# GNU libgomp

## Short Table of Contents

- 1 Enabling OpenMP
- 2 Runtime Library Routines
- 3 Environment Variables
- 4 The libgomp ABI
- 5 Reporting Bugs
- GNU GENERAL PUBLIC LICENSE
- GNU Free Documentation License
- Funding Free Software
- Index

## Table of Contents

- 1 Enabling OpenMP
- 2 Runtime Library Routines
  - 2.1 `omp_get_active_level` – Number of parallel regions
  - 2.2 `omp_get_ancestor_thread_num` – Ancestor thread ID
  - 2.3 `omp_get_dynamic` – Dynamic teams setting
  - 2.4 `omp_get_level` – Obtain the current nesting level
  - 2.5 `omp_get_max_active_levels` – Maximum number of active regions
  - 2.6 `omp_get_max_threads` – Maximum number of threads of parallel region
  - 2.7 `omp_get_nested` – Nested parallel regions
  - 2.8 `omp_get_num_procs` – Number of processors online
  - 2.9 `omp_get_num_threads` – Size of the active team
  - 2.10 `omp_get_schedule` – Obtain the runtime scheduling method
  - 2.11 `omp_get_team_size` – Number of threads in a team
  - 2.12 `omp_get_thread_limit` – Maximum number of threads
  - 2.13 `omp_get_thread_num` – Current thread ID
  - 2.14 `omp_in_parallel` – Whether a parallel region is active
  - 2.15 `omp_in_final` – Whether in final or included task region
  - 2.16 `omp_set_dynamic` – Enable/disable dynamic teams
  - 2.17 `omp_set_max_active_levels` – Limits the number of active parallel regions
  - 2.18 `omp_set_nested` – Enable/disable nested parallel regions
  - 2.19 `omp_set_num_threads` – Set upper team size limit
  - 2.20 `omp_set_schedule` – Set the runtime scheduling method
  - 2.21 `omp_init_lock` – Initialize simple lock
  - 2.22 `omp_set_lock` – Wait for and set simple lock
  - 2.23 `omp_test_lock` – Test and set simple lock if available
  - 2.24 `omp_unset_lock` – Unset simple lock
  - 2.25 `omp_destroy_lock` – Destroy simple lock
  - 2.26 `omp_init_nest_lock` – Initialize nested lock
  - 2.27 `omp_set_nest_lock` – Wait for and set nested lock
  - 2.28 `omp_test_nest_lock` – Test and set nested lock if available
  - 2.29 `omp_unset_nest_lock` – Unset nested lock
  - 2.30 `omp_destroy_nest_lock` – Destroy nested lock
  - 2.31 `omp_get_wtick` – Get timer precision
  - 2.32 `omp_get_wtime` – Elapsed wall clock time
- 3 Environment Variables
  - 3.1 `OMP_DYNAMIC` – Dynamic adjustment of threads
  - 3.2 `OMP_MAX_ACTIVE_LEVELS` – Set the maximum number of nested parallel regions
  - 3.3 `OMP_NESTED` – Nested parallel regions
  - 3.4 `OMP_NUM_THREADS` – Specifies the number of threads to use
  - 3.5 `OMP_SCHEDULE` – How threads are scheduled
  - 3.6 `OMP_STACKSIZE` – Set default thread stack size
  - 3.7 `OMP_THREAD_LIMIT` – Set the maximum number of threads
  - 3.8 `OMP_WAIT_POLICY` – How waiting threads are handled
  - 3.9 `OMP_PROC_BIND` – Whether theads may be moved between CPUs
  - 3.10 `GOMP_CPU_AFFINITY` – Bind threads to specific CPUs
  - 3.11 `GOMP_STACKSIZE` – Set default thread stack size
- 4 The libgomp ABI
  - 4.1 Implementing MASTER construct
  - 4.2 Implementing CRITICAL construct
  - 4.3 Implementing ATOMIC construct
  - 4.4 Implementing FLUSH construct
  - 4.5 Implementing BARRIER construct
  - 4.6 Implementing THREADPRIVATE construct
  - 4.7 Implementing PRIVATE clause
  - 4.8 Implementing FIRSTPRIVATE LASTPRIVATE COPYIN and COPYPRIVATE clauses
  - 4.9 Implementing REDUCTION clause
  - 4.10 Implementing PARALLEL construct
  - 4.11 Implementing FOR construct
  - 4.12 Implementing ORDERED construct
  - 4.13 Implementing SECTIONS construct
  - 4.14 Implementing SINGLE construct
- 5 Reporting Bugs
- GNU GENERAL PUBLIC LICENSE
  - Preamble
  - Appendix: How to Apply These Terms to Your New Programs
- GNU Free Documentation License
  - ADDENDUM: How to use this License for your documents
- Funding Free Software
- Index

