一起学JUCE之Atomic

　　Atomic功能是提供简单的类保持原始值，并且提供对其执行原子操作；Atomic是线程安全的，类型的实现比较简单，就是通过各种措施保证变量的操作达到原子操作，有一点需要注意Atomic使用的时候只支持长度是32位或者64位的类或者类型，其他类型会出现问题。这里对类中用到的一些系统函数进行一些说明。

类型转换

 template <typename Dest, typename Source>

    static inline Dest castTo (Source value) noexcept         { union { Dest d; Source s; } u; u.s = value; return u.d; }

    static inline Type castFrom32Bit (int32 value) noexcept   { return castTo <Type, int32> (value); }

    static inline Type castFrom64Bit (int64 value) noexcept   { return castTo <Type, int64> (value); }

    static inline int32 castTo32Bit (Type value) noexcept     { return castTo <int32, Type> (value); }

    static inline int64 castTo64Bit (Type value) noexcept     { return castTo <int64, Type> (value); }

以上类型转换比较巧妙，直接使用联合体进行两个变量的转换不用再对类型进行判断，Dest和Source占用的内存空间都位4或者8

以下对各个系统使用到的api做些说明
MAC：

原子操作

 #include <libkern/OSAtomic.h>

 int32_t

     OSAtomicAdd32(int32_t theAmount, volatile int32_t *theValue);

     int32_t

     OSAtomicAdd32Barrier(int32_t theAmount, volatile int32_t *theValue);

     int32_t

     OSAtomicIncrement32(volatile int32_t *theValue);

     int32_t

     OSAtomicIncrement32Barrier(volatile int32_t *theValue);

     int32_t

     OSAtomicDecrement32(volatile int32_t *theValue);

     int32_t

     OSAtomicDecrement32Barrier(volatile int32_t *theValue);

     int32_t

     OSAtomicOr32(uint32_t theMask, volatile uint32_t *theValue);

     int32_t

     OSAtomicOr32Barrier(uint32_t theMask, volatile uint32_t *theValue);

     int32_t

     OSAtomicAnd32(uint32_t theMask, volatile uint32_t *theValue);

     int32_t

     OSAtomicAnd32Barrier(uint32_t theMask, volatile uint32_t *theValue);

     int32_t

     OSAtomicXor32(uint32_t theMask, volatile uint32_t *theValue);

     int32_t

     OSAtomicXor32Barrier(uint32_t theMask, volatile uint32_t *theValue);

     int32_t

     OSAtomicOr32Orig(uint32_t theMask, volatile uint32_t *theValue);

     int32_t

     OSAtomicOr32OrigBarrier(uint32_t theMask, volatile uint32_t *theValue);

     int32_t

     OSAtomicAnd32Orig(uint32_t theMask, volatile uint32_t *theValue);

     int32_t

     OSAtomicAnd32OrigBarrier(uint32_t theMask, volatile uint32_t *theValue);

     int32_t

     OSAtomicXor32Orig(uint32_t theMask, volatile uint32_t *theValue);

     int32_t

     OSAtomicXor32OrigBarrier(uint32_t theMask, volatile uint32_t *theValue);

     int64_t

     OSAtomicAdd64(int64_t theAmount, volatile int64_t *theValue);

     int64_t

     OSAtomicAdd64Barrier(int64_t theAmount, volatile int64_t *theValue);

     int64_t

     OSAtomicIncrement64(volatile int64_t *theValue);

     int64_t

     OSAtomicIncrement64Barrier(volatile int64_t *theValue);

     int64_t

     OSAtomicDecrement64(volatile int64_t *theValue);

     int64_t

     OSAtomicDecrement64Barrier(volatile int64_t *theValue);

     bool

     OSAtomicCompareAndSwapInt(int oldValue, int newValue,

         volatile int *theValue);

     bool

     OSAtomicCompareAndSwapIntBarrier(int oldValue, int newValue,

         volatile int *theValue);

     bool

     OSAtomicCompareAndSwapLong(long oldValue, long newValue,

         volatile long *theValue);

     bool

     OSAtomicCompareAndSwapLongBarrier(long oldValue, long newValue,

         volatile long *theValue);

     bool

     OSAtomicCompareAndSwapPtr(void* oldValue, void* newValue,

         void* volatile *theValue);

     bool

     OSAtomicCompareAndSwapPtrBarrier(void* oldValue, void* newValue,

         void* volatile *theValue);

     bool

     OSAtomicCompareAndSwap32(int32_t oldValue, int32_t newValue,

         volatile int32_t *theValue);

     bool

     OSAtomicCompareAndSwap32Barrier(int32_t oldValue, int32_t newValue,

         volatile int32_t *theValue);

     bool

     OSAtomicCompareAndSwap64(int64_t oldValue, int64_t newValue,

         volatile int64_t *theValue);

     bool

     OSAtomicCompareAndSwap64Barrier(int64_t oldValue, int64_t newValue,

         volatile int64_t *theValue);

     bool

     OSAtomicTestAndSet(uint32_t n, volatile void *theAddress);

     bool

     OSAtomicTestAndSetBarrier(uint32_t n, volatile void *theAddress);

     bool

     OSAtomicTestAndClear(uint32_t n, volatile void *theAddress);

     bool

     OSAtomicTestAndClearBarrier(uint32_t n, volatile void *theAddress);

     bool

     OSSpinLockTry(OSSpinLock *lock);

     void

     OSSpinLockLock(OSSpinLock *lock);

     void

     OSSpinLockUnlock(OSSpinLock *lock);

     void

     OSAtomicEnqueue(OSQueueHead *list, void *new, size_t offset);

     void*

     OSAtomicDequeue(OSQueueHead *list, size_t offset);

LINUX：

原子操作

type __sync_fetch_and_add (type *ptr, type value);

type __sync_fetch_and_sub (type *ptr, type value);

type __sync_fetch_and_or (type *ptr, type value);

type __sync_fetch_and_and (type *ptr, type value);

type __sync_fetch_and_xor (type *ptr, type value);

type __sync_fetch_and_nand (type *ptr, type value);

type __sync_add_and_fetch (type *ptr, type value);

type __sync_sub_and_fetch (type *ptr, type value);

type __sync_or_and_fetch (type *ptr, type value);

type __sync_and_and_fetch (type *ptr, type value);

type __sync_xor_and_fetch (type *ptr, type value);

type __sync_nand_and_fetch (type *ptr, type value);

WINDOWS：

原子操作

LONG InterLockedIncrement(

　　LPLONG lpAddend // variable address

　　);

LONG InterlockedDecrement(

　　LPLONG lpAddend // variable address

　　);

LONG__cdeclInterlockedExchangeAdd(

_Inout_LONGvolatile*Addend,

_In_LONGValue

);

 LONG InterlockedCompareExchange(

LPLONG Destination, LONG Exchange, LONG Comperand );

 PVOID InterlockedCompareExchangePointer(

PVOID *Destination, PVOID Exchange, PVOID Comperand );

总体的原子操作完全是依赖于系统API来实现的，留一下相关系统的原子操作api即可