libgomp/libgomp.info

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below).  A copy of the license is included in the section entitled "GNU
Free Documentation License".

   (a) The FSF's Front-Cover Text is:

   A GNU Manual

   (b) The FSF's Back-Cover Text is:

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INFO-DIR-SECTION GNU Libraries
START-INFO-DIR-ENTRY
* libgomp: (libgomp).                    GNU OpenMP runtime library
END-INFO-DIR-ENTRY

   This manual documents the GNU implementation of the OpenMP API for
multi-platform shared-memory parallel programming in C/C++ and Fortran.

   Published by the Free Software Foundation 51 Franklin Street, Fifth
Floor Boston, MA 02110-1301 USA

   Copyright (C) 2006, 2007, 2008 Free Software Foundation, Inc.

   Permission is granted to copy, distribute and/or modify this document
under the terms of the GNU Free Documentation License, Version 1.2 or
any later version published by the Free Software Foundation; with the
Invariant Sections being "Funding Free Software", the Front-Cover texts
being (a) (see below), and with the Back-Cover Texts being (b) (see
below).  A copy of the license is included in the section entitled "GNU
Free Documentation License".

   (a) The FSF's Front-Cover Text is:

   A GNU Manual

   (b) The FSF's Back-Cover Text is:

   You have freedom to copy and modify this GNU Manual, like GNU
software.  Copies published by the Free Software Foundation raise
funds for GNU development.


File: libgomp.info,  Node: Top,  Next: Enabling OpenMP,  Up: (dir)

Introduction
************

This manual documents the usage of libgomp, the GNU implementation of
the OpenMP (http://www.openmp.org) Application Programming Interface
(API) for multi-platform shared-memory parallel programming in C/C++
and Fortran.

* Menu:

* Enabling OpenMP::            How to enable OpenMP for your applications.
* Runtime Library Routines::   The OpenMP runtime application programming
                               interface.
* Environment Variables::      Influencing runtime behavior with environment
                               variables.
* The libgomp ABI::            Notes on the external ABI presented by libgomp.
* Reporting Bugs::             How to report bugs in GNU OpenMP.
* Copying::                    GNU general public license says
                               how you can copy and share libgomp.
* GNU Free Documentation License::
                               How you can copy and share this manual.
* Funding::                    How to help assure continued work for free
                               software.
* Index::                      Index of this documentation.


File: libgomp.info,  Node: Enabling OpenMP,  Next: Runtime Library Routines,  Prev: Top,  Up: Top

1 Enabling OpenMP
*****************

To activate the OpenMP extensions for C/C++ and Fortran, the
compile-time flag `-fopenmp' must be specified. This enables the OpenMP
directive `#pragma omp' in C/C++ and `!$omp' directives in free form,
`c$omp', `*$omp' and `!$omp' directives in fixed form, `!$' conditional
compilation sentinels in free form and `c$', `*$' and `!$' sentinels in
fixed form, for Fortran. The flag also arranges for automatic linking
of the OpenMP runtime library (*note Runtime Library Routines::).

   A complete description of all OpenMP directives accepted may be
found in the OpenMP Application Program Interface
(http://www.openmp.org) manual, version 3.0.


File: libgomp.info,  Node: Runtime Library Routines,  Next: Environment Variables,  Prev: Enabling OpenMP,  Up: Top

2 Runtime Library Routines
**************************

The runtime routines described here are defined by section 3 of the
OpenMP specifications in version 3.0. The routines are structured in
following three parts:

   Control threads, processors and the parallel environment.

* Menu:

* omp_get_active_level::        Number of active parallel regions
* omp_get_ancestor_thread_num:: Ancestor thread ID
* omp_get_dynamic::             Dynamic teams setting
* omp_get_level::               Number of parallel regions
* omp_get_max_active_levels::   Maximal number of active regions
* omp_get_max_threads::         Maximal number of threads of parallel region
* omp_get_nested::              Nested parallel regions
* omp_get_num_procs::           Number of processors online
* omp_get_num_threads::         Size of the active team
* omp_get_schedule::            Obtain the runtime scheduling method
* omp_get_team_size::           Number of threads in a team
* omp_get_thread_limit::        Maximal number of threads
* omp_get_thread_num::          Current thread ID
* omp_in_parallel::             Whether a parallel region is active
* omp_set_dynamic::             Enable/disable dynamic teams
* omp_set_max_active_levels::   Limits the number of active parallel regions
* omp_set_nested::              Enable/disable nested parallel regions
* omp_set_num_threads::         Set upper team size limit
* omp_set_schedule::            Set the runtime scheduling method

   Initialize, set, test, unset and destroy simple and nested locks.

* Menu:

* omp_init_lock::            Initialize simple lock
* omp_set_lock::             Wait for and set simple lock
* omp_test_lock::            Test and set simple lock if available
* omp_unset_lock::           Unset simple lock
* omp_destroy_lock::         Destroy simple lock
* omp_init_nest_lock::       Initialize nested lock
* omp_set_nest_lock::        Wait for and set simple lock
* omp_test_nest_lock::       Test and set nested lock if available
* omp_unset_nest_lock::      Unset nested lock
* omp_destroy_nest_lock::    Destroy nested lock

   Portable, thread-based, wall clock timer.

* Menu:

* omp_get_wtick::            Get timer precision.
* omp_get_wtime::            Elapsed wall clock time.


File: libgomp.info,  Node: omp_get_active_level,  Next: omp_get_ancestor_thread_num,  Up: Runtime Library Routines

2.1 `omp_get_active_level' - Number of parallel regions
=======================================================

_Description_:
     This function returns the nesting level for the active parallel
     blocks, which enclose the calling call.

_C/C++_
     _Prototype_:  `int omp_get_active_level();'

_Fortran_:
     _Interface_:  `integer omp_get_active_level()'

_See also_:
     *note omp_get_level::, *note omp_get_max_active_levels::, *note
     omp_set_max_active_levels::

_Reference_:
     OpenMP specifications v3.0 (http://www.openmp.org/), section
     3.2.19.


File: libgomp.info,  Node: omp_get_ancestor_thread_num,  Next: omp_get_dynamic,  Prev: omp_get_active_level,  Up: Runtime Library Routines

2.2 `omp_get_ancestor_thread_num' - Ancestor thread ID
======================================================

_Description_:
     This function returns the thread identification number for the
     given nesting level of the current thread. For values of LEVEL
     outside zero to `omp_get_level' -1 is returned; if LEVEL is
     `omp_get_level' the result is identical to `omp_get_thread_num'.

_C/C++_
     _Prototype_:  `int omp_get_ancestor_thread_num(int level);'

_Fortran_:
     _Interface_:  `integer omp_ancestor_thread_num(level)'
                   `integer level'

_See also_:
     *note omp_get_level::, *note omp_get_thread_num::, *note
     omp_get_team_size::

_Reference_:
     OpenMP specifications v3.0 (http://www.openmp.org/), section
     3.2.17.


File: libgomp.info,  Node: omp_get_dynamic,  Next: omp_get_level,  Prev: omp_get_ancestor_thread_num,  Up: Runtime Library Routines

2.3 `omp_get_dynamic' - Dynamic teams setting
=============================================

_Description_:
     This function returns `true' if enabled, `false' otherwise.  Here,
     `true' and `false' represent their language-specific counterparts.

     The dynamic team setting may be initialized at startup by the
     `OMP_DYNAMIC' environment variable or at runtime using
     `omp_set_dynamic'. If undefined, dynamic adjustment is disabled by
     default.

_C/C++_:
     _Prototype_:  `int omp_get_dynamic();'

_Fortran_:
     _Interface_:  `logical function omp_get_dynamic()'

_See also_:
     *note omp_set_dynamic::, *note OMP_DYNAMIC::

_Reference_:
     OpenMP specifications v3.0 (http://www.openmp.org/), section 3.2.8.


File: libgomp.info,  Node: omp_get_level,  Next: omp_get_max_active_levels,  Prev: omp_get_dynamic,  Up: Runtime Library Routines

2.4 `omp_get_level' - Obtain the current nesting level
======================================================

_Description_:
     This function returns the nesting level for the parallel blocks,
     which enclose the calling call.

