Java从JDK源码角度对Object进行实例分析

public class Object {
	private static native void registerNatives();
	static {
		registerNatives();
	}
	public final native Class<?> getClass();
	public native int hashCode();
	public Boolean equals(Object obj) {
		return (this == obj);
	}
	protected native Object clone() throws CloneNotSupportedException;
	public String toString() {
		return getClass().getName() + "@" + Integer.toHexString(hashCode());
	}
	public final native void notify();
	public final native void notifyAll();
	public final native void wait(long timeout) throws InterruptedException;
	public final void wait(long timeout, int nanos) throws InterruptedException {
		if (timeout < 0) {
			throw new IllegalArgumentException("timeout value is negative");
		}
		if (nanos < 0 || nanos > 999999) {
			throw new IllegalArgumentException("nanosecond timeout value out of range");
		}
		if (nanos > 0) {
			timeout++;
		}
		wait(timeout);
	}
	public final void wait() throws InterruptedException {
		wait(0);
	}
	protected void finalize() throws Throwable {
	}
}

JNIEXPORT void JNICALL
Java_java_lang_Object_registerNatives(JNIEnv *env, jclass cls)
{
	(*env)->RegisterNatives(env, cls,
	methods, sizeof(methods)/sizeof(methods[0]));
}

static JNINativeMethod methods[] = {
  {"hashCode",  "()I",          (void *)&JVM_IHashCode},
  {"wait",    "(J)V",          (void *)&JVM_MonitorWait},
  {"notify",   "()V",          (void *)&JVM_MonitorNotify},
  {"notifyAll",  "()V",          (void *)&JVM_MonitorNotifyAll},
  {"clone",    "()Ljava/lang/Object;",  (void *)&JVM_Clone},
};

JNIEXPORT jclass JNICALL
Java_java_lang_Object_getClass(JNIEnv *env, jobject this)
{
  if (this == NULL) {
    JNU_ThrowNullPointerException(env, NULL);
    return 0;
  } else {
    return (*env)->GetObjectClass(env, this);
  }
}

JNI_ENTRY(jclass, jni_GetObjectClass(JNIEnv *env, jobject obj))
 JNIWrapper("GetObjectClass");
 DTRACE_PROBE2(hotspot_jni, GetObjectClass__entry, env, obj);
 klassOop k = JNIHandles::resolve_non_null(obj)->klass();
 jclass ret =
  (jclass) JNIHandles::make_local(env, Klass::cast(k)->java_mirror());
 DTRACE_PROBE1(hotspot_jni, GetObjectClass__return, ret);
 return ret;
JNI_END

JVM_ENTRY(jint, JVM_IHashCode(JNIEnv* env, jobject handle))
 JVMWrapper("JVM_IHashCode");
 // as implemented in the classic virtual machine; return 0 if object is NULL
 return handle == NULL ? 0 : ObjectSynchronizer::FastHashCode (THREAD, JNIHandles::resolve_non_null(handle)) ;
JVM_END

static inline intptr_t get_next_hash(Thread * Self, oop obj) {
	intptr_t value = 0 ;
	if (hashCode == 0) {
		value = os::random() ;
	} else
	 if (hashCode == 1) {
		intptr_t addrBits = intptr_t(obj) >> 3 ;
		value = addrBits ^ (addrBits >> 5) ^ GVars.stwRandom ;
	} else
	 if (hashCode == 2) {
		value = 1 ;
		// for sensitivity testing
	} else
	 if (hashCode == 3) {
		value = ++GVars.hcSequence ;
	} else
	 if (hashCode == 4) {
		value = intptr_t(obj) ;
	} else {
		unsigned t = Self->_hashStateX ;
		t ^= (t << 11) ;
		Self->_hashStateX = Self->_hashStateY ;
		Self->_hashStateY = Self->_hashStateZ ;
		Self->_hashStateZ = Self->_hashStateW ;
		unsigned v = Self->_hashStateW ;
		v = (v ^ (v >> 19)) ^ (t ^ (t >> 8)) ;
		Self->_hashStateW = v ;
		value = v ;
	}
	value &= markOopDesc::hash_mask;
	if (value == 0) value = 0xBAD ;
	assert (value != markOopDesc::no_hash, "invariant") ;
	TEVENT (hashCode: GENERATE) ;
	return value;
}

JVM_ENTRY(jobject, JVM_Clone(JNIEnv* env, jobject handle))
 JVMWrapper("JVM_Clone");
Handle obj(THREAD, JNIHandles::resolve_non_null(handle));
const KlassHandle klass (THREAD, obj->klass());
JvmtiVMObjectAllocEventCollector oam;
if (!klass->is_cloneable()) {
	ResourceMark rm(THREAD);
	THROW_MSG_0(vmSymbols::java_lang_CloneNotSupportedException(), klass->external_name());
}
const int size = obj->size();
oop new_obj = NULL;
if (obj->is_javaArray()) {
	const int length = ((arrayOop)obj())->length();
	new_obj = CollectedHeap::array_allocate(klass, size, length, CHECK_NULL);
} else {
	new_obj = CollectedHeap::obj_allocate(klass, size, CHECK_NULL);
}
Copy::conjoint_jlongs_atomic((jlong*)obj(), (jlong*)new_obj,
                (size_t)align_object_size(size) / HeapWordsPerlong);
new_obj->init_mark();
BarrierSet* bs = Universe::heap()->barrier_set();
assert(bs->has_write_region_opt(), "Barrier set does not have write_region");
bs->write_region(MemRegion((HeapWord*)new_obj, size));
if (klass->has_finalizer()) {
	assert(obj->is_instance(), "should be instanceOop");
	new_obj = instanceKlass::register_finalizer(instanceOop(new_obj), CHECK_NULL);
}
return JNIHandles::make_local(env, oop(new_obj));
JVM_END

