pthread(3) Library Functions Manual pthread(3)
NAME
pthread, pthread_intro - Introduction to POSIX Threads
DESCRIPTION
DECthreads, a multithreading run-time library, provides a set of interfaces for building multithreaded programs. The POSIX threads inter-
face provides routines that implement the IEEE Std 1003.1c-1995, POSIX System Application Program Interface, also known as POSIX Standard
1003.1c or POSIX.1c.
This version of DECthreads also includes additional routines specified in the document X/Open CAE Specification, System Interfaces and
Headers, Issue 5 published by the Open Group. The additional routines support creating and operating on read-write locks and defining
mutexes, condition variables, and read-write locks as shareable across processes, via those objects' "pshared" attribute.
Note that POSIX Standard 1003.1c now supersedes the POSIX draft standard 1003.4a. Users of previous versions of DECthreads should be aware
that applications based on the POSIX draft standard 1003.4a/D4 interface (also known as the "d4" interface or "DCE threads") require sig-
nificant modifications to be upgraded to the POSIX threads interface. See the discussion in the Guide to DECthreads.
The Guide to DECthreads describes important considerations for threaded application development, particularly for the Tru64 UNIX operating
system.
A thread is a single, sequential flow of control within a program. Within a single thread, there is a single point of execution. Most
traditional programs consist of a single thread.
Using the DECthreads POSIX threads interface, a programmer can create more than one thread within a program. Threads execute concurrently,
and, within a multithreaded program, there are at any time multiple points of execution. The threads in a given process execute within and
share a single address space; therefore, threads read and write the same memory locations. Synchronization objects such as mutexes, condi-
tion variables, and read-write locks ensure that data objects shared among threads are accessed correctly. DECthreads provides routines
that allow you to create and use these synchronization objects. Mutexes, condition variables, and read-write locks are discussed in the
Guide to DECthreads.
DECthreads POSIX threads interface routines whose names have the _np suffix are "not portable." That is, such a routine might operate dif-
ferently, or might not be available, in other vendor implementations of POSIX Standard 1003.1c.
For users of the Compaq C and C++ compilers, compile a multithreaded application as follows:
cc -c myprog.c -pthread
For users of C and C++ compilers without support for the -pthread switch, you must ensure that that the C preprocessor symbol _REENTRANT is
defined before including any system header file. One way to accomplish this is to compile the application as follows:
cc -c myprog.c -D_REENTRANT
For users of the Compaq C and C++ compilers, when linking your multithreaded application that use DECthreads, include only the -pthread
switch in the linker command line. Note that this switch also directs the linker to search for thread-reentrant variants (named with the
"_r" suffix) of any libraries it searches.
For users of other language environments or C and C++ compilers that do not support the -pthread linker switch, include these switches at
the end of the linker command line:
ld -o myprog myprog.o -lpthread -lexc -lc crt0.o
or
gcc -o myprog myprog.o -lpthread -lexc
In this case, the -lpthread and -lexc switches direct the linker explicitly to use the DECthreads run-time and exception-handling
libraries. These switches must immediately precede the -lc switch (if specified), which directs the linker to use the libc run-time
library. If your application also requires specific thread-reentrant variants of libraries (such as the C run-time libraries), your linker
command line must explicitly identify them or a search path for them.
Each C module that utilizes DECthreads exceptions must include the pthread_exception.h header file. The Guide to DECthreads describes the
use of DECthreads exceptions.
Note that previous versions of DECthreads provided a DECthreads-specific debugging interface. However, for this version and future ver-
sions of DECthreads, you must use the Ladebug debugger (or other thread-aware debugger, such as TotalView) for debugging DECthreads-based
multithreaded applications.
You can also use the Visual Threads tool for troubleshooting and debugging a multithreaded application. Visual Threads is part of the
Developer's Toolkit product.
