//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 1.6.0
static 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.cpp
unsigned 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.hpp
inline 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
}
}
cmpxchg解釋
