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23 
24 // See bug 5094825 / ClassLoadDeadlock.sh
25 
26 import java.net.*;
27 
28 import java.security.*;
29 
30 public class ClassLoaderDeadlock {
31 
main(String[] args)32     public static void main(String[] args) throws Exception {
33         // create a new classloader
34         URL url = new URL("file:provider/");
35         final DelayClassLoader cl = new DelayClassLoader(url);
36 
37         // install a provider on the custom class loader as the most prefered provider
38         Class clazz = cl.loadClass("HashProvider");
39         Provider p = (Provider)clazz.newInstance();
40         Security.insertProviderAt(p, 1);
41 
42         // add a delay in class loading for reproducability
43         cl.delay = 1000;
44 
45         new Thread() {
46             public void run() {
47                 try {
48                     // load a random system class
49                     // this locks the DelayClassLoader and after the delay the system class loader
50                     Class c1 = cl.loadClass("java.lang.String");
51                     System.out.println(c1);
52                 } catch (Exception e) {
53                     e.printStackTrace();
54                 }
55             }
56         }.start();
57 
58         // make sure the other thread got a chance to run and grab the lock
59         Thread.sleep(200);
60 
61         // load a random class from a signed JAR file to trigger JAR signature verification
62         // locks system class loader first and then tries to lock DelayClassLoader to load the hashes
63         // DEADLOCK HAPPENS HERE
64         Class c2 = Class.forName("com.abc.Tst1");
65 
66         // NOT REACHED
67         System.out.println(c2);
68 
69         System.out.println("OK");
70     }
71 
72     static class DelayClassLoader extends URLClassLoader {
73 
74         volatile int delay;
75 
DelayClassLoader(URL url)76         DelayClassLoader(URL url) {
77             super(new URL[] {url});
78         }
79 
loadClass(String name, boolean resolve)80         protected synchronized Class loadClass(String name, boolean resolve) throws ClassNotFoundException {
81             System.out.println("-loadClass(" + name + "," + resolve + ")");
82             try {
83                 // delay so that we hold the lock for a longer period
84                 // makes it much easier to reproduce
85                 Thread.sleep(delay);
86             } catch (InterruptedException e) { e.printStackTrace(); }
87             return super.loadClass(name, resolve);
88         }
89     }
90 
91 }
92