|
|
} |
413 |
|
|
} |
414 |
jsr166 |
1.5 |
|
415 |
dl |
1.9 |
/** |
416 |
|
|
* Tries to unsplice the cancelled node held in cleanMe that was |
417 |
|
|
* previously uncleanable because it was at tail. |
418 |
jsr166 |
1.17 |
* |
419 |
dl |
1.9 |
* @return current cleanMe node (or null) |
420 |
|
|
*/ |
421 |
jsr166 |
1.25 |
private Node<E> reclean() { |
422 |
jsr166 |
1.10 |
/* |
423 |
dl |
1.9 |
* cleanMe is, or at one time was, predecessor of cancelled |
424 |
|
|
* node s that was the tail so could not be unspliced. If s |
425 |
|
|
* is no longer the tail, try to unsplice if necessary and |
426 |
|
|
* make cleanMe slot available. This differs from similar |
427 |
|
|
* code in clean() because we must check that pred still |
428 |
|
|
* points to a cancelled node that must be unspliced -- if |
429 |
|
|
* not, we can (must) clear cleanMe without unsplicing. |
430 |
|
|
* This can loop only due to contention on casNext or |
431 |
jsr166 |
1.10 |
* clearing cleanMe. |
432 |
dl |
1.9 |
*/ |
433 |
jsr166 |
1.25 |
Node<E> pred; |
434 |
dl |
1.9 |
while ((pred = cleanMe.get()) != null) { |
435 |
jsr166 |
1.25 |
Node<E> t = getValidatedTail(); |
436 |
|
|
Node<E> s = pred.next; |
437 |
jsr166 |
1.10 |
if (s != t) { |
438 |
jsr166 |
1.25 |
Node<E> sn; |
439 |
dl |
1.9 |
if (s == null || s == pred || s.get() != s || |
440 |
|
|
(sn = s.next) == s || pred.casNext(s, sn)) |
441 |
|
|
cleanMe.compareAndSet(pred, null); |
442 |
dl |
1.1 |
} |
443 |
dl |
1.9 |
else // s is still tail; cannot clean |
444 |
|
|
break; |
445 |
dl |
1.1 |
} |
446 |
dl |
1.9 |
return pred; |
447 |
dl |
1.1 |
} |
448 |
jsr166 |
1.5 |
|
449 |
dl |
1.1 |
/** |
450 |
jsr166 |
1.11 |
* Creates an initially empty {@code LinkedTransferQueue}. |
451 |
dl |
1.1 |
*/ |
452 |
|
|
public LinkedTransferQueue() { |
453 |
jsr166 |
1.25 |
Node<E> dummy = new Node<E>(null, false); |
454 |
|
|
head = new PaddedAtomicReference<Node<E>>(dummy); |
455 |
|
|
tail = new PaddedAtomicReference<Node<E>>(dummy); |
456 |
|
|
cleanMe = new PaddedAtomicReference<Node<E>>(null); |
457 |
dl |
1.1 |
} |
458 |
|
|
|
459 |
|
|
/** |
460 |
jsr166 |
1.11 |
* Creates a {@code LinkedTransferQueue} |
461 |
dl |
1.1 |
* initially containing the elements of the given collection, |
462 |
|
|
* added in traversal order of the collection's iterator. |
463 |
jsr166 |
1.17 |
* |
464 |
dl |
1.1 |
* @param c the collection of elements to initially contain |
465 |
|
|
* @throws NullPointerException if the specified collection or any |
466 |
|
|
* of its elements are null |
467 |
|
|
*/ |
468 |
|
|
public LinkedTransferQueue(Collection<? extends E> c) { |
469 |
dl |
1.7 |
this(); |
470 |
dl |
1.1 |
addAll(c); |
471 |
|
|
} |
472 |
|
|
|
473 |
jsr166 |
1.29 |
