Mercurial > hg > blitz_stable

annotate src/EDU/oswego/cs/dl/util/concurrent/LinkedQueue.java @ 32:243c74d599bf

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author Dan Creswell <dan.creswell@gmail.com>
date Sat, 12 Jun 2010 10:41:47 +0100
parents 3dc0c5604566
children
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1 /*
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2 File: LinkedQueue.java
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3
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4 Originally written by Doug Lea and released into the public domain.
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5 This may be used for any purposes whatsoever without acknowledgment.
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6 Thanks for the assistance and support of Sun Microsystems Labs,
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7 and everyone contributing, testing, and using this code.
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8
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9 History:
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10 Date Who What
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11 11Jun1998 dl Create public version
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12 25aug1998 dl added peek
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13 10dec1998 dl added isEmpty
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14 10oct1999 dl lock on node object to ensure visibility
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15 */
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16
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17 package EDU.oswego.cs.dl.util.concurrent;
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18
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19 /**
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20 * A linked list based channel implementation.
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21 * The algorithm avoids contention between puts
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22 * and takes when the queue is not empty.
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23 * Normally a put and a take can proceed simultaneously.
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24 * (Although it does not allow multiple concurrent puts or takes.)
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25 * This class tends to perform more efficently than
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26 * other Channel implementations in producer/consumer
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27 * applications.
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28 * <p>[<a href="http://gee.cs.oswego.edu/dl/classes/EDU/oswego/cs/dl/util/concurrent/intro.html"> Introduction to this package. </a>]
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29 **/
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30
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31 public class LinkedQueue implements Channel {
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32
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33
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34 /**
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35 * Dummy header node of list. The first actual node, if it exists, is always
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36 * at head_.next. After each take, the old first node becomes the head.
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37 **/
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38 protected LinkedNode head_;
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39
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40 /**
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41 * Helper monitor for managing access to last node.
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42 **/
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43 protected final Object putLock_ = new Object();
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44
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45 /**
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46 * The last node of list. Put() appends to list, so modifies last_
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47 **/
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48 protected LinkedNode last_;
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49
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50 /**
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51 * The number of threads waiting for a take.
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52 * Notifications are provided in put only if greater than zero.
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53 * The bookkeeping is worth it here since in reasonably balanced
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54 * usages, the notifications will hardly ever be necessary, so
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55 * the call overhead to notify can be eliminated.
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56 **/
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57 protected int waitingForTake_ = 0;
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58
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59 public LinkedQueue() {
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60 head_ = new LinkedNode(null);
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61 last_ = head_;
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62 }
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63
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64 /** Main mechanics for put/offer **/
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65 protected void insert(Object x) {
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66 synchronized(putLock_) {
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67 LinkedNode p = new LinkedNode(x);
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68 synchronized(last_) {
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69 last_.next = p;
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70 last_ = p;
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71 }
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72 if (waitingForTake_ > 0)
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73 putLock_.notify();
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74 }
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75 }
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76
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77 /** Main mechanics for take/poll **/
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78 protected synchronized Object extract() {
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79 synchronized(head_) {
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80 Object x = null;
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81 LinkedNode first = head_.next;
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82 if (first != null) {
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83 x = first.value;
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84 first.value = null;
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85 head_ = first;
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86 }
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87 return x;
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88 }
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89 }
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90
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91
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92 public void put(Object x) throws InterruptedException {
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93 if (x == null) throw new IllegalArgumentException();
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94 if (Thread.interrupted()) throw new InterruptedException();
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95 insert(x);
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96 }
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97
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98 public boolean offer(Object x, long msecs) throws InterruptedException {
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99 if (x == null) throw new IllegalArgumentException();
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100 if (Thread.interrupted()) throw new InterruptedException();
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101 insert(x);
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102 return true;
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103 }
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104
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105 public Object take() throws InterruptedException {
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106 if (Thread.interrupted()) throw new InterruptedException();
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107 // try to extract. If fail, then enter wait-based retry loop
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108 Object x = extract();
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109 if (x != null)
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110 return x;
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111 else {
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112 synchronized(putLock_) {
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113 try {
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114 ++waitingForTake_;
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115 for (;;) {
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116 x = extract();
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117 if (x != null) {
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118 --waitingForTake_;
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119 return x;
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120 }
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121 else {
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122 putLock_.wait();
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123 }
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124 }
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125 }
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126 catch(InterruptedException ex) {
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127 --waitingForTake_;
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128 putLock_.notify();
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129 throw ex;
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130 }
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131 }
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132 }
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133 }
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134
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135 public Object peek() {
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136 synchronized(head_) {
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137 LinkedNode first = head_.next;
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Dan Creswell <dan.creswell@gmail.com>
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138 if (first != null)
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Dan Creswell <dan.creswell@gmail.com>
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139 return first.value;
3dc0c5604566 Initial checkin of blitz 2.0 fcs - no installer yet.
