GCC __builtin_expect的作用

https://blog.csdn.net/shuimuniao/article/details/8017971

#define LIKELY(x) __builtin_expect(!!(x), 1) //x很可能为真
#define UNLIKELY(x) __builtin_expect(!!(x), 0) //x很可能为假

CurrentThread.h

namespace CurrentThread
{
    // internal
    extern __thread int t_cachedTid;
    extern __thread char t_tidString[];
    extern __thread int t_tidStringLength;
    extern __thread const char* t_threadName;
    void cacheTid();
    inline int tid()
    {
        if (__builtin_expect(t_cachedTid == , ))
        {
            cacheTid();
        }
        return t_cachedTid;
    }

    inline const char* tidString() // for logging
    {
        return t_tidString;
    }

    inline int tidStringLength() // for logging
    {
        return t_tidStringLength;
    }

    inline const char* name()
    {
        return t_threadName;
    }
}