cas调用链

//java.util.concurrent.atomic.AtomicInteger.java public final boolean compareAndSet(int expect, int update) { return unsafe.compareAndSwapInt(this, valueOffset, expect, update); }//sun.misc.Unsafe.java public final native boolean compareAndSwapInt(Object o, long offset, int expected, int x);// http://hg.openjdk.java.net/jdk8u/jdk8u/ \hotspot\src\share\vm\prims\unsafe.cpp// These are the methods prior to the JSR 166 changes in 1.6.0static JNINativeMethod methods_15[] = {//… {CC “compareAndSwapInt”, CC “(” OBJ “J"“I"“I”")Z”, FN_PTR(Unsafe_CompareAndSwapInt)},//…};UNSAFE_ENTRY(jboolean, Unsafe_CompareAndSwapInt(JNIEnv env, jobject unsafe, jobject obj, jlong offset, jint e, jint x)) UnsafeWrapper(“Unsafe_CompareAndSwapInt”); oop p = JNIHandles::resolve(obj); jint addr = (jint ) index_oop_from_field_offset_long(p, offset); return (jint)(Atomic::cmpxchg(x, addr, e)) == e;UNSAFE_END// http://hg.openjdk.java.net/jdk8u/jdk8u/ \hotspot\src\share\vm\runtime\atomic.cppunsigned Atomic::cmpxchg(unsigned int exchange_value, volatile unsigned int dest, unsigned int compare_value) { assert(sizeof(unsigned int) == sizeof(jint), “more work to do”); return (unsigned int)Atomic::cmpxchg((jint)exchange_value, (volatile jint*)dest, (jint)compare_value);}// http://hg.openjdk.java.net/jdk8u/jdk8u/ \hotspot\src\os_cpu\windows_x86\vm\atomic_windows_x86.inline.hppinline jint Atomic::cmpxchg (jint exchange_value, volatile jint* dest, jint compare_value) { // alternative for InterlockedCompareExchange int mp = os::is_MP(); __asm { mov edx, dest mov ecx, exchange_value mov eax, compare_value LOCK_IF_MP(mp) cmpxchg dword ptr [edx], ecx }}