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1 | \input texinfo @c -*-texinfo-*- |
2 | ||
3 | @c %**start of header | |
4 | @setfilename libgomp.info | |
5 | @settitle GNU libgomp | |
6 | @c %**end of header | |
7 | ||
8 | ||
9 | @copying | |
10 | Copyright @copyright{} 2006 Free Software Foundation, Inc. | |
11 | ||
12 | Permission is granted to copy, distribute and/or modify this document | |
13 | under the terms of the GNU Free Documentation License, Version 1.1 or | |
14 | any later version published by the Free Software Foundation; with the | |
15 | Invariant Sections being ``GNU General Public License'' and ``Funding | |
16 | Free Software'', the Front-Cover | |
17 | texts being (a) (see below), and with the Back-Cover Texts being (b) | |
18 | (see below). A copy of the license is included in the section entitled | |
19 | ``GNU Free Documentation License''. | |
20 | ||
21 | (a) The FSF's Front-Cover Text is: | |
22 | ||
23 | A GNU Manual | |
24 | ||
25 | (b) The FSF's Back-Cover Text is: | |
26 | ||
27 | You have freedom to copy and modify this GNU Manual, like GNU | |
28 | software. Copies published by the Free Software Foundation raise | |
29 | funds for GNU development. | |
30 | @end copying | |
31 | ||
32 | @ifinfo | |
33 | @dircategory GNU Libraries | |
34 | @direntry | |
35 | * libgomp: (libgomp). GNU OpenMP runtime library | |
36 | @end direntry | |
37 | ||
38 | This manual documents the GNU implementation of the OpenMP API for | |
39 | multi-platform shared-memory parallel programming in C/C++ and Fortran. | |
40 | ||
41 | Published by the Free Software Foundation | |
42 | 51 Franklin Street, Fifth Floor | |
43 | Boston, MA 02110-1301 USA | |
44 | ||
45 | @insertcopying | |
46 | @end ifinfo | |
47 | ||
48 | ||
49 | @setchapternewpage odd | |
50 | ||
51 | @titlepage | |
52 | @title The GNU OpenMP Implementation | |
53 | @page | |
54 | @vskip 0pt plus 1filll | |
55 | @comment For the @value{version-GCC} Version* | |
56 | @sp 1 | |
57 | Published by the Free Software Foundation @* | |
58 | 51 Franklin Street, Fifth Floor@* | |
59 | Boston, MA 02110-1301, USA@* | |
60 | @sp 1 | |
61 | @insertcopying | |
62 | @end titlepage | |
63 | ||
64 | @summarycontents | |
65 | @contents | |
66 | @page | |
67 | ||
68 | ||
69 | @node Top | |
70 | @top Introduction | |
71 | @cindex Introduction | |
72 | ||
73 | This manual documents the usage of libgomp, the GNU implementation of the | |
74 | @uref{http://www.openmp.org, OpenMP} Application Programming Interface (API) | |
75 | for multi-platform shared-memory parallel programming in C/C++ and Fortran. | |
76 | ||
77 | ||
78 | ||
79 | @comment | |
80 | @comment When you add a new menu item, please keep the right hand | |
81 | @comment aligned to the same column. Do not use tabs. This provides | |
82 | @comment better formatting. | |
83 | @comment | |
84 | @menu | |
85 | * Enabling OpenMP:: How to enable OpenMP for your applications. | |
86 | * Runtime Library Routines:: The OpenMP runtime application programming | |
87 | interface. | |
88 | * Environment Variables:: Influencing runtime behavior with environment | |
89 | variables. | |
90 | * The libgomp ABI:: Notes on the external ABI presented by libgomp. | |
91 | * Reporting Bugs:: How to report bugs in GNU OpenMP. | |
92 | * Copying:: GNU general public license says | |
93 | how you can copy and share libgomp. | |
94 | * GNU Free Documentation License:: | |
95 | How you can copy and share this manual. | |
96 | * Funding:: How to help assure continued work for free | |
97 | software. | |
98 | * Index:: Index of this documentation. | |
99 | @end menu | |
100 | ||
101 | ||
102 | @c --------------------------------------------------------------------- | |
103 | @c Enabling OpenMP | |
104 | @c --------------------------------------------------------------------- | |
105 | ||
106 | @node Enabling OpenMP | |
107 | @chapter Enabling OpenMP | |
108 | ||
109 | To activate the OpenMP extensions for C/C++ and Fortran, the compile-time | |
110 | flag @command{-fopenmp} must be specified. This enables the OpenMP directive | |
111 | @code{#pragma omp} in C/C++ and @code{!$omp} directives in free form, | |
112 | @code{c$omp}, @code{*$omp} and @code{!$omp} directives in fixed form, | |
113 | @code{!$} conditional compilation sentinels in free form and @code{c$}, | |
114 | @code{*$} and @code{!$} sentinels in fixed form, for Fortran. The flag also | |
115 | arranges for automatic linking of the OpenMP runtime library | |
116 | (@ref{Runtime Library Routines}). | |
117 | ||
118 | A complete description of all OpenMP directives accepted may be found in | |
119 | the @uref{http://www.openmp.org, OpenMP Application Program Interface} manual, | |
120 | version 2.5. | |
121 | ||
122 | ||
123 | @c --------------------------------------------------------------------- | |
124 | @c Runtime Library Routines | |
125 | @c --------------------------------------------------------------------- | |
126 | ||
127 | @node Runtime Library Routines | |
128 | @chapter Runtime Library Routines | |
129 | ||
130 | The runtime routines described here are defined by section 3 of the OpenMP | |
131 | specifications in version 2.5. | |
132 | ||
133 | Control threads, processors and the parallel environment. | |
134 | ||
135 | @menu | |
136 | * omp_get_dynamic:: Dynamic teams setting | |
137 | * omp_get_max_threads:: Maximum number of threads | |
138 | * omp_get_nested:: Nested parallel regions | |
139 | * omp_get_num_procs:: Number of processors online | |
140 | * omp_get_num_threads:: Size of the active team | |
141 | * omp_get_thread_num:: Current thread ID | |
142 | * omp_in_parallel:: Whether a parallel region is active | |
143 | * omp_set_dynamic:: Enable/disable dynamic teams | |
144 | * omp_set_nested:: Enable/disable nested parallel regions | |
145 | * omp_set_num_threads:: Set upper team size limit | |
146 | @end menu | |
147 | ||
148 | Initialize, set, test, unset and destroy simple and nested locks. | |
149 | ||
150 | @menu | |
151 | * omp_init_lock:: Initialize simple lock | |
152 | * omp_set_lock:: Wait for and set simple lock | |
153 | * omp_test_lock:: Test and set simple lock if available | |
154 | * omp_unset_lock:: Unset simple lock | |
155 | * omp_destroy_lock:: Destroy simple lock | |