_C/C++_
     _Prototype_:  `int omp_get level();'

_Fortran_:
     _Interface_:  `integer omp_level()'

_See also_:
     *note omp_get_active_level::

_Reference_:
     OpenMP specifications v3.0 (http://www.openmp.org/), section
     3.2.16.


File: libgomp.info,  Node: omp_get_max_active_levels,  Next: omp_get_max_threads,  Prev: omp_get_level,  Up: Runtime Library Routines

2.5 `omp_set_max_active_levels' - Maximal number of active regions
==================================================================

_Description_:
     This function obtains the maximally allowed number of nested,
     active parallel regions.

_C/C++_
     _Prototype_:  `int omp_get_max_active_levels();'

_Fortran_:
     _Interface_:  `int omp_get_max_active_levels()'

_See also_:
     *note omp_set_max_active_levels::, *note omp_get_active_level::

_Reference_:
     OpenMP specifications v3.0 (http://www.openmp.org/), section
     3.2.14.


File: libgomp.info,  Node: omp_get_max_threads,  Next: omp_get_nested,  Prev: omp_get_max_active_levels,  Up: Runtime Library Routines

2.6 `omp_get_max_threads' - Maximal number of threads of parallel region
========================================================================

_Description_:
     Return the maximal number of threads used for the current parallel
     region that does not use the clause `num_threads'.

_C/C++_:
     _Prototype_:  `int omp_get_max_threads();'

_Fortran_:
     _Interface_:  `integer function omp_get_max_threads()'

_See also_:
     *note omp_set_num_threads::, *note omp_set_dynamic::, *note
     omp_get_thread_limit::

_Reference_:
     OpenMP specifications v3.0 (http://www.openmp.org/), section 3.2.3.


File: libgomp.info,  Node: omp_get_nested,  Next: omp_get_num_procs,  Prev: omp_get_max_threads,  Up: Runtime Library Routines

2.7 `omp_get_nested' - Nested parallel regions
==============================================

_Description_:
     This function returns `true' if nested parallel regions are
     enabled, `false' otherwise. Here, `true' and `false' represent
     their language-specific counterparts.

     Nested parallel regions may be initialized at startup by the
     `OMP_NESTED' environment variable or at runtime using
     `omp_set_nested'. If undefined, nested parallel regions are
     disabled by default.

_C/C++_:
     _Prototype_:  `int omp_get_nested();'

_Fortran_:
     _Interface_:  `integer function omp_get_nested()'

_See also_:
     *note omp_set_nested::, *note OMP_NESTED::

_Reference_:
     OpenMP specifications v3.0 (http://www.openmp.org/), section
     3.2.10.


File: libgomp.info,  Node: omp_get_num_procs,  Next: omp_get_num_threads,  Prev: omp_get_nested,  Up: Runtime Library Routines

2.8 `omp_get_num_procs' - Number of processors online
=====================================================

_Description_:
     Returns the number of processors online.

_C/C++_:
     _Prototype_:  `int omp_get_num_procs();'

_Fortran_:
     _Interface_:  `integer function omp_get_num_procs()'

_Reference_:
     OpenMP specifications v3.0 (http://www.openmp.org/), section 3.2.5.


File: libgomp.info,  Node: omp_get_num_threads,  Next: omp_get_schedule,  Prev: omp_get_num_procs,  Up: Runtime Library Routines

2.9 `omp_get_num_threads' - Size of the active team
===================================================

_Description_:
     The number of threads in the current team. In a sequential section
     of the program `omp_get_num_threads' returns 1.

     The default team size may be initialized at startup by the
     `OMP_NUM_THREADS' environment variable. At runtime, the size of
     the current team may be set either by the `NUM_THREADS' clause or
     by `omp_set_num_threads'. If none of the above were used to define
     a specific value and `OMP_DYNAMIC' is disabled, one thread per CPU
     online is used.

_C/C++_:
     _Prototype_:  `int omp_get_num_threads();'

_Fortran_:
     _Interface_:  `integer function omp_get_num_threads()'

_See also_:
     *note omp_get_max_threads::, *note omp_set_num_threads::, *note
     OMP_NUM_THREADS::

_Reference_:
     OpenMP specifications v3.0 (http://www.openmp.org/), section 3.2.2.


File: libgomp.info,  Node: omp_get_schedule,  Next: omp_get_team_size,  Prev: omp_get_num_threads,  Up: Runtime Library Routines

2.10 `omp_get_schedule' - Obtain the runtime scheduling method
==============================================================

_Description_:
     Obtain runtime the scheduling method. The KIND argument will be
     set to the value `omp_sched_static', `omp_sched_dynamic',
     `opm_sched_guided' or `auto'. The second argument, MODIFIER, is
     set to the chunk size.

_C/C++_
     _Prototype_:  `omp_schedule(omp_sched_t * kind, int *modifier);'

_Fortran_:
     _Interface_:  `subroutine omp_schedule(kind, modifier)'
                   `integer(kind=omp_sched_kind) kind'
                   `integer modifier'

_See also_:
     *note omp_set_schedule::, *note OMP_SCHEDULE::

_Reference_:
     OpenMP specifications v3.0 (http://www.openmp.org/), section
     3.2.12.


File: libgomp.info,  Node: omp_get_team_size,  Next: omp_get_thread_limit,  Prev: omp_get_schedule,  Up: Runtime Library Routines

2.11 `omp_get_team_size' - Number of threads in a team
======================================================

_Description_:
     This function returns the number of threads in a thread team to
     which either the current thread or its ancestor belongs. For
     values of LEVEL outside zero to `omp_get_level' -1 is returned; if
     LEVEL is zero 1 is returned and for `omp_get_level' the result is
     identical to `omp_get_num_threads'.

_C/C++_:
     _Prototype_:  `int omp_get_time_size(int level);'

_Fortran_:
     _Interface_:  `integer function omp_get_team_size(level)'
                   `integer level'

_See also_:
     *note omp_get_num_threads::, *note omp_get_level::, *note
     omp_get_ancestor_thread_num::

_Reference_:
     OpenMP specifications v3.0 (http://www.openmp.org/), section
     3.2.18.


File: libgomp.info,  Node: omp_get_thread_limit,  Next: omp_get_thread_num,  Prev: omp_get_team_size,  Up: Runtime Library Routines

2.12 `omp_get_thread_limit' - Maximal number of threads
=======================================================

_Description_:
     Return the maximal number of threads of the program.

_C/C++_:
     _Prototype_:  `int omp_get_thread_limit();'

_Fortran_:
     _Interface_:  `integer function omp_get_thread_limit()'

_See also_:
     *note omp_get_max_threads::, *note OMP_THREAD_LIMIT::

_Reference_:
     OpenMP specifications v3.0 (http://www.openmp.org/), section
     3.2.13.


File: libgomp.info,  Node: omp_get_thread_num,  Next: omp_in_parallel,  Prev: omp_get_thread_limit,  Up: Runtime Library Routines

2.13 `omp_get_thread_num' - Current thread ID
=============================================

_Description_:
     Unique thread identification number within the current team.  In a
     sequential parts of the program, `omp_get_thread_num' always
     returns 0. In parallel regions the return value varies from 0 to
     `omp_get_num_threads'-1 inclusive. The return value of the master
     thread of a team is always 0.

_C/C++_:
     _Prototype_:  `int omp_get_thread_num();'

_Fortran_:
     _Interface_:  `integer function omp_get_thread_num()'

_See also_:
     *note omp_get_num_threads::, *note omp_get_ancestor_thread_num::

_Reference_:
     OpenMP specifications v3.0 (http://www.openmp.org/), section 3.2.4.


File: libgomp.info,  Node: omp_in_parallel,  Next: omp_set_dynamic,  Prev: omp_get_thread_num,  Up: Runtime Library Routines

2.14 `omp_in_parallel' - Whether a parallel region is active
============================================================

_Description_:
     This function returns `true' if currently running in parallel,
     `false' otherwise. Here, `true' and `false' represent their
     language-specific counterparts.