# Introduction

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

## 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 (Runtime Library Routines).

A complete description of all OpenMP directives accepted may be found in the OpenMP Application Program Interface manual, version 3.1.

## 2 Runtime Library Routines

The runtime routines described here are defined by section 3 of the OpenMP specifications in version 3.1. The routines are structured in following three parts:

Control threads, processors and the parallel environment.

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

Portable, thread-based, wall clock timer.

### 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(void);`

Fortran:

  Interface: | `integer function omp_get_active_level()`

See also:

  omp_get_level, omp_get_max_active_levels, omp_set_max_active_levels

Reference:

  OpenMP specifications v3.1, section 3.2.19.

### 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 function omp_get_ancestor_thread_num(level)`
  | `integer level`

See also:

  omp_get_level, omp_get_thread_num, omp_get_team_size

Reference:

  OpenMP specifications v3.1, section 3.2.17.

### 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(void);`

Fortran:

  Interface: | `logical function omp_get_dynamic()`

See also:

  omp_set_dynamic, OMP_DYNAMIC

Reference:

  OpenMP specifications v3.1, section 3.2.8.

### 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(void);`

Fortran:

  Interface: | `integer function omp_level()`

See also:

  omp_get_active_level

Reference:

  OpenMP specifications v3.1, section 3.2.16.

### 2.5 `omp_get_max_active_levels` – Maximum number of active regions

Description:

  This function obtains the maximum allowed number of nested, active parallel regions.

C/C++

  Prototype: | `int omp_get_max_active_levels(void);`

Fortran:

  Interface: | `integer function omp_get_max_active_levels()`

See also:

  omp_set_max_active_levels, omp_get_active_level

Reference:

  OpenMP specifications v3.1, section 3.2.15.

### 2.6 `omp_get_max_threads` – Maximum number of threads of parallel region

Description:

  Return the maximum 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(void);`

Fortran:

  Interface: | `integer function omp_get_max_threads()`

See also:

  omp_set_num_threads, omp_set_dynamic, omp_get_thread_limit

Reference:

  OpenMP specifications v3.1, section 3.2.3.

### 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(void);`

Fortran:

  Interface: | `logical function omp_get_nested()`

See also:

  omp_set_nested, OMP_NESTED

Reference:

  OpenMP specifications v3.1, section 3.2.10.

### 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(void);`

Fortran:

  Interface: | `integer function omp_get_num_procs()`

Reference:

  OpenMP specifications v3.1, section 3.2.5.

### 2.9 `omp_get_num_threads` – Size of the active team

Description:

  Returns 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(void);`

Fortran:

  Interface: | `integer function omp_get_num_threads()`

See also:

  omp_get_max_threads, omp_set_num_threads, OMP_NUM_THREADS

Reference:

  OpenMP specifications v3.1, section 3.2.2.

### 2.10 `omp_get_schedule` – Obtain the runtime scheduling method

Description:

  Obtain the runtime scheduling method. The kind argument will be set to the value `omp_sched_static`, `omp_sched_dynamic`, `omp_sched_guided` or `omp_sched_auto`. The second argument, modifier, is set to the chunk size.

