HP-UX Reference (11i v1 05/09) - 3 Library Functions N-Z (vol 7)

p
pthread(3T) pthread(3T)
(Pthread Library)
Detached Thread
A thread whose resources are automatically released by the system when the thread terminates. A
detached thread cannot be joined by another thread. Consequently, detached threads cannot return an exit
status.
Joinable Thread
A thread whose termination can be waited for by another thread. Joinable threads can return an exit status
to a joining thread. Joinable threads maintain some state after termination until they are joined by another
thread.
Kernel Mode
A mode of operation where all operations are allowed. While a thread is executing a system call it is execut-
ing in kernel mode.
Kernel Space
The kernel program exists in this space. Kernel code is executed in this space at the highest privilege level.
In general, there are two privilege levels: one for user code (user mode) and the other for kernel code (ker-
nel mode).
Kernel Stack
When a thread makes a system call, it executes in kernel mode. While in kernel mode, it does not use the
stack allocated for use by the application. Instead, a separate kernel stack is used while in the system call.
Each kernel-scheduled entity, whether a process, kernel thread or lightweight process, contains a kernel
stack. See Stack for a generic description of a stack.
Kernel Thread
Kernel threads are created by the thread functions in the threads library. Kernel threads are kernel-
scheduled entities that are visible to the operating system kernel. A kernel thread typically supports one or
more user threads. Kernel threads execute kernel code or system calls on behalf of user threads. Some sys-
tems may call the equivalent of a kernel thread a lightweight process. See Thread for a generic description
of a thread.
Lightweight Process
A kernel-scheduled entity. Some systems may call the equivalent of a lightweight process a kernel thread.
Each process contains one or more lightweight process. How many lightweight processes a process contains
depends on whether and how the process is multithreaded. See Thread for a generic description of a
thread.
Multiprocessor
A system with two or more processors (CPUs). Multiprocessors allow multithreaded applications to obtain
true parallelism.
Multithreading
A programming model that allows an application to have multiple threads of execution. Multithreading
allows an application to have concurrency and parallelism (on multiprocessor systems).
Mutex
A mutex is a mutual exclusion synchronization primitive. Mutexes provide threads with the ability to regu-
late or serialize access to process shared data and resources. When a thread locks a mutex, other threads
trying to lock the mutex block until the owning thread unlocks the mutex.
POSIX
Portable Operating System Interface. POSIX defines a set of standards that multiple vendors conform to in
order to provide for application portability. The Pthreads standard (POSIX 1003.1c) provides a set of port-
able multithreading APIs to application developers.
Priority Inversion
A situation where a low-priority thread has acquired a resource that is needed by a higher priority thread.
As the resource cannot be acquired, the higher priority thread must wait for the resource. The end result is
that a low-priority thread blocks a high-priority thread.
HP-UX 11i Version 1: September 2005 − 9 − Hewlett-Packard Company Section 3−−675