_C/C++_:
     _Prototype_:  `int omp_in_parallel();'

_Fortran_:
     _Interface_:  `logical function omp_in_parallel()'

_Reference_:
     OpenMP specifications v3.0 (http://www.openmp.org/), section 3.2.6.


File: libgomp.info,  Node: omp_set_dynamic,  Next: omp_set_max_active_levels,  Prev: omp_in_parallel,  Up: Runtime Library Routines

2.15 `omp_set_dynamic' - Enable/disable dynamic teams
=====================================================

_Description_:
     Enable or disable the dynamic adjustment of the number of threads
     within a team. The function takes the language-specific equivalent
     of `true' and `false', where `true' enables dynamic adjustment of
     team sizes and `false' disables it.

_C/C++_:
     _Prototype_:  `void omp_set_dynamic(int);'

_Fortran_:
     _Interface_:  `subroutine omp_set_dynamic(set)'
                   `integer, intent(in) :: set'

_See also_:
     *note OMP_DYNAMIC::, *note omp_get_dynamic::

_Reference_:
     OpenMP specifications v3.0 (http://www.openmp.org/), section 3.2.7.


File: libgomp.info,  Node: omp_set_max_active_levels,  Next: omp_set_nested,  Prev: omp_set_dynamic,  Up: Runtime Library Routines

2.16 `omp_set_max_active_levels' - Limits the number of active parallel regions
===============================================================================

_Description_:
     This function limits the maximally allowed number of nested,
     active parallel regions.

_C/C++_
     _Prototype_:  `omp_set_max_active_levels(int max_levels);'

_Fortran_:
     _Interface_:  `omp_max_active_levels(max_levels)'
                   `integer max_levels'

_See also_:
     *note omp_get_max_active_levels::, *note omp_get_active_level::

_Reference_:
     OpenMP specifications v3.0 (http://www.openmp.org/), section
     3.2.14.


File: libgomp.info,  Node: omp_set_nested,  Next: omp_set_num_threads,  Prev: omp_set_max_active_levels,  Up: Runtime Library Routines

2.17 `omp_set_nested' - Enable/disable nested parallel regions
==============================================================

_Description_:
     Enable or disable nested parallel regions, i.e., whether team
     members are allowed to create new teams. The function takes the
     language-specific equivalent of `true' and `false', where `true'
     enables dynamic adjustment of team sizes and `false' disables it.

_C/C++_:
     _Prototype_:  `void omp_set_dynamic(int);'

_Fortran_:
     _Interface_:  `subroutine omp_set_dynamic(set)'
                   `integer, intent(in) :: set'

_See also_:
     *note OMP_NESTED::, *note omp_get_nested::

_Reference_:
     OpenMP specifications v3.0 (http://www.openmp.org/), section 3.2.9.


File: libgomp.info,  Node: omp_set_num_threads,  Next: omp_set_schedule,  Prev: omp_set_nested,  Up: Runtime Library Routines

2.18 `omp_set_num_threads' - Set upper team size limit
======================================================

_Description_:
     Specifies the number of threads used by default in subsequent
     parallel sections, if those do not specify a `num_threads' clause.
     The argument of `omp_set_num_threads' shall be a positive integer.

_C/C++_:
     _Prototype_:  `void omp_set_num_threads(int);'

_Fortran_:
     _Interface_:  `subroutine omp_set_num_threads(set)'
                   `integer, intent(in) :: set'

_See also_:
     *note OMP_NUM_THREADS::, *note omp_get_num_threads::, *note
     omp_get_max_threads::

_Reference_:
     OpenMP specifications v3.0 (http://www.openmp.org/), section 3.2.1.


File: libgomp.info,  Node: omp_set_schedule,  Next: omp_init_lock,  Prev: omp_set_num_threads,  Up: Runtime Library Routines

2.19 `omp_set_schedule' - Set the runtime scheduling method
===========================================================

_Description_:
     Sets the runtime scheduling method. The KIND argument can have the
     value `omp_sched_static', `omp_sched_dynamic', `opm_sched_guided'
     or `omp_sched_auto'. Except for `omp_sched_auto', the chunk size
     is set to the value of MODIFIER if positive or to the default
     value if zero or negative.  For `omp_sched_auto' the MODIFIER
     argument is ignored.

_C/C++_
     _Prototype_:  `int omp_schedule(omp_sched_t * kind, int *modifier);'

_Fortran_:
     _Interface_:  `subroutine omp_schedule(kind, modifier)'
                   `integer(kind=omp_sched_kind) kind'
                   `integer modifier'

_See also_:
     *note omp_get_schedule:: *note OMP_SCHEDULE::

_Reference_:
     OpenMP specifications v3.0 (http://www.openmp.org/), section
     3.2.11.


File: libgomp.info,  Node: omp_init_lock,  Next: omp_set_lock,  Prev: omp_set_schedule,  Up: Runtime Library Routines

2.20 `omp_init_lock' - Initialize simple lock
=============================================

_Description_:
     Initialize a simple lock. After initialization, the lock is in an
     unlocked state.

_C/C++_:
     _Prototype_:  `void omp_init_lock(omp_lock_t *lock);'

_Fortran_:
     _Interface_:  `subroutine omp_init_lock(lock)'
                   `integer(omp_lock_kind), intent(out) :: lock'

_See also_:
     *note omp_destroy_lock::

_Reference_:
     OpenMP specifications v3.0 (http://www.openmp.org/), section 3.3.1.


File: libgomp.info,  Node: omp_set_lock,  Next: omp_test_lock,  Prev: omp_init_lock,  Up: Runtime Library Routines

2.21 `omp_set_lock' - Wait for and set simple lock
==================================================

_Description_:
     Before setting a simple lock, the lock variable must be
     initialized by `omp_init_lock'. The calling thread is blocked
     until the lock is available. If the lock is already held by the
     current thread, a deadlock occurs.

_C/C++_:
     _Prototype_:  `void omp_set_lock(omp_lock_t *lock);'

_Fortran_:
     _Interface_:  `subroutine omp_set_lock(lock)'
                   `integer(omp_lock_kind), intent(out) :: lock'

_See also_:
     *note omp_init_lock::, *note omp_test_lock::, *note
     omp_unset_lock::

_Reference_:
     OpenMP specifications v3.0 (http://www.openmp.org/), section 3.3.3.


File: libgomp.info,  Node: omp_test_lock,  Next: omp_unset_lock,  Prev: omp_set_lock,  Up: Runtime Library Routines

2.22 `omp_test_lock' - Test and set simple lock if available
============================================================

_Description_:
     Before setting a simple lock, the lock variable must be
     initialized by `omp_init_lock'. Contrary to `omp_set_lock',
     `omp_test_lock' does not block if the lock is not available. This
     function returns `true' upon success, `false' otherwise. Here,
     `true' and `false' represent their language-specific counterparts.

_C/C++_:
     _Prototype_:  `int omp_test_lock(omp_lock_t *lock);'

_Fortran_:
     _Interface_:  `subroutine omp_test_lock(lock)'
                   `logical(omp_logical_kind) :: omp_test_lock'
                   `integer(omp_lock_kind), intent(out) :: lock'

_See also_:
     *note omp_init_lock::, *note omp_set_lock::, *note omp_set_lock::

_Reference_:
     OpenMP specifications v3.0 (http://www.openmp.org/), section 3.3.5.


File: libgomp.info,  Node: omp_unset_lock,  Next: omp_destroy_lock,  Prev: omp_test_lock,  Up: Runtime Library Routines

2.23 `omp_unset_lock' - Unset simple lock
=========================================

_Description_:
     A simple lock about to be unset must have been locked by
     `omp_set_lock' or `omp_test_lock' before. In addition, the lock
     must be held by the thread calling `omp_unset_lock'. Then, the
     lock becomes unlocked. If one ore more threads attempted to set
     the lock before, one of them is chosen to, again, set the lock for
     itself.

