pthread_attr_destroy(3p) — Linux manual page

PROLOG | NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | ERRORS | EXAMPLES | APPLICATION USAGE | RATIONALE | FUTURE DIRECTIONS | SEE ALSO | COPYRIGHT

PTHREAD_ATTR_DESTROY(3P)POSIX Programmer's ManualTHREAD_ATTR_DESTROY(3P)

PROLOG         top

       This manual page is part of the POSIX Programmer's Manual.  The
       Linux implementation of this interface may differ (consult the
       corresponding Linux manual page for details of Linux behavior),
       or the interface may not be implemented on Linux.

NAME         top

       pthread_attr_destroy, pthread_attr_init — destroy and initialize
       the thread attributes object

SYNOPSIS         top

       #include <pthread.h>

       int pthread_attr_destroy(pthread_attr_t *attr);
       int pthread_attr_init(pthread_attr_t *attr);

DESCRIPTION         top

       The pthread_attr_destroy() function shall destroy a thread
       attributes object. An implementation may cause
       pthread_attr_destroy() to set attr to an implementation-defined
       invalid value. A destroyed attr attributes object can be
       reinitialized using pthread_attr_init(); the results of otherwise
       referencing the object after it has been destroyed are undefined.

       The pthread_attr_init() function shall initialize a thread
       attributes object attr with the default value for all of the
       individual attributes used by a given implementation.

       The resulting attributes object (possibly modified by setting
       individual attribute values) when used by pthread_create()
       defines the attributes of the thread created. A single attributes
       object can be used in multiple simultaneous calls to
       pthread_create().  Results are undefined if pthread_attr_init()
       is called specifying an already initialized attr attributes
       object.

       The behavior is undefined if the value specified by the attr
       argument to pthread_attr_destroy() does not refer to an
       initialized thread attributes object.

RETURN VALUE         top

       Upon successful completion, pthread_attr_destroy() and
       pthread_attr_init() shall return a value of 0; otherwise, an
       error number shall be returned to indicate the error.

ERRORS         top

       The pthread_attr_init() function shall fail if:

       ENOMEM Insufficient memory exists to initialize the thread
              attributes object.

       These functions shall not return an error code of [EINTR].

       The following sections are informative.

EXAMPLES         top

       None.

APPLICATION USAGE         top

       None.

RATIONALE         top

       Attributes objects are provided for threads, mutexes, and
       condition variables as a mechanism to support probable future
       standardization in these areas without requiring that the
       function itself be changed.

       Attributes objects provide clean isolation of the configurable
       aspects of threads. For example, ``stack size'' is an important
       attribute of a thread, but it cannot be expressed portably. When
       porting a threaded program, stack sizes often need to 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.

       Attributes objects can be used to set up ``classes' of threads
       with similar attributes; for example, ``threads with large stacks
       and high priority'' or ``threads with minimal stacks''. These
       classes can be defined in a single place and then referenced
       wherever threads need to be created. Changes to ``class''
       decisions become straightforward, and detailed analysis of each
       pthread_create() call is not required.

       The attributes objects are defined as opaque types as an aid to
       extensibility. If these objects had been specified as structures,
       adding new attributes would force recompilation of all multi-
       threaded programs when the attributes objects are extended; this
       might not be possible if different program components were
       supplied by different vendors.

       Additionally, opaque attributes objects present opportunities for
       improving performance. Argument validity can be checked once when
       attributes are set, rather than each time a thread is created.
       Implementations often need to cache kernel objects that are
       expensive to create. Opaque attributes objects provide an
       efficient mechanism to detect when cached objects become invalid
       due to attribute changes.

       Since assignment is not necessarily defined on a given opaque
       type, implementation-defined default values cannot be defined in
       a portable way. The solution to this problem is to allow
       attributes objects to be initialized dynamically by attributes
       object initialization functions, so that default values can be
       supplied automatically by the implementation.