156 | * omp_init_nest_lock:: Initialize nested lock | |
157 | * omp_set_nest_lock:: Wait for and set simple lock | |
158 | * omp_test_nest_lock:: Test and set nested lock if available | |
159 | * omp_unset_nest_lock:: Unset nested lock | |
160 | * omp_destroy_nest_lock:: Destroy nested lock | |
161 | @end menu | |
162 | ||
163 | Portable, thread-based, wall clock timer. | |
164 | ||
165 | @menu | |
166 | * omp_get_wtick:: Get timer precision. | |
167 | * omp_get_wtime:: Elapsed wall clock time. | |
168 | @end menu | |
169 | ||
170 | @node omp_get_dynamic | |
171 | @section @code{omp_get_dynamic} -- Dynamic teams setting | |
172 | @table @asis | |
173 | @item @emph{Description}: | |
174 | This function returns @code{true} if enabled, @code{false} otherwise. | |
175 | Here, @code{true} and @code{false} represent their language-specific | |
176 | counterparts. | |
177 | ||
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178 | The dynamic team setting may be initialized at startup by the |
179 | @code{OMP_DYNAMIC} environment variable or at runtime using | |
180 | @code{omp_set_dynamic}. If undefined, dynamic adjustment is | |
181 | disabled by default. | |
182 | ||
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183 | @item @emph{C/C++}: |
184 | @multitable @columnfractions .20 .80 | |
185 | @item @emph{Prototype}: @tab @code{int omp_get_dynamic();} | |
186 | @end multitable | |
187 | ||
188 | @item @emph{Fortran}: | |
189 | @multitable @columnfractions .20 .80 | |
190 | @item @emph{Interface}: @tab @code{logical function omp_get_dynamic()} | |
191 | @end multitable | |
192 | ||
193 | @item @emph{See also}: | |
14734fc7 | 194 | @ref{omp_set_dynamic}, @ref{OMP_DYNAMIC} |
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195 | |
196 | @item @emph{Reference}: | |
197 | @uref{http://www.openmp.org/, OpenMP specifications v2.5}, section 3.2.8. | |
198 | @end table | |
199 | ||
200 | ||
201 | ||
202 | @node omp_get_max_threads | |
203 | @section @code{omp_get_max_threads} -- Maximum number of threads | |
204 | @table @asis | |
205 | @item @emph{Description}: | |
206 | Return the maximum number of threads used for parallel regions that do | |
207 | not use the clause @code{num_threads}. | |
208 | ||
209 | @item @emph{C/C++}: | |
210 | @multitable @columnfractions .20 .80 | |
211 | @item @emph{Prototype}: @tab @code{int omp_get_max_threads();} | |
212 | @end multitable | |
213 | ||
214 | @item @emph{Fortran}: | |
215 | @multitable @columnfractions .20 .80 | |
216 | @item @emph{Interface}: @tab @code{integer function omp_get_max_threads()} | |
217 | @end multitable | |
218 | ||
219 | @item @emph{See also}: | |
220 | @ref{omp_set_num_threads}, @ref{omp_set_dynamic} | |
221 | ||
222 | @item @emph{Reference}: | |
223 | @uref{http://www.openmp.org/, OpenMP specifications v2.5}, section 3.2.3. | |
224 | @end table | |
225 | ||
226 | ||
227 | ||
228 | @node omp_get_nested | |
229 | @section @code{omp_get_nested} -- Nested parallel regions | |
230 | @table @asis | |
231 | @item @emph{Description}: | |
232 | This function returns @code{true} if nested parallel regions are | |
233 | enabled, @code{false} otherwise. Here, @code{true} and @code{false} | |
234 | represent their language-specific counterparts. | |
235 | ||
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236 | Nested parallel regions may be initialized at startup by the |
237 | @code{OMP_NESTED} environment variable or at runtime using | |
238 | @code{omp_set_nested}. If undefined, nested parallel regions are | |
239 | disabled by default. | |
240 | ||
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241 | @item @emph{C/C++}: |
242 | @multitable @columnfractions .20 .80 | |
243 | @item @emph{Prototype}: @tab @code{int omp_get_nested();} | |
244 | @end multitable | |
245 | ||
246 | @item @emph{Fortran}: | |
247 | @multitable @columnfractions .20 .80 | |
248 | @item @emph{Interface}: @tab @code{integer function omp_get_nested()} | |
249 | @end multitable | |
250 | ||
251 | @item @emph{See also}: | |
14734fc7 | 252 | @ref{omp_set_nested}, @ref{OMP_NESTED} |
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253 | |
254 | @item @emph{Reference}: | |
255 | @uref{http://www.openmp.org/, OpenMP specifications v2.5}, section 3.2.10. | |
256 | @end table | |
257 | ||
258 | ||
259 | ||
260 | @node omp_get_num_procs | |
261 | @section @code{omp_get_num_procs} -- Number of processors online | |
262 | @table @asis | |
263 | @item @emph{Description}: | |
264 | Returns the number of processors online. | |
265 | ||
266 | @item @emph{C/C++}: | |
267 | @multitable @columnfractions .20 .80 | |
268 | @item @emph{Prototype}: @tab @code{int omp_get_num_procs();} | |
269 | @end multitable | |
270 | ||
271 | @item @emph{Fortran}: | |
272 | @multitable @columnfractions .20 .80 | |
273 | @item @emph{Interface}: @tab @code{integer function omp_get_num_procs()} | |
274 | @end multitable | |
275 | ||
276 | @item @emph{Reference}: | |
277 | @uref{http://www.openmp.org/, OpenMP specifications v2.5}, section 3.2.5. | |
278 | @end table | |
279 | ||
280 | ||
281 | ||
282 | @node omp_get_num_threads | |
283 | @section @code{omp_get_num_threads} -- Size of the active team | |
284 | @table @asis | |
285 | @item @emph{Description}: | |
286 | The number of threads in the current team. In a sequential section of | |
287 | the program @code{omp_get_num_threads} returns 1. | |
288 | ||
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289 | The default team size may be initialized at startup by the |
290 | @code{OMP_NUM_THREADS} environment variable. At runtime, the size | |
291 | of the current team may be set either by the @code{NUM_THREADS} | |
292 | clause or by @code{omp_set_num_threads}. If none of the above were | |
293 | used to define a specific value and @code{OMP_DYNAMIC} is disabled, | |
294 | one thread per CPU online is used. | |
295 | ||
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296 | @item @emph{C/C++}: |
297 | @multitable @columnfractions .20 .80 | |
298 | @item @emph{Prototype}: @tab @code{int omp_get_num_threads();} | |
299 | @end multitable | |
300 | ||
301 | @item @emph{Fortran}: | |
302 | @multitable @columnfractions .20 .80 | |
303 | @item @emph{Interface}: @tab @code{integer function omp_get_num_threads()} | |
