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23 
24 /*
25  * @test KeepAliveClass
26  * @summary This test case uses a java.lang.Class instance to keep a class alive.
27  * @library /testlibrary /testlibrary/whitebox /runtime/testlibrary
28  * @library classes
29  * @build KeepAliveClass test.Empty
30  * @build ClassUnloadCommon
31  * @run main ClassFileInstaller sun.hotspot.WhiteBox
32  * @run main/othervm -Xbootclasspath/a:. -Xmn8m -XX:+UnlockDiagnosticVMOptions -XX:+WhiteBoxAPI KeepAliveClass
33  */
34 
35 import java.lang.ref.SoftReference;
36 import sun.hotspot.WhiteBox;
37 
38 /**
39  * Test that verifies that classes are not unloaded when specific types of references are kept to them.
40  */
41 public class KeepAliveClass {
42   private static final String className = "test.Empty";
43   private static final WhiteBox wb = WhiteBox.getWhiteBox();
44   public static Object escape = null;
45 
main(String... args)46   public static void main(String... args) throws Exception {
47     ClassLoader cl = ClassUnloadCommon.newClassLoader();
48     Class<?> c = cl.loadClass(className);
49     Object o = c.newInstance();
50     o = null; cl = null;
51     escape = c;
52 
53     {
54         boolean isAlive = wb.isClassAlive(className);
55         System.out.println("testClass (1) alive: " + isAlive);
56 
57         ClassUnloadCommon.failIf(!isAlive, "should be alive");
58     }
59 
60     ClassUnloadCommon.triggerUnloading();
61 
62     {
63         boolean isAlive = wb.isClassAlive(className);
64         System.out.println("testClass (2) alive: " + isAlive);
65 
66         ClassUnloadCommon.failIf(!isAlive, "should be alive");
67     }
68     c = null;
69     escape = null;
70     ClassUnloadCommon.triggerUnloading();
71 
72     {
73         boolean isAlive = wb.isClassAlive(className);
74         System.out.println("testClass (3) alive: " + isAlive);
75         ClassUnloadCommon.failIf(isAlive, "should be unloaded");
76     }
77 
78   }
79 }
80