DECthreads POSIX threads interface routines are grouped in the following functional categories: General threads routines Thread attributes
object routines Thread cancelation routines Thread priority, concurrency, and scheduling routines Thread-specific data routines Mutex rou-
tines Mutex attributes object routines Condition variable routines Condition variable attributes object routines Read-write lock routines
Read-write lock attributes object routines
Other DECthreads Pthread routines implement nonportable extensions to POSIX Standard 1003.1c. These routines are grouped into these func-
tional categories: Thread execution routines Thread attributes object routines Thread-specific data routines DECthreads global mutex rou-
tines Mutex routines Mutex attributes object routines Condition variable routines Read-write lock routines Processor subset object routines
DECthreads exception object routines
General Threads Routines
Declares fork handler routines to be called. Creates a thread object and thread. Marks a thread object for deletion when its thread ter-
minates. Compares one thread identifier to another. Terminates the calling thread. Causes the calling thread to wait for the termination
of another thread and to detach it. Delivers a signal to a specified thread. Calls an initialization routine to be executed only once.
Obtains the identifier of the calling thread. Examines or changes the calling thread's signal mask.
Thread Attributes Object Routines
Destroys a thread attributes object. Obtains the detachstate attribute of the specified thread attributes object. Obtains the guardsize
attribute of the specified thread attributes object. (Supersedes pthread_attr_getguardsize_np.) Obtains the inherit scheduling attribute
of the specified thread attributes object. Obtains the scheduling parameters for an attribute of the specified thread attributes object.
Obtains the scheduling policy attribute of the specified thread attributes object. Obtains the contention scope attribute of the specified
thread attributes object. Obtains the stackaddr attribute of the specified thread attributes object. (See also pthread_attr_getstack-
addr_np.) Obtains the stacksize attribute of the specified thread attributes object. Initializes a thread attributes object. Changes the
detachstate attribute of the specified thread attributes object. Changes the guardsize attribute of the specified thread attributes
object. (Supersedes pthread_attr_setguardsize_np.) Changes the inherit scheduling attribute of the specified thread attributes object.
Changes the values of the parameters associated with the scheduling policy attribute of the specified thread attributes object. Changes
the scheduling policy attribute of the specified thread attributes object. Changes the contention scope attribute of the specified thread
attributes object. Changes the stackaddr attribute of the specified thread attributes object. (See also pthread_attr_setstackaddr_np.)
Changes the stacksize attribute of the specified thread attributes object.
Thread Cancelation Routines
Requests that a thread terminate its execution. Removes a cleanup handler routine from the calling thread's cleanup stack and optionally
executes it. Establishes a cleanup handler routine to be executed when the calling thread exits or is canceled. Sets the calling thread's
cancelability state. Sets the calling thread's cancelability type. Requests delivery of any pending cancelation requests to the calling
thread.
Thread Priority, Concurrency, and Scheduling Routines
Obtains the current concurrency level hint parameter for the calling thread's process. Obtains the current scheduling policy and schedul-
ing parameters of a thread. Changes the current concurrency level hint for the calling thread's process. Changes the current scheduling
policy and scheduling parameters of a thread.
Thread-Specific Data Routines
Obtains the thread-specific data associated with the specified key. Generates a unique thread-specific data key. Deletes a thread-spe-
cific data key. Sets the thread-specific data value associated with the specified key for the calling thread.
Mutex Routines
Destroys a mutex object. Initializes a mutex object with attributes in the specified mutex attributes object. Locks an unlocked mutex; if
already locked, the caller waits for the mutex to become available. Attempts to lock a mutex; returns immediately if mutex is already
locked. Unlocks a locked mutex.
Mutex Attributes Object Routines
Initializes a mutex attributes object. Destroys a mutex attributes object. Obtains the process-shared attribute of the specified mutex
attributes object. Obtains the mutex type attribute of the specified mutex attributes object. (Supersedes pthread_mutexattr_gettype_np.)
Changes the process-shared attribute of the specified mutex attributes object. Changes the mutex type attribute of the specified mutex
attributes object. (Supersedes pthread_mutexattr_settype_np.)