304 | @end multitable | |
305 | ||
306 | @item @emph{See also}: | |
307 | @ref{omp_get_max_threads}, @ref{omp_set_num_threads}, @ref{OMP_NUM_THREADS} | |
308 | ||
309 | @item @emph{Reference}: | |
310 | @uref{http://www.openmp.org/, OpenMP specifications v2.5}, section 3.2.2. | |
311 | @end table | |
312 | ||
313 | ||
314 | ||
315 | @node omp_get_thread_num | |
316 | @section @code{omp_get_thread_num} -- Current thread ID | |
317 | @table @asis | |
318 | @item @emph{Description}: | |
319 | Unique thread identification number. In a sequential parts of the program, | |
320 | @code{omp_get_thread_num} always returns 0. In parallel regions the return | |
321 | value varies from 0 to @code{omp_get_max_threads}-1 inclusive. The return | |
322 | value of the master thread of a team is always 0. | |
323 | ||
324 | @item @emph{C/C++}: | |
325 | @multitable @columnfractions .20 .80 | |
326 | @item @emph{Prototype}: @tab @code{int omp_get_thread_num();} | |
327 | @end multitable | |
328 | ||
329 | @item @emph{Fortran}: | |
330 | @multitable @columnfractions .20 .80 | |
331 | @item @emph{Interface}: @tab @code{integer function omp_get_thread_num()} | |
332 | @end multitable | |
333 | ||
334 | @item @emph{See also}: | |
335 | @ref{omp_get_max_threads} | |
336 | ||
337 | @item @emph{Reference}: | |
338 | @uref{http://www.openmp.org/, OpenMP specifications v2.5}, section 3.2.4. | |
339 | @end table | |
340 | ||
341 | ||
342 | ||
343 | @node omp_in_parallel | |
344 | @section @code{omp_in_parallel} -- Whether a parallel region is active | |
345 | @table @asis | |
346 | @item @emph{Description}: | |
347 | This function returns @code{true} if currently running in parallel, | |
348 | @code{false} otherwise. Here, @code{true} and @code{false} represent | |
349 | their language-specific counterparts. | |
350 | ||
351 | @item @emph{C/C++}: | |
352 | @multitable @columnfractions .20 .80 | |
353 | @item @emph{Prototype}: @tab @code{int omp_in_parallel();} | |
354 | @end multitable | |
355 | ||
356 | @item @emph{Fortran}: | |
357 | @multitable @columnfractions .20 .80 | |
358 | @item @emph{Interface}: @tab @code{logical function omp_in_parallel()} | |
359 | @end multitable | |
360 | ||
361 | @item @emph{Reference}: | |
362 | @uref{http://www.openmp.org/, OpenMP specifications v2.5}, section 3.2.6. | |
363 | @end table | |
364 | ||
365 | ||
366 | @node omp_set_dynamic | |
367 | @section @code{omp_set_dynamic} -- Enable/disable dynamic teams | |
368 | @table @asis | |
369 | @item @emph{Description}: | |
370 | Enable or disable the dynamic adjustment of the number of threads | |
371 | within a team. The function takes the language-specific equivalent | |
372 | of @code{true} and @code{false}, where @code{true} enables dynamic | |
373 | adjustment of team sizes and @code{false} disables it. | |
374 | ||
375 | @item @emph{C/C++}: | |
376 | @multitable @columnfractions .20 .80 | |
377 | @item @emph{Prototype}: @tab @code{void omp_set_dynamic(int);} | |
378 | @end multitable | |
379 | ||
380 | @item @emph{Fortran}: | |
381 | @multitable @columnfractions .20 .80 | |
382 | @item @emph{Interface}: @tab @code{subroutine omp_set_dynamic(set)} | |
383 | @item @tab @code{integer, intent(in) :: set} | |
384 | @end multitable | |
385 | ||
386 | @item @emph{See also}: | |
387 | @ref{OMP_DYNAMIC}, @ref{omp_get_dynamic} | |
388 | ||
389 | @item @emph{Reference}: | |
390 | @uref{http://www.openmp.org/, OpenMP specifications v2.5}, section 3.2.7. | |
391 | @end table | |
392 | ||
393 | ||
394 | ||
395 | @node omp_set_nested | |
396 | @section @code{omp_set_nested} -- Enable/disable nested parallel regions | |
397 | @table @asis | |
398 | @item @emph{Description}: | |
f1b0882e | 399 | Enable or disable nested parallel regions, i.e., whether team members |
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400 | are allowed to create new teams. The function takes the language-specific |
401 | equivalent of @code{true} and @code{false}, where @code{true} enables | |
402 | dynamic adjustment of team sizes and @code{false} disables it. | |
403 | ||
404 | @item @emph{C/C++}: | |
405 | @multitable @columnfractions .20 .80 | |
406 | @item @emph{Prototype}: @tab @code{void omp_set_dynamic(int);} | |
407 | @end multitable | |
408 | ||
409 | @item @emph{Fortran}: | |
410 | @multitable @columnfractions .20 .80 | |
411 | @item @emph{Interface}: @tab @code{subroutine omp_set_dynamic(set)} | |
412 | @item @tab @code{integer, intent(in) :: set} | |
413 | @end multitable | |
414 | ||
415 | @item @emph{See also}: | |
416 | @ref{OMP_NESTED}, @ref{omp_get_nested} | |
417 | ||
418 | @item @emph{Reference}: | |
419 | @uref{http://www.openmp.org/, OpenMP specifications v2.5}, section 3.2.9. | |
420 | @end table | |
421 | ||
422 | ||
423 | ||
424 | @node omp_set_num_threads | |
425 | @section @code{omp_set_num_threads} -- Set upper team size limit | |
426 | @table @asis | |
427 | @item @emph{Description}: | |
428 | Specifies the number of threads used by default in subsequent parallel | |
429 | sections, if those do not specify a @code{num_threads} clause. The | |
430 | argument of @code{omp_set_num_threads} shall be a positive integer. | |
431 | ||
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432 | @item @emph{C/C++}: |
433 | @multitable @columnfractions .20 .80 | |
434 | @item @emph{Prototype}: @tab @code{void omp_set_num_threads(int);} | |
435 | @end multitable | |
436 | ||
437 | @item @emph{Fortran}: | |
438 | @multitable @columnfractions .20 .80 | |
439 | @item @emph{Interface}: @tab @code{subroutine omp_set_num_threads(set)} | |
440 | @item @tab @code{integer, intent(in) :: set} | |
441 | @end multitable | |
442 | ||
443 | @item @emph{See also}: | |
444 | @ref{OMP_NUM_THREADS}, @ref{omp_get_num_threads}, @ref{omp_get_max_threads} | |
445 | ||
446 | @item @emph{Reference}: | |
447 | @uref{http://www.openmp.org/, OpenMP specifications v2.5}, section 3.2.1. | |
448 | @end table | |
449 | ||
450 | ||
451 | ||
452 | @node omp_init_lock | |
453 | @section @code{omp_init_lock} -- Initialize simple lock | |
454 | @table @asis | |
455 | @item @emph{Description}: | |
456 | Initialize a simple lock. After initialization, the lock is in | |
457 | an unlocked state. | |
458 | ||
459 | @item @emph{C/C++}: | |