/** |
474 |
|
|
* @throws InterruptedException {@inheritDoc} |
475 |
|
|
* @throws NullPointerException {@inheritDoc} |
476 |
|
|
*/ |
477 |
dl |
1.1 |
public void put(E e) throws InterruptedException { |
478 |
|
|
if (e == null) throw new NullPointerException(); |
479 |
|
|
if (Thread.interrupted()) throw new InterruptedException(); |
480 |
|
|
xfer(e, NOWAIT, 0); |
481 |
|
|
} |
482 |
|
|
|
483 |
jsr166 |
1.29 |
/** |
484 |
|
|
* @throws InterruptedException {@inheritDoc} |
485 |
|
|
* @throws NullPointerException {@inheritDoc} |
486 |
|
|
*/ |
487 |
jsr166 |
1.5 |
public boolean offer(E e, long timeout, TimeUnit unit) |
488 |
dl |
1.1 |
throws InterruptedException { |
489 |
|
|
if (e == null) throw new NullPointerException(); |
490 |
|
|
if (Thread.interrupted()) throw new InterruptedException(); |
491 |
|
|
xfer(e, NOWAIT, 0); |
492 |
|
|
return true; |
493 |
|
|
} |
494 |
|
|
|
495 |
jsr166 |
1.29 |
/** |
496 |
|
|
* @throws NullPointerException {@inheritDoc} |
497 |
|
|
*/ |
498 |
dl |
1.1 |
public boolean offer(E e) { |
499 |
|
|
if (e == null) throw new NullPointerException(); |
500 |
|
|
xfer(e, NOWAIT, 0); |
501 |
|
|
return true; |
502 |
|
|
} |
503 |
|
|
|
504 |
jsr166 |
1.29 |
/** |
505 |
|
|
* @throws NullPointerException {@inheritDoc} |
506 |
|
|
*/ |
507 |
dl |
1.15 |
public boolean add(E e) { |
508 |
|
|
if (e == null) throw new NullPointerException(); |
509 |
|
|
xfer(e, NOWAIT, 0); |
510 |
|
|
return true; |
511 |
|
|
} |
512 |
|
|
|
513 |
jsr166 |
1.29 |
/** |
514 |
|
|
* @throws InterruptedException {@inheritDoc} |
515 |
|
|
* @throws NullPointerException {@inheritDoc} |
516 |
|
|
*/ |
517 |
dl |
1.1 |
public void transfer(E e) throws InterruptedException { |
518 |
|
|
if (e == null) throw new NullPointerException(); |
519 |
|
|
if (xfer(e, WAIT, 0) == null) { |
520 |
jsr166 |
1.6 |
Thread.interrupted(); |
521 |
dl |
1.1 |
throw new InterruptedException(); |
522 |
jsr166 |
1.6 |
} |
523 |
dl |
1.1 |
} |
524 |
|
|
|
525 |
jsr166 |
1.29 |
/** |
526 |
|
|
* @throws InterruptedException {@inheritDoc} |
527 |
|
|
* @throws NullPointerException {@inheritDoc} |
528 |
|
|
*/ |
529 |
dl |
1.1 |
public boolean tryTransfer(E e, long timeout, TimeUnit unit) |
530 |
|
|
throws InterruptedException { |
531 |
|
|
if (e == null) throw new NullPointerException(); |
532 |
|
|
if (xfer(e, TIMEOUT, unit.toNanos(timeout)) != null) |
533 |
|
|
return true; |
534 |
|
|
if (!Thread.interrupted()) |
535 |
|
|
return false; |
536 |
|
|
throw new InterruptedException(); |
537 |
|
|
} |
538 |
|
|
|
539 |
jsr166 |
1.29 |
/** |
540 |
|
|
* @throws NullPointerException {@inheritDoc} |
541 |
|
|
*/ |
542 |
dl |
1.1 |
public boolean tryTransfer(E e) { |
543 |
|
|
if (e == null) throw new NullPointerException(); |