_C/C++_:
     _Prototype_:  `void omp_unset_lock(omp_lock_t *lock);'

_Fortran_:
     _Interface_:  `subroutine omp_unset_lock(lock)'
                   `integer(omp_lock_kind), intent(out) :: lock'

_See also_:
     *note omp_set_lock::, *note omp_test_lock::

_Reference_:
     OpenMP specifications v3.0 (http://www.openmp.org/), section 3.3.4.


File: libgomp.info,  Node: omp_destroy_lock,  Next: omp_init_nest_lock,  Prev: omp_unset_lock,  Up: Runtime Library Routines

2.24 `omp_destroy_lock' - Destroy simple lock
=============================================

_Description_:
     Destroy a simple lock. In order to be destroyed, a simple lock
     must be in the unlocked state.

_C/C++_:
     _Prototype_:  `void omp_destroy_lock(omp_lock_t *);'

_Fortran_:
     _Interface_:  `subroutine omp_destroy_lock(lock)'
                   `integer(omp_lock_kind), intent(inout) :: lock'

_See also_:
     *note omp_init_lock::

_Reference_:
     OpenMP specifications v3.0 (http://www.openmp.org/), section 3.3.2.


File: libgomp.info,  Node: omp_init_nest_lock,  Next: omp_set_nest_lock,  Prev: omp_destroy_lock,  Up: Runtime Library Routines

2.25 `omp_init_nest_lock' - Initialize nested lock
==================================================

_Description_:
     Initialize a nested lock. After initialization, the lock is in an
     unlocked state and the nesting count is set to zero.

_C/C++_:
     _Prototype_:  `void omp_init_nest_lock(omp_nest_lock_t *lock);'

_Fortran_:
     _Interface_:  `subroutine omp_init_nest_lock(lock)'
                   `integer(omp_nest_lock_kind), intent(out) :: lock'

_See also_:
     *note omp_destroy_nest_lock::

_Reference_:
     OpenMP specifications v3.0 (http://www.openmp.org/), section 3.3.1.


File: libgomp.info,  Node: omp_set_nest_lock,  Next: omp_test_nest_lock,  Prev: omp_init_nest_lock,  Up: Runtime Library Routines

2.26 `omp_set_nest_lock' - Wait for and set simple lock
=======================================================

_Description_:
     Before setting a nested lock, the lock variable must be
     initialized by `omp_init_nest_lock'. The calling thread is blocked
     until the lock is available. If the lock is already held by the
     current thread, the nesting count for the lock in incremented.

_C/C++_:
     _Prototype_:  `void omp_set_nest_lock(omp_nest_lock_t *lock);'

_Fortran_:
     _Interface_:  `subroutine omp_set_nest_lock(lock)'
                   `integer(omp_nest_lock_kind), intent(out) :: lock'

_See also_:
     *note omp_init_nest_lock::, *note omp_unset_nest_lock::

_Reference_:
     OpenMP specifications v3.0 (http://www.openmp.org/), section 3.3.3.


File: libgomp.info,  Node: omp_test_nest_lock,  Next: omp_unset_nest_lock,  Prev: omp_set_nest_lock,  Up: Runtime Library Routines

2.27 `omp_test_nest_lock' - Test and set nested lock if available
=================================================================

_Description_:
     Before setting a nested lock, the lock variable must be
     initialized by `omp_init_nest_lock'. Contrary to
     `omp_set_nest_lock', `omp_test_nest_lock' does not block if the
     lock is not available.  If the lock is already held by the current
     thread, the new nesting count is returned. Otherwise, the return
     value equals zero.

_C/C++_:
     _Prototype_:  `int omp_test_nest_lock(omp_nest_lock_t *lock);'

_Fortran_:
     _Interface_:  `integer function omp_test_nest_lock(lock)'
                   `integer(omp_integer_kind) :: omp_test_nest_lock'
                   `integer(omp_nest_lock_kind), intent(inout) :: lock'

_See also_:
     *note omp_init_lock::, *note omp_set_lock::, *note omp_set_lock::

_Reference_:
     OpenMP specifications v3.0 (http://www.openmp.org/), section 3.3.5.


File: libgomp.info,  Node: omp_unset_nest_lock,  Next: omp_destroy_nest_lock,  Prev: omp_test_nest_lock,  Up: Runtime Library Routines

2.28 `omp_unset_nest_lock' - Unset nested lock
==============================================

_Description_:
     A nested lock about to be unset must have been locked by
     `omp_set_nested_lock' or `omp_test_nested_lock' before. In
     addition, the lock must be held by the thread calling
     `omp_unset_nested_lock'. If the nesting count drops to zero, the
     lock becomes unlocked. If one ore more threads attempted to set
     the lock before, one of them is chosen to, again, set the lock for
     itself.

_C/C++_:
     _Prototype_:  `void omp_unset_nest_lock(omp_nest_lock_t *lock);'

_Fortran_:
     _Interface_:  `subroutine omp_unset_nest_lock(lock)'
                   `integer(omp_nest_lock_kind), intent(out) :: lock'

_See also_:
     *note omp_set_nest_lock::

_Reference_:
     OpenMP specifications v3.0 (http://www.openmp.org/), section 3.3.4.


File: libgomp.info,  Node: omp_destroy_nest_lock,  Next: omp_get_wtick,  Prev: omp_unset_nest_lock,  Up: Runtime Library Routines

2.29 `omp_destroy_nest_lock' - Destroy nested lock
==================================================

_Description_:
     Destroy a nested lock. In order to be destroyed, a nested lock
     must be in the unlocked state and its nesting count must equal
     zero.

_C/C++_:
     _Prototype_:  `void omp_destroy_nest_lock(omp_nest_lock_t *);'

_Fortran_:
     _Interface_:  `subroutine omp_destroy_nest_lock(lock)'
                   `integer(omp_nest_lock_kind), intent(inout) :: lock'

_See also_:
     *note omp_init_lock::

_Reference_:
     OpenMP specifications v3.0 (http://www.openmp.org/), section 3.3.2.


File: libgomp.info,  Node: omp_get_wtick,  Next: omp_get_wtime,  Prev: omp_destroy_nest_lock,  Up: Runtime Library Routines

2.30 `omp_get_wtick' - Get timer precision
==========================================

_Description_:
     Gets the timer precision, i.e., the number of seconds between two
     successive clock ticks.

_C/C++_:
     _Prototype_:  `double omp_get_wtick();'

_Fortran_:
     _Interface_:  `double precision function omp_get_wtick()'

_See also_:
     *note omp_get_wtime::

_Reference_:
     OpenMP specifications v3.0 (http://www.openmp.org/), section 3.4.2.


File: libgomp.info,  Node: omp_get_wtime,  Prev: omp_get_wtick,  Up: Runtime Library Routines

2.31 `omp_get_wtime' - Elapsed wall clock time
==============================================

_Description_:
     Elapsed wall clock time in seconds. The time is measured per
     thread, no guarantee can bee made that two distinct threads
     measure the same time.  Time is measured from some "time in the
     past". On POSIX compliant systems the seconds since the Epoch
     (00:00:00 UTC, January 1, 1970) are returned.

_C/C++_:
     _Prototype_:  `double omp_get_wtime();'

_Fortran_:
     _Interface_:  `double precision function omp_get_wtime()'

_See also_:
     *note omp_get_wtick::

_Reference_:
     OpenMP specifications v3.0 (http://www.openmp.org/), section 3.4.1.


File: libgomp.info,  Node: Environment Variables,  Next: The libgomp ABI,  Prev: Runtime Library Routines,  Up: Top

3 Environment Variables
***********************

The variables `OMP_DYNAMIC', `OMP_MAX_ACTIVE_LEVELS', `OMP_NESTED',
`OMP_NUM_THREADS', `OMP_SCHEDULE', `OMP_STACKSIZE',`OMP_THREAD_LIMIT'
and `OMP_WAIT_POLICY' are defined by section 4 of the OpenMP
specifications in version 3.0, while `GOMP_CPU_AFFINITY' and
`GOMP_STACKSIZE' are GNU extensions.