460 | @multitable @columnfractions .20 .80 | |
461 | @item @emph{Prototype}: @tab @code{void omp_init_lock(omp_lock_t *lock);} | |
462 | @end multitable | |
463 | ||
464 | @item @emph{Fortran}: | |
465 | @multitable @columnfractions .20 .80 | |
466 | @item @emph{Interface}: @tab @code{subroutine omp_init_lock(lock)} | |
467 | @item @tab @code{integer(omp_lock_kind), intent(out) :: lock} | |
468 | @end multitable | |
469 | ||
470 | @item @emph{See also}: | |
471 | @ref{omp_destroy_lock} | |
472 | ||
473 | @item @emph{Reference}: | |
474 | @uref{http://www.openmp.org/, OpenMP specifications v2.5}, section 3.3.1. | |
475 | @end table | |
476 | ||
477 | ||
478 | ||
479 | @node omp_set_lock | |
480 | @section @code{omp_set_lock} -- Wait for and set simple lock | |
481 | @table @asis | |
482 | @item @emph{Description}: | |
483 | Before setting a simple lock, the lock variable must be initialized by | |
484 | @code{omp_init_lock}. The calling thread is blocked until the lock | |
485 | is available. If the lock is already held by the current thread, | |
486 | a deadlock occurs. | |
487 | ||
488 | @item @emph{C/C++}: | |
489 | @multitable @columnfractions .20 .80 | |
490 | @item @emph{Prototype}: @tab @code{void omp_set_lock(omp_lock_t *lock);} | |
491 | @end multitable | |
492 | ||
493 | @item @emph{Fortran}: | |
494 | @multitable @columnfractions .20 .80 | |
495 | @item @emph{Interface}: @tab @code{subroutine omp_set_lock(lock)} | |
496 | @item @tab @code{integer(omp_lock_kind), intent(out) :: lock} | |
497 | @end multitable | |
498 | ||
499 | @item @emph{See also}: | |
500 | @ref{omp_init_lock}, @ref{omp_test_lock}, @ref{omp_unset_lock} | |
501 | ||
502 | @item @emph{Reference}: | |
503 | @uref{http://www.openmp.org/, OpenMP specifications v2.5}, section 3.3.3. | |
504 | @end table | |
505 | ||
506 | ||
507 | ||
508 | @node omp_test_lock | |
509 | @section @code{omp_test_lock} -- Test and set simple lock if available | |
510 | @table @asis | |
511 | @item @emph{Description}: | |
512 | Before setting a simple lock, the lock variable must be initialized by | |
513 | @code{omp_init_lock}. Contrary to @code{omp_set_lock}, @code{omp_test_lock} | |
514 | does not block if the lock is not available. This function returns | |
515 | @code{true} upon success,@code{false} otherwise. Here, @code{true} and | |
516 | @code{false} represent their language-specific counterparts. | |
517 | ||
518 | @item @emph{C/C++}: | |
519 | @multitable @columnfractions .20 .80 | |
520 | @item @emph{Prototype}: @tab @code{int omp_test_lock(omp_lock_t *lock);} | |
521 | @end multitable | |
522 | ||
523 | @item @emph{Fortran}: | |
524 | @multitable @columnfractions .20 .80 | |
525 | @item @emph{Interface}: @tab @code{subroutine omp_test_lock(lock)} | |
526 | @item @tab @code{logical(omp_logical_kind) :: omp_test_lock} | |
527 | @item @tab @code{integer(omp_lock_kind), intent(out) :: lock} | |
528 | @end multitable | |
529 | ||
530 | @item @emph{See also}: | |
531 | @ref{omp_init_lock}, @ref{omp_set_lock}, @ref{omp_set_lock} | |
532 | ||
533 | @item @emph{Reference}: | |
534 | @uref{http://www.openmp.org/, OpenMP specifications v2.5}, section 3.3.5. | |
535 | @end table | |
536 | ||
537 | ||
538 | ||
539 | @node omp_unset_lock | |
540 | @section @code{omp_unset_lock} -- Unset simple lock | |
541 | @table @asis | |
542 | @item @emph{Description}: | |
543 | A simple lock about to be unset must have been locked by @code{omp_set_lock} | |
544 | or @code{omp_test_lock} before. In addition, the lock must be held by the | |
545 | thread calling @code{omp_unset_lock}. Then, the lock becomes unlocked. If one | |
546 | ore more threads attempted to set the lock before, one of them is chosen to, | |
547 | again, set the lock for itself. | |
548 | ||
549 | @item @emph{C/C++}: | |
550 | @multitable @columnfractions .20 .80 | |
551 | @item @emph{Prototype}: @tab @code{void omp_unset_lock(omp_lock_t *lock);} | |
552 | @end multitable | |
553 | ||
554 | @item @emph{Fortran}: | |
555 | @multitable @columnfractions .20 .80 | |
556 | @item @emph{Interface}: @tab @code{subroutine omp_unset_lock(lock)} | |
557 | @item @tab @code{integer(omp_lock_kind), intent(out) :: lock} | |
558 | @end multitable | |
559 | ||
560 | @item @emph{See also}: | |
561 | @ref{omp_set_lock}, @ref{omp_test_lock} | |
562 | ||
563 | @item @emph{Reference}: | |
564 | @uref{http://www.openmp.org/, OpenMP specifications v2.5}, section 3.3.4. | |
565 | @end table | |
566 | ||
567 | ||
568 | ||
569 | @node omp_destroy_lock | |
570 | @section @code{omp_destroy_lock} -- Destroy simple lock | |
571 | @table @asis | |
572 | @item @emph{Description}: | |
573 | Destroy a simple lock. In order to be destroyed, a simple lock must be | |
574 | in the unlocked state. | |
575 | ||
576 | @item @emph{C/C++}: | |
577 | @multitable @columnfractions .20 .80 | |
578 | @item @emph{Prototype}: @tab @code{void omp_destroy_lock(omp_lock_t *);} | |
579 | @end multitable | |
580 | ||
581 | @item @emph{Fortran}: | |
582 | @multitable @columnfractions .20 .80 | |
583 | @item @emph{Interface}: @tab @code{subroutine omp_destroy_lock(lock)} | |
584 | @item @tab @code{integer(omp_lock_kind), intent(inout) :: lock} | |
585 | @end multitable | |
586 | ||
587 | @item @emph{See also}: | |
588 | @ref{omp_init_lock} | |
589 | ||
590 | @item @emph{Reference}: | |
591 | @uref{http://www.openmp.org/, OpenMP specifications v2.5}, section 3.3.2. | |
592 | @end table | |
593 | ||
594 | ||
595 | ||
596 | @node omp_init_nest_lock | |
597 | @section @code{omp_init_nest_lock} -- Initialize nested lock | |
598 | @table @asis | |
599 | @item @emph{Description}: | |
600 | Initialize a nested lock. After initialization, the lock is in | |
601 | an unlocked state and the nesting count is set to zero. | |
602 | ||
603 | @item @emph{C/C++}: | |
604 | @multitable @columnfractions .20 .80 | |
605 | @item @emph{Prototype}: @tab @code{void omp_init_nest_lock(omp_nest_lock_t *lock);} | |
606 | @end multitable | |
607 | ||
608 | @item @emph{Fortran}: | |
609 | @multitable @columnfractions .20 .80 | |
610 | @item @emph{Interface}: @tab @code{subroutine omp_init_nest_lock(lock)} | |
611 | @item @tab @code{integer(omp_nest_lock_kind), intent(out) :: lock} | |
612 | @end multitable | |
613 | ||
614 | @item @emph{See also}: | |