C/C++

  Prototype: | `void 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:

  omp_set_schedule, OMP_SCHEDULE

Reference:

  OpenMP specifications v3.1, section 3.2.12.

### 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_team_size(int level);`

Fortran:

  Interface: | `integer function omp_get_team_size(level)`
  | `integer level`

See also:

  omp_get_num_threads, omp_get_level, omp_get_ancestor_thread_num

Reference:

  OpenMP specifications v3.1, section 3.2.18.

### 2.12 `omp_get_thread_limit` – Maximum number of threads

Description:

  Return the maximum number of threads of the program.

C/C++:

  Prototype: | `int omp_get_thread_limit(void);`

Fortran:

  Interface: | `integer function omp_get_thread_limit()`

See also:

  omp_get_max_threads, OMP_THREAD_LIMIT

Reference:

  OpenMP specifications v3.1, section 3.2.13.

### 2.13 `omp_get_thread_num` – Current thread ID

Description:

  Returns a 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(void);`

Fortran:

  Interface: | `integer function omp_get_thread_num()`

See also:

  omp_get_num_threads, omp_get_ancestor_thread_num

Reference:

  OpenMP specifications v3.1, section 3.2.4.

### 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(void);`

Fortran:

  Interface: | `logical function omp_in_parallel()`

Reference:

  OpenMP specifications v3.1, section 3.2.6.

### 2.15 `omp_in_final` – Whether in final or included task region

Description:

  This function returns `true` if currently running in a final or included task region, `false` otherwise. Here, `true` and `false` represent their language-specific counterparts.

C/C++:

  Prototype: | `int omp_in_final(void);`

Fortran:

  Interface: | `logical function omp_in_final()`

Reference:

  OpenMP specifications v3.1, section 3.2.20.

### 2.16 `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 set);`

Fortran:

  Interface: | `subroutine omp_set_dynamic(set)`
  | `logical, intent(in) :: set`

See also:

  OMP_DYNAMIC, omp_get_dynamic

Reference:

  OpenMP specifications v3.1, section 3.2.7.

### 2.17 `omp_set_max_active_levels` – Limits the number of active parallel regions

Description:

  This function limits the maximum allowed number of nested, active parallel regions.

C/C++

  Prototype: | `void omp_set_max_active_levels(int max_levels);`

Fortran:

  Interface: | `subroutine omp_set_max_active_levels(max_levels)`
  | `integer max_levels`

See also:

  omp_get_max_active_levels, omp_get_active_level

Reference:

  OpenMP specifications v3.1, section 3.2.14.

### 2.18 `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_nested(int set);`

Fortran:

  Interface: | `subroutine omp_set_nested(set)`
  | `logical, intent(in) :: set`

See also:

  OMP_NESTED, omp_get_nested

Reference:

  OpenMP specifications v3.1, section 3.2.9.

### 2.19 `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 n);`

Fortran:

  Interface: | `subroutine omp_set_num_threads(n)`
  | `integer, intent(in) :: n`

See also:

  OMP_NUM_THREADS, omp_get_num_threads, omp_get_max_threads

Reference:

  OpenMP specifications v3.1, section 3.2.1.

### 2.20 `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`, `omp_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: | `void omp_set_schedule(omp_sched_t *kind, int *modifier);`

Fortran:

  Interface: | `subroutine omp_set_schedule(kind, modifier)`
  | `integer(kind=omp_sched_kind) kind`
  | `integer modifier`

See also:

  omp_get_schedule OMP_SCHEDULE

Reference:

  OpenMP specifications v3.1, section 3.2.11.

### 2.21 `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:

  omp_destroy_lock

Reference:

  OpenMP specifications v3.1, section 3.3.1.

### 2.22 `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(inout) :: lock`

See also:

  omp_init_lock, omp_test_lock, omp_unset_lock

Reference:

  OpenMP specifications v3.1, section 3.3.3.