* Menu:

* OMP_DYNAMIC::           Dynamic adjustment of threads
* OMP_MAX_ACTIVE_LEVELS:: Set the maximal number of nested parallel regions
* OMP_NESTED::            Nested parallel regions
* OMP_NUM_THREADS::       Specifies the number of threads to use
* OMP_STACKSIZE::         Set default thread stack size
* OMP_SCHEDULE::          How threads are scheduled
* OMP_THREAD_LIMIT::      Set the maximal number of threads
* OMP_WAIT_POLICY::       How waiting threads are handled
* GOMP_CPU_AFFINITY::     Bind threads to specific CPUs
* GOMP_STACKSIZE::        Set default thread stack size


File: libgomp.info,  Node: OMP_DYNAMIC,  Next: OMP_MAX_ACTIVE_LEVELS,  Up: Environment Variables

3.1 `OMP_DYNAMIC' - Dynamic adjustment of threads
=================================================

_Description_:
     Enable or disable the dynamic adjustment of the number of threads
     within a team. The value of this environment variable shall be
     `TRUE' or `FALSE'. If undefined, dynamic adjustment is disabled by
     default.

_See also_:
     *note omp_set_dynamic::

_Reference_:
     OpenMP specifications v3.0 (http://www.openmp.org/), section 4.3


File: libgomp.info,  Node: OMP_MAX_ACTIVE_LEVELS,  Next: OMP_NESTED,  Prev: OMP_DYNAMIC,  Up: Environment Variables

3.2 `OMP_MAX_ACTIVE_LEVELS' - Set the maximal number of nested parallel regions
===============================================================================

_Description_:
     Specifies the initial value for the maximal number of nested
     parallel regions. The value of this variable shall be positive
     integer.  If undefined, the number of active levels is unlimited.

_See also_:
     *note omp_set_max_active_levels::

_Reference_:
     OpenMP specifications v3.0 (http://www.openmp.org/), section 4.7


File: libgomp.info,  Node: OMP_NESTED,  Next: OMP_NUM_THREADS,  Prev: OMP_MAX_ACTIVE_LEVELS,  Up: Environment Variables

3.3 `OMP_NESTED' - Nested parallel regions
==========================================

_Description_:
     Enable or disable nested parallel regions, i.e., whether team
     members are allowed to create new teams. The value of this
     environment variable shall be `TRUE' or `FALSE'. If undefined,
     nested parallel regions are disabled by default.

_See also_:
     *note omp_set_nested::

_Reference_:
     OpenMP specifications v3.0 (http://www.openmp.org/), section 4.4


File: libgomp.info,  Node: OMP_NUM_THREADS,  Next: OMP_STACKSIZE,  Prev: OMP_NESTED,  Up: Environment Variables

3.4 `OMP_NUM_THREADS' - Specifies the number of threads to use
==============================================================

_Description_:
     Specifies the default number of threads to use in parallel
     regions. The value of this variable shall be positive integer. If
     undefined one thread per CPU online is used.

_See also_:
     *note omp_set_num_threads::

_Reference_:
     OpenMP specifications v3.0 (http://www.openmp.org/), section 4.2


File: libgomp.info,  Node: OMP_SCHEDULE,  Next: OMP_THREAD_LIMIT,  Prev: OMP_STACKSIZE,  Up: Environment Variables

3.5 `OMP_SCHEDULE' - How threads are scheduled
==============================================

_Description_:
     Allows to specify `schedule type' and `chunk size'.  The value of
     the variable shall have the form: `type[,chunk]' where `type' is
     one of `static', `dynamic', `guided' or `auto' The optional
     `chunk' size shall be a positive integer. If undefined, dynamic
     scheduling and a chunk size of 1 is used.

_See also_:
     *note omp_set_schedule::

_Reference_:
     OpenMP specifications v3.0 (http://www.openmp.org/), sections
     2.5.1 and 4.1


File: libgomp.info,  Node: OMP_STACKSIZE,  Next: OMP_SCHEDULE,  Prev: OMP_NUM_THREADS,  Up: Environment Variables

3.6 `OMP_STACKSIZE' - Set default thread stack size
===================================================

_Description_:
     Set the default thread stack size in kilobytes, unless the number
     is suffixed by `B', `K', `M' or `G', in which case the size is,
     respectively, in bytes, kilobytes, megabytes or gigabytes. This is
     different from `pthread_attr_setstacksize' which gets the number
     of bytes as an argument. If the stacksize can not be set due to
     system constraints, an error is reported and the initial stacksize
     is left unchanged. If undefined, the stack size is system
     dependent.

_Reference_:
     OpenMP specifications v3.0 (http://www.openmp.org/), sections 4.5


File: libgomp.info,  Node: OMP_THREAD_LIMIT,  Next: OMP_WAIT_POLICY,  Prev: OMP_SCHEDULE,  Up: Environment Variables

3.7 `OMP_THREAD_LIMIT' - Set the maximal number of threads
==========================================================

_Description_:
     Specifies the number of threads to use for the whole program. The
     value of this variable shall be positive integer. If undefined,
     the number of threads is not limited.

_See also_:
     *note OMP_NUM_THREADS:: *note omp_get_thread_limit::

_Reference_:
     OpenMP specifications v3.0 (http://www.openmp.org/), section 4.8


File: libgomp.info,  Node: OMP_WAIT_POLICY,  Next: GOMP_CPU_AFFINITY,  Prev: OMP_THREAD_LIMIT,  Up: Environment Variables

3.8 `OMP_WAIT_POLICY' - How waiting threads are handled
=======================================================

_Description_:
     Specifies whether waiting threads should be active or passive. If
     the value is `PASSIVE', waiting threads should not consume CPU
     power while waiting; while the value is `ACTIVE' specifies that
     they should.

_Reference_:
     OpenMP specifications v3.0 (http://www.openmp.org/), sections 4.6


File: libgomp.info,  Node: GOMP_CPU_AFFINITY,  Next: GOMP_STACKSIZE,  Prev: OMP_WAIT_POLICY,  Up: Environment Variables

3.9 `GOMP_CPU_AFFINITY' - Bind threads to specific CPUs
=======================================================

_Description_:
     Binds threads to specific CPUs. The variable should contain a
     space- or comma-separated list of CPUs. This list may contain
     different kind of entries: either single CPU numbers in any order,
     a range of CPUs (M-N) or a range with some stride (M-N:S). CPU
     numbers are zero based. For example, `GOMP_CPU_AFFINITY="0 3 1-2
     4-15:2"' will bind the initial thread to CPU 0, the second to CPU
     3, the third to CPU 1, the fourth to CPU 2, the fifth to CPU 4,
     the sixth through tenth to CPUs 6, 8, 10, 12, and 14 respectively
     and then start assigning back from the beginning of the list.
     `GOMP_CPU_AFFINITY=0' binds all threads to CPU 0.

     There is no GNU OpenMP library routine to determine whether a CPU
     affinity specification is in effect. As a workaround,
     language-specific library functions, e.g., `getenv' in C or
     `GET_ENVIRONMENT_VARIABLE' in Fortran, may be used to query the
     setting of the `GOMP_CPU_AFFINITY' environment variable. A defined
     CPU affinity on startup cannot be changed or disabled during the
     runtime of the application.

     If this environment variable is omitted, the host system will
     handle the assignment of threads to CPUs.


File: libgomp.info,  Node: GOMP_STACKSIZE,  Prev: GOMP_CPU_AFFINITY,  Up: Environment Variables

3.10 `GOMP_STACKSIZE' - Set default thread stack size
=====================================================

_Description_:
     Set the default thread stack size in kilobytes. This is different
     from `pthread_attr_setstacksize' which gets the number of bytes as
     an argument. If the stacksize can not be set due to system
     constraints, an error is reported and the initial stacksize is
     left unchanged. If undefined, the stack size is system dependent.

