java系列 - System

简介

java.lang.System.java

跟踪arraycopy

public static native void arraycopy(Object src, int srcPos, Object dest, int destPos, int length);

System.c

// jdk/src/share/native/java/lang/System.c

/* Only register the performance-critical methods */
static JNINativeMethod methods[] = {
    {"currentTimeMillis", "()J",              (void *)&JVM_CurrentTimeMillis},
    {"nanoTime",          "()J",              (void *)&JVM_NanoTime},
    {"arraycopy",     "(" OBJ "I" OBJ "II)V", (void *)&JVM_ArrayCopy},
};

jvm.cpp

// src/share/vm/prims/jvm.cpp

JVM_ENTRY(void, JVM_ArrayCopy(JNIEnv *env, jclass ignored, jobject src, jint src_pos,
                               jobject dst, jint dst_pos, jint length))
  JVMWrapper("JVM_ArrayCopy");
  // Check if we have null pointers
  if (src == NULL || dst == NULL) {
    THROW(vmSymbols::java_lang_NullPointerException());
  }
  arrayOop s = arrayOop(JNIHandles::resolve_non_null(src));
  arrayOop d = arrayOop(JNIHandles::resolve_non_null(dst));
  assert(s->is_oop(), "JVM_ArrayCopy: src not an oop");
  assert(d->is_oop(), "JVM_ArrayCopy: dst not an oop");
  // Do copy
  Klass::cast(s->klass())->copy_array(s, src_pos, d, dst_pos, length, thread);
JVM_END