- rwlock->__data.__nr_readers = 0;
- rwlock->__data.__writer = 0;
- rwlock->__data.__readers_wakeup = 0;
- rwlock->__data.__writer_wakeup = 0;
- rwlock->__data.__nr_readers_queued = 0;
- rwlock->__data.__nr_writers_queued = 0;
+
+ /* The __SHARED field is computed to minimize the work that needs to
+ be done while handling the futex. There are two inputs: the
+ availability of private futexes and whether the rwlock is shared
+ or private. Unfortunately the value of a private rwlock is
+ fixed: it must be zero. The PRIVATE_FUTEX flag has the value
+ 0x80 in case private futexes are available and zero otherwise.
+ This leads to the following table:
+
+ | pshared | result
+ | shared private | shared private |
+ ------------+-----------------+-----------------+
+ !avail 0 | 0 0 | 0 0 |
+ avail 0x80 | 0x80 0 | 0 0x80 |
+
+ If the pshared value is in locking functions XORed with avail
+ we get the expected result. */
+#ifdef __ASSUME_PRIVATE_FUTEX
+ rwlock->__data.__shared = (iattr->pshared == PTHREAD_PROCESS_PRIVATE
+ ? 0 : FUTEX_PRIVATE_FLAG);
+#else
+ rwlock->__data.__shared = (iattr->pshared == PTHREAD_PROCESS_PRIVATE
+ ? 0
+ : THREAD_GETMEM (THREAD_SELF,
+ header.private_futex));
+#endif