544 |
|
|
return fulfill(e) != null; |
545 |
|
|
} |
546 |
|
|
|
547 |
jsr166 |
1.29 |
/** |
548 |
|
|
* @throws InterruptedException {@inheritDoc} |
549 |
|
|
*/ |
550 |
dl |
1.1 |
public E take() throws InterruptedException { |
551 |
|
|
Object e = xfer(null, WAIT, 0); |
552 |
|
|
if (e != null) |
553 |
jsr166 |
1.22 |
return (E) e; |
554 |
jsr166 |
1.6 |
Thread.interrupted(); |
555 |
dl |
1.1 |
throw new InterruptedException(); |
556 |
|
|
} |
557 |
|
|
|
558 |
jsr166 |
1.29 |
/** |
559 |
|
|
* @throws InterruptedException {@inheritDoc} |
560 |
|
|
*/ |
561 |
dl |
1.1 |
public E poll(long timeout, TimeUnit unit) throws InterruptedException { |
562 |
|
|
Object e = xfer(null, TIMEOUT, unit.toNanos(timeout)); |
563 |
|
|
if (e != null || !Thread.interrupted()) |
564 |
jsr166 |
1.22 |
return (E) e; |
565 |
dl |
1.1 |
throw new InterruptedException(); |
566 |
|
|
} |
567 |
|
|
|
568 |
|
|
public E poll() { |
569 |
jsr166 |
1.25 |
return fulfill(null); |
570 |
dl |
1.1 |
} |
571 |
|
|
|
572 |
jsr166 |
1.29 |
/** |
573 |
jsr166 |
1.30 |
* @throws NullPointerException {@inheritDoc} |
574 |
|
|
* @throws IllegalArgumentException {@inheritDoc} |
575 |
jsr166 |
1.29 |
*/ |
576 |
dl |
1.1 |
public int drainTo(Collection<? super E> c) { |
577 |
|
|
if (c == null) |
578 |
|
|
throw new NullPointerException(); |
579 |
|
|
if (c == this) |
580 |
|
|
throw new IllegalArgumentException(); |
581 |
|
|
int n = 0; |
582 |
|
|
E e; |
583 |
|
|
while ( (e = poll()) != null) { |
584 |
|
|
c.add(e); |
585 |
|
|
++n; |
586 |
|
|
} |
587 |
|
|
return n; |
588 |
|
|
} |
589 |
|
|
|
590 |
jsr166 |
1.29 |
/** |
591 |
jsr166 |
1.30 |
* @throws NullPointerException {@inheritDoc} |
592 |
|
|
* @throws IllegalArgumentException {@inheritDoc} |
593 |
jsr166 |
1.29 |
*/ |
594 |
dl |
1.1 |
public int drainTo(Collection<? super E> c, int maxElements) { |
595 |
|
|
if (c == null) |
596 |
|
|
throw new NullPointerException(); |
597 |
|
|
if (c == this) |
598 |
|
|
throw new IllegalArgumentException(); |
599 |
|
|
int n = 0; |
600 |
|
|
E e; |
601 |
|
|
while (n < maxElements && (e = poll()) != null) { |
602 |
|
|
c.add(e); |
603 |
|
|
++n; |
604 |
|
|
} |
605 |
|
|
return n; |
606 |
|
|
} |
607 |
|
|
|
608 |
|
|
// Traversal-based methods |
609 |
|
|
|
610 |
|
|
/** |
611 |
jsr166 |
1.17 |
* Returns head after performing any outstanding helping steps. |
612 |
dl |
1.1 |
*/ |
613 |
jsr166 |
1.25 |
private Node<E> traversalHead() { |
614 |
dl |
1.1 |
for (;;) { |
615 |
jsr166 |
1.25 |
Node<E> t = tail.get(); |
616 |
|
|
Node<E> h = head.get(); |
617 |
dl |
1.1 |
if (h != null && t != null) { |
618 |
jsr166 |
1.25 |
Node<E> last = t.next; |
619 |
|
|
Node<E> first = h.next; |
620 |
dl |
1.1 |
