src/hotspot/share/runtime/objectMonitor.inline.hpp

rev 54415 : 8222295: more baseline cleanups from Async Monitor Deflation project
rev 54416 : Checkpoint latest preliminary review patches for full OpenJDK review; merge with 8222295.patch.
rev 54417 : imported patch dcubed.monitor_deflate_conc.v2.01

*** 54,86 ****
    void* owner = _owner;
    return owner != DEFLATER_MARKER ? owner : NULL;
  }
  
  inline void ObjectMonitor::clear() {
    assert(_contentions == 0, "must be 0: contentions=%d", _contentions);
    assert(_owner == NULL, "must be NULL: owner=" INTPTR_FORMAT, p2i(_owner));
  
    clear_using_JT();
  }
  
  inline void ObjectMonitor::clear_using_JT() {
!   // When clearing using a JavaThread, we leave _owner == DEFLATER_MARKER
!   // and _contentions < 0 to force any racing threads to retry. Unlike other
!   // *_using_JT() functions, we cannot assert AsyncDeflateIdleMonitors
!   // or Thread::current()->is_Java_thread() because clear() calls this
!   // function for the rest of its checks.
! 
!   assert(_header != NULL, "must be non-NULL");
    assert(_waiters == 0, "must be 0: waiters=%d", _waiters);
    assert(_recursions == 0, "must be 0: recursions=" INTPTR_FORMAT, _recursions);
    assert(_object != NULL, "must be non-NULL");
    // Do not assert _ref_count == 0 here because a racing thread could
    // increment _ref_count, observe _owner == DEFLATER_MARKER and then
    // decrement _ref_count.
  
    set_allocation_state(Free);
-   _header = NULL;
    _object = NULL;
    // Do not clear _ref_count here because _ref_count is for indicating
    // that the ObjectMonitor* is in use which is orthogonal to whether
    // the ObjectMonitor itself is in use for a locking operation.
  }
--- 54,98 ----
    void* owner = _owner;
    return owner != DEFLATER_MARKER ? owner : NULL;
  }
  
  inline void ObjectMonitor::clear() {
+   assert(_header != NULL, "must be non-NULL");
    assert(_contentions == 0, "must be 0: contentions=%d", _contentions);
    assert(_owner == NULL, "must be NULL: owner=" INTPTR_FORMAT, p2i(_owner));
  
+   _header = NULL;
+ 
    clear_using_JT();
  }
  
  inline void ObjectMonitor::clear_using_JT() {
!   // Unlike other *_using_JT() functions, we cannot assert
!   // AsyncDeflateIdleMonitors or Thread::current()->is_Java_thread()
!   // because clear() calls this function for the rest of its checks.
! 
!   if (AsyncDeflateIdleMonitors) {
!     // Async deflation protocol uses the _header, _contentions and _owner
!     // fields. While the ObjectMonitor being deflated is on the global free
!     // list, we leave those three fields alone; _owner == DEFLATER_MARKER
!     // and _contentions < 0 will force any racing threads to retry. The
!     // _header field is used by install_displaced_markword_in_object()
!     // in the last part of the deflation protocol so we cannot check
!     // its values here.
!     guarantee(_owner == NULL || _owner == DEFLATER_MARKER,
!               "must be NULL or DEFLATER_MARKER: owner=" INTPTR_FORMAT,
!               p2i(_owner));
!     guarantee(_contentions <= 0, "must be <= 0: contentions=%d", _contentions);
!   }
    assert(_waiters == 0, "must be 0: waiters=%d", _waiters);
    assert(_recursions == 0, "must be 0: recursions=" INTPTR_FORMAT, _recursions);
    assert(_object != NULL, "must be non-NULL");
    // Do not assert _ref_count == 0 here because a racing thread could
    // increment _ref_count, observe _owner == DEFLATER_MARKER and then
    // decrement _ref_count.
  
    set_allocation_state(Free);
    _object = NULL;
    // Do not clear _ref_count here because _ref_count is for indicating
    // that the ObjectMonitor* is in use which is orthogonal to whether
    // the ObjectMonitor itself is in use for a locking operation.
  }
*** 146,179 ****
  inline bool ObjectMonitor::is_new() const {
    return _allocation_state == New;
  }
  
  inline void ObjectMonitor::dec_ref_count() {
!   // The decrement needs to be MO_ACQ_REL. At the moment, the Atomic::dec
!   // backend on PPC does not yet conform to these requirements. Therefore
!   // the decrement is simulated with an Atomic::sub(1, &addr). Without
!   // this MO_ACQ_REL Atomic::dec simulation, AsyncDeflateIdleMonitors is
!   // not safe.
!   Atomic::sub((jint)1, &_ref_count);
    guarantee(_ref_count >= 0, "sanity check: ref_count=%d", _ref_count);
  }
  
  inline void ObjectMonitor::inc_ref_count() {
!   // The increment needs to be MO_SEQ_CST. At the moment, the Atomic::inc
!   // backend on PPC does not yet conform to these requirements. Therefore
!   // the increment is simulated with a load phi; cas phi + 1; loop.
!   // Without this MO_SEQ_CST Atomic::inc simulation, AsyncDeflateIdleMonitors
!   // is not safe.
!   for (;;) {
!     jint sample = OrderAccess::load_acquire(&_ref_count);
!     guarantee(sample >= 0, "sanity check: sample=%d", (int)sample);
!     if (Atomic::cmpxchg(sample + 1, &_ref_count, sample) == sample) {
!       // Incremented _ref_count without interference.
!       return;
!     }
!     // Implied else: Saw interference so loop and try again.
!   }
  }
  
  inline jint ObjectMonitor::ref_count() const {
    return OrderAccess::load_acquire(&_ref_count);
  }
--- 158,179 ----
  inline bool ObjectMonitor::is_new() const {
    return _allocation_state == New;
  }
  
  inline void ObjectMonitor::dec_ref_count() {
!   // The decrement only needs to be MO_ACQ_REL since the reference
!   // counter is volatile.
!   Atomic::dec(&_ref_count);
    guarantee(_ref_count >= 0, "sanity check: ref_count=%d", _ref_count);
  }
  
  inline void ObjectMonitor::inc_ref_count() {
!   // The increment needs to be MO_SEQ_CST so that the reference
!   // counter update is seen as soon as possible in a race with the
!   // async deflation protocol.
!   Atomic::inc(&_ref_count);
!   guarantee(_ref_count > 0, "sanity check: ref_count=%d", _ref_count);
  }
  
  inline jint ObjectMonitor::ref_count() const {
    return OrderAccess::load_acquire(&_ref_count);
  }