java native调用

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Object

Object

registerNatives()
getClass()
hashCode()
equals()
clone()
toString()
notify()
notifyAll()
wait(long timeout)
wait(long timeout, int nanos)
wait()
finalize()

Object就这几个方法,其中除equals和toString,其他都是native方法.

本文就以Object来探讨下java的native,源码基于openjdk7

Object native方法的声明在openjdk/jdk/src/share/native/java/lang/Object.c中

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},};

JNINativeMethod的结构体如下:

typedef struct {    char *name;    char *signature;    void *fnPtr;} JNINativeMethod;

name Object的方法名称
signature 方法签名
fnPtr native实现的函数指针

对应的native实现在openjdk/hotspot/src/share/vm/prims/jvm.cpp

hashCode():

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

wait():

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, THREAD);JVM_END

…

JVM_ENTRY的结构体定义在openjdk/hotspot/src/share/vm/runtime/interfaceSupport.hpp

#define JVM_ENTRY(result_type, header)                               \extern "C" {                                                         \  result_type JNICALL header {                                       \    JavaThread* thread=JavaThread::thread_from_jni_environment(env); \    ThreadInVMfromNative __tiv(thread);                              \    debug_only(VMNativeEntryWrapper __vew;)                          \    VM_ENTRY_BASE(result_type, header, thread)

JVM_END

#define JVM_END } }

Object