_See also_:
     *note GOMP_STACKSIZE::

_Reference_:
     GCC Patches Mailinglist
     (http://gcc.gnu.org/ml/gcc-patches/2006-06/msg00493.html), GCC
     Patches Mailinglist
     (http://gcc.gnu.org/ml/gcc-patches/2006-06/msg00496.html)


File: libgomp.info,  Node: The libgomp ABI,  Next: Reporting Bugs,  Prev: Environment Variables,  Up: Top

4 The libgomp ABI
*****************

The following sections present notes on the external ABI as presented
by libgomp. Only maintainers should need them.

* Menu:

* Implementing MASTER construct::
* Implementing CRITICAL construct::
* Implementing ATOMIC construct::
* Implementing FLUSH construct::
* Implementing BARRIER construct::
* Implementing THREADPRIVATE construct::
* Implementing PRIVATE clause::
* Implementing FIRSTPRIVATE LASTPRIVATE COPYIN and COPYPRIVATE clauses::
* Implementing REDUCTION clause::
* Implementing PARALLEL construct::
* Implementing FOR construct::
* Implementing ORDERED construct::
* Implementing SECTIONS construct::
* Implementing SINGLE construct::


File: libgomp.info,  Node: Implementing MASTER construct,  Next: Implementing CRITICAL construct,  Up: The libgomp ABI

4.1 Implementing MASTER construct
=================================

     if (omp_get_thread_num () == 0)
       block

   Alternately, we generate two copies of the parallel subfunction and
only include this in the version run by the master thread.  Surely
that's not worthwhile though...


File: libgomp.info,  Node: Implementing CRITICAL construct,  Next: Implementing ATOMIC construct,  Prev: Implementing MASTER construct,  Up: The libgomp ABI

4.2 Implementing CRITICAL construct
===================================

Without a specified name,

       void GOMP_critical_start (void);
       void GOMP_critical_end (void);

   so that we don't get COPY relocations from libgomp to the main
application.

   With a specified name, use omp_set_lock and omp_unset_lock with name
being transformed into a variable declared like

       omp_lock_t gomp_critical_user_<name> __attribute__((common))

   Ideally the ABI would specify that all zero is a valid unlocked
state, and so we wouldn't actually need to initialize this at startup.


File: libgomp.info,  Node: Implementing ATOMIC construct,  Next: Implementing FLUSH construct,  Prev: Implementing CRITICAL construct,  Up: The libgomp ABI

4.3 Implementing ATOMIC construct
=================================

The target should implement the `__sync' builtins.

   Failing that we could add

       void GOMP_atomic_enter (void)
       void GOMP_atomic_exit (void)

   which reuses the regular lock code, but with yet another lock object
private to the library.


File: libgomp.info,  Node: Implementing FLUSH construct,  Next: Implementing BARRIER construct,  Prev: Implementing ATOMIC construct,  Up: The libgomp ABI

4.4 Implementing FLUSH construct
================================

Expands to the `__sync_synchronize' builtin.


File: libgomp.info,  Node: Implementing BARRIER construct,  Next: Implementing THREADPRIVATE construct,  Prev: Implementing FLUSH construct,  Up: The libgomp ABI

4.5 Implementing BARRIER construct
==================================

       void GOMP_barrier (void)


File: libgomp.info,  Node: Implementing THREADPRIVATE construct,  Next: Implementing PRIVATE clause,  Prev: Implementing BARRIER construct,  Up: The libgomp ABI

4.6 Implementing THREADPRIVATE construct
========================================

In _most_ cases we can map this directly to `__thread'.  Except that
OMP allows constructors for C++ objects.  We can either refuse to
support this (how often is it used?) or we can implement something akin
to .ctors.

   Even more ideally, this ctor feature is handled by extensions to the
main pthreads library.  Failing that, we can have a set of entry points
to register ctor functions to be called.


File: libgomp.info,  Node: Implementing PRIVATE clause,  Next: Implementing FIRSTPRIVATE LASTPRIVATE COPYIN and COPYPRIVATE clauses,  Prev: Implementing THREADPRIVATE construct,  Up: The libgomp ABI

4.7 Implementing PRIVATE clause
===============================

In association with a PARALLEL, or within the lexical extent of a
PARALLEL block, the variable becomes a local variable in the parallel
subfunction.

   In association with FOR or SECTIONS blocks, create a new automatic
variable within the current function.  This preserves the semantic of
new variable creation.


File: libgomp.info,  Node: Implementing FIRSTPRIVATE LASTPRIVATE COPYIN and COPYPRIVATE clauses,  Next: Implementing REDUCTION clause,  Prev: Implementing PRIVATE clause,  Up: The libgomp ABI

4.8 Implementing FIRSTPRIVATE LASTPRIVATE COPYIN and COPYPRIVATE clauses
========================================================================

Seems simple enough for PARALLEL blocks.  Create a private struct for
communicating between parent and subfunction.  In the parent, copy in
values for scalar and "small" structs; copy in addresses for others
TREE_ADDRESSABLE types.  In the subfunction, copy the value into the
local variable.

   Not clear at all what to do with bare FOR or SECTION blocks.  The
only thing I can figure is that we do something like

     #pragma omp for firstprivate(x) lastprivate(y)
     for (int i = 0; i < n; ++i)
       body;

   which becomes

     {
       int x = x, y;

       // for stuff

       if (i == n)
         y = y;
     }

   where the "x=x" and "y=y" assignments actually have different uids
for the two variables, i.e. not something you could write directly in
C.  Presumably this only makes sense if the "outer" x and y are global
variables.

   COPYPRIVATE would work the same way, except the structure broadcast
would have to happen via SINGLE machinery instead.


File: libgomp.info,  Node: Implementing REDUCTION clause,  Next: Implementing PARALLEL construct,  Prev: Implementing FIRSTPRIVATE LASTPRIVATE COPYIN and COPYPRIVATE clauses,  Up: The libgomp ABI

4.9 Implementing REDUCTION clause
=================================

The private struct mentioned in the previous section should have a
pointer to an array of the type of the variable, indexed by the
thread's TEAM_ID.  The thread stores its final value into the array,
and after the barrier the master thread iterates over the array to
collect the values.


File: libgomp.info,  Node: Implementing PARALLEL construct,  Next: Implementing FOR construct,  Prev: Implementing REDUCTION clause,  Up: The libgomp ABI

4.10 Implementing PARALLEL construct
====================================

       #pragma omp parallel
       {
         body;
       }

   becomes

       void subfunction (void *data)
       {
         use data;
         body;
       }

       setup data;
       GOMP_parallel_start (subfunction, &data, num_threads);
       subfunction (&data);
       GOMP_parallel_end ();

       void GOMP_parallel_start (void (*fn)(void *), void *data, unsigned num_threads)

   The FN argument is the subfunction to be run in parallel.

   The DATA argument is a pointer to a structure used to communicate
data in and out of the subfunction, as discussed above with respect to
FIRSTPRIVATE et al.

   The NUM_THREADS argument is 1 if an IF clause is present and false,
or the value of the NUM_THREADS clause, if present, or 0.

   The function needs to create the appropriate number of threads
and/or launch them from the dock.  It needs to create the team
structure and assign team ids.

       void GOMP_parallel_end (void)

   Tears down the team and returns us to the previous
`omp_in_parallel()' state.


File: libgomp.info,  Node: Implementing FOR construct,  Next: Implementing ORDERED construct,  Prev: Implementing PARALLEL construct,  Up: The libgomp ABI

4.11 Implementing FOR construct
===============================

       #pragma omp parallel for
       for (i = lb; i <= ub; i++)
         body;

   becomes

       void subfunction (void *data)
       {
         long _s0, _e0;
         while (GOMP_loop_static_next (&_s0, &_e0))
         {
           long _e1 = _e0, i;
           for (i = _s0; i < _e1; i++)
             body;
         }
         GOMP_loop_end_nowait ();
       }

       GOMP_parallel_loop_static (subfunction, NULL, 0, lb, ub+1, 1, 0);
       subfunction (NULL);
       GOMP_parallel_end ();

       #pragma omp for schedule(runtime)
       for (i = 0; i < n; i++)
         body;

   becomes

       {
         long i, _s0, _e0;
         if (GOMP_loop_runtime_start (0, n, 1, &_s0, &_e0))
           do {
             long _e1 = _e0;
             for (i = _s0, i < _e0; i++)
               body;
           } while (GOMP_loop_runtime_next (&_s0, _&e0));
         GOMP_loop_end ();
       }

   Note that while it looks like there is trickyness to propagating a
non-constant STEP, there isn't really.  We're explicitly allowed to
evaluate it as many times as we want, and any variables involved should
automatically be handled as PRIVATE or SHARED like any other variables.
So the expression should remain evaluable in the subfunction.  We can
also pull it into a local variable if we like, but since its supposed
to remain unchanged, we can also not if we like.

