I found these in open JDK (System.c file)
static JNINativeMethod methods[] = {
{"currentTimeMillis", "()J", (void *)&JVM_CurrentTimeMillis},
{"nanoTime", "()J", (void *)&JVM_NanoTime},
{"arraycopy", "(" OBJ "I" OBJ "II)V", (void *)&JVM_ArrayCopy},
};
#undef OBJ
JNIEXPORT void JNICALL
Java_java_lang_System_registerNatives(JNIEnv *env, jclass cls)
{
(*env)->RegisterNatives(env, cls,
methods, sizeof(methods)/sizeof(methods[0]));
}
but I was not able to find the native implemetations of these functions currentTimeMillis nanoTime arraycopy
Form where can I get the native implementations of these functions ? Is that available in open JDK?
Native methods are implemented mostly in C and compiled to native code which runs directly on the machine. This is in contrast to normal methods, which are implemented in Java and compiled to Java byte code, which is executed by the Java Virtual Machine (JVM).
Native methods are Java™ methods that start in a language other than Java. Native methods can access system-specific functions and APIs that are not available directly in Java. The use of native methods limits the portability of an application, because it involves system-specific code.
Native Method Libraries are libraries that are written in other programming languages, such as C, C++, and assembly. These libraries can be loaded through JNI. So, the picture you posted is saying that JNI allows access to Native Method Libraries.
if found it in
jdk7/hotspot/src/share/vm/prims/jvm.cpp:229
JVM_LEAF(jlong, JVM_CurrentTimeMillis(JNIEnv *env, jclass ignored))
JVMWrapper("JVM_CurrentTimeMillis");
return os::javaTimeMillis();
JVM_END
the real implementation (for linux) is in
/jdk7/hotspot/src/os/linux/vm/os_linux.cpp
the other methods are just below it
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