The AS/400 threads support takes the same implementation route that the Single Unix Specification suggests, and also causes the thread to deadlock when it attempts to relock a normal (non-recursive) mutex. Because many users of pthreads don't check return codes from functions, the deadlock scenario will protect applications from corrupted data that might result if they attempt to relock an already held mutex, then unlock the mutex as if the lock was successful.

See "pthread_mutexattr_gettype()--Get Mutex Type Attribute" and "pthread_mutexattr_settype()--Set Mutex Type Attribute" if your application requires error checking mutexes.