### 2.23 `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: | `logical function omp_test_lock(lock)`
  | `integer(omp_lock_kind), intent(inout) :: lock`

See also:

  omp_init_lock, omp_set_lock, omp_set_lock

Reference:

  OpenMP specifications v3.1, section 3.3.5.

### 2.24 `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 or more threads attempted to set the lock before, one of them is chosen to, again, set the lock to itself.

C/C++:

  Prototype: | `void omp_unset_lock(omp_lock_t *lock);`

Fortran:

  Interface: | `subroutine omp_unset_lock(lock)`
  | `integer(omp_lock_kind), intent(inout) :: lock`

See also:

  omp_set_lock, omp_test_lock

Reference:

  OpenMP specifications v3.1, section 3.3.4.

### 2.25 `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 *lock);`

Fortran:

  Interface: | `subroutine omp_destroy_lock(lock)`
  | `integer(omp_lock_kind), intent(inout) :: lock`

See also:

  omp_init_lock

Reference:

  OpenMP specifications v3.1, section 3.3.2.

### 2.26 `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:

  omp_destroy_nest_lock

Reference:

  OpenMP specifications v3.1, section 3.3.1.

### 2.27 `omp_set_nest_lock` – Wait for and set nested 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 is 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(inout) :: lock`

See also:

  omp_init_nest_lock, omp_unset_nest_lock

Reference:

  OpenMP specifications v3.1, section 3.3.3.

### 2.28 `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: | `logical function omp_test_nest_lock(lock)`
  | `integer(omp_nest_lock_kind), intent(inout) :: lock`

See also:

  omp_init_lock, omp_set_lock, omp_set_lock

Reference:

  OpenMP specifications v3.1, section 3.3.5.

### 2.29 `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 to 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(inout) :: lock`

See also:

  omp_set_nest_lock

Reference:

  OpenMP specifications v3.1, section 3.3.4.

### 2.30 `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:

  omp_init_lock

Reference:

  OpenMP specifications v3.1, section 3.3.2.

### 2.31 `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(void);`

Fortran:

  Interface: | `double precision function omp_get_wtick()`

See also:

  omp_get_wtime

Reference:

  OpenMP specifications v3.1, section 3.4.2.

### 2.32 `omp_get_wtime` – Elapsed wall clock time

Description:

  Elapsed wall clock time in seconds. The time is measured per thread, no guarantee can be made that two distinct threads measure the same time. Time is measured from some "time in the past", which is an arbitrary time guaranteed not to change during the execution of the program.

C/C++:

  Prototype: | `double omp_get_wtime(void);`

Fortran:

  Interface: | `double precision function omp_get_wtime()`

See also:

  omp_get_wtick

Reference:

  OpenMP specifications v3.1, section 3.4.1.

## 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 3.1, while `GOMP_CPU_AFFINITY` and `GOMP_STACKSIZE` are GNU extensions.

### 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:

  omp_set_dynamic

Reference:

  OpenMP specifications v3.1, section 4.3

### 3.2 `OMP_MAX_ACTIVE_LEVELS` – Set the maximum number of nested parallel regions

Description:

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

See also:

  omp_set_max_active_levels

Reference:

  OpenMP specifications v3.1, section 4.8

### 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:

  omp_set_nested

Reference:

  OpenMP specifications v3.1, section 4.5

### 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 a comma-separated list of positive integers; the value specified the number of threads to use for the corresponding nested level. If undefined one thread per CPU is used.

See also:

  omp_set_num_threads

Reference:

  OpenMP specifications v3.1, section 4.2

### 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:

  omp_set_schedule

Reference:

  OpenMP specifications v3.1, sections 2.5.1 and 4.1

### 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 stack size cannot be set due to system constraints, an error is reported and the initial stack size is left unchanged. If undefined, the stack size is system dependent.