615 | @ref{omp_destroy_nest_lock} | |
616 | ||
617 | @item @emph{Reference}: | |
618 | @uref{http://www.openmp.org/, OpenMP specifications v2.5}, section 3.3.1. | |
619 | @end table | |
620 | ||
621 | ||
622 | @node omp_set_nest_lock | |
623 | @section @code{omp_set_nest_lock} -- Wait for and set simple lock | |
624 | @table @asis | |
625 | @item @emph{Description}: | |
626 | Before setting a nested lock, the lock variable must be initialized by | |
627 | @code{omp_init_nest_lock}. The calling thread is blocked until the lock | |
628 | is available. If the lock is already held by the current thread, the | |
629 | nesting count for the lock in incremented. | |
630 | ||
631 | @item @emph{C/C++}: | |
632 | @multitable @columnfractions .20 .80 | |
633 | @item @emph{Prototype}: @tab @code{void omp_set_nest_lock(omp_nest_lock_t *lock);} | |
634 | @end multitable | |
635 | ||
636 | @item @emph{Fortran}: | |
637 | @multitable @columnfractions .20 .80 | |
638 | @item @emph{Interface}: @tab @code{subroutine omp_set_nest_lock(lock)} | |
639 | @item @tab @code{integer(omp_nest_lock_kind), intent(out) :: lock} | |
640 | @end multitable | |
641 | ||
642 | @item @emph{See also}: | |
643 | @ref{omp_init_nest_lock}, @ref{omp_unset_nest_lock} | |
644 | ||
645 | @item @emph{Reference}: | |
646 | @uref{http://www.openmp.org/, OpenMP specifications v2.5}, section 3.3.3. | |
647 | @end table | |
648 | ||
649 | ||
650 | ||
651 | @node omp_test_nest_lock | |
652 | @section @code{omp_test_nest_lock} -- Test and set nested lock if available | |
653 | @table @asis | |
654 | @item @emph{Description}: | |
655 | Before setting a nested lock, the lock variable must be initialized by | |
656 | @code{omp_init_nest_lock}. Contrary to @code{omp_set_nest_lock}, | |
657 | @code{omp_test_nest_lock} does not block if the lock is not available. | |
658 | If the lock is already held by the current thread, the new nesting count | |
659 | is returned. Otherwise, the return value equals zero. | |
660 | ||
661 | @item @emph{C/C++}: | |
662 | @multitable @columnfractions .20 .80 | |
663 | @item @emph{Prototype}: @tab @code{int omp_test_nest_lock(omp_nest_lock_t *lock);} | |
664 | @end multitable | |
665 | ||
666 | @item @emph{Fortran}: | |
667 | @multitable @columnfractions .20 .80 | |
668 | @item @emph{Interface}: @tab @code{integer function omp_test_nest_lock(lock)} | |
669 | @item @tab @code{integer(omp_integer_kind) :: omp_test_nest_lock} | |
670 | @item @tab @code{integer(omp_nest_lock_kind), intent(inout) :: lock} | |
671 | @end multitable | |
672 | ||
673 | ||
674 | @item @emph{See also}: | |
675 | @ref{omp_init_lock}, @ref{omp_set_lock}, @ref{omp_set_lock} | |
676 | ||
677 | @item @emph{Reference}: | |
678 | @uref{http://www.openmp.org/, OpenMP specifications v2.5}, section 3.3.5. | |
679 | @end table | |
680 | ||
681 | ||
682 | ||
683 | @node omp_unset_nest_lock | |
684 | @section @code{omp_unset_nest_lock} -- Unset nested lock | |
685 | @table @asis | |
686 | @item @emph{Description}: | |
687 | A nested lock about to be unset must have been locked by @code{omp_set_nested_lock} | |
688 | or @code{omp_test_nested_lock} before. In addition, the lock must be held by the | |
689 | thread calling @code{omp_unset_nested_lock}. If the nesting count drops to zero, the | |
690 | lock becomes unlocked. If one ore more threads attempted to set the lock before, | |
691 | one of them is chosen to, again, set the lock for itself. | |
692 | ||
693 | @item @emph{C/C++}: | |
694 | @multitable @columnfractions .20 .80 | |
695 | @item @emph{Prototype}: @tab @code{void omp_unset_nest_lock(omp_nest_lock_t *lock);} | |
696 | @end multitable | |
697 | ||
698 | @item @emph{Fortran}: | |
699 | @multitable @columnfractions .20 .80 | |
700 | @item @emph{Interface}: @tab @code{subroutine omp_unset_nest_lock(lock)} | |
701 | @item @tab @code{integer(omp_nest_lock_kind), intent(out) :: lock} | |
702 | @end multitable | |
703 | ||
704 | @item @emph{See also}: | |
705 | @ref{omp_set_nest_lock} | |
706 | ||
707 | @item @emph{Reference}: | |
708 | @uref{http://www.openmp.org/, OpenMP specifications v2.5}, section 3.3.4. | |
709 | @end table | |
710 | ||
711 | ||
712 | ||
713 | @node omp_destroy_nest_lock | |
714 | @section @code{omp_destroy_nest_lock} -- Destroy nested lock | |
715 | @table @asis | |
716 | @item @emph{Description}: | |
717 | Destroy a nested lock. In order to be destroyed, a nested lock must be | |
718 | in the unlocked state and its nesting count must equal zero. | |
719 | ||
720 | @item @emph{C/C++}: | |
721 | @multitable @columnfractions .20 .80 | |
722 | @item @emph{Prototype}: @tab @code{void omp_destroy_nest_lock(omp_nest_lock_t *);} | |
723 | @end multitable | |
724 | ||
725 | @item @emph{Fortran}: | |
726 | @multitable @columnfractions .20 .80 | |
727 | @item @emph{Interface}: @tab @code{subroutine omp_destroy_nest_lock(lock)} | |
728 | @item @tab @code{integer(omp_nest_lock_kind), intent(inout) :: lock} | |
729 | @end multitable | |
730 | ||
731 | @item @emph{See also}: | |
732 | @ref{omp_init_lock} | |
733 | ||
734 | @item @emph{Reference}: | |
735 | @uref{http://www.openmp.org/, OpenMP specifications v2.5}, section 3.3.2. | |
736 | @end table | |
737 | ||
738 | ||
739 | ||
740 | @node omp_get_wtick | |
741 | @section @code{omp_get_wtick} -- Get timer precision | |
742 | @table @asis | |
743 | @item @emph{Description}: | |
f1b0882e | 744 | Gets the timer precision, i.e., the number of seconds between two |
3721b9e1 DF |
745 | successive clock ticks. |
746 | ||
747 | @item @emph{C/C++}: | |
748 | @multitable @columnfractions .20 .80 | |
749 | @item @emph{Prototype}: @tab @code{double omp_get_wtick();} | |
750 | @end multitable | |
751 | ||
752 | @item @emph{Fortran}: | |
753 | @multitable @columnfractions .20 .80 | |
754 | @item @emph{Interface}: @tab @code{double precision function omp_get_wtick()} | |
755 | @end multitable | |
756 | ||
757 | @item @emph{See also}: | |
758 | @ref{omp_get_wtime} | |
759 | ||
760 | @item @emph{Reference}: | |
761 | @uref{http://www.openmp.org/, OpenMP specifications v2.5}, section 3.4.2. | |
762 | @end table | |
763 | ||
764 | ||
765 | ||
766 | @node omp_get_wtime | |
767 | @section @code{omp_get_wtime} -- Elapsed wall clock time | |
768 | @table @asis | |
769 | @item @emph{Description}: | |
