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PTHREAD_ATTR_DESTROY(3P) POSIX Programmer's Manual PTHREAD_ATTR_DESTROY(3P)
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.
pthread_attr_destroy, pthread_attr_init — destroy and initialize the
thread attributes object
#include <pthread.h>
int pthread_attr_destroy(pthread_attr_t *attr);
int pthread_attr_init(pthread_attr_t *attr);
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.
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.
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.
None.
None.
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.1‐2008 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.
None.
pthread_attr_getstacksize(3p), pthread_attr_getdetachstate(3p),
pthread_create(3p)
The Base Definitions volume of POSIX.1‐2008, pthread.h(0p)
Portions of this text are reprinted and reproduced in electronic form
from IEEE Std 1003.1, 2013 Edition, Standard for Information
Technology -- Portable Operating System Interface (POSIX), The Open
Group Base Specifications Issue 7, Copyright (C) 2013 by the
Institute of Electrical and Electronics Engineers, Inc and The Open
Group. (This is POSIX.1-2008 with the 2013 Technical Corrigendum 1
applied.) 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.unix.org/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 2013 PTHREAD_ATTR_DESTROY(3P)
Pages that refer to this page: pthread.h(0p), pthread_attr_getdetachstate(3p), pthread_attr_getinheritsched(3p), pthread_attr_getschedparam(3p), pthread_attr_getschedpolicy(3p), pthread_attr_getscope(3p), pthread_attr_getstack(3p), pthread_attr_getstacksize(3p), pthread_attr_init(3p), pthread_condattr_destroy(3p), pthread_mutexattr_destroy(3p)
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