Reference:

  OpenMP specifications v3.1, sections 4.6

### 3.7 `OMP_THREAD_LIMIT` – Set the maximum number of threads

Description:

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

See also:

  OMP_NUM_THREADS omp_get_thread_limit

Reference:

  OpenMP specifications v3.1, section 4.9

### 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 v3.1, sections 4.7

### 3.9 `OMP_PROC_BIND` – Whether theads may be moved between CPUs

Description:

  Specifies whether threads may be moved between processors. If set to `true`, OpenMP theads should not be moved, if set to `false` they may be moved.

See also:

  GOMP_CPU_AFFINITY

Reference:

  OpenMP specifications v3.1, sections 4.4

### 3.10 `GOMP_CPU_AFFINITY` – Bind threads to specific CPUs

Description:

  Binds threads to specific CPUs. The variable should contain a space-separated or comma-separated list of CPUs. This list may contain different kinds 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.

See also:

  OMP_PROC_BIND

### 3.11 `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 stack size cannot be set due to system constraints, an error is reported and the initial stack size is left unchanged. If undefined, the stack size is system dependent.

See also:

  OMP_STACKSIZE

Reference:

  GCC Patches Mailinglist, GCC Patches Mailinglist

## 4 The libgomp ABI

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

### 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 this is not worthwhile though...

### 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 need to initialize this at startup.

### 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.

### 4.4 Implementing FLUSH construct

Expands to the `__sync_synchronize` builtin.

### 4.5 Implementing BARRIER construct

      void GOMP_barrier (void)

### 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.

### 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.

### 4.8 Implementing FIRSTPRIVATE LASTPRIVATE COPYIN and COPYPRIVATE clauses

This seems simple enough for PARALLEL blocks. Create a private struct for communicating between the 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.

It is not clear 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.

### 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.

### 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.

### 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 trickiness 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...

### 4.12 Implementing ORDERED construct

      void GOMP_ordered_start (void)
      void GOMP_ordered_end (void)

### 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 ();

### 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 ();

## 5 Reporting Bugs

Bugs in the GNU OpenMP implementation should be reported via bugzilla. For all cases, please add "openmp" to the keywords field in the bug report.

## GNU GENERAL PUBLIC LICENSE

Version 2, June 1991

    Copyright © 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

The licenses for most software are designed to take away your freedom to share and change it. By contrast, the GNU General Public License is intended to guarantee your freedom to share and change free software—to make sure the software is free for all its users. This General Public License applies to most of the Free Software Foundation’s software and to any other program whose authors commit to using it. (Some other Free Software Foundation software is covered by the GNU Library General Public License instead.) You can apply it to your programs, too.

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We protect your rights with two steps: (1) copyright the software, and (2) offer you this license which gives you legal permission to copy, distribute and/or modify the software.

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TERMS AND CONDITIONS FOR COPYING, DISTRIBUTION AND MODIFICATION

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    NO WARRANTY
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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 terms.

To do so, attach the following notices to the program. It is safest to attach them to the start of each source file to most effectively convey the exclusion of warranty; and each file should have at least the “copyright” line and a pointer to where the full notice is found.

    one line to give the program's name and a brief idea of what it does.
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    This program is free software; you can redistribute it and/or modify
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    the Free Software Foundation; either version 2 of the License, or
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    This program is distributed in the hope that it will be useful,
    but WITHOUT ANY WARRANTY; without even the implied warranty of
    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
    GNU General Public License for more details.

    You should have received a copy of the GNU General Public License
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Also add information on how to contact you by electronic and paper mail.

If the program is interactive, make it output a short notice like this when it starts in an interactive mode:

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The hypothetical commands ‘`show w`’ and ‘`show c`’ should show the appropriate parts of the General Public License. Of course, the commands you use may be called something other than ‘`show w`’ and ‘`show c`’; they could even be mouse-clicks or menu items—whatever suits your program.

You should also get your employer (if you work as a programmer) or your school, if any, to sign a “copyright disclaimer” for the program, if necessary. Here is a sample; alter the names:

    Yoyodyne, Inc., hereby disclaims all copyright interest in the program
    `Gnomovision' (which makes passes at compilers) written by James Hacker.

    signature of Ty Coon, 1 April 1989
    Ty Coon, President of Vice

This General Public License does not permit incorporating your program into proprietary programs. If your program is a subroutine library, you may consider it more useful to permit linking proprietary applications with the library. If this is what you want to do, use the GNU Library General Public License instead of this License.