if (t == tail.get()) { |
621 |
jsr166 |
1.5 |
if (last != null) |
622 |
dl |
1.1 |
tail.compareAndSet(t, last); |
623 |
|
|
else if (first != null) { |
624 |
|
|
Object x = first.get(); |
625 |
jsr166 |
1.5 |
if (x == first) |
626 |
|
|
advanceHead(h, first); |
627 |
dl |
1.1 |
else |
628 |
|
|
return h; |
629 |
|
|
} |
630 |
|
|
else |
631 |
|
|
return h; |
632 |
|
|
} |
633 |
|
|
} |
634 |
dl |
1.15 |
reclean(); |
635 |
dl |
1.1 |
} |
636 |
|
|
} |
637 |
|
|
|
638 |
|
|
|
639 |
|
|
public Iterator<E> iterator() { |
640 |
|
|
return new Itr(); |
641 |
|
|
} |
642 |
|
|
|
643 |
|
|
/** |
644 |
jsr166 |
1.4 |
* Iterators. Basic strategy is to traverse list, treating |
645 |
dl |
1.1 |
* non-data (i.e., request) nodes as terminating list. |
646 |
|
|
* Once a valid data node is found, the item is cached |
647 |
|
|
* so that the next call to next() will return it even |
648 |
|
|
* if subsequently removed. |
649 |
|
|
*/ |
650 |
|
|
class Itr implements Iterator<E> { |
651 |
jsr166 |
1.25 |
Node<E> next; // node to return next |
652 |
|
|
Node<E> pnext; // predecessor of next |
653 |
|
|
Node<E> snext; // successor of next |
654 |
|
|
Node<E> curr; // last returned node, for remove() |
655 |
|
|
Node<E> pcurr; // predecessor of curr, for remove() |
656 |
jsr166 |
1.18 |
E nextItem; // Cache of next item, once committed to in next |
657 |
jsr166 |
1.5 |
|
658 |
dl |
1.1 |
Itr() { |
659 |
dl |
1.15 |
findNext(); |
660 |
dl |
1.1 |
} |
661 |
jsr166 |
1.5 |
|
662 |
dl |
1.15 |
/** |
663 |
jsr166 |
1.17 |
* Ensures next points to next valid node, or null if none. |
664 |
dl |
1.15 |
*/ |
665 |
|
|
void findNext() { |
666 |
dl |
1.1 |
for (;;) { |
667 |
jsr166 |
1.25 |
Node<E> pred = pnext; |
668 |
|
|
Node<E> q = next; |
669 |
dl |
1.15 |
if (pred == null || pred == q) { |
670 |
|
|
pred = traversalHead(); |
671 |
|
|
q = pred.next; |
672 |
|
|
} |
673 |
|
|
if (q == null || !q.isData) { |
674 |
|
|
next = null; |
675 |
|
|
return; |
676 |
|
|
} |
677 |
|
|
Object x = q.get(); |
678 |
jsr166 |
1.25 |
Node<E> s = q.next; |
679 |
dl |
1.15 |
if (x != null && q != x && q != s) { |
680 |
jsr166 |
1.22 |
nextItem = (E) x; |
681 |
dl |
1.15 |
snext = s; |
682 |
|
|
pnext = pred; |
683 |
|
|
next = q; |
684 |
|
|
return; |
685 |
dl |
1.1 |
} |
686 |
dl |
1.15 |
pnext = q; |
687 |
|
|
next = s; |
688 |
dl |
1.1 |
} |
689 |
|
|
} |
690 |
jsr166 |
1.5 |
|
691 |
dl |
1.1 |
public boolean hasNext() { |
692 |
dl |
1.15 |
return next != null; |
693 |
dl |
1.1 |
} |
694 |
jsr166 |
1.5 |
|
695 |
dl |
1.1 |
public E next() { |
696 |
dl |
1.15 |
if (next == null) throw new NoSuchElementException(); |
697 |
|
|
pcurr = pnext; |
698 |
|
|
curr = next; |
699 |
|
|
pnext = next; |
700 |
|
|
next = snext; |
701 |