Dan Creswell <dan.creswell@gmail.com>
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140 else
3dc0c5604566 Initial checkin of blitz 2.0 fcs - no installer yet.
Dan Creswell <dan.creswell@gmail.com>
parents:
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141 return null;
3dc0c5604566 Initial checkin of blitz 2.0 fcs - no installer yet.
Dan Creswell <dan.creswell@gmail.com>
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142 }
3dc0c5604566 Initial checkin of blitz 2.0 fcs - no installer yet.
Dan Creswell <dan.creswell@gmail.com>
parents:
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143 }
3dc0c5604566 Initial checkin of blitz 2.0 fcs - no installer yet.
Dan Creswell <dan.creswell@gmail.com>
parents:
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144
3dc0c5604566 Initial checkin of blitz 2.0 fcs - no installer yet.
Dan Creswell <dan.creswell@gmail.com>
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145
3dc0c5604566 Initial checkin of blitz 2.0 fcs - no installer yet.
Dan Creswell <dan.creswell@gmail.com>
parents:
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146 public boolean isEmpty() {
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Dan Creswell <dan.creswell@gmail.com>
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147 synchronized(head_) {
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Dan Creswell <dan.creswell@gmail.com>
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148 return head_.next == null;
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Dan Creswell <dan.creswell@gmail.com>
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149 }
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Dan Creswell <dan.creswell@gmail.com>
parents:
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150 }
3dc0c5604566 Initial checkin of blitz 2.0 fcs - no installer yet.
Dan Creswell <dan.creswell@gmail.com>
parents:
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151
3dc0c5604566 Initial checkin of blitz 2.0 fcs - no installer yet.
Dan Creswell <dan.creswell@gmail.com>
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152 public Object poll(long msecs) throws InterruptedException {
3dc0c5604566 Initial checkin of blitz 2.0 fcs - no installer yet.
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153 if (Thread.interrupted()) throw new InterruptedException();
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Dan Creswell <dan.creswell@gmail.com>
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154 Object x = extract();
3dc0c5604566 Initial checkin of blitz 2.0 fcs - no installer yet.
Dan Creswell <dan.creswell@gmail.com>
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155 if (x != null)
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Dan Creswell <dan.creswell@gmail.com>
parents:
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156 return x;
3dc0c5604566 Initial checkin of blitz 2.0 fcs - no installer yet.
Dan Creswell <dan.creswell@gmail.com>
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157 else {
3dc0c5604566 Initial checkin of blitz 2.0 fcs - no installer yet.
Dan Creswell <dan.creswell@gmail.com>
parents:
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158 synchronized(putLock_) {
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Dan Creswell <dan.creswell@gmail.com>
parents:
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159 try {
3dc0c5604566 Initial checkin of blitz 2.0 fcs - no installer yet.
Dan Creswell <dan.creswell@gmail.com>
parents:
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160 long waitTime = msecs;
3dc0c5604566 Initial checkin of blitz 2.0 fcs - no installer yet.
Dan Creswell <dan.creswell@gmail.com>
parents:
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161 long start = (msecs <= 0)? 0 : System.currentTimeMillis();
3dc0c5604566 Initial checkin of blitz 2.0 fcs - no installer yet.
