[LTP] Question about priority of pthread rwlock on linux

[Kang Kai <Kai.Kang@windriver.com>]

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Hello everyone,

I am working on Yocto( a kind of  embedded linux) to make POSIX test 
cases pass. It uses kernel 3.0 and eglibc 2.3.

There are 3 failed test cases about pthread rwlock:
pthread_rwlock_rdlock/2-1 pthread_rwlock_rdlock/2-2  
pthread_rwlock_unlock/3-1

In pthread_rwlock_rdlock/2-1,  main thread*read lock* a rwlock,  child 
thread1 *write lock* the rwlock with a medium priority, so it should be 
blocked. child thread2 try to *read lock *the rwlock with low priority, 
the case says child thread2 should block too. But in Yocto linux child 
thread2 doesn't block and then read lock the rwlock, that make test case 
fail.

In eglibc nptl implementation, rwlock has a element "__flags" to 
identify prefer write lock or read lock, default is to prefer read lock. 
If change __flags to prefer write lock, the test case will pass.

My questions are:
1 What is the test case base on? I checked the  POSIX.1-2008 but didn't 
find description priority about the pthread rwlock? Could anyone give me 
a source that make me to understand it better?
2 Which C library or platform can make this case pass? So that I can 
compare it with eglibc.

Thanks a lot!
Kai




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