|
|
E x = nextItem; |
702 |
|
|
findNext(); |
703 |
|
|
return x; |
704 |
dl |
1.1 |
} |
705 |
jsr166 |
1.5 |
|
706 |
dl |
1.1 |
public void remove() { |
707 |
jsr166 |
1.25 |
Node<E> p = curr; |
708 |
dl |
1.15 |
if (p == null) |
709 |
dl |
1.1 |
throw new IllegalStateException(); |
710 |
|
|
Object x = p.get(); |
711 |
|
|
if (x != null && x != p && p.compareAndSet(x, p)) |
712 |
dl |
1.15 |
clean(pcurr, p); |
713 |
dl |
1.1 |
} |
714 |
|
|
} |
715 |
|
|
|
716 |
|
|
public E peek() { |
717 |
|
|
for (;;) { |
718 |
jsr166 |
1.25 |
Node<E> h = traversalHead(); |
719 |
|
|
Node<E> p = h.next; |
720 |
dl |
1.1 |
if (p == null) |
721 |
|
|
return null; |
722 |
|
|
Object x = p.get(); |
723 |
|
|
if (p != x) { |
724 |
|
|
if (!p.isData) |
725 |
|
|
return null; |
726 |
|
|
if (x != null) |
727 |
jsr166 |
1.22 |
return (E) x; |
728 |
dl |
1.1 |
} |
729 |
|
|
} |
730 |
|
|
} |
731 |
|
|
|
732 |
dl |
1.2 |
public boolean isEmpty() { |
733 |
|
|
for (;;) { |
734 |
jsr166 |
1.25 |
Node<E> h = traversalHead(); |
735 |
|
|
Node<E> p = h.next; |
736 |
dl |
1.2 |
if (p == null) |
737 |
|
|
return true; |
738 |
|
|
Object x = p.get(); |
739 |
|
|
if (p != x) { |
740 |
|
|
if (!p.isData) |
741 |
|
|
return true; |
742 |
|
|
if (x != null) |
743 |
|
|
return false; |
744 |
|
|
} |
745 |
|
|
} |
746 |
|
|
} |
747 |
|
|
|
748 |
dl |
1.1 |
public boolean hasWaitingConsumer() { |
749 |
|
|
for (;;) { |
750 |
jsr166 |
1.25 |
Node<E> h = traversalHead(); |
751 |
|
|
Node<E> p = h.next; |
752 |
dl |
1.1 |
if (p == null) |
753 |
|
|
return false; |
754 |
|
|
Object x = p.get(); |
755 |
jsr166 |
1.5 |
if (p != x) |
756 |
dl |
1.1 |
return !p.isData; |
757 |
|
|
} |
758 |
|
|
} |
759 |
jsr166 |
1.5 |
|
760 |
dl |
1.1 |
/** |
761 |
|
|
* Returns the number of elements in this queue. If this queue |
762 |
jsr166 |
1.11 |
* contains more than {@code Integer.MAX_VALUE} elements, returns |
763 |
|
|
* {@code Integer.MAX_VALUE}. |
764 |
dl |
1.1 |
* |
765 |
|
|
* <p>Beware that, unlike in most collections, this method is |
766 |
|
|
* <em>NOT</em> a constant-time operation. Because of the |
767 |
|
|
* asynchronous nature of these queues, determining the current |
768 |
|
|
* number of elements requires an O(n) traversal. |
769 |
|
|
* |
770 |
|
|
* @return the number of elements in this queue |
771 |
|
|
*/ |
772 |
|
|
public int size() { |
773 |
|
|
int count = 0; |
774 |
jsr166 |
1.25 |
Node<E> h = traversalHead(); |
775 |
|
|
for (Node<E> p = h.next; p != null && p.isData; p = p.next) { |
776 |
dl |
1.1 |
Object x = p.get(); |
777 |
jsr166 |
1.5 |
if (x != null && x != p) { |
778 |
dl |
1.1 |
if (++count == Integer.MAX_VALUE) // saturated |
779 |
|
|
break; |
780 |
|
|
} |
781 |
|
|
} |
782 |
|
|
return count; |