JVM_ENTRY(void, JVM_MonitorNotify(JNIEnv* env, jobject handle))
 JVMWrapper("JVM_MonitorNotify");
 Handle obj(THREAD, JNIHandles::resolve_non_null(handle));
 assert(obj->is_instance() || obj->is_array(), "JVM_MonitorNotify must apply to an object");
 ObjectSynchronizer::notify(obj, CHECK);
JVM_END

void ObjectMonitor::notify(TRAPS) {
	CHECK_OWNER();
	if (_WaitSet == NULL) {
		TEVENT (Empty-Notify) ;
		return ;
	}
	DTRACE_MONITOR_PROBE(notify, this, object(), THREAD);
	int Policy = Knob_MoveNotifyee ;
	Thread::SpinAcquire (&_WaitSetLock, "WaitSet - notify") ;
	ObjectWaiter * iterator = DequeueWaiter() ;
	if (iterator != NULL) {
		TEVENT (Notify1 - Transfer) ;
		guarantee (iterator->TState == ObjectWaiter::TS_WAIT, "invariant") ;
		guarantee (iterator->_notified == 0, "invariant") ;
		if (Policy != 4) {
			iterator->TState = ObjectWaiter::TS_ENTER ;
		}
		iterator->_notified = 1 ;
		ObjectWaiter * List = _EntryList ;
		if (List != NULL) {
			assert (List->_prev == NULL, "invariant") ;
			assert (List->TState == ObjectWaiter::TS_ENTER, "invariant") ;
			assert (List != iterator, "invariant") ;
		}
		if (Policy == 0) {
			// prepend to EntryList
			if (List == NULL) {
				iterator->_next = iterator->_prev = NULL ;
				_EntryList = iterator ;
			} else {
				List->_prev = iterator ;
				iterator->_next = List ;
				iterator->_prev = NULL ;
				_EntryList = iterator ;
			}
		} else
		   if (Policy == 1) {
			// append to EntryList
			if (List == NULL) {
				iterator->_next = iterator->_prev = NULL ;
				_EntryList = iterator ;
			} else {
				// CONSIDER: finding the tail currently requires a linear-time walk of
				// the EntryList. We can make tail access constant-time by converting to
				// a CDLL instead of using our current DLL.
				ObjectWaiter * Tail ;
				for (Tail = List ; Tail->_next != NULL ; Tail = Tail->_next) ;
				assert (Tail != NULL && Tail->_next == NULL, "invariant") ;
				Tail->_next = iterator ;
				iterator->_prev = Tail ;
				iterator->_next = NULL ;
			}
		} else
		   if (Policy == 2) {
			// prepend to cxq
			// prepend to cxq
			if (List == NULL) {
				iterator->_next = iterator->_prev = NULL ;
				_EntryList = iterator ;
			} else {
				iterator->TState = ObjectWaiter::TS_CXQ ;
				for (;;) {
					ObjectWaiter * Front = _cxq ;
					iterator->_next = Front ;
					if (Atomic::cmpxchg_ptr (iterator, &_cxq, Front) == Front) {
						break ;
					}
				}
			}
		} else
		   if (Policy == 3) {
			// append to cxq
			iterator->TState = ObjectWaiter::TS_CXQ ;
			for (;;) {
				ObjectWaiter * Tail ;
				Tail = _cxq ;
				if (Tail == NULL) {
					iterator->_next = NULL ;
					if (Atomic::cmpxchg_ptr (iterator, &_cxq, NULL) == NULL) {
						break ;
					}
				} else {
					while (Tail->_next != NULL) Tail = Tail->_next ;
					Tail->_next = iterator ;
					iterator->_prev = Tail ;
					iterator->_next = NULL ;
					break ;
				}
			}
		} else {
			ParkEvent * ev = iterator->_event ;
			iterator->TState = ObjectWaiter::TS_RUN ;
			OrderAccess::fence() ;
			ev->unpark() ;
		}
		if (Policy < 4) {
			iterator->wait_reenter_begin(this);
		}
		// _WaitSetLock protects the wait queue, not the EntryList. We could
		// move the add-to-EntryList operation, above, outside the critical section
		// protected by _WaitSetLock. In practice that's not useful. With the
		// exception of wait() timeouts and interrupts the monitor owner
		// is the only thread that grabs _WaitSetLock. There's almost no contention
		// on _WaitSetLock so it's not profitable to reduce the length of the
		// critical section.
	}
	Thread::SpinRelease (&_WaitSetLock) ;
	if (iterator != NULL && ObjectMonitor::_sync_Notifications != NULL) {
		ObjectMonitor::_sync_Notifications->inc() ;
	}
}

JVM_ENTRY(void, JVM_MonitorWait(JNIEnv* env, jobject handle, jlong ms))
 JVMWrapper("JVM_MonitorWait");
 Handle obj(THREAD, JNIHandles::resolve_non_null(handle));
 assert(obj->is_instance() || obj->is_array(), "JVM_MonitorWait must apply to an object");
 JavaThreadInObjectWaitState jtiows(thread, ms != 0);
 if (JvmtiExport::should_post_monitor_wait()) {
  JvmtiExport::post_monitor_wait((JavaThread *)THREAD, (oop)obj(), ms);
 }
 ObjectSynchronizer::wait(obj, ms, CHECK);
JVM_END