Finding an unnamed union in a struct

Question

I have to find an unnamed union in struct _pthread_rwlock in pthread.h in the Haiku open source project. I began this assignment with some knowledge of c++ (past inheritance, polymorphism, and classes), but I find that what I learned do not help at all in my situation. I've opened the header file, and a source file named pthread_rwlock.cpp, and tried to look for the unnamed union, but there seems to be no unions in either file. What would be the correct way to find the problem?

Answer 1

In pthreads.h, the structure you are looking for goes by the name of pthread_rwlock_t. If you follow the include files backwards, you'll see the following in sys/types.h:

typedef struct  _pthread_rwlock    pthread_rwlock_t;
...
struct _pthread_rwlock {
    __haiku_std_uint32     flags;
    __haiku_std_int32      owner;
    union {
        struct {
            __haiku_std_int32    sem;
        } shared;
        struct {
            __haiku_std_int32    lock_sem;
            __haiku_std_int32    lock_count;
            __haiku_std_int32    reader_count;
            __haiku_std_int32    writer_count;
            void*                waiters[2];
        } local;
    } u;
};

I'm assuming that the union in here is the one that you are looking for. As of the version I'm looking at (d06f5808), the union is no longer anonymous.