natobject.cc

gcc的组建

        heavy_lock_finalization_proc (hl);
#     endif
    }
}

// We hold the lock on he, and heavy_count is 0.
// Release the lock by replacing the address with new_address_val.
// Remove all heavy locks on the list.  Note that the only possible way
// in which a lock may still be in use is if it's in the process of
// being unlocked.
// FIXME:  Why does this unlock the hash entry?  I think that
// could now be done more cleanly in MonitorExit.
static void
remove_all_heavy (hash_entry *he, obj_addr_t new_address_val)
{
  JvAssert(he -> heavy_count == 0);
  JvAssert(he -> address & LOCKED);
  heavy_lock *hl = he -> heavy_locks;
  he -> heavy_locks = 0;
  // We would really like to release the lock bit here.  Unfortunately, that
  // Creates a race between or finalizer removal, and the potential
  // reinstallation of a new finalizer as a new heavy lock is created.
  // This may need to be revisited.
  for(; 0 != hl; hl = hl->next)
    {
      obj_addr_t obj = hl -> address;
      JvAssert(0 != obj);  // If this was previously finalized, it should no
			   // longer appear on our list.
      hl -> address = 0; // Finalization proc might still see it after we
      			 // finish.
      GC_finalization_proc old_finalization_proc = hl -> old_finalization_proc;
      void * old_client_data = hl -> old_client_data;
#     ifdef HAVE_BOEHM_GC
	// Remove our finalization procedure.
        // Reregister the clients if applicable.
          GC_REGISTER_FINALIZER_NO_ORDER((GC_PTR)obj, old_finalization_proc,
			  		 old_client_data, 0, 0);
      	  // Note that our old finalization procedure may have been
          // previously determined to be runnable, and may still run.
      	  // FIXME - direct dependency on boehm GC.
#     endif
#     if defined (_Jv_HaveCondDestroy) || defined (_Jv_HaveMutexDestroy)
        // Wait for a possible lock holder to finish unlocking it.
        // This is only an issue if we have to explicitly destroy the mutex
        // or possibly if we have to destroy a condition variable that is
        // still being notified.
          _Jv_MutexLock(&(hl->si.mutex));
          _Jv_MutexUnlock(&(hl->si.mutex));
          heavy_lock_finalization_proc (hl);
#     endif
    }
  release_set(&(he -> address), new_address_val);
}

// We hold the lock on he and heavy_count is 0.
// We release it by replacing the address field with new_address_val.
// Remove all heavy locks on the list if the list is sufficiently long.
// This is called periodically to avoid very long lists of heavy locks.
// This seems to otherwise become an issue with SPECjbb, for example.
static inline void
maybe_remove_all_heavy (hash_entry *he, obj_addr_t new_address_val)
{
  static const int max_len = 5;
  heavy_lock *hl = he -> heavy_locks;

  for (int i = 0; i < max_len; ++i)
    {
      if (0 == hl) 
	{
  	  release_set(&(he -> address), new_address_val);
	  return;
	}
      hl = hl -> next;
    }
  remove_all_heavy(he, new_address_val);
}

// Allocate a new heavy lock for addr, returning its address.
// Assumes we already have the hash_entry locked, and there
// is currently no lightweight or allocated lock for addr.
// We register a finalizer for addr, which is responsible for
// removing the heavy lock when addr goes away, in addition
// to the responsibilities of any prior finalizer.
// This unfortunately holds the lock bit for the hash entry while it
// allocates two objects (on for the finalizer).
// It would be nice to avoid that somehow ...
static heavy_lock *
alloc_heavy(obj_addr_t addr, hash_entry *he)
{
  heavy_lock * hl = (heavy_lock *) _Jv_AllocTraceTwo(sizeof (heavy_lock));
  
  hl -> address = addr;
  _Jv_MutexInit (&(hl -> si.mutex));
  _Jv_CondInit (&(hl -> si.condition));
# if defined (_Jv_HaveCondDestroy) || defined (_Jv_HaveMutexDestroy)
    hl->si.init = true;  // needed ?
# endif
  hl -> next = he -> heavy_locks;
  he -> heavy_locks = hl;
  // FIXME: The only call that cheats and goes directly to the GC interface.
# ifdef HAVE_BOEHM_GC
    GC_REGISTER_FINALIZER_NO_ORDER(
		    	  (void *)addr, heavy_lock_obj_finalization_proc,
			  hl, &hl->old_finalization_proc,
			  &hl->old_client_data);
# endif /* HAVE_BOEHM_GC */
  return hl;
}

