Hello,

I find that all pthread-related interfaces directly access the input
parameter `pthread_t` without any check. If I pass an invalid thread ID
(e.g. an exited thread ID) to these interfaces, then segment fault
happens.

Both glibc and freebsd can do simple detection of thread ID(pthread_t)
passed by user and return ESRCH when no thread can be found. They
put all threads in a list or hash table, and update this list or table every
time a thread is created or exits.

From the user's point of view, segment fault is unbearable and is not
*         recoverable in most cases. Instead, returning an error of ESRCH
*         seems more acceptable.