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The following applies only if the symbol _POSIX_THREAD_PRIO_INHERIT is defined, and the mutex attributes object attr
should be used only to initialize mutexes that will also be initialized
with the protocol attribute having the value PTHREAD_PRIO_INHERIT. See pthread_mutexattr_getprotocol(3THR).
The pthread_mutexattr_setrobust_np() and pthread_mutexattr_getrobust_np() functions set and get the robustness attribute of a mutex attribute object pointed to
by attr that was previously created by the function pthread_mutexattr_init(3THR).
The robustness attribute defines the behavior
when the owner of a mutex dies. The value of robustness
may be ether PTHREAD_MUTEX_ROBUST_NP or PTHREAD_MUTEX_STALLED_NP, which are defined by the header <pthread.h>. The default value of the robustness
attribute is PTHREAD_MUTEX_STALLED_NP.
When the owner of a mutex with the PTHREAD_MUTEX_STALLED_NP robustness attribute dies, all future
calls to pthread_mutex_lock(3THR)
for this mutex will be blocked from progress in an unspecified manner.
When the owner of a mutex with the PTHREAD_MUTEX_ROBUST_NP robustness attribute dies, the mutex is
unlocked. The next owner of this mutex acquires it with an error value
of EOWNERDEAD. Note that the application must always
check the return value from pthread_mutex_lock() for
a mutex initialized with the PTHREAD_MUTEX_ROBUST_NP robustness attribute. The new owner of this mutex should then
attempt to make the state protected by the mutex consistent, since this
state could have been left inconsistent when the last owner died. If the
new owner is able to make the state consistent, it should call pthread_mutex_consistent_np(3THR) for the mutex and then unlock the mutex.
If for any reason the new owner is not able to make the state consistent,
it should not call pthread_mutex_consistent_np() for
the mutex, but should simply unlock the mutex. In the latter scenario, all
waiters will be awakened and all subsequent calls to pthread_mutex_lock() will fail in acquiring the mutex with an error value of ENOTRECOVERABLE. The mutex can then be made consistent by uninitializing
the mutex with the pthread_mutex_destroy() function and
reinitializing it with the pthread_mutex_init() function.
If the thread that acquired the lock with EOWNERDEAD
dies, the next owner will acquire the lock with an error value of EOWNERDEAD.
Note that the mutex may be in memory shared between processes or in
memory private to a process, i.e. the "owner" referenced above is a thread,
either within or outside the requestor's process.
The mutex memory must be zeroed before initialization.
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