HP-UX Reference (11i v1 00/12) - 3 Library Functions N-Z (vol 7)

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pthread(3T) pthread(3T)

(Pthread Library)

NAME

pthread - Introduction To POSIX.1c Threads

DESCRIPTION

The POSIX.1c library developed by HP enables the creation of processes that can exploit application and

multi-processor platform parallelism. The pthread library libpthread consists of over 90 standardized inter-

faces for developing concurrent applications and synchronizing their actions within processes or between

them. This manual page presents an overview of libpthread including terminology and how to compile and

link programs which use threads.

COMPILATION SUMMARY

A multi-threaded application must deﬁne the appropriate POSIX revision level (199506) at compile time

and link againstthe pthread library via -lpthread. For example:

cc -D_POSIX_C_SOURCE=199506L -o myapp myapp.c -lpthread

All program sources must also include the header ﬁle <pthread.h>.

Note: When explicitly specifying ANSI compilation (via "-Aa"), deﬁning the POSIX revision level restricts

the program to using interfaces within the POSIX namespaces. If interfaces in the larger X/Open

namespace are to be called, either of the compiler options,

-D_XOPEN_SOURCE_EXTENDED

-D_HPUX_SOURCE, must be speciﬁed in addition to

-D_POSIX_C_SOURCE=199506L. Alternatively,

compiling with -Ae (or not specifying "-A") will implicitly specify

-D_HPUX_SOURCE

Note: Some documentation will recommend the use of

-D_REENTRANT for compilation. While this also

functions properly, it is considered an obsolescent form.

THREAD OVERVIEW

A thread is an independent ﬂow of control within a process, composed of a context (which includes a regis-

ter set and a program counter) and a sequence of instructions to execute.

All processes consist of at least one thread. Multi-threaded processes contain several threads. All threads

share the common address space allocated for the process. A program using the POSIX pthread APIs

creates and manipulates what are called user threads.Akernel thread is a kernel-schedulable entity which

may support one or more user threads. Currently, the HP-UX threads implementation supports only a

one-to-one mapping between user and kernel threads.

Each thread is assigned a unique identiﬁer of type pthread_t upon creation. The thread id is a process-

private value and implementation-dependent. It is considered to be an opaque handle for the thread. Its

value should not be used by the application.

NOTES ON INTERFACES

The HP-UX system provides some non-standard extensions to the pthread API. These will always have a

distinguishing sufﬁx of _np or _NP (non-portable).

The programmer should always consult the manpages for the functions being used. Some standard-

speciﬁed functions are not available or may have no effect in some implementations.

THREAD CREATION/DESTRUCTION

A program creates a thread using the

pthread_create()

function. When the thread has completed its

work, it may optionally call the

pthread_exit()

function, or simply return from its initial function. A

thread can detect the completion of another by using the

pthread_join()

function.

pthread_create() Creates a thread and assigns a unique identiﬁer, pthread_t. The caller provides

a function which will be executed by the thread. Optionally, the call may expli-

citly specify some attributes for the thread (see PTHREAD ATTRIBUTES

below).

pthread_exit() Called by a thread when it completes. This function does not return.

pthread_join() This is analogous to wait(), but for pthreads. Any thread may join any other

thread in the process, there is no parent/child relationship. It returns when a

speciﬁed thread terminates, and the thread resources have been reaped.

pthread_detach() Makes it unnecessary to "join" the thread. Thread resources are reaped by the

system at the time the thread terminates.

HP-UX Release 11i: December 2000 − 1 − Section 3−−631

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