Name: vsR10008 Date: 09/07/2003



The JLS Second edition says:
[14.18 The synchronized Statement]
<SynchronizedStatement>:
    synchronized ( <Expression> ) <Block>

"If execution of the <Block> completes abruptly for any reason,
the the lock is unlocked and the synchronized statement then
completes abruptly for the same reason"

It is very important for compiler to generate correct bytecode
that properly locks/unlocks monitors, even in the presence of
asynchronous exceptions (see RFE 4639704).

There are several cases when compiler doesn't generate enclosing
"guard" exception ranges for monitorenter/monitorexit instructions
which protect monitor from remaining locked.

To reproduce the bug please compile the following source:

---- File: test.java ------------------------------------------------
public class test {
void t1(int arg) {
     int loc = 0;
     label0:
     synchronized (new Integer(arg)) {
         label1:
         {
             label2:
             {
                 break label2;
             }
         }
     }
}

void t2(int arg) {
     int loc = 0;
     label0:
     synchronized (new Integer(arg)) {
         label1:
         {
             label2:
             do {
                 break label2;
             } while (arg != 0);
         }
     }
}

void t3(int arg) {
     int loc = 0;
     label0:
     synchronized (new Integer(arg)) {
         label1:
         try {
             label2:
             {
                 break label2;
             }
         } catch (Throwable t474) {
         }
     }
}

void t4(int arg) {
     int loc = 0;
     label0:
     synchronized (new Integer(arg)) {
         label1:
         try {
             label2:
             do {
                 break label2;
             } while (arg != 0);
         } catch (Throwable t482) {
         }
     }
}

}
---------------------------------------------------------------------

Looking at generated bytecode (see for example method t4)
we can see that it is not correct:

Method t4:"(I)V"
     stack 3 locals 4
{
     iconst_0;
     istore_2;
     new class java/lang/Integer;
     dup;
     iload_1;
     invokespecial Method java/lang/Integer."<init>":"(I)V";
     dup;
     astore_3;
     monitorenter;
*** aload_3;
     monitorexit;
     return;
}

If asynchronous exception occurs at the point marked with "***"
the monitor will remain locked.

The same is true for methods t1,t2,t3 either.

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