## GNU Free Documentation License

Version 1.3, 3 November 2008

    Copyright © 2000, 2001, 2002, 2007, 2008 Free Software Foundation, Inc.
    http://fsf.org/

    Everyone is permitted to copy and distribute verbatim copies
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   A “Transparent” copy of the Document means a machine-readable copy, represented in a format whose specification is available to the general public, that is suitable for revising the document straightforwardly with generic text editors or (for images composed of pixels) generic paint programs or (for drawings) some widely available drawing editor, and that is suitable for input to text formatters or for automatic translation to a variety of formats suitable for input to text formatters. A copy made in an otherwise Transparent file format whose markup, or absence of markup, has been arranged to thwart or discourage subsequent modification by readers is not Transparent. An image format is not Transparent if used for any substantial amount of text. A copy that is not “Transparent” is called “Opaque”.

   Examples of suitable formats for Transparent copies include plain ASCII without markup, Texinfo input format, LaTeX input format, SGML or XML using a publicly available DTD, and standard-conforming simple HTML, PostScript or PDF designed for human modification. Examples of transparent image formats include PNG, XCF and JPG. Opaque formats include proprietary formats that can be read and edited only by proprietary word processors, SGML or XML for which the DTD and/or processing tools are not generally available, and the machine-generated HTML, PostScript or PDF produced by some word processors for output purposes only.

   The “Title Page” means, for a printed book, the title page itself, plus such following pages as are needed to hold, legibly, the material this License requires to appear in the title page. For works in formats which do not have any title page as such, “Title Page” means the text near the most prominent appearance of the work’s title, preceding the beginning of the body of the text.

   The “publisher” means any person or entity that distributes copies of the Document to the public.

   A section “Entitled XYZ” means a named subunit of the Document whose title either is precisely XYZ or contains XYZ in parentheses following text that translates XYZ in another language. (Here XYZ stands for a specific section name mentioned below, such as “Acknowledgements”, “Dedications”, “Endorsements”, or “History”.) To “Preserve the Title” of such a section when you modify the Document means that it remains a section “Entitled XYZ” according to this definition.

   The Document may include Warranty Disclaimers next to the notice which states that this License applies to the Document. These Warranty Disclaimers are considered to be included by reference in this License, but only as regards disclaiming warranties: any other implication that these Warranty Disclaimers may have is void and has no effect on the meaning of this License.

3. VERBATIM COPYING

   You may copy and distribute the Document in any medium, either commercially or noncommercially, provided that this License, the copyright notices, and the license notice saying this License applies to the Document are reproduced in all copies, and that you add no other conditions whatsoever to those of this License. You may not use technical measures to obstruct or control the reading or further copying of the copies you make or distribute. However, you may accept compensation in exchange for copies. If you distribute a large enough number of copies you must also follow the conditions in section 3.

   You may also lend copies, under the same conditions stated above, and you may publicly display copies.

4. COPYING IN QUANTITY

   If you publish printed copies (or copies in media that commonly have printed covers) of the Document, numbering more than 100, and the Document’s license notice requires Cover Texts, you must enclose the copies in covers that carry, clearly and legibly, all these Cover Texts: Front-Cover Texts on the front cover, and Back-Cover Texts on the back cover. Both covers must also clearly and legibly identify you as the publisher of these copies. The front cover must present the full title with all words of the title equally prominent and visible. You may add other material on the covers in addition. Copying with changes limited to the covers, as long as they preserve the title of the Document and satisfy these conditions, can be treated as verbatim copying in other respects.

   If the required texts for either cover are too voluminous to fit legibly, you should put the first ones listed (as many as fit reasonably) on the actual cover, and continue the rest onto adjacent pages.

