JAVASSIST-242: Demonstrates a race condition in DefineClassHelper + proposed fix

src/main/javassist/util/proxy/DefineClassHelper.java

@@ -219,9 +219,6 @@ Class<?> defineClass(String name, byte[] b, int off, int len, Class<?> neighbor,
                 if (e instanceof RuntimeException) throw (RuntimeException) e;
                 throw new CannotCompileException(e);
             }
-            finally {
-                SecurityActions.setAccessible(defineClass, false);
-            }
         }
     }
 

src/main/javassist/util/proxy/DefinePackageHelper.java

@@ -128,9 +128,6 @@ Package definePackage(ClassLoader loader, String name, String specTitle,
                 }
                 if (e instanceof RuntimeException) throw (RuntimeException) e;
             }
-            finally {
-                definePackage.setAccessible(false);
-            }
             return null;
         }
     };

src/test/javassist/ConcurrentClassDefinitionTest.java

@@ -0,0 +1,75 @@
+package javassist;
+
+import javassist.bytecode.ClassFile;
+import org.junit.Test;
+import org.junit.runner.RunWith;
+import org.junit.runners.Parameterized;
+
+@RunWith(Parameterized.class)
+public class ConcurrentClassDefinitionTest {
+
+  @Parameterized.Parameter
+  public int N;
+
+  @Parameterized.Parameters
+  public static Object[] data() {
+    return new Object[] {
+            1, // single threaded - should pass
+            Runtime.getRuntime().availableProcessors() * 2
+    };
+  }
+
+  @Test
+  public void showDefineClassRaceCondition() throws Exception{
+    Worker[] workers = new Worker[N];
+    for (int i = 0; i < N; i++) {
+      workers[i] = new Worker(N + "_ " + i, 100);
+      workers[i].start();
+    }
+    for (Worker w : workers) {
+      w.join();
+    }
+    for (Worker w : workers) {
+      if (w.e != null) {
+        throw w.e;
+      }
+    }
+  }
+
+  private static class Worker extends Thread {
+    String id;
+    int count;
+    Exception e;
+
+    Worker(String id, int count) {
+      this.id = id;
+      this.count = count;
+    }
+
+    @Override
+    public void run() {
+      try {
+        for (int i = 0; i < count; i++) {
+          Class c = makeClass(id + "_" + i);
+          assert c != null;
+        }
+      } catch (Exception e) {
+        this.e = e;
+      }
+    }
+
+    @Override
+    public void interrupt() {
+      super.interrupt();
+    }
+  }
+
+  private static Class makeClass(String id) throws Exception {
+    ClassFile cf = new ClassFile(
+            false, "com.example.JavassistGeneratedClass_" + id, null);
+    ClassPool classPool = ClassPool.getDefault();
+    return classPool.makeClass(cf).toClass();
+  }
+
+
+}