// Return the heavy lock for addr, allocating if necessary.
// Assumes we have the cache entry locked, and there is no lightweight
// lock for addr.
static heavy_lock *
get_heavy(obj_addr_t addr, hash_entry *he)
{
  heavy_lock *hl = find_heavy(addr, he);
  if (0 == hl)
    hl = alloc_heavy(addr, he);
  return hl;
}

void
_Jv_MonitorEnter (jobject obj)
{
#ifdef JV_LINKER_CANNOT_8BYTE_ALIGN_STATICS
  obj_addr_t addr = (obj_addr_t)obj & ~((obj_addr_t)FLAGS);
#else
  obj_addr_t addr = (obj_addr_t)obj;
#endif
  obj_addr_t address;
  unsigned hash = JV_SYNC_HASH(addr);
  hash_entry * he = light_locks + hash;
  _Jv_ThreadId_t self = _Jv_ThreadSelf();
  unsigned count;
  const unsigned N_SPINS = 18;

  // We need to somehow check that addr is not NULL on the fast path.
  // A very predictable
  // branch on a register value is probably cheaper than dereferencing addr.
  // We could also permanently lock the NULL entry in the hash table.
  // But it's not clear that's cheaper either.
  if (__builtin_expect(!addr, false))
    throw new java::lang::NullPointerException;
   
  JvAssert(!(addr & FLAGS));
retry:
  if (__builtin_expect(compare_and_swap(&(he -> address),
					0, addr),true))
    {
      JvAssert(he -> light_thr_id == INVALID_THREAD_ID);
      JvAssert(he -> light_count == 0);
      he -> light_thr_id = self;
      // Count fields are set correctly.  Heavy_count was also zero,
      // but can change asynchronously.
      // This path is hopefully both fast and the most common.
      LOG(ACQ_LIGHT, addr, self);
      return;
    }
  address = he -> address;
  if ((address & ~(HEAVY | REQUEST_CONVERSION)) == addr)
    {
      if (he -> light_thr_id == self)
	{
	  // We hold the lightweight lock, and it's for the right
	  // address.
	  count = he -> light_count;
	  if (count == USHRT_MAX)
	    {
	      // I think most JVMs don't check for this.
	      // But I'm not convinced I couldn't turn this into a security
	      // hole, even with a 32 bit counter.
	      throw new java::lang::IllegalMonitorStateException(
		JvNewStringLatin1("maximum monitor nesting level exceeded")); 
	    }
	  he -> light_count = count + 1;
	  return;
	}
      else
	{
	  JvAssert(!(address & LOCKED));
	  // Lightweight lock is held, but by somone else.
          // Spin a few times.  This avoids turning this into a heavyweight
    	  // lock if the current holder is about to release it.
	  // FIXME: Does this make sense on a uniprocessor, where
	  // it actually yields?  It's probably cheaper to convert.
          for (unsigned int i = 0; i < N_SPINS; ++i)
	    {
	      if ((he -> address & ~LOCKED) != address) goto retry;
	      spin(i);
            }
	  if (!compare_and_swap(&(he -> address), address, address | LOCKED ))
	    {
	      wait_unlocked(he);      
	      goto retry;
	    }
	  heavy_lock *hl = get_heavy(addr, he);
	  ++ (he -> heavy_count);
	  // The hl lock acquisition can't block for long, since it can
	  // only be held by other threads waiting for conversion, and
	  // they, like us, drop it quickly without blocking.
	  _Jv_MutexLock(&(hl->si.mutex));
	  JvAssert(he -> address == address | LOCKED );
	  release_set(&(he -> address), (address | REQUEST_CONVERSION | HEAVY));
				// release lock on he
	  LOG(REQ_CONV, (address | REQUEST_CONVERSION | HEAVY), self);
	  // If _Jv_CondWait is interrupted, we ignore the interrupt, but
	  // restore the thread's interrupt status flag when done.
	  jboolean interrupt_flag = false;
	  while ((he -> address & ~FLAGS) == (address & ~FLAGS))
	    {
	      // Once converted, the lock has to retain heavyweight
	      // status, since heavy_count > 0.
	      int r = _Jv_CondWait (&(hl->si.condition), &(hl->si.mutex), 0, 0);
	      if (r == _JV_INTERRUPTED)
	        {
		  interrupt_flag = true;
		  Thread::currentThread()->interrupt_flag = false;
		}
	    }
	  if (interrupt_flag)
	    Thread::currentThread()->interrupt_flag = interrupt_flag;
	  keep_live(addr);
		// Guarantee that hl doesn't get unlinked by finalizer.
		// This is only an issue if the client fails to release
		// the lock, which is unlikely.
	  JvAssert(he -> address & HEAVY);
	  // Lock has been converted, we hold the heavyweight lock,
	  // heavy_count has been incremented.
	  return;
        }
    }
  obj_addr_t was_heavy = (address & HEAVY);
  if ((address & LOCKED) ||
      !compare_and_swap(&(he -> address), address, (address | LOCKED )))
    {
      wait_unlocked(he);
      goto retry;
    }
  if ((address & ~(HEAVY | REQUEST_CONVERSION)) == 0)
    {
      // Either was_heavy is true, or something changed out from under us,
      // since the initial test for 0 failed.
      JvAssert(!(address & REQUEST_CONVERSION));
	// Can't convert a nonexistent lightweight lock.
      heavy_lock *hl;
      hl = (was_heavy? find_heavy(addr, he) : 0);
        // The CAS succeeded, so was_heavy is still accurate.
      if (0 == hl)
        {
	  // It is OK to use the lighweight lock, since either the
	  // heavyweight lock does not exist, or none of the
	  // heavyweight locks are currently in use.  Future threads
	  // trying to acquire the lock will see the lightweight
	  // one first and use that.
	  he -> light_thr_id = self;  // OK, since nobody else can hold
				      // light lock or do this at the same time.
	  JvAssert(he -> light_count == 0);
	  JvAssert(was_heavy == (he -> address & HEAVY));
	  release_set(&(he -> address), (addr | was_heavy));
	  LOG(ACQ_LIGHT2, addr | was_heavy, self);
        }
      else
	{
	  // Must use heavy lock.
	  ++ (he -> heavy_count);
	  JvAssert(0 == (address & ~HEAVY));
          release_set(&(he -> address), HEAVY);
	  LOG(ACQ_HEAVY, addr | was_heavy, self);
          _Jv_MutexLock(&(hl->si.mutex));
	  keep_live(addr);
        }
      return;
    }
  // Lightweight lock is held, but does not correspond to this object.
  // We hold the lock on the hash entry, and he -> address can't
  // change from under us.  Neither can the chain of heavy locks.
    {
      JvAssert(0 == he -> heavy_count || (address & HEAVY));
      heavy_lock *hl = get_heavy(addr, he);
      ++ (he -> heavy_count);
      release_set(&(he -> address), address | HEAVY);
      LOG(ACQ_HEAVY2, address | HEAVY, self);
      _Jv_MutexLock(&(hl->si.mutex));
      keep_live(addr);
    }
}


