#define __ONCE_ALIGNMENT的作用是什么?

Question

在pthread源码中x86_64-linux-gnu/bits/pthreadtypes.h

typedef int __ONCE_ALIGNMENT pthread_once_t;

宏__ONCE_ALIGNMENT在x86_64-linux-gnu/bits/pthreadtypes-arch.h中定义:

#define __ONCE_ALIGNMENT

我很疑惑这里的__ONCE_ALIGNMENT的作用? 还望各位大神解答！先提前表示感谢!!!

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Answer 1

glibc/sysdeps/nptl/bits/thread-shared-types.h :

       The additional macro defines any constraint for the lock alignment
       inside the thread structures:
    
       __LOCK_ALIGNMENT - for internal lock/futex usage.
    
       Same idea but for the once locking primitive:
    
       __ONCE_ALIGNMENT - for pthread_once_t/once_flag definition.

glibc/sysdeps/nptl/bits/pthreadtypes.h ：

       /* Once-only execution */
       typedef int __ONCE_ALIGNMENT pthread_once_t;

Maybe just an once_flag in threads call_once functions. (*~・ω・)~