标签：turn hand atomic post error date jin exception volatile
鼠篇写的基本都是理论基础，最近在研究Unsafe的源码，大致看了看，还没有太深入这篇牛篇，只能算是做个资源记录吧。
从AtomicInteger类源码看起来。
AtomicInteger源码部分：
// setup to use Unsafe.compareAndSwapInt for updates private static final Unsafe unsafe = Unsafe.getUnsafe(); private static final long valueOffset; static { try { valueOffset = unsafe.objectFieldOffset (AtomicInteger.class.getDeclaredField("value")); } catch (Exception ex) { throw new Error(ex); } } private volatile int value;
这里比较神奇的是：unsafe.objectFieldOffset 这个方法，方法的参数是Field类型。这里就是声明的volatile类型的value属性。
跟踪到Hotspot源码里可以看到：
Unsafe.cpp
UNSAFE_ENTRY(jlong, Unsafe_ObjectFieldOffset(JNIEnv *env, jobject unsafe, jobject field)) UnsafeWrapper("Unsafe_ObjectFieldOffset"); return find_field_offset(field, 0, THREAD); UNSAFE_END
jint find_field_offset(jobject field, int must_be_static, TRAPS) { if (field == NULL) { THROW_0(vmSymbols::java_lang_NullPointerException()); } oop reflected = JNIHandles::resolve_non_null(field); oop mirror = java_lang_reflect_Field::clazz(reflected); klassOop k = java_lang_Class::as_klassOop(mirror); int slot = java_lang_reflect_Field::slot(reflected); int modifiers = java_lang_reflect_Field::modifiers(reflected); if (must_be_static >= 0) { int really_is_static = ((modifiers & JVM_ACC_STATIC) != 0); if (must_be_static != really_is_static) { THROW_0(vmSymbols::java_lang_IllegalArgumentException()); } } int offset = instanceKlass::cast(k)->offset_from_fields(slot); return field_offset_from_byte_offset(offset); }
想看懂这段代码，必须看懂java在jvm里的对象体系了。
这篇文章很不错，对此做了一个大概况介绍 http://www.sczyh30.com/posts/Java/jvm-klass-oop/
标签：turn hand atomic post error date jin exception volatile
原文地址：http://www.cnblogs.com/aquariusm/p/7212658.html
