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23 
24 /* @test
25  * @bug 4076287
26  * @summary Invoking get on a SoftReference shouldn't pin the referent
27  * @run main/othervm -ms16m -mx16m Pin
28  * @author Peter Jones
29  * @author Mark Reinhold
30  */
31 
32 
33 import java.lang.ref.SoftReference;
34 
35 public class Pin {
36 
37     static final int NUM_BLOCKS = 128;
38     static final int BLOCK_SIZE = 32768;
39 
main(String[] args)40     public static void main(String[] args) throws Exception {
41 
42         SoftReference[] blocks = new SoftReference[NUM_BLOCKS];
43 
44         byte[] block;
45 
46         System.err.println("Filling array with " + NUM_BLOCKS +
47                            " SoftReferences to blocks of " +
48                            BLOCK_SIZE + " bytes.");
49 
50         for (int i = 0; i < NUM_BLOCKS; ++ i) {
51             block = new byte[BLOCK_SIZE];
52             SoftReference ref = new SoftReference(block);
53             blocks[i] = ref;
54         }
55         block = null;
56 
57         System.err.println("Allowing SoftReferences to be enqueued.");
58         System.gc();
59         Thread.sleep(1000);
60 
61         /* -- Commenting out the following section will hide the bug -- */
62         System.err.println("Invoking get() on SoftReferences.");
63         for (int i = 0; i < NUM_BLOCKS; ++ i) {
64             block = (byte[]) blocks[i].get();
65         }
66         block = null;
67         /* -- end -- */
68 
69         System.err.println("Forcing desperate garbage collection...");
70         java.util.Vector chain = new java.util.Vector();
71         try {
72             while (true) {
73                 System.gc();
74                 int[] hungry = new int[65536];
75                 chain.addElement(hungry);
76                 Thread.sleep(100);              // yield, for what it's worth
77             }
78         } catch (OutOfMemoryError e) {
79             chain = null; // Free memory for further work.
80             System.err.println("Got OutOfMemoryError, as expected.");
81         }
82 
83         int emptyCount = 0, fullCount = 0;
84         System.err.print("Examining contents of array:");
85         for (int i = 0; i < NUM_BLOCKS; ++ i) {
86             block = (byte[]) blocks[i].get();
87             if (block == null) {
88                 emptyCount++;
89             } else {
90                 fullCount++;
91             }
92         }
93         System.err.println(" " + emptyCount + " empty, " +
94                            fullCount + " full.");
95         if (emptyCount == 0)
96             throw new Exception("No SoftReference instances were cleared");
97     }
98 
99 }
100