   If you publish or distribute Opaque copies of the Document numbering more than 100, you must either include a machine-readable Transparent copy along with each Opaque copy, or state in or with each Opaque copy a computer-network location from which the general network-using public has access to download using public-standard network protocols a complete Transparent copy of the Document, free of added material. If you use the latter option, you must take reasonably prudent steps, when you begin distribution of Opaque copies in quantity, to ensure that this Transparent copy will remain thus accessible at the stated location until at least one year after the last time you distribute an Opaque copy (directly or through your agents or retailers) of that edition to the public.

   It is requested, but not required, that you contact the authors of the Document well before redistributing any large number of copies, to give them a chance to provide you with an updated version of the Document.

5. MODIFICATIONS

   You may copy and distribute a Modified Version of the Document under the conditions of sections 2 and 3 above, provided that you release the Modified Version under precisely this License, with the Modified Version filling the role of the Document, thus licensing distribution and modification of the Modified Version to whoever possesses a copy of it. In addition, you must do these things in the Modified Version:

   1. Use in the Title Page (and on the covers, if any) a title distinct from that of the Document, and from those of previous versions (which should, if there were any, be listed in the History section of the Document). You may use the same title as a previous version if the original publisher of that version gives permission.
   2. List on the Title Page, as authors, one or more persons or entities responsible for authorship of the modifications in the Modified Version, together with at least five of the principal authors of the Document (all of its principal authors, if it has fewer than five), unless they release you from this requirement.
   3. State on the Title page the name of the publisher of the Modified Version, as the publisher.
   4. Preserve all the copyright notices of the Document.
   5. Add an appropriate copyright notice for your modifications adjacent to the other copyright notices.
   6. Include, immediately after the copyright notices, a license notice giving the public permission to use the Modified Version under the terms of this License, in the form shown in the Addendum below.
   7. Preserve in that license notice the full lists of Invariant Sections and required Cover Texts given in the Document’s license notice.
   8. Include an unaltered copy of this License.
   9. Preserve the section Entitled “History”, Preserve its Title, and add to it an item stating at least the title, year, new authors, and publisher of the Modified Version as given on the Title Page. If there is no section Entitled “History” in the Document, create one stating the title, year, authors, and publisher of the Document as given on its Title Page, then add an item describing the Modified Version as stated in the previous sentence.
   10. Preserve the network location, if any, given in the Document for public access to a Transparent copy of the Document, and likewise the network locations given in the Document for previous versions it was based on. These may be placed in the “History” section. You may omit a network location for a work that was published at least four years before the Document itself, or if the original publisher of the version it refers to gives permission.
   11. For any section Entitled “Acknowledgements” or “Dedications”, Preserve the Title of the section, and preserve in the section all the substance and tone of each of the contributor acknowledgements and/or dedications given therein.
   12. Preserve all the Invariant Sections of the Document, unaltered in their text and in their titles. Section numbers or the equivalent are not considered part of the section titles.
   13. Delete any section Entitled “Endorsements”. Such a section may not be included in the Modified Version.
   14. Do not retitle any existing section to be Entitled “Endorsements” or to conflict in title with any Invariant Section.
   15. 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 parties—for example, statements of peer review or that the text has been approved by an organization as the authoritative definition of a standard.

   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 of the list of Cover Texts in the Modified Version. Only one passage of Front-Cover Text and one of Back-Cover Text may be added by (or through arrangements made by) any one entity. If the Document already includes a cover text for the same cover, previously added by you or by arrangement made by the same entity you are acting on behalf of, you may not add another; but you may 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.

6. 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 but different contents, make the title of each such section unique 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 unique number. Make the same adjustment to the section titles in 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.”

7. 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.

8. 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 electronic equivalent of covers if the Document is in electronic form. Otherwise they must appear on printed covers that bracket the whole aggregate.