770 | Elapsed wall clock time in seconds. The time is measured per thread, no | |
771 | guarantee can bee made that two distinct threads measure the same time. | |
772 | Time is measured from some "time in the past". On POSIX compliant systems | |
773 | the seconds since the Epoch (00:00:00 UTC, January 1, 1970) are returned. | |
774 | ||
775 | @item @emph{C/C++}: | |
776 | @multitable @columnfractions .20 .80 | |
777 | @item @emph{Prototype}: @tab @code{double omp_get_wtime();} | |
778 | @end multitable | |
779 | ||
780 | @item @emph{Fortran}: | |
781 | @multitable @columnfractions .20 .80 | |
782 | @item @emph{Interface}: @tab @code{double precision function omp_get_wtime()} | |
783 | @end multitable | |
784 | ||
785 | @item @emph{See also}: | |
786 | @ref{omp_get_wtick} | |
787 | ||
788 | @item @emph{Reference}: | |
789 | @uref{http://www.openmp.org/, OpenMP specifications v2.5}, section 3.4.1. | |
790 | @end table | |
791 | ||
792 | ||
793 | ||
794 | @c --------------------------------------------------------------------- | |
795 | @c Environment Variables | |
796 | @c --------------------------------------------------------------------- | |
797 | ||
798 | @node Environment Variables | |
799 | @chapter Environment Variables | |
800 | ||
801 | The variables @env{OMP_DYNAMIC}, @env{OMP_NESTED}, @env{OMP_NUM_THREADS} and | |
802 | @env{OMP_SCHEDULE} are defined by section 4 of the OpenMP specifications in | |
803 | version 2.5, while @env{GOMP_CPU_AFFINITY} and @env{GOMP_STACKSIZE} are GNU | |
804 | extensions. | |
805 | ||
806 | @menu | |
807 | * OMP_DYNAMIC:: Dynamic adjustment of threads | |
808 | * OMP_NESTED:: Nested parallel regions | |
809 | * OMP_NUM_THREADS:: Specifies the number of threads to use | |
810 | * OMP_SCHEDULE:: How threads are scheduled | |
811 | * GOMP_CPU_AFFINITY:: Bind threads to specific CPUs | |
812 | * GOMP_STACKSIZE:: Set default thread stack size | |
813 | @end menu | |
814 | ||
815 | ||
816 | @node OMP_DYNAMIC | |
817 | @section @env{OMP_DYNAMIC} -- Dynamic adjustment of threads | |
818 | @cindex Environment Variable | |
14734fc7 | 819 | @cindex Implementation specific setting |
3721b9e1 DF |
820 | @table @asis |
821 | @item @emph{Description}: | |
822 | Enable or disable the dynamic adjustment of the number of threads | |
823 | within a team. The value of this environment variable shall be | |
7c2b7f45 DF |
824 | @code{TRUE} or @code{FALSE}. If undefined, dynamic adjustment is |
825 | disabled by default. | |
3721b9e1 DF |
826 | |
827 | @item @emph{See also}: | |
828 | @ref{omp_set_dynamic} | |
829 | ||
830 | @item @emph{Reference}: | |
831 | @uref{http://www.openmp.org/, OpenMP specifications v2.5}, section 4.3 | |
832 | @end table | |
833 | ||
834 | ||
835 | ||
836 | @node OMP_NESTED | |
837 | @section @env{OMP_NESTED} -- Nested parallel regions | |
838 | @cindex Environment Variable | |
14734fc7 | 839 | @cindex Implementation specific setting |
3721b9e1 DF |
840 | @table @asis |
841 | @item @emph{Description}: | |
f1b0882e | 842 | Enable or disable nested parallel regions, i.e., whether team members |
3721b9e1 | 843 | are allowed to create new teams. The value of this environment variable |
7c2b7f45 DF |
844 | shall be @code{TRUE} or @code{FALSE}. If undefined, nested parallel |
845 | regions are disabled by default. | |
3721b9e1 DF |
846 | |
847 | @item @emph{See also}: | |
848 | @ref{omp_set_nested} | |
849 | ||
850 | @item @emph{Reference}: | |
851 | @uref{http://www.openmp.org/, OpenMP specifications v2.5}, section 4.4 | |
852 | @end table | |
853 | ||
854 | ||
855 | ||
856 | @node OMP_NUM_THREADS | |
857 | @section @env{OMP_NUM_THREADS} -- Specifies the number of threads to use | |
858 | @cindex Environment Variable | |
14734fc7 | 859 | @cindex Implementation specific setting |
3721b9e1 DF |
860 | @table @asis |
861 | @item @emph{Description}: | |
14734fc7 DF |
862 | Specifies the default number of threads to use in parallel regions. The |
863 | value of this variable shall be positive integer. If undefined one thread | |
864 | per CPU online is used. | |
3721b9e1 DF |
865 | |
866 | @item @emph{See also}: | |
867 | @ref{omp_set_num_threads} | |
868 | ||
869 | @item @emph{Reference}: | |
870 | @uref{http://www.openmp.org/, OpenMP specifications v2.5}, section 4.2 | |
871 | @end table | |
872 | ||
873 | ||
874 | ||
875 | @node OMP_SCHEDULE | |
876 | @section @env{OMP_SCHEDULE} -- How threads are scheduled | |
877 | @cindex Environment Variable | |
14734fc7 | 878 | @cindex Implementation specific setting |
3721b9e1 DF |
879 | @table @asis |
880 | @item @emph{Description}: | |
881 | Allows to specify @code{schedule type} and @code{chunk size}. | |
882 | The value of the variable shall have the form: @code{type[,chunk]} where | |
883 | @code{type} is one of @code{static}, @code{dynamic} or @code{guided}. | |
7c2b7f45 DF |
884 | The optional @code{chunk size} shall be a positive integer. If undefined, |
885 | dynamic scheduling and a chunk size of 1 is used. | |
3721b9e1 DF |
886 | |
887 | @item @emph{Reference}: | |
7c2b7f45 | 888 | @uref{http://www.openmp.org/, OpenMP specifications v2.5}, sections 2.5.1 and 4.1 |
3721b9e1 DF |
889 | @end table |
890 | ||
891 | ||
892 | ||
893 | @node GOMP_CPU_AFFINITY | |
894 | @section @env{GOMP_CPU_AFFINITY} -- Bind threads to specific CPUs | |
895 | @cindex Environment Variable | |
896 | @table @asis | |
897 | @item @emph{Description}: | |
898 | A patch for this extension has been submitted, but was not yet applied at the | |
899 | time of writing. | |
900 | ||
901 | @item @emph{Reference}: | |
902 | @uref{http://gcc.gnu.org/ml/gcc-patches/2006-05/msg00982.html, | |
903 | GCC Patches Mailinglist} | |
904 | @uref{http://gcc.gnu.org/ml/gcc-patches/2006-05/msg01133.html, | |
905 | GCC Patches Mailinglist} | |
906 | @end table | |
907 | ||
908 | ||
909 | ||
910 | @node GOMP_STACKSIZE | |
911 | @section @env{GOMP_STACKSIZE} -- Set default thread stack size | |
912 | @cindex Environment Variable | |
14734fc7 | 913 | @cindex Implementation specific setting |
3721b9e1 DF |
914 | @table @asis |
915 | @item @emph{Description}: | |
916 | Set the default thread stack size in kilobytes. This is in opposition | |
917 | to @code{pthread_attr_setstacksize} which gets the number of bytes as an | |
