pthread_attr_init(3T)          DG/UX R4.11MU05         pthread_attr_init(3T)


NAME
       pthread_attr_init, pthread_attr_destroy - thread attributes objects

SYNOPSIS
       #include <pthread.h>

       int pthread_attr_init(pthread_attr_t *attr);

       int pthread_attr_destroy(pthread_attr_t *attr);

   where:
       attr        A pointer to a thread attributes object

DESCRIPTION
       Thread attributes objects are opaque collections of thread attributes
       that are used to override the default creation attributes, such as
       the stack size, in calls to pthread_create().  They can also be used
       to change certain scheduling attributes, such as scheduling policy
       and priority, of existing threads in calls to pthread_setschedattr().

       Thread attributes objects are manipulated only by object-oriented
       functions described here and in other man pages listed below.  The
       use of opaque attributes objects provides a clean isolation of the
       configurable aspects of threads and an extensible mechanism for
       adding vendor-specific attributes and future standard attributes.

       Typically, an application initializes one or more attributes objects
       in a well-isolated, possibly vendor-specific, place in its code.
       Then those attributes objects are passed, in a standard way, to
       pthread_create().  Hence most of the application code remains
       portable, while a small portion may change to take advantage of the
       underlying operating system.  Moreover, different attributes objects
       can be used to set up "classes" of threads with similar attributes.

       For example, stack size is an important attribute of a thread, but it
       cannot be expressed portably.  When porting a threaded program, stack
       sizes must often be adjusted.  The use of attributes objects can help
       by allowing the changes to be isolated in a single place, rather than
       being spread across every instance of thread creation.

       Standard attributes are provided to specify the size of the thread's
       stack, whether or not the thread is created as detached, and how it
       will will be scheduled.  The scheduling attributes are the only
       attributes that can be modified or retrieved for an existing thread.

       DG/UX provides an additional attribute that can be used to create
       threads in specific DG thread groups for purposes of maximizing the
       affinity of computationally related threads.  While this attribute is
       DG-specific, its manipulation, like that of other attributes, can be
       well-isolated in an application.

       Before a thread attributes object can be used, it must be initialized
       by a call to pthread_attr_init().  After it has been initialized,
       individual attributes are specified by other object-oriented calls,
       and then the attributes object is passed to a call to
       pthread_create() or pthread_setschedattr().  Upon return from such a
       call, the attributes object is no longer associated with the affected
       thread, and can be destroyed by a call to pthread_attr_destroy().  If
       desired, the attributes object can instead be used in subsequent
       calls to pthread_create() or pthread_setschedattr().

       The following functions initialize and destroy thread attributes
       objects:

   pthread_attr_init()
       This function initializes the thread attributes object pointed to by
       attr with the default values for all thread attributes.  Consult the
       other man pages below for the default values under DG/UX.

   pthread_attr_destroy()
       This function destroys the thread attributes object pointed to by
       attr.  The attributes object should have been initialized by a
       previous call to pthread_attr_init().  The behavior of using the
       attributes object after it has been destroyed is undefined.  If DG/UX
       detects that an attributes object is uninitialized or destroyed, it
       will cause the using function to fail with EINVAL.

DIAGNOSTICS
   Returns
       If successful, these functions return 0.  Otherwise they return -1
       and set errno to indicate the error.

   Errors
       For each of the following conditions, pthread_attr_destroy() returns
       -1 and sets errno to the corresponding value:

       [EINVAL]  An invalid attributes object has been specified.  This
                 occurs when DG/UX has detected that the attributes object
                 pointed to by attr has not been initialized by a previous
                 call to pthread_attr_init() or has been corrupted.

SEE ALSO
       pthread_attr_setstacksize(3T), pthread_attr_getstacksize(3T),
       pthread_attr_setdetachstate(3T), pthread_attr_getdetachstate(3T),
       pthread_attr_setinheritsched(3T), pthread_attr_getinheritsched(3T),
       pthread_attr_setsched(3T), pthread_attr_getsched(3T),
       pthread_attr_setprio(3T), pthread_attr_getprio(3T),
       pthread_create(3T), pthread_setschedattr(3T),
       pthread_getschedattr(3T), dg_pthread_group_create(3T),
       dg_pthread_attr_setgroup(3T), dg_pthread_attr_getgroup(3T).

NOTES
       Attributes objects are provided for threads, mutexes, condition
       variables, and DG thread groups.   While the attributes vary from
       entity to entity, the style of the interfaces is consistent.   For DG
       thread groups, scheduling attributes similar to those for threads are
       provided, but they affect the global scheduling of the target thread
       group.

       The effect of passing a NULL pointer to pthread_create() is the same
       as passing a pointer to a newly initialized thread attributes object.
       Both cases cause the default attributes to be used.


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