9. TRANSLATION

   Translation is considered a kind of modification, so you may distribute translations of the Document under the terms of section 4. Replacing Invariant Sections with translations requires special permission from their copyright holders, but you may include translations of some or all Invariant Sections in addition to the original versions of these Invariant Sections. You may include a 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 this License or a notice or disclaimer, the original version will prevail.

   If a section in the Document is Entitled “Acknowledgements”, “Dedications”, or “History”, the requirement (section 4) to Preserve its Title (section 1) will typically require changing the actual title.

10. TERMINATION

    You may not copy, modify, sublicense, or distribute the Document except as expressly provided under this License. Any attempt otherwise to copy, modify, sublicense, or distribute it is void, and will automatically terminate your rights under this License.

    However, if you cease all violation of this License, then your license from a particular copyright holder is reinstated (a) provisionally, unless and until the copyright holder explicitly and finally terminates your license, and (b) permanently, if the copyright holder fails to notify you of the violation by some reasonable means prior to 60 days after the cessation.

    Moreover, your license from a particular copyright holder is reinstated permanently if the copyright holder notifies you of the violation by some reasonable means, this is the first time you have received notice of violation of this License (for any work) from that copyright holder, and you cure the violation prior to 30 days after your receipt of the notice.

    Termination of your rights under this section does not terminate the licenses of parties who have received copies or rights from you under this License. If your rights have been terminated and not permanently reinstated, receipt of a copy of some or all of the same material does not give you any rights to use it.

11. 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. If the Document specifies that a proxy can decide which future versions of this License can be used, that proxy’s public statement of acceptance of a version permanently authorizes you to choose that version for the Document.

12. RELICENSING

    “Massive Multiauthor Collaboration Site” (or “MMC Site”) means any World Wide Web server that publishes copyrightable works and also provides prominent facilities for anybody to edit those works. A public wiki that anybody can edit is an example of such a server. A “Massive Multiauthor Collaboration” (or “MMC”) contained in the site means any set of copyrightable works thus published on the MMC site.

    “CC-BY-SA” means the Creative Commons Attribution-Share Alike 3.0 license published by Creative Commons Corporation, a not-for-profit corporation with a principal place of business in San Francisco, California, as well as future copyleft versions of that license published by that same organization.

    “Incorporate” means to publish or republish a Document, in whole or in part, as part of another Document.

    An MMC is “eligible for relicensing” if it is licensed under this License, and if all works that were first published under this License somewhere other than this MMC, and subsequently incorporated in whole or in part into the MMC, (1) had no cover texts or invariant sections, and (2) were thus incorporated prior to November 1, 2008.

    The operator of an MMC Site may republish an MMC contained in the site under CC-BY-SA on the same site at any time before August 1, 2009, provided the MMC is eligible for relicensing.

### 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 1.3
      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.

## 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 © 1994 Free Software Foundation, Inc.
    Verbatim copying and redistribution of this section is permitted
    without royalty; alteration is not permitted.

## Index

Jump to: | E F I

| Index Entry |  | Section

E |  |
| Environment Variable: |  | OMP_DYNAMIC
| Environment Variable: |  | OMP_MAX_ACTIVE_LEVELS
| Environment Variable: |  | OMP_NESTED
| Environment Variable: |  | OMP_NUM_THREADS
| Environment Variable: |  | OMP_SCHEDULE
| Environment Variable: |  | OMP_STACKSIZE
| Environment Variable: |  | OMP_THREAD_LIMIT
| Environment Variable: |  | OMP_WAIT_POLICY
| Environment Variable: |  | OMP_PROC_BIND
| Environment Variable: |  | GOMP_CPU_AFFINITY
| Environment Variable: |  | GOMP_STACKSIZE

F |  |
| FDL, GNU Free Documentation License: |  | GNU Free Documentation License

I |  |
| Implementation specific setting: |  | OMP_NESTED
| Implementation specific setting: |  | OMP_NUM_THREADS
| Implementation specific setting: |  | OMP_SCHEDULE
| Implementation specific setting: |  | GOMP_STACKSIZE
| Introduction: |  | Top

Jump to: | E F I