38 /**
39 * Constructs a new reference-object queue.
40 */
41 public ReferenceQueue() { }
42
43 private static class Null extends ReferenceQueue {
44 boolean enqueue(Reference r) {
45 return false;
46 }
47 }
48
49 static ReferenceQueue NULL = new Null();
50 static ReferenceQueue ENQUEUED = new Null();
51
52 static private class Lock { };
53 private Lock lock = new Lock();
54 private volatile Reference<? extends T> head = null;
55 private long queueLength = 0;
56
57 boolean enqueue(Reference<? extends T> r) { /* Called only by Reference class */
58 synchronized (r) {
59 if (r.queue == ENQUEUED) return false;
60 synchronized (lock) {
61 r.queue = ENQUEUED;
62 r.next = (head == null) ? r : head;
63 head = r;
64 queueLength++;
65 if (r instanceof FinalReference) {
66 sun.misc.VM.addFinalRefCount(1);
67 }
68 lock.notifyAll();
69 return true;
70 }
71 }
72 }
73
74 private Reference<? extends T> reallyPoll() { /* Must hold lock */
75 if (head != null) {
76 Reference<? extends T> r = head;
77 head = (r.next == r) ? null : r.next;
78 r.queue = NULL;
79 r.next = r;
80 queueLength--;
81 if (r instanceof FinalReference) {
82 sun.misc.VM.addFinalRefCount(-1);
83 }
84 return r;
85 }
86 return null;
87 }
88
89 /**
90 * Polls this queue to see if a reference object is available. If one is
91 * available without further delay then it is removed from the queue and
92 * returned. Otherwise this method immediately returns <tt>null</tt>.
93 *
94 * @return A reference object, if one was immediately available,
95 * otherwise <code>null</code>
96 */
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38 /**
39 * Constructs a new reference-object queue.
40 */
41 public ReferenceQueue() { }
42
43 private static class Null extends ReferenceQueue {
44 boolean enqueue(Reference r) {
45 return false;
46 }
47 }
48
49 static ReferenceQueue NULL = new Null();
50 static ReferenceQueue ENQUEUED = new Null();
51
52 static private class Lock { };
53 private Lock lock = new Lock();
54 private volatile Reference<? extends T> head = null;
55 private long queueLength = 0;
56
57 boolean enqueue(Reference<? extends T> r) { /* Called only by Reference class */
58 synchronized (lock) {
59 // Check that since getting the lock this reference hasn't already been
60 // enqueued (and even then removed)
61 ReferenceQueue queue = r.queue;
62 if ((queue == NULL) || (queue == ENQUEUED)) {
63 return false;
64 }
65 assert queue == this;
66 r.queue = ENQUEUED;
67 r.next = (head == null) ? r : head;
68 head = r;
69 queueLength++;
70 if (r instanceof FinalReference) {
71 sun.misc.VM.addFinalRefCount(1);
72 }
73 lock.notifyAll();
74 return true;
75 }
76 }
77
78 private Reference<? extends T> reallyPoll() { /* Must hold lock */
79 Reference<? extends T> r = head;
80 if (r != null) {
81 head = (r.next == r) ? null : r.next;
82 r.queue = NULL;
83 r.next = r;
84 queueLength--;
85 if (r instanceof FinalReference) {
86 sun.misc.VM.addFinalRefCount(-1);
87 }
88 return r;
89 }
90 return null;
91 }
92
93 /**
94 * Polls this queue to see if a reference object is available. If one is
95 * available without further delay then it is removed from the queue and
96 * returned. Otherwise this method immediately returns <tt>null</tt>.
97 *
98 * @return A reference object, if one was immediately available,
99 * otherwise <code>null</code>
100 */
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