       The following proposal was provided as a suggested alternative to
       the supplied attributes:

        1. Maintain the style of passing a parameter formed by the
           bitwise-inclusive OR of flags to the initialization routines
           (pthread_create(), pthread_mutex_init(),
           pthread_cond_init()).  The parameter containing the flags
           should be an opaque type for extensibility. If no flags are
           set in the parameter, then the objects are created with
           default characteristics. An implementation may specify
           implementation-defined flag values and associated behavior.

        2. If further specialization of mutexes and condition variables
           is necessary, implementations may specify additional
           procedures that operate on the pthread_mutex_t and
           pthread_cond_t objects (instead of on attributes objects).

       The difficulties with this solution are:

        1. A bitmask is not opaque if bits have to be set into bitvector
           attributes objects using explicitly-coded bitwise-inclusive
           OR operations. If the set of options exceeds an int,
           application programmers need to know the location of each
           bit. If bits are set or read by encapsulation (that is, get
           and set functions), then the bitmask is merely an
           implementation of attributes objects as currently defined and
           should not be exposed to the programmer.

        2. Many attributes are not Boolean or very small integral
           values. For example, scheduling policy may be placed in 3-bit
           or 4-bit, but priority requires 5-bit or more, thereby taking
           up at least 8 bits out of a possible 16 bits on machines with
           16-bit integers. Because of this, the bitmask can only
           reasonably control whether particular attributes are set or
           not, and it cannot serve as the repository of the value
           itself. The value needs to be specified as a function
           parameter (which is non-extensible), or by setting a
           structure field (which is non-opaque), or by get and set
           functions (making the bitmask a redundant addition to the
           attributes objects).

       Stack size is defined as an optional attribute because the very
       notion of a stack is inherently machine-dependent. Some
       implementations may not be able to change the size of the stack,
       for example, and others may not need to because stack pages may
       be discontiguous and can be allocated and released on demand.

       The attribute mechanism has been designed in large measure for
       extensibility. Future extensions to the attribute mechanism or to
       any attributes object defined in this volume of POSIX.1‐2017 has
       to be done with care so as not to affect binary-compatibility.

       Attributes objects, even if allocated by means of dynamic
       allocation functions such as malloc(), may have their size fixed
       at compile time. This means, for example, a pthread_create() in
       an implementation with extensions to pthread_attr_t cannot look
       beyond the area that the binary application assumes is valid.
       This suggests that implementations should maintain a size field
       in the attributes object, as well as possibly version
       information, if extensions in different directions (possibly by
       different vendors) are to be accommodated.

       If an implementation detects that the value specified by the attr
       argument to pthread_attr_destroy() does not refer to an
       initialized thread attributes object, it is recommended that the
       function should fail and report an [EINVAL] error.

       If an implementation detects that the value specified by the attr
       argument to pthread_attr_init() refers to an already initialized
       thread attributes object, it is recommended that the function
       should fail and report an [EBUSY] error.

FUTURE DIRECTIONS         top

       None.

SEE ALSO         top

       pthread_attr_getstacksize(3p), pthread_attr_getdetachstate(3p),
       pthread_create(3p)

       The Base Definitions volume of POSIX.1‐2017, pthread.h(0p)

COPYRIGHT         top

       Portions of this text are reprinted and reproduced in electronic
       form from IEEE Std 1003.1-2017, Standard for Information
       Technology -- Portable Operating System Interface (POSIX), The
       Open Group Base Specifications Issue 7, 2018 Edition, Copyright
       (C) 2018 by the Institute of Electrical and Electronics
       Engineers, Inc and The Open Group.  In the event of any
       discrepancy between this version and the original IEEE and The
       Open Group Standard, the original IEEE and The Open Group
       Standard is the referee document. The original Standard can be
       obtained online at http://www.opengroup.org/unix/online.html .

       Any typographical or formatting errors that appear in this page
       are most likely to have been introduced during the conversion of
       the source files to man page format. To report such errors, see
       https://www.kernel.org/doc/man-pages/reporting_bugs.html .

IEEE/The Open Group               2017          PTHREAD_ATTR_DESTROY(3P)

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