1 /*
2 * Copyright (c) 2011, 2013, Oracle and/or its affiliates. All rights reserved.
3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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5 * This code is free software; you can redistribute it and/or modify it
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22 */
23
24 /* @test
25 * @bug 4243978
26 * @summary Test if Reference.enqueue() works properly with pending references
27 */
28 import java.lang.ref.*;
29
30 public class ReferenceEnqueuePending {
31 static class NumberedWeakReference extends WeakReference<Integer> {
32 // Add an integer to identify the weak reference object.
33 int number;
34
35 NumberedWeakReference(Integer referent, ReferenceQueue<Integer> q, int i) {
36 super(referent, q);
37 number = i;
38 }
39 }
40
41 static final boolean debug = System.getProperty("test.debug") != null;
42 static final int iterations = 1000;
43 static final int gc_trigger = 99;
44 static int[] a = new int[2 * iterations];
45 // Keep all weak references alive with the following array.
46 static NumberedWeakReference[] b = new NumberedWeakReference[iterations];
47
48 public static void main(String[] argv) throws Exception {
49 if (debug) {
50 System.out.println("Starting the test.");
51 }
52 // Raise thread priority to match the referenceHandler
53 // priority, so that they can race also on a uniprocessor.
54 raisePriority();
55
56 ReferenceQueue<Integer> refQueue = new ReferenceQueue<>();
57
58 // Our objective is to let the mutator enqueue
59 // a Reference object that may already be in the
60 // pending state because of having been identified
61 // as weakly reachable at a previous garbage collection.
62 // To this end, we create many Reference objects, each with a
63 // a unique integer object as its referant.
64 // We let the referents become eligible for collection,
65 // while racing with the garbage collector which may
66 // have pended some of these Reference objects.
67 // Finally we check that all of the Reference objects
68 // end up on the their queue. The test was originally
69 // submitted to show that such races could break the
70 // pending list and/or the reference queue, because of sharing
71 // the same link ("next") for maintaining both lists, thus
72 // losing some of the Reference objects on either queue.
73
74 Integer obj = new Integer(0);
75 NumberedWeakReference weaky = new NumberedWeakReference(obj, refQueue, 0);
76 for (int i = 1; i < iterations; i++) {
77 // Create a new object, dropping the onlY strong reference to
78 // the previous Integer object.
79 obj = new Integer(i);
80 // Trigger gc each gc_trigger iterations.
81 if ((i % gc_trigger) == 0) {
82 forceGc(0);
83 }
84 // Enqueue every other weaky.
85 if ((i % 2) == 0) {
86 weaky.enqueue();
87 }
88 // Remember the Reference objects, for testing later.
89 b[i - 1] = weaky;
90 // Get a new weaky for the Integer object just
91 // created, which may be explicitly enqueued in
92 // our next trip around the loop.
93 weaky = new NumberedWeakReference(obj, refQueue, i);
94 }
95
96 // Do a final collection to discover and process all
97 // Reference objects created above, allowing enough time
98 // for the ReferenceHandler thread to queue the References.
99 forceGc(100);
100 forceGc(100);
101
102 // Verify that all WeakReference objects ended up queued.
103 checkResult(refQueue, obj, iterations-1);
104 System.out.println("Test passed.");
105 }
106
107 private static void checkResult(ReferenceQueue<Integer> queue,
108 Integer obj,
109 int expected) {
110 if (debug) {
111 System.out.println("Reading the queue");
112 }
113
114 // Empty the queue and record numbers into a[];
115 NumberedWeakReference weakRead = (NumberedWeakReference) queue.poll();
116 int length = 0;
117 while (weakRead != null) {
118 a[length++] = weakRead.number;
119 weakRead = (NumberedWeakReference) queue.poll();
120 }
121 if (debug) {
122 System.out.println("Reference Queue had " + length + " elements");
123 }
124 // Use the last Reference object of those created above, so as to keep it "alive".
125 System.out.println("I must write " + obj + " to prevent compiler optimizations.");
126
127
128 // verify the queued references: all but the last Reference object
129 // should have been in the queue.
130 if (debug) {
131 System.out.println("Start of final check");
132 }
133
134 // Sort the first "length" elements in array "a[]".
135 sort(length);
136
137 boolean fail = (length != expected);
138 for (int i = 0; i < length; i++) {
139 if (a[i] != i) {
140 if (debug) {
141 System.out.println("a[" + i + "] is not " + i + " but " + a[i]);
142 }
143 fail = true;
144 }
145 }
146 if (fail) {
147 printMissingElements(length, expected);
148 throw new RuntimeException("TEST FAILED: only " + length
149 + " reference objects have been queued out of "
150 + expected);
151 }
152 }
153
154 private static void printMissingElements(int length, int expected) {
155 System.out.println("The following numbers were not found in the reference queue: ");
156 int missing = 0;
157 int element = 0;
158 for (int i = 0; i < length; i++) {
159 while ((a[i] != element) & (element < expected)) {
160 System.out.print(element + " ");
161 if (missing % 20 == 19) {
162 System.out.println(" ");
163 }
164 missing++;
165 element++;
166 }
167 element++;
168 }
169 System.out.print("\n");
170 }
171
172 private static void forceGc(long millis) throws InterruptedException {
173 Runtime.getRuntime().gc();
174 Thread.sleep(millis);
175 }
176
177 // Bubble sort the first "length" elements in array "a".
178 private static void sort(int length) {
179 int hold;
180 if (debug) {
181 System.out.println("Sorting. Length=" + length);
182 }
183 for (int pass = 1; pass < length; pass++) { // passes over the array
184 for (int i = 0; i < length - pass; i++) { // a single pass
185 if (a[i] > a[i + 1]) { // then swap
186 hold = a[i];
187 a[i] = a[i + 1];
188 a[i + 1] = hold;
189 }
190 } // End of i loop
191 } // End of pass loop
192 }
193
194 // Raise thread priority so as to increase the
195 // probability of the mutator succeeding in enqueueing
196 // an object that is still in the pending state.
197 // This is (probably) only required for a uniprocessor.
198 static void raisePriority() {
199 Thread tr = Thread.currentThread();
200 tr.setPriority(Thread.MAX_PRIORITY);
201 }
202 } // End of class ReferenceEnqueuePending