783 |
|
|
} |
784 |
|
|
|
785 |
|
|
public int getWaitingConsumerCount() { |
786 |
|
|
int count = 0; |
787 |
jsr166 |
1.25 |
Node<E> h = traversalHead(); |
788 |
|
|
for (Node<E> p = h.next; p != null && !p.isData; p = p.next) { |
789 |
dl |
1.1 |
if (p.get() == null) { |
790 |
|
|
if (++count == Integer.MAX_VALUE) |
791 |
|
|
break; |
792 |
|
|
} |
793 |
|
|
} |
794 |
|
|
return count; |
795 |
|
|
} |
796 |
|
|
|
797 |
|
|
public int remainingCapacity() { |
798 |
|
|
return Integer.MAX_VALUE; |
799 |
|
|
} |
800 |
|
|
|
801 |
dl |
1.15 |
public boolean remove(Object o) { |
802 |
|
|
if (o == null) |
803 |
|
|
return false; |
804 |
|
|
for (;;) { |
805 |
jsr166 |
1.25 |
Node<E> pred = traversalHead(); |
806 |
dl |
1.15 |
for (;;) { |
807 |
jsr166 |
1.25 |
Node<E> q = pred.next; |
808 |
dl |
1.15 |
if (q == null || !q.isData) |
809 |
|
|
return false; |
810 |
|
|
if (q == pred) // restart |
811 |
|
|
break; |
812 |
|
|
Object x = q.get(); |
813 |
jsr166 |
1.17 |
if (x != null && x != q && o.equals(x) && |
814 |
dl |
1.15 |
q.compareAndSet(x, q)) { |
815 |
|
|
clean(pred, q); |
816 |
|
|
return true; |
817 |
|
|
} |
818 |
|
|
pred = q; |
819 |
|
|
} |
820 |
|
|
} |
821 |
|
|
} |
822 |
|
|
|
823 |
dl |
1.1 |
/** |
824 |
|
|
* Save the state to a stream (that is, serialize it). |
825 |
|
|
* |
826 |
jsr166 |
1.11 |
* @serialData All of the elements (each an {@code E}) in |
827 |
dl |
1.1 |
* the proper order, followed by a null |
828 |
|
|
* @param s the stream |
829 |
|
|
*/ |
830 |
|
|
private void writeObject(java.io.ObjectOutputStream s) |
831 |
|
|
throws java.io.IOException { |
832 |
|
|
s.defaultWriteObject(); |
833 |
jsr166 |
1.16 |
for (E e : this) |
834 |
|
|
s.writeObject(e); |
835 |
dl |
1.1 |
// Use trailing null as sentinel |
836 |
|
|
s.writeObject(null); |
837 |
|
|
} |
838 |
|
|
|
839 |
|
|
/** |
840 |
|
|
* Reconstitute the Queue instance from a stream (that is, |
841 |
|
|
* deserialize it). |
842 |
jsr166 |
1.19 |
* |
843 |
dl |
1.1 |
* @param s the stream |
844 |
|
|
*/ |
845 |
|
|
private void readObject(java.io.ObjectInputStream s) |
846 |
|
|
throws java.io.IOException, ClassNotFoundException { |
847 |
|
|
s.defaultReadObject(); |
848 |
dl |
1.7 |
resetHeadAndTail(); |
849 |
dl |
1.1 |
for (;;) { |
850 |
jsr166 |
1.25 |
@SuppressWarnings("unchecked") E item = (E) s.readObject(); |
851 |
dl |
1.1 |
if (item == null) |
852 |
|
|
break; |
853 |
|
|
else |
854 |
|
|
offer(item); |
855 |
|
|
} |
856 |
|
|
} |
857 |
dl |
1.7 |
|
858 |
|
|
// Support for resetting head/tail while deserializing |
859 |
dl |
1.12 |
private void resetHeadAndTail() { |
860 |
jsr166 |
1.25 |
Node<E> dummy = new Node<E>(null, false); |
861 |
jsr166 |
1.20 |
UNSAFE.putObjectVolatile(this, headOffset, |
