Java并发编程笔记（一）--volatile, CAS, Atomic变量
#include <gcj/cni.h>#include <gcj/field.h>#include <gcj/javaprims.h>#include <jvm.h>#include <sun/misc/Unsafe.h>#include <java/lang/System.h>#include <java/lang/InterruptedException.h>#include <java/lang/Thread.h>#include <java/lang/Long.h>#include "sysdep/locks.h"// Use a spinlock for multi-word accessesclass spinlock{ static volatile obj_addr_t lock;public:spinlock () { while (! compare_and_swap (&lock, 0, 1)) _Jv_ThreadYield (); } ~spinlock () { release_set (&lock, 0); }};// This is a single lock that is used for all synchronized accesses if// the compiler can't generate inline compare-and-swap operations. In// most cases it'll never be used, but the i386 needs it for 64-bit// locked accesses and so does PPC32. It's worth building libgcj with// target=i486 (or above) to get the inlines.volatile obj_addr_t spinlock::lock;static inline boolcompareAndSwap (volatile jint *addr, jint old, jint new_val){ jboolean result = false; spinlock lock; if ((result = (*addr == old))) *addr = new_val; return result;}static inline boolcompareAndSwap (volatile jlong *addr, jlong old, jlong new_val){ jboolean result = false; spinlock lock; if ((result = (*addr == old))) *addr = new_val; return result;}static inline boolcompareAndSwap (volatile jobject *addr, jobject old, jobject new_val){ jboolean result = false; spinlock lock; if ((result = (*addr == old))) *addr = new_val; return result;}jlongsun::misc::Unsafe::objectFieldOffset (::java::lang::reflect::Field *field){ _Jv_Field *fld = _Jv_FromReflectedField (field); // FIXME: what if it is not an instance field? return fld->getOffset();}jintsun::misc::Unsafe::arrayBaseOffset (jclass arrayClass){ // FIXME: assert that arrayClass is array. jclass eltClass = arrayClass->getComponentType(); return (jint)(jlong) _Jv_GetArrayElementFromElementType (NULL, eltClass);}jintsun::misc::Unsafe::arrayIndexScale (jclass arrayClass){ // FIXME: assert that arrayClass is array. jclass eltClass = arrayClass->getComponentType(); if (eltClass->isPrimitive()) return eltClass->size(); return sizeof (void *);}// These methods are used when the compiler fails to generate inline// versions of the compare-and-swap primitives.jbooleansun::misc::Unsafe::compareAndSwapInt (jobject obj, jlong offset, jint expect, jint update){ jint *addr = (jint *)((char *)obj + offset); return compareAndSwap (addr, expect, update);}jbooleansun::misc::Unsafe::compareAndSwapLong (jobject obj, jlong offset, jlong expect, jlong update){ volatile jlong *addr = (jlong*)((char *) obj + offset); return compareAndSwap (addr, expect, update);}jbooleansun::misc::Unsafe::compareAndSwapObject (jobject obj, jlong offset, jobject expect, jobject update){ jobject *addr = (jobject*)((char *) obj + offset); return compareAndSwap (addr, expect, update);}voidsun::misc::Unsafe::putOrderedInt (jobject obj, jlong offset, jint value){ volatile jint *addr = (jint *) ((char *) obj + offset); *addr = value;}voidsun::misc::Unsafe::putOrderedLong (jobject obj, jlong offset, jlong value){ volatile jlong *addr = (jlong *) ((char *) obj + offset); spinlock lock; *addr = value;}voidsun::misc::Unsafe::putOrderedObject (jobject obj, jlong offset, jobject value){ volatile jobject *addr = (jobject *) ((char *) obj + offset); *addr = value;}voidsun::misc::Unsafe::putIntVolatile (jobject obj, jlong offset, jint value){ write_barrier (); volatile jint *addr = (jint *) ((char *) obj + offset); *addr = value;}voidsun::misc::Unsafe::putLongVolatile (jobject obj, jlong offset, jlong value){ volatile jlong *addr = (jlong *) ((char *) obj + offset); spinlock lock; *addr = value;}voidsun::misc::Unsafe::putObjectVolatile (jobject obj, jlong offset, jobject value){ write_barrier (); volatile jobject *addr = (jobject *) ((char *) obj + offset); *addr = value;}#if 0 // FIXMEvoidsun::misc::Unsafe::putInt (jobject obj, jlong offset, jint value){ jint *addr = (jint *) ((char *) obj + offset); *addr = value;}#endifvoidsun::misc::Unsafe::putLong (jobject obj, jlong offset, jlong value){ jlong *addr = (jlong *) ((char *) obj + offset); spinlock lock; *addr = value;}voidsun::misc::Unsafe::putObject (jobject obj, jlong offset, jobject value){ jobject *addr = (jobject *) ((char *) obj + offset); *addr = value;}jintsun::misc::Unsafe::getIntVolatile (jobject obj, jlong offset){ volatile jint *addr = (jint *) ((char *) obj + offset); jint result = *addr; read_barrier (); return result;}jobjectsun::misc::Unsafe::getObjectVolatile (jobject obj, jlong offset){ volatile jobject *addr = (jobject *) ((char *) obj + offset); jobject result = *addr; read_barrier (); return result;}jlongsun::misc::Unsafe::getLong (jobject obj, jlong offset){ jlong *addr = (jlong *) ((char *) obj + offset); spinlock lock; return *addr;}jlongsun::misc::Unsafe::getLongVolatile (jobject obj, jlong offset){ volatile jlong *addr = (jlong *) ((char *) obj + offset); spinlock lock; return *addr;}voidsun::misc::Unsafe::unpark (::java::lang::Thread *thread){ natThread *nt = (natThread *) thread->data; nt->park_helper.unpark ();}voidsun::misc::Unsafe::park (jboolean isAbsolute, jlong time){ using namespace ::java::lang; Thread *thread = Thread::currentThread(); natThread *nt = (natThread *) thread->data; nt->park_helper.park (isAbsolute, time);}
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