测试用例地址：
测试用用例运行error log：
| conformance/interfaces/pthread_rwlock_rdlock/pthread_rwlock_rdlock_2-1: execution: FAILED: Output: main: has priority: 3 main: attempt read lock main: acquired read lock main: create wr_thread, with priority: 2 wr_thread: attempt write lock main: create rd_thread, with priority: 1 rd_thread: attempt read lock rd_thread: acquired read lock rd_thread: unlock read lock Test FAILED: rd_thread did not block on read lock, when a reader owns the lock, and a higher priority writer is waiting for the lock |
通过走查glibc库源码 和kernel的futex源码。在内核中添加了一些调试信息来观察futex在锁竞争时，分析唤醒任务的流程。
/tmp/ltp/conformance/interfaces/pthread_rwlock_unlock # ./pthread_rwlock_unlock_3-1.run-test
==========================main 268,===============================
==========================writer1 269,===============================
==========================reader1 270,===============================
==========================writer2 271,===============================
main: write lock --主程序占有锁
main: create writer1, with priority: 3
writer1: attempt write lock
[futex_wait_in][2682]:current->comm=pthread_rwlock_,pid=269,hb=0x7b770b00 --writer1进入futex_wait等待unlock
main: create reader, with priority: 3
reader: attempt read lock
[futex_wait_in][2682]:current->comm=pthread_rwlock_,pid=270,hb=0x7b775880 --reader1进入futex_wait等待unlock 哈希桶不同
main: create writer2, with priority: 1
writer2: attempt write lock
[futex_wait_in][2682]:current->comm=pthread_rwlock_,pid=271,hb=0x7b770b00 --writer2进入futex_wait等待unlock 哈希桶和writer1相同
main: release write lock --主程序释放锁
[futex_wake][1560]:current->comm=pthread_rwlock_,pid=268,hb=0x7b770b00
[mark_wake_futex][1569]:task->comm=pthread_rwlock_,pid=269,this->bitset=-1,bitset=-1
[mark_wake_futex][1575]:this->comm=pthread_rwlock_,pid=269,this->bitset=-1,bitset=-1
[futex_wait_out][2686]:current->comm=pthread_rwlock_,pid=269,hb=0x7b770b00 --writer1(269)拿到了锁
writer1: acquired write lock
[futex_wait_in][2682]:current->comm=pthread_rwlock_,pid=268,hb=0x7b7747c0 --主程序调用了pthread_join,等待writer1(269)退出。
[futex_wake][1560]:current->comm=pthread_rwlock_,pid=269,hb=0x7b770b00 --writer1(269)开始释放锁
writer1: unlock write lock
[mark_wake_futex][1569]:task->comm=pthread_rwlock_,pid=271,this->bitset=-1,bitset=-1
[mark_wake_futex][1575]:this->comm=pthread_rwlock_,pid=271,this->bitset=-1,bitset=-1 --writer(269)唤醒了writer2
[futex_wait_out][2686]:current->comm=pthread_rwlock_,pid=271,hb=0x7b770b00 --writer2拿到了锁。
writer2: acquired writer lock
[futex_wake][1560]:current->comm=pthread_rwlock_,pid=269,hb=0x7b7747c0 --write1线程退出，唤醒了主程序。
[mark_wake_futex][1569]:task->comm=pthread_rwlock_,pid=268,this->bitset=-1,bitset=-1
[mark_wake_futex][1575]:this->comm=pthread_rwlock_,pid=268,this->bitset=-1,bitset=-1
[futex_wait_out][2686]:current->comm=pthread_rwlock_,pid=268,hb=0x7b7747c0 --主程序继续运行。
Test failed: reader did not get the lock when writer1 release the lock --由于测试用例要求高优先级的读者获取锁，导致失败。
[futex_wait_out][2686]:current->comm=pthread_rwlock_,pid=270,hb=0x7b775880
/tmp/ltp/conformance/interfaces/pthread_rwlock_unlock #
/tmp/ltp/conformance/interfaces/pthread_rwlock_unlock #
初步分析结论：
pthread各种锁的原理，是采用了用户态与内核态混合同步方式，也就是内核futex机制，rwlock锁和普通的锁还不太一样，rwlock包含了reader，writer成员，对应内核态，读者和写者挂在了不同的等待队列上。
当多个进程在一把锁上发生竞争时，由内核态进行仲裁，内核通过用户态传来的futex参数来判断是唤醒读者还是写者。
读写锁的用例场景比较多，发生竞争时：读优先，还是写优先？同优先级读者写者哪个应该先拿到？不同优先级的读者写者，哪个先拿到？如果读者或写者设置了锁优先级继承，又会怎样？读者还涉及递归拿锁，等等等。
此项用例，需要根据posix标准，以及内核的对应实现，在下结论。