918 | argument. If the stacksize can not be set due to system constraints, an | |
7c2b7f45 DF |
919 | error is reported and the initial stacksize is left unchanged. If undefined, |
920 | the stack size is system dependent. | |
3721b9e1 DF |
921 | |
922 | @item @emph{Reference}: | |
923 | @uref{http://gcc.gnu.org/ml/gcc-patches/2006-06/msg00493.html, | |
924 | GCC Patches Mailinglist}, | |
925 | @uref{http://gcc.gnu.org/ml/gcc-patches/2006-06/msg00496.html, | |
926 | GCC Patches Mailinglist} | |
927 | @end table | |
928 | ||
929 | ||
930 | ||
931 | @c --------------------------------------------------------------------- | |
932 | @c The libgomp ABI | |
933 | @c --------------------------------------------------------------------- | |
934 | ||
935 | @node The libgomp ABI | |
936 | @chapter The libgomp ABI | |
937 | ||
938 | The following sections present notes on the external ABI as | |
939 | presented by libgomp. Only maintainers should need them. | |
940 | ||
941 | @menu | |
942 | * Implementing MASTER construct:: | |
943 | * Implementing CRITICAL construct:: | |
944 | * Implementing ATOMIC construct:: | |
945 | * Implementing FLUSH construct:: | |
946 | * Implementing BARRIER construct:: | |
947 | * Implementing THREADPRIVATE construct:: | |
948 | * Implementing PRIVATE clause:: | |
949 | * Implementing FIRSTPRIVATE LASTPRIVATE COPYIN and COPYPRIVATE clauses:: | |
950 | * Implementing REDUCTION clause:: | |
951 | * Implementing PARALLEL construct:: | |
952 | * Implementing FOR construct:: | |
953 | * Implementing ORDERED construct:: | |
954 | * Implementing SECTIONS construct:: | |
955 | * Implementing SINGLE construct:: | |
956 | @end menu | |
957 | ||
958 | ||
959 | @node Implementing MASTER construct | |
960 | @section Implementing MASTER construct | |
961 | ||
962 | @smallexample | |
963 | if (omp_get_thread_num () == 0) | |
964 | block | |
965 | @end smallexample | |
966 | ||
967 | Alternately, we generate two copies of the parallel subfunction | |
968 | and only include this in the version run by the master thread. | |
969 | Surely that's not worthwhile though... | |
970 | ||
971 | ||
972 | ||
973 | @node Implementing CRITICAL construct | |
974 | @section Implementing CRITICAL construct | |
975 | ||
976 | Without a specified name, | |
977 | ||
978 | @smallexample | |
979 | void GOMP_critical_start (void); | |
980 | void GOMP_critical_end (void); | |
981 | @end smallexample | |
982 | ||
983 | so that we don't get COPY relocations from libgomp to the main | |
984 | application. | |
985 | ||
986 | With a specified name, use omp_set_lock and omp_unset_lock with | |
987 | name being transformed into a variable declared like | |
988 | ||
989 | @smallexample | |
990 | omp_lock_t gomp_critical_user_<name> __attribute__((common)) | |
991 | @end smallexample | |
992 | ||
993 | Ideally the ABI would specify that all zero is a valid unlocked | |
994 | state, and so we wouldn't actually need to initialize this at | |
995 | startup. | |
996 | ||
997 | ||
998 | ||
999 | @node Implementing ATOMIC construct | |
1000 | @section Implementing ATOMIC construct | |
1001 | ||
1002 | The target should implement the @code{__sync} builtins. | |
1003 | ||
1004 | Failing that we could add | |
1005 | ||
1006 | @smallexample | |
1007 | void GOMP_atomic_enter (void) | |
1008 | void GOMP_atomic_exit (void) | |
1009 | @end smallexample | |
1010 | ||
1011 | which reuses the regular lock code, but with yet another lock | |
1012 | object private to the library. | |
1013 | ||
1014 | ||
1015 | ||
1016 | @node Implementing FLUSH construct | |
1017 | @section Implementing FLUSH construct | |
1018 | ||
1019 | Expands to the @code{__sync_synchronize} builtin. | |
1020 | ||
1021 | ||
1022 | ||
1023 | @node Implementing BARRIER construct | |
1024 | @section Implementing BARRIER construct | |
1025 | ||
1026 | @smallexample | |
1027 | void GOMP_barrier (void) | |
1028 | @end smallexample | |
1029 | ||
1030 | ||
1031 | @node Implementing THREADPRIVATE construct | |
1032 | @section Implementing THREADPRIVATE construct | |
1033 | ||
1034 | In _most_ cases we can map this directly to @code{__thread}. Except | |
1035 | that OMP allows constructors for C++ objects. We can either | |
1036 | refuse to support this (how often is it used?) or we can | |
1037 | implement something akin to .ctors. | |
1038 | ||
1039 | Even more ideally, this ctor feature is handled by extensions | |
1040 | to the main pthreads library. Failing that, we can have a set | |
1041 | of entry points to register ctor functions to be called. | |
1042 | ||
1043 | ||
1044 | ||
1045 | @node Implementing PRIVATE clause | |
1046 | @section Implementing PRIVATE clause | |
1047 | ||
1048 | In association with a PARALLEL, or within the lexical extent | |
1049 | of a PARALLEL block, the variable becomes a local variable in | |
1050 | the parallel subfunction. | |
1051 | ||
1052 | In association with FOR or SECTIONS blocks, create a new | |
1053 | automatic variable within the current function. This preserves | |
1054 | the semantic of new variable creation. | |
1055 | ||
1056 | ||
1057 | ||
1058 | @node Implementing FIRSTPRIVATE LASTPRIVATE COPYIN and COPYPRIVATE clauses | |
1059 | @section Implementing FIRSTPRIVATE LASTPRIVATE COPYIN and COPYPRIVATE clauses | |
1060 | ||
1061 | Seems simple enough for PARALLEL blocks. Create a private | |
1062 | struct for communicating between parent and subfunction. | |
1063 | In the parent, copy in values for scalar and "small" structs; | |
1064 | copy in addresses for others TREE_ADDRESSABLE types. In the | |
1065 | subfunction, copy the value into the local variable. | |
1066 | ||
1067 | Not clear at all what to do with bare FOR or SECTION blocks. | |
1068 | The only thing I can figure is that we do something like | |
1069 | ||
1070 | @smallexample | |
1071 | #pragma omp for firstprivate(x) lastprivate(y) | |
1072 | for (int i = 0; i < n; ++i) | |
1073 | body; | |
1074 | @end smallexample | |
1075 | ||
1076 | which becomes | |
1077 | ||
1078 | @smallexample | |
1079 | @{ | |
1080 | int x = x, y; | |
1081 | ||
1082 | // for stuff | |
1083 | ||
1084 | if (i == n) | |
1085 | y = y; | |
1086 | @} | |
1087 | @end smallexample | |
1088 | ||
1089 | where the "x=x" and "y=y" assignments actually have different | |
