碎片化知识

运算符可以用于宏函数的替换部分 粘合符合

__builtin_expect
example: 预测值 ,实际值

#define likely(x) __builtin_expect(!!(x), 1)
#define fastpath(x) ((typeof(x))__builtin_expect(_safe_cast_to_long(x), ~0l))
#define slowpath(x) ((typeof(x))__builtin_expect(_safe_cast_to_long(x), 0l))

数值交换

os_atomic_cmpxchg
os_atomic_store2o
os_atomic_inc_orig

Block Implementation Specification

struct Block_literal_1 {
    void *isa; // initialized to &_NSConcreteStackBlock or &_NSConcreteGlobalBlock
    int flags;
    int reserved;
    void (*invoke)(void *, ...);
    struct Block_descriptor_1 {
    unsigned long int reserved;         // NULL
        unsigned long int size;         // sizeof(struct Block_literal_1)
        // optional helper functions
        void (*copy_helper)(void *dst, void *src);     // IFF (1<<25)
        void (*dispose_helper)(void *src);             // IFF (1<<25)
        // required ABI.2010.3.16
        const char *signature;                         // IFF (1<<30)
    } *descriptor;
    // imported variables
};

enum {
    // Set to true on blocks that have captures (and thus are not true
    // global blocks) but are known not to escape for various other
    // reasons. For backward compatiblity with old runtimes, whenever
    // BLOCK_IS_NOESCAPE is set, BLOCK_IS_GLOBAL is set too. Copying a
    // non-escaping block returns the original block and releasing such a
    // block is a no-op, which is exactly how global blocks are handled.
    BLOCK_IS_NOESCAPE      =  (1 << 23),

    BLOCK_HAS_COPY_DISPOSE =  (1 << 25),
    BLOCK_HAS_CTOR =          (1 << 26), // helpers have C++ code
    BLOCK_IS_GLOBAL =         (1 << 28),
    BLOCK_HAS_STRET =         (1 << 29), // IFF BLOCK_HAS_SIGNATURE
    BLOCK_HAS_SIGNATURE =     (1 << 30),
};

Swift operator

• overflow operator * (&+ &- &*) *
• backtick ``

参考
浅谈iOS多线程(源码)
Block Implementation Specification