Name: akC45999 Date: 03/12/99



The chapter 6 "The Java Virtual Machine Instruction Set" of revised
VM specification reads:
...
Otherwise, if the virtual machine implementation enforces the rules on
structured use of locks described in 8.13 and if the first of those
rules is violated during invocation of the current method, then return
throws an IllegalMonitorStateException.
...

The chapter 8.13 "Locks and Synchronization" of revised VM specification reads:
...
Let T be a thread and L be a lock. Then:

 1.The number of lock operations performed by T on L during a method
    invocation must equal the number of unlock operations performed by T on L
    during the method invocation whether the method invocation completes
    normally or abruptly.
 2.At no point during a method invocation may the number of unlock operations
    performed by T on L since the method invocation exceed the number of lock
    operations performed by T on L since the method invocation.

In less formal terms, during a method invocation every unlock operation on L
must match some preceding lock operation on L.
...

The following test shows JDK-1.2-V does not check violation of this rule.
The same concerns JDK-1.2fcsQ.

------------------------------------- test.java --------------------------------

import java.io.PrintStream;

class test {

  public static void main(String argv[]) {

try {
Class.forName("BadClass");
System.out.println("Expected exception was not thrown");
} catch(Throwable e) {
System.out.println(e);
}
  }
}

----------------------------------- BadClass.jasm ------------------------------

class BadClass
{

static Method "<clinit>":"()V"
stack 2 locals 1
{
new class java/lang/Object;
dup;
invokespecial Method java/lang/Object."<init>":"()V";
monitorenter;
return;
}
}

--------------------------------------------------------------------------------

novo48% javac test.java
novo48% jasm BadClass.jasm
novo48% java -fullversion
java full version "JDK-1.2-V"
novo48% java test
Expected exception was not thrown
 
======================================================================

======================================================================