   If we have SCHEDULE(STATIC), and no ORDERED, then we ought to be
able to get away with no work-sharing context at all, since we can
simply perform the arithmetic directly in each thread to divide up the
iterations.  Which would mean that we wouldn't need to call any of
these routines.

   There are separate routines for handling loops with an ORDERED
clause.  Bookkeeping for that is non-trivial...


File: libgomp.info,  Node: Implementing ORDERED construct,  Next: Implementing SECTIONS construct,  Prev: Implementing FOR construct,  Up: The libgomp ABI

4.12 Implementing ORDERED construct
===================================

       void GOMP_ordered_start (void)
       void GOMP_ordered_end (void)


File: libgomp.info,  Node: Implementing SECTIONS construct,  Next: Implementing SINGLE construct,  Prev: Implementing ORDERED construct,  Up: The libgomp ABI

4.13 Implementing SECTIONS construct
====================================

A block as

       #pragma omp sections
       {
         #pragma omp section
         stmt1;
         #pragma omp section
         stmt2;
         #pragma omp section
         stmt3;
       }

   becomes

       for (i = GOMP_sections_start (3); i != 0; i = GOMP_sections_next ())
         switch (i)
           {
           case 1:
             stmt1;
             break;
           case 2:
             stmt2;
             break;
           case 3:
             stmt3;
             break;
           }
       GOMP_barrier ();


File: libgomp.info,  Node: Implementing SINGLE construct,  Prev: Implementing SECTIONS construct,  Up: The libgomp ABI

4.14 Implementing SINGLE construct
==================================

A block like

       #pragma omp single
       {
         body;
       }

   becomes

       if (GOMP_single_start ())
         body;
       GOMP_barrier ();

   while

       #pragma omp single copyprivate(x)
         body;

   becomes

       datap = GOMP_single_copy_start ();
       if (datap == NULL)
         {
           body;
           data.x = x;
           GOMP_single_copy_end (&data);
         }
       else
         x = datap->x;
       GOMP_barrier ();


File: libgomp.info,  Node: Reporting Bugs,  Next: Copying,  Prev: The libgomp ABI,  Up: Top

5 Reporting Bugs
****************

Bugs in the GNU OpenMP implementation should be reported via bugzilla
(http://gcc.gnu.org/bugzilla/). In all cases, please add "openmp" to
the keywords field in the bug report.


File: libgomp.info,  Node: Copying,  Next: GNU Free Documentation License,  Prev: Reporting Bugs,  Up: Top

GNU GENERAL PUBLIC LICENSE
**************************

                         Version 2, June 1991

     Copyright (C) 1989, 1991 Free Software Foundation, Inc.
     51 Franklin Street, Fifth Floor, Boston, MA  02110-1301, USA

     Everyone is permitted to copy and distribute verbatim copies
     of this license document, but changing it is not allowed.

Preamble
========

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                      END OF TERMS AND CONDITIONS
Appendix: How to Apply These Terms to Your New Programs
=======================================================

If you develop a new program, and you want it to be of the greatest
possible use to the public, the best way to achieve this is to make it
free software which everyone can redistribute and change under these
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     ONE LINE TO GIVE THE PROGRAM'S NAME AND A BRIEF IDEA OF WHAT IT DOES.
     Copyright (C) YEAR  NAME OF AUTHOR

     This program is free software; you can redistribute it and/or modify
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     This program is distributed in the hope that it will be useful,
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   Also add information on how to contact you by electronic and paper
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     SIGNATURE OF TY COON, 1 April 1989
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   This General Public License does not permit incorporating your
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File: libgomp.info,  Node: GNU Free Documentation License,  Next: Funding,  Prev: Copying,  Up: Top

GNU Free Documentation License
******************************

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          unaltered in their text and in their titles.  Section numbers
          or the equivalent are not considered part of the section
          titles.

       M. Delete any section Entitled "Endorsements".  Such a section
          may not be included in the Modified Version.

       N. Do not retitle any existing section to be Entitled
          "Endorsements" or to conflict in title with any Invariant
          Section.

       O. Preserve any Warranty Disclaimers.

     If the Modified Version includes new front-matter sections or
     appendices that qualify as Secondary Sections and contain no
     material copied from the Document, you may at your option
     designate some or all of these sections as invariant.  To do this,
     add their titles to the list of Invariant Sections in the Modified
     Version's license notice.  These titles must be distinct from any
     other section titles.

     You may add a section Entitled "Endorsements", provided it contains
     nothing but endorsements of your Modified Version by various
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     You may add a passage of up to five words as a Front-Cover Text,
     and a passage of up to 25 words as a Back-Cover Text, to the end
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     added by (or through arrangements made by) any one entity.  If the
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     replace the old one, on explicit permission from the previous
     publisher that added the old one.

     The author(s) and publisher(s) of the Document do not by this
     License give permission to use their names for publicity for or to
     assert or imply endorsement of any Modified Version.

  5. COMBINING DOCUMENTS

     You may combine the Document with other documents released under
     this License, under the terms defined in section 4 above for
     modified versions, provided that you include in the combination
     all of the Invariant Sections of all of the original documents,
     unmodified, and list them all as Invariant Sections of your
     combined work in its license notice, and that you preserve all
     their Warranty Disclaimers.

     The combined work need only contain one copy of this License, and
     multiple identical Invariant Sections may be replaced with a single
     copy.  If there are multiple Invariant Sections with the same name
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     by adding at the end of it, in parentheses, the name of the
     original author or publisher of that section if known, or else a
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     the list of Invariant Sections in the license notice of the
     combined work.

     In the combination, you must combine any sections Entitled
     "History" in the various original documents, forming one section
     Entitled "History"; likewise combine any sections Entitled
     "Acknowledgements", and any sections Entitled "Dedications".  You
     must delete all sections Entitled "Endorsements."

  6. COLLECTIONS OF DOCUMENTS

     You may make a collection consisting of the Document and other
     documents released under this License, and replace the individual
     copies of this License in the various documents with a single copy
     that is included in the collection, provided that you follow the
     rules of this License for verbatim copying of each of the
     documents in all other respects.

     You may extract a single document from such a collection, and
     distribute it individually under this License, provided you insert
     a copy of this License into the extracted document, and follow
     this License in all other respects regarding verbatim copying of
     that document.

  7. AGGREGATION WITH INDEPENDENT WORKS

     A compilation of the Document or its derivatives with other
     separate and independent documents or works, in or on a volume of
     a storage or distribution medium, is called an "aggregate" if the
     copyright resulting from the compilation is not used to limit the
     legal rights of the compilation's users beyond what the individual
     works permit.  When the Document is included in an aggregate, this
     License does not apply to the other works in the aggregate which
     are not themselves derivative works of the Document.

     If the Cover Text requirement of section 3 is applicable to these
     copies of the Document, then if the Document is less than one half
     of the entire aggregate, the Document's Cover Texts may be placed
     on covers that bracket the Document within the aggregate, or the
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  8. TRANSLATION

     Translation is considered a kind of modification, so you may
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     translations of some or all Invariant Sections in addition to the
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     translation of this License, and all the license notices in the
     Document, and any Warranty Disclaimers, provided that you also
     include the original English version of this License and the
     original versions of those notices and disclaimers.  In case of a
     disagreement between the translation and the original version of
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     prevail.

     If a section in the Document is Entitled "Acknowledgements",
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     Preserve its Title (section 1) will typically require changing the
     actual title.