Dan Creswell <dan.creswell@gmail.com>
parents:
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162 ++waitingForTake_;
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Dan Creswell <dan.creswell@gmail.com>
parents:
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163 for (;;) {
3dc0c5604566 Initial checkin of blitz 2.0 fcs - no installer yet.
Dan Creswell <dan.creswell@gmail.com>
parents:
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164 x = extract();
3dc0c5604566 Initial checkin of blitz 2.0 fcs - no installer yet.
Dan Creswell <dan.creswell@gmail.com>
parents:
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165 if (x != null || waitTime <= 0) {
3dc0c5604566 Initial checkin of blitz 2.0 fcs - no installer yet.
Dan Creswell <dan.creswell@gmail.com>
parents:
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166 --waitingForTake_;
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Dan Creswell <dan.creswell@gmail.com>
parents:
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167 return x;
3dc0c5604566 Initial checkin of blitz 2.0 fcs - no installer yet.
Dan Creswell <dan.creswell@gmail.com>
parents:
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168 }
3dc0c5604566 Initial checkin of blitz 2.0 fcs - no installer yet.
Dan Creswell <dan.creswell@gmail.com>
parents:
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169 else {
3dc0c5604566 Initial checkin of blitz 2.0 fcs - no installer yet.
Dan Creswell <dan.creswell@gmail.com>
parents:
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170 putLock_.wait(waitTime);
3dc0c5604566 Initial checkin of blitz 2.0 fcs - no installer yet.
Dan Creswell <dan.creswell@gmail.com>
parents:
diff changeset
171 waitTime = msecs - (System.currentTimeMillis() - start);
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Dan Creswell <dan.creswell@gmail.com>
parents:
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172 }
3dc0c5604566 Initial checkin of blitz 2.0 fcs - no installer yet.
Dan Creswell <dan.creswell@gmail.com>
parents:
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173 }
3dc0c5604566 Initial checkin of blitz 2.0 fcs - no installer yet.
Dan Creswell <dan.creswell@gmail.com>
parents:
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174 }
3dc0c5604566 Initial checkin of blitz 2.0 fcs - no installer yet.
Dan Creswell <dan.creswell@gmail.com>
parents:
diff changeset
175 catch(InterruptedException ex) {
3dc0c5604566 Initial checkin of blitz 2.0 fcs - no installer yet.
Dan Creswell <dan.creswell@gmail.com>
parents:
diff changeset
176 --waitingForTake_;
3dc0c5604566 Initial checkin of blitz 2.0 fcs - no installer yet.
Dan Creswell <dan.creswell@gmail.com>
parents:
diff changeset
177 putLock_.notify();
3dc0c5604566 Initial checkin of blitz 2.0 fcs - no installer yet.
Dan Creswell <dan.creswell@gmail.com>
parents:
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178 throw ex;
3dc0c5604566 Initial checkin of blitz 2.0 fcs - no installer yet.
Dan Creswell <dan.creswell@gmail.com>
parents:
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179 }
3dc0c5604566 Initial checkin of blitz 2.0 fcs - no installer yet.
Dan Creswell <dan.creswell@gmail.com>
parents:
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180 }
3dc0c5604566 Initial checkin of blitz 2.0 fcs - no installer yet.
Dan Creswell <dan.creswell@gmail.com>
parents:
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181 }
3dc0c5604566 Initial checkin of blitz 2.0 fcs - no installer yet.
Dan Creswell <dan.creswell@gmail.com>
parents:
diff changeset
182 }
3dc0c5604566 Initial checkin of blitz 2.0 fcs - no installer yet.
Dan Creswell <dan.creswell@gmail.com>
parents:
diff changeset
183 }
3dc0c5604566 Initial checkin of blitz 2.0 fcs - no installer yet.
Dan Creswell <dan.creswell@gmail.com>
parents:
diff changeset
184
3dc0c5604566 Initial checkin of blitz 2.0 fcs - no installer yet.
Dan Creswell <dan.creswell@gmail.com>
parents:
diff changeset
185