862 |
jsr166 |
1.25 |
new PaddedAtomicReference<Node<E>>(dummy)); |
863 |
jsr166 |
1.20 |
UNSAFE.putObjectVolatile(this, tailOffset, |
864 |
jsr166 |
1.25 |
new PaddedAtomicReference<Node<E>>(dummy)); |
865 |
jsr166 |
1.20 |
UNSAFE.putObjectVolatile(this, cleanMeOffset, |
866 |
jsr166 |
1.25 |
new PaddedAtomicReference<Node<E>>(null)); |
867 |
dl |
1.12 |
} |
868 |
dl |
1.7 |
|
869 |
jsr166 |
1.28 |
// Unsafe mechanics |
870 |
|
|
|
871 |
|
|
private static final sun.misc.Unsafe UNSAFE = getUnsafe(); |
872 |
|
|
private static final long headOffset = |
873 |
jsr166 |
1.31 |
objectFieldOffset(UNSAFE, "head", LinkedTransferQueue.class); |
874 |
jsr166 |
1.28 |
private static final long tailOffset = |
875 |
jsr166 |
1.31 |
objectFieldOffset(UNSAFE, "tail", LinkedTransferQueue.class); |
876 |
jsr166 |
1.28 |
private static final long cleanMeOffset = |
877 |
jsr166 |
1.31 |
objectFieldOffset(UNSAFE, "cleanMe", LinkedTransferQueue.class); |
878 |
|
|
|
879 |
jsr166 |
1.28 |
|
880 |
jsr166 |
1.31 |
static long objectFieldOffset(sun.misc.Unsafe UNSAFE, |
881 |
|
|
String field, Class<?> klazz) { |
882 |
jsr166 |
1.28 |
try { |
883 |
|
|
return UNSAFE.objectFieldOffset(klazz.getDeclaredField(field)); |
884 |
|
|
} catch (NoSuchFieldException e) { |
885 |
|
|
// Convert Exception to corresponding Error |
886 |
|
|
NoSuchFieldError error = new NoSuchFieldError(field); |
887 |
|
|
error.initCause(e); |
888 |
|
|
throw error; |
889 |
|
|
} |
890 |
|
|
} |
891 |
|
|
|
892 |
|
|
/** |
893 |
|
|
* Returns a sun.misc.Unsafe. Suitable for use in a 3rd party package. |
894 |
|
|
* Replace with a simple call to Unsafe.getUnsafe when integrating |
895 |
|
|
* into a jdk. |
896 |
|
|
* |
897 |
|
|
* @return a sun.misc.Unsafe |
898 |
|
|
*/ |
899 |
jsr166 |
1.25 |
private static sun.misc.Unsafe getUnsafe() { |
900 |
jsr166 |
1.13 |
try { |
901 |
jsr166 |
1.25 |
return sun.misc.Unsafe.getUnsafe(); |
902 |
jsr166 |
1.13 |
} catch (SecurityException se) { |
903 |
|
|
try { |
904 |
|
|
return java.security.AccessController.doPrivileged |
905 |
jsr166 |
1.28 |
(new java.security |
906 |
|
|
.PrivilegedExceptionAction<sun.misc.Unsafe>() { |
907 |
jsr166 |
1.25 |
public sun.misc.Unsafe run() throws Exception { |
908 |
jsr166 |
1.28 |
java.lang.reflect.Field f = sun.misc |
909 |
|
|
.Unsafe.class.getDeclaredField("theUnsafe"); |
910 |
|
|
f.setAccessible(true); |
911 |
|
|
return (sun.misc.Unsafe) f.get(null); |
912 |
jsr166 |
1.13 |
}}); |
913 |
|
|
} catch (java.security.PrivilegedActionException e) { |
914 |
jsr166 |
1.25 |
throw new RuntimeException("Could not initialize intrinsics", |
915 |
|
|
e.getCause()); |
916 |
jsr166 |
1.13 |
} |
917 |
|
|
} |
918 |
|
|
} |
919 |
dl |
1.1 |
} |