RFR 8217223 [lworld][c1] monitorenter on value object should throw IllegalMonitorStateException

Ioi Lam ioi.lam at oracle.com
Wed Jan 16 06:32:29 UTC 2019


https://bugs.openjdk.java.net/browse/JDK-8217223
http://cr.openjdk.java.net/~iklam/valhalla/8217223-c1-monitorenter-throw-imse.v01/

Here's a fix for C1 to properly throw IllegalMonitorStateException
when synchronizing on value objects.

Ideally, we should just call into Runtime1::monitorenter(), which
handles the IMSE throwing. However, due to C1's limitation, when
an exception happens inside Runtime1::monitorenter(), there's no
way for the current method to catch this exception, so for code
like this:

     try {
         synchronized(vt) {}
     } catch (Throwable t) {
         foo();
     }

foo() is never called and the exception is thrown to the method's
caller.

As a work around, I added an explicit check in MonitorEnterStub to
call a SimpleExceptionStub to throw the IMSE.

Here's what the generated code looks like. The instructions marked
by "+" are added by this patch.


+UseBiasedLocking case:
======================

  ;; MonitorEnterStub slow case
   0x00007fe788e285f0: mov    (%rsi),%rdi
+ 0x00007fe788e285f3: test   $0x405,%edi
        ;; 0x405 = markOopDesc::always_locked_pattern
+ 0x00007fe788e285f9: jne    0x00007fe788e28612
   0x00007fe788e285ff: mov    %rsi,0x8(%rsp)
   0x00007fe788e28604: mov    %rdx,(%rsp)
   0x00007fe788e28608: callq  0x00007fe7889d8840
        ;;{runtime_call monitorenter_nofpu}

   0x00007fe788e2860d: jmpq   0x00007fe788e28381
  ;; SimpleExceptionStub slow case
+ 0x00007fe788e28612: callq  0x00007fe7889d7e40
        ;;{runtime_call throw_illegal_monitor_state_exception}


-UseBiasedLocking case:
======================

   0x00007fe1e8e2828c: lea    0x20(%rsp),%rdx
   0x00007fe1e8e28291: mov    %rsi,0x8(%rdx)
   0x00007fe1e8e28295: mov    (%rsi),%rax
+ 0x00007fe1e8e28298: test   $0x405,%eax
+ 0x00007fe1e8e2829d: jne    0x00007fe1e8e28528 ;; MonitorEnterStub
   0x00007fe1e8e282a3: or     $0x1,%rax
   0x00007fe1e8e282a7: mov    %rax,(%rdx)
   0x00007fe1e8e282aa: lock cmpxchg %rdx,(%rsi)

(the MonitorEnterStub looks identical to the +UseBiasedLocking case).

Thanks
- Ioi




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