  9. TERMINATION

     You may not copy, modify, sublicense, or distribute the Document
     except as expressly provided for under this License.  Any other
     attempt to copy, modify, sublicense or distribute the Document is
     void, and will automatically terminate your rights under this
     License.  However, parties who have received copies, or rights,
     from you under this License will not have their licenses
     terminated so long as such parties remain in full compliance.

 10. FUTURE REVISIONS OF THIS LICENSE

     The Free Software Foundation may publish new, revised versions of
     the GNU Free Documentation License from time to time.  Such new
     versions will be similar in spirit to the present version, but may
     differ in detail to address new problems or concerns.  See
     `http://www.gnu.org/copyleft/'.

     Each version of the License is given a distinguishing version
     number.  If the Document specifies that a particular numbered
     version of this License "or any later version" applies to it, you
     have the option of following the terms and conditions either of
     that specified version or of any later version that has been
     published (not as a draft) by the Free Software Foundation.  If
     the Document does not specify a version number of this License,
     you may choose any version ever published (not as a draft) by the
     Free Software Foundation.

ADDENDUM: How to use this License for your documents
====================================================

To use this License in a document you have written, include a copy of
the License in the document and put the following copyright and license
notices just after the title page:

       Copyright (C)  YEAR  YOUR NAME.
       Permission is granted to copy, distribute and/or modify this document
       under the terms of the GNU Free Documentation License, Version 1.2
       or any later version published by the Free Software Foundation;
       with no Invariant Sections, no Front-Cover Texts, and no Back-Cover
       Texts.  A copy of the license is included in the section entitled ``GNU
       Free Documentation License''.

   If you have Invariant Sections, Front-Cover Texts and Back-Cover
Texts, replace the "with...Texts." line with this:

         with the Invariant Sections being LIST THEIR TITLES, with
         the Front-Cover Texts being LIST, and with the Back-Cover Texts
         being LIST.

   If you have Invariant Sections without Cover Texts, or some other
combination of the three, merge those two alternatives to suit the
situation.

   If your document contains nontrivial examples of program code, we
recommend releasing these examples in parallel under your choice of
free software license, such as the GNU General Public License, to
permit their use in free software.


File: libgomp.info,  Node: Funding,  Next: Index,  Prev: GNU Free Documentation License,  Up: Top

Funding Free Software
*********************

If you want to have more free software a few years from now, it makes
sense for you to help encourage people to contribute funds for its
development.  The most effective approach known is to encourage
commercial redistributors to donate.

   Users of free software systems can boost the pace of development by
encouraging for-a-fee distributors to donate part of their selling price
to free software developers--the Free Software Foundation, and others.

   The way to convince distributors to do this is to demand it and
expect it from them.  So when you compare distributors, judge them
partly by how much they give to free software development.  Show
distributors they must compete to be the one who gives the most.

   To make this approach work, you must insist on numbers that you can
compare, such as, "We will donate ten dollars to the Frobnitz project
for each disk sold."  Don't be satisfied with a vague promise, such as
"A portion of the profits are donated," since it doesn't give a basis
for comparison.

   Even a precise fraction "of the profits from this disk" is not very
meaningful, since creative accounting and unrelated business decisions
can greatly alter what fraction of the sales price counts as profit.
If the price you pay is $50, ten percent of the profit is probably less
than a dollar; it might be a few cents, or nothing at all.

   Some redistributors do development work themselves.  This is useful
too; but to keep everyone honest, you need to inquire how much they do,
and what kind.  Some kinds of development make much more long-term
difference than others.  For example, maintaining a separate version of
a program contributes very little; maintaining the standard version of a
program for the whole community contributes much.  Easy new ports
contribute little, since someone else would surely do them; difficult
ports such as adding a new CPU to the GNU Compiler Collection
contribute more; major new features or packages contribute the most.

   By establishing the idea that supporting further development is "the
proper thing to do" when distributing free software for a fee, we can
assure a steady flow of resources into making more free software.

     Copyright (C) 1994 Free Software Foundation, Inc.
     Verbatim copying and redistribution of this section is permitted
     without royalty; alteration is not permitted.


File: libgomp.info,  Node: Index,  Prev: Funding,  Up: Top

Index
*****

�[index�]
* Menu:

* Environment Variable <1>:              GOMP_STACKSIZE.        (line 6)
* Environment Variable <2>:              GOMP_CPU_AFFINITY.     (line 6)
* Environment Variable <3>:              OMP_WAIT_POLICY.       (line 6)
* Environment Variable <4>:              OMP_THREAD_LIMIT.      (line 6)
* Environment Variable <5>:              OMP_STACKSIZE.         (line 6)
* Environment Variable <6>:              OMP_SCHEDULE.          (line 6)
* Environment Variable <7>:              OMP_NUM_THREADS.       (line 6)
* Environment Variable <8>:              OMP_NESTED.            (line 6)
* Environment Variable <9>:              OMP_MAX_ACTIVE_LEVELS. (line 6)
* Environment Variable:                  OMP_DYNAMIC.           (line 6)
* FDL, GNU Free Documentation License:   GNU Free Documentation License.
                                                                (line 6)
* Implementation specific setting <1>:   GOMP_STACKSIZE.        (line 6)
* Implementation specific setting <2>:   OMP_SCHEDULE.          (line 6)
* Implementation specific setting <3>:   OMP_NUM_THREADS.       (line 6)
* Implementation specific setting:       OMP_NESTED.            (line 6)
* Introduction:                          Top.                   (line 6)



Tag Table:
Node: Top2039
Node: Enabling OpenMP3233
Node: Runtime Library Routines4018
Node: omp_get_active_level6393
Node: omp_get_ancestor_thread_num7084
Node: omp_get_dynamic7998
Node: omp_get_level8872
Node: omp_get_max_active_levels9483
Node: omp_get_max_threads10171
Node: omp_get_nested10923
Node: omp_get_num_procs11831
Node: omp_get_num_threads12345
Node: omp_get_schedule13415
Node: omp_get_team_size14322
Node: omp_get_thread_limit15280
Node: omp_get_thread_num15899
Node: omp_in_parallel16753
Node: omp_set_dynamic17399
Node: omp_set_max_active_levels18235
Node: omp_set_nested18997
Node: omp_set_num_threads19874
Node: omp_set_schedule20712
Node: omp_init_lock21756
Node: omp_set_lock22406
Node: omp_test_lock23255
Node: omp_unset_lock24282
Node: omp_destroy_lock25208
Node: omp_init_nest_lock25878
Node: omp_set_nest_lock26610
Node: omp_test_nest_lock27519
Node: omp_unset_nest_lock28617
Node: omp_destroy_nest_lock29626
Node: omp_get_wtick30374
Node: omp_get_wtime30961
Node: Environment Variables31744
Node: OMP_DYNAMIC32805
Node: OMP_MAX_ACTIVE_LEVELS33373
Node: OMP_NESTED34010
Node: OMP_NUM_THREADS34614
Node: OMP_SCHEDULE35187
Node: OMP_STACKSIZE35881
Node: OMP_THREAD_LIMIT36706
Node: OMP_WAIT_POLICY37299
Node: GOMP_CPU_AFFINITY37864
Node: GOMP_STACKSIZE39348
Node: The libgomp ABI40158
Node: Implementing MASTER construct40956
Node: Implementing CRITICAL construct41369
Node: Implementing ATOMIC construct42117
Node: Implementing FLUSH construct42598
Node: Implementing BARRIER construct42869
Node: Implementing THREADPRIVATE construct43138
Node: Implementing PRIVATE clause43790
Node: Implementing FIRSTPRIVATE LASTPRIVATE COPYIN and COPYPRIVATE clauses44371
Node: Implementing REDUCTION clause45686
Node: Implementing PARALLEL construct46242
Node: Implementing FOR construct47499
Node: Implementing ORDERED construct49497
Node: Implementing SECTIONS construct49803
Node: Implementing SINGLE construct50569
Node: Reporting Bugs51231
Node: Copying51539
Node: GNU Free Documentation License70749
Node: Funding93160
Node: Index95677

End Tag Table