JVM_ENTRY在OpenJDK源代码上

JVM_ENTRY on OpenJDK source code

本文关键字：源代码 OpenJDK ENTRY JVM      更新时间：2023-10-16

我读取在热点OpenJDK 7中抛出异常的代码，并跟踪哪些类使用了它们。它们最终出现在实现JVM_ENTRY(result_type, header)的类中，例如在jvm.cpp、java.cpp等中。 我的问题是JVM_ENTRY的功能是什么，它是如何工作的？

下面是jvm.cpp中的示例

JVM_ENTRY(jobject, JVM_AllocateNewObject(JNIEnv *env, jobject receiver, jclass currClass, jclass initClass))
JVMWrapper("JVM_AllocateNewObject");
JvmtiVMObjectAllocEventCollector oam;
// Receiver is not used
oop curr_mirror = JNIHandles::resolve_non_null(currClass);
oop init_mirror = JNIHandles::resolve_non_null(initClass);
// Cannot instantiate primitive types
if (java_lang_Class::is_primitive(curr_mirror) || java_lang_Class::is_primitive(init_mirror)) {
ResourceMark rm(THREAD);
THROW_0(vmSymbols::java_lang_InvalidClassException());
}
// Arrays not allowed here, must use JVM_AllocateNewArray
if (Klass::cast(java_lang_Class::as_klassOop(curr_mirror))->oop_is_javaArray() ||
Klass::cast(java_lang_Class::as_klassOop(init_mirror))->oop_is_javaArray()) {
ResourceMark rm(THREAD);
THROW_0(vmSymbols::java_lang_InvalidClassException());
}
instanceKlassHandle curr_klass (THREAD, java_lang_Class::as_klassOop(curr_mirror));
instanceKlassHandle init_klass (THREAD, java_lang_Class::as_klassOop(init_mirror));
assert(curr_klass->is_subclass_of(init_klass()), "just checking");
// Interfaces, abstract classes, and java.lang.Class classes cannot be instantiated directly.
curr_klass->check_valid_for_instantiation(false, CHECK_NULL);
// Make sure klass is initialized, since we are about to instantiate one of them.
curr_klass->initialize(CHECK_NULL);
methodHandle m (THREAD,
init_klass->find_method(vmSymbols::object_initializer_name(),
vmSymbols::void_method_signature()));
if (m.is_null()) {
ResourceMark rm(THREAD);
THROW_MSG_0(vmSymbols::java_lang_NoSuchMethodError(),
methodOopDesc::name_and_sig_as_C_string(Klass::cast(init_klass()),
vmSymbols::object_initializer_name(),
vmSymbols::void_method_signature()));
}
if (curr_klass ==  init_klass && !m->is_public()) {
// Calling the constructor for class 'curr_klass'.
// Only allow calls to a public no-arg constructor.
// This path corresponds to creating an Externalizable object.
THROW_0(vmSymbols::java_lang_IllegalAccessException());
}
if (!force_verify_field_access(curr_klass(), init_klass(), m->access_flags(), false)) {
// subclass 'curr_klass' does not have access to no-arg constructor of 'initcb'
THROW_0(vmSymbols::java_lang_IllegalAccessException());
}
Handle obj = curr_klass->allocate_instance_handle(CHECK_NULL);
// Call constructor m. This might call a constructor higher up in the hierachy
JavaCalls::call_default_constructor(thread, m, obj, CHECK_NULL);
return JNIHandles::make_local(obj());
JVM_END

我在hotspot/src/share/vm/runtime/interfaceSupport.hpp找到了JVM_ENTRY的定义

#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_ENTRY是一个预处理器宏，它添加了一些HotSpot JVM API的所有功能通用的样板代码。此 API 是 JDK 类库的本机代码和 JVM 之间的连接层。

JVM_ENTRY宏的作用：

  1. 从参数获取指向当前JavaThreadJNIEnv*指针。
  2. 执行从_thread_in_native到_thread_in_vm的线程状态转换，必要时在安全点阻塞。
  3. 在函数退出时清除 JNI 本地引用。
  4. 负责 JVM 调试版本中的调试跟踪和验证。
相关文章：