Condition Variable Routines
Wakes all threads waiting on a condition variable. Destroys a condition variable object. Initializes a condition variable object. Wakes
at least one thread that is waiting on a condition variable. Causes a thread to wait for a specified period of time for a condition vari-
able to be signaled or broadcast. Causes a thread to wait for a condition variable to be signaled or broadcast.
Condition Variable Attributes Object Routines
Destroys a condition variable attributes object. Obtains the process-shared attribute of the specified condition variable attributes
object. Initializes a condition variable attributes object. Changes the process-shared attribute of the specified condition variable
attributes object.
Read-Write Lock Routines
Destroys a read-write lock object. Initializes a read-write lock object. Acquires a read-write lock for read access, after waiting if
necessary. Attempts to acquire, without waiting, a read-write lock for read access. Attempts to acquire, without waiting, a read-write
lock for write access. Releases one acquisition by the calling thread of a read-write lock for read access or write access. Acquires a
read-write lock for write access, after waiting if necessary.
Read-Write Lock Attributes Object Routines
Destroys a read-write lock attributes object. Obtains the process-shared attribute of the specified read-write lock attributes object.
Initializes a read-write lock attributes object. Changes the process-shared attribute of the specified read-write lock attributes object.
Non-Portable Extensions: Thread Execution Routines
Causes a thread to delay execution. Obtains a value representing a desired expiration time. Obtains the object name of the specified
thread object. Obtains a thread's sequence number. Changes the object name of the specified thread object.
Non-Portable Extensions: Thread Attributes Object Routines
Obtains the object name attribute of the specified thread attributes object. Obtains the processor subset attribute of the specified
thread attributes object. Obtains the stackaddr attribute of the specified thread attributes object as low address and size. (See also
pthread_attr_getstackaddr.) Changes the object name attribute of the specified thread attributes object. Changes the processor subset
attribute of the specified thread attributes object. Changes the stackaddr attribute of the specified thread attributes object by specify-
ing low address and size. (See also pthread_attr_setstackaddr.)
Non-Portable Extensions: Thread-Specific Data Routines
Obtains the object name of a thread-specific data key object. Changes the object name of a thread-specific data key object.
Non-Portable Extensions: DECthreads Global Mutex Routines
Locks the DECthreads global mutex if it is unlocked. Unlocks the DECthreads global mutex if it is locked.
Non-Portable Extensions: Mutex Routines
Obtains the object name of a mutex object. Changes the object name of a mutex object.
Non-Portable Extensions: Condition Variable Routines
Obtains the object name of a condition variable object. Changes the object name of a condition variable object. Wakes one thread that is
waiting on a condition variable (called from interrupt level only). Wakes one thread that is waiting on the specified condition variable
(called from interrupt level only).
Non-Portable Extensions: Read-Write Lock Routines
Obtains the object name of a read-write lock object. Changes the object name of a read-write lock object.
Non-Portable Extensions: Processor Subset Object Routines
Stores the combined CPU resource descriptions from two processor subset objects into a third. Destroys a processor subset object. Deter-
mines whether the CPU resource descriptions of two processor subset objects are equivalent. Obtains CPU resource information in a thread
object and stores it in the specified processor subset object. Initializes a processor subset object based on a processor subset
attributes object. Returns the number of processors described in the specified processor subset object. Stores the CPU resource descrip-
tions from a processor subset object into a thread object. Sets the contents of two processor subset objects by splitting the contents of
a third.
Non-Portable Extensions: DECthreads Exception Object Routines
Obtains a system-defined error status from a DECthreads status exception object. Determines whether two DECthreads exception objects are
identical. Produces a message that reports what a specified DECthreads status exception object represents. Imports a system-defined error
status into a DECthreads address exception object.
Non-Portable Extensions: Thread Priority, Concurrency, and Scheduling Routines
Notifies the scheduler that the current thread is willing to release its processor to other threads of the same or higher priority. delim
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pthread(3)