void
_Jv_MonitorExit (jobject obj)
{
#ifdef JV_LINKER_CANNOT_8BYTE_ALIGN_STATICS
  obj_addr_t addr = (obj_addr_t)obj & ~((obj_addr_t)FLAGS);
#else
  obj_addr_t addr = (obj_addr_t)obj;
#endif
  _Jv_ThreadId_t self = _Jv_ThreadSelf();
  unsigned hash = JV_SYNC_HASH(addr);
  hash_entry * he = light_locks + hash;
  _Jv_ThreadId_t light_thr_id;
  unsigned count;
  obj_addr_t address;

retry:
  light_thr_id = he -> light_thr_id;
  // Unfortunately, it turns out we always need to read the address
  // first.  Even if we are going to update it with compare_and_swap,
  // we need to reset light_thr_id, and that's not safe unless we know
  // that we hold the lock.
  address = he -> address;
  // First the (relatively) fast cases:
  if (__builtin_expect(light_thr_id == self, true))
    // Above must fail if addr == 0 .
    {
      count = he -> light_count;
      if (__builtin_expect((address & ~HEAVY) == addr, true))
	{
          if (count != 0)
            {
	      // We held the lightweight lock all along.  Thus the values
	      // we saw for light_thr_id and light_count must have been valid. 
	      he -> light_count = count - 1;
	      return;
            }
	  else
	    {
	      // We hold the lightweight lock once.
	      he -> light_thr_id = INVALID_THREAD_ID;
              if (compare_and_swap_release(&(he -> address), address,
					   address & HEAVY))
		{
		  LOG(REL_LIGHT, address & HEAVY, self);
	          return;
		}
	      else
		{
	          he -> light_thr_id = light_thr_id; // Undo prior damage.
	          goto retry;
	        }
            }
        }
      // else lock is not for this address, conversion is requested,
      // or the lock bit in the address field is set.
    }
  else
    {
      if (__builtin_expect(!addr, false))
	throw new java::lang::NullPointerException;
      if ((address & ~(HEAVY | REQUEST_CONVERSION)) == addr)
	{
#	  ifdef LOCK_DEBUG
	    fprintf(stderr, "Lightweight lock held by other thread\n\t"
			    "light_thr_id = 0x%lx, self = 0x%lx, "
			    "address = 0x%lx, heavy_count = %d, pid = %d\n",
			    light_thr_id, self, (unsigned long)address,
			    he -> heavy_count, getpid());
	    print_he(he);
	    for(;;) {}
#	  endif
	  // Someone holds the lightweight lock for this object, and
	  // it can't be us.
	  throw new java::lang::IllegalMonitorStateException(
			JvNewStringLatin1("current thread not owner"));
        }
      else