1090 | uids for the two variables, i.e. not something you could write | |
1091 | directly in C. Presumably this only makes sense if the "outer" | |
1092 | x and y are global variables. | |
1093 | ||
1094 | COPYPRIVATE would work the same way, except the structure | |
1095 | broadcast would have to happen via SINGLE machinery instead. | |
1096 | ||
1097 | ||
1098 | ||
1099 | @node Implementing REDUCTION clause | |
1100 | @section Implementing REDUCTION clause | |
1101 | ||
1102 | The private struct mentioned in the previous section should have | |
1103 | a pointer to an array of the type of the variable, indexed by the | |
1104 | thread's @var{team_id}. The thread stores its final value into the | |
1105 | array, and after the barrier the master thread iterates over the | |
1106 | array to collect the values. | |
1107 | ||
1108 | ||
1109 | @node Implementing PARALLEL construct | |
1110 | @section Implementing PARALLEL construct | |
1111 | ||
1112 | @smallexample | |
1113 | #pragma omp parallel | |
1114 | @{ | |
1115 | body; | |
1116 | @} | |
1117 | @end smallexample | |
1118 | ||
1119 | becomes | |
1120 | ||
1121 | @smallexample | |
1122 | void subfunction (void *data) | |
1123 | @{ | |
1124 | use data; | |
1125 | body; | |
1126 | @} | |
1127 | ||
1128 | setup data; | |
1129 | GOMP_parallel_start (subfunction, &data, num_threads); | |
1130 | subfunction (&data); | |
1131 | GOMP_parallel_end (); | |
1132 | @end smallexample | |
1133 | ||
1134 | @smallexample | |
1135 | void GOMP_parallel_start (void (*fn)(void *), void *data, unsigned num_threads) | |
1136 | @end smallexample | |
1137 | ||
1138 | The @var{FN} argument is the subfunction to be run in parallel. | |
1139 | ||
1140 | The @var{DATA} argument is a pointer to a structure used to | |
1141 | communicate data in and out of the subfunction, as discussed | |
f1b0882e | 1142 | above with respect to FIRSTPRIVATE et al. |
3721b9e1 DF |
1143 | |
1144 | The @var{NUM_THREADS} argument is 1 if an IF clause is present | |
1145 | and false, or the value of the NUM_THREADS clause, if | |
1146 | present, or 0. | |
1147 | ||
1148 | The function needs to create the appropriate number of | |
1149 | threads and/or launch them from the dock. It needs to | |
1150 | create the team structure and assign team ids. | |
1151 | ||
1152 | @smallexample | |
1153 | void GOMP_parallel_end (void) | |
1154 | @end smallexample | |
1155 | ||
1156 | Tears down the team and returns us to the previous @code{omp_in_parallel()} state. | |
1157 | ||
1158 | ||
1159 | ||
1160 | @node Implementing FOR construct | |
1161 | @section Implementing FOR construct | |
1162 | ||
1163 | @smallexample | |
1164 | #pragma omp parallel for | |
1165 | for (i = lb; i <= ub; i++) | |
1166 | body; | |
1167 | @end smallexample | |
1168 | ||
1169 | becomes | |
1170 | ||
1171 | @smallexample | |
1172 | void subfunction (void *data) | |
1173 | @{ | |
1174 | long _s0, _e0; | |
1175 | while (GOMP_loop_static_next (&_s0, &_e0)) | |
1176 | @{ | |
1177 | long _e1 = _e0, i; | |
1178 | for (i = _s0; i < _e1; i++) | |
1179 | body; | |
1180 | @} | |
1181 | GOMP_loop_end_nowait (); | |
1182 | @} | |
1183 | ||
1184 | GOMP_parallel_loop_static (subfunction, NULL, 0, lb, ub+1, 1, 0); | |
1185 | subfunction (NULL); | |
1186 | GOMP_parallel_end (); | |
1187 | @end smallexample | |
1188 | ||
1189 | @smallexample | |
1190 | #pragma omp for schedule(runtime) | |
1191 | for (i = 0; i < n; i++) | |
1192 | body; | |
1193 | @end smallexample | |
1194 | ||
1195 | becomes | |
1196 | ||
1197 | @smallexample | |
1198 | @{ | |
1199 | long i, _s0, _e0; | |
1200 | if (GOMP_loop_runtime_start (0, n, 1, &_s0, &_e0)) | |
1201 | do @{ | |
1202 | long _e1 = _e0; | |
1203 | for (i = _s0, i < _e0; i++) | |
1204 | body; | |
1205 | @} while (GOMP_loop_runtime_next (&_s0, _&e0)); | |
1206 | GOMP_loop_end (); | |
1207 | @} | |
1208 | @end smallexample | |
1209 | ||
1210 | Note that while it looks like there is trickyness to propagating | |
1211 | a non-constant STEP, there isn't really. We're explicitly allowed | |
1212 | to evaluate it as many times as we want, and any variables involved | |
1213 | should automatically be handled as PRIVATE or SHARED like any other | |
1214 | variables. So the expression should remain evaluable in the | |
1215 | subfunction. We can also pull it into a local variable if we like, | |
1216 | but since its supposed to remain unchanged, we can also not if we like. | |
1217 | ||
1218 | If we have SCHEDULE(STATIC), and no ORDERED, then we ought to be | |
1219 | able to get away with no work-sharing context at all, since we can | |
1220 | simply perform the arithmetic directly in each thread to divide up | |
1221 | the iterations. Which would mean that we wouldn't need to call any | |
1222 | of these routines. | |
1223 | ||
1224 | There are separate routines for handling loops with an ORDERED | |
1225 | clause. Bookkeeping for that is non-trivial... | |
1226 | ||
1227 | ||
1228 | ||
1229 | @node Implementing ORDERED construct | |
1230 | @section Implementing ORDERED construct | |
1231 | ||
1232 | @smallexample | |
1233 | void GOMP_ordered_start (void) | |
1234 | void GOMP_ordered_end (void) | |
1235 | @end smallexample | |
1236 | ||
1237 | ||
1238 | ||
1239 | @node Implementing SECTIONS construct | |
1240 | @section Implementing SECTIONS construct | |
1241 | ||
1242 | A block as | |
1243 | ||
1244 | @smallexample | |
1245 | #pragma omp sections | |
1246 | @{ | |
1247 | #pragma omp section | |
1248 | stmt1; | |
1249 | #pragma omp section | |
1250 | stmt2; | |
1251 | #pragma omp section | |
1252 | stmt3; | |
1253 | @} | |
1254 | @end smallexample | |
1255 | ||
1256 | becomes | |
1257 | ||
1258 | @smallexample | |
1259 | for (i = GOMP_sections_start (3); i != 0; i = GOMP_sections_next ()) | |
1260 | switch (i) | |
1261 | @{ | |
1262 | case 1: | |
1263 | stmt1; | |
1264 | break; | |
1265 | case 2: | |
1266 | stmt2; | |
1267 | break; | |
1268 | case 3: | |
1269 | stmt3; | |
1270 | break; | |
1271 | @} | |
1272 | GOMP_barrier (); | |
1273 | @end smallexample | |
1274 | ||
1275 | ||
1276 | @node Implementing SINGLE construct | |
1277 | @section Implementing SINGLE construct | |
1278 | ||
1279 | A block like | |
1280 | ||
1281 | @smallexample | |
1282 | #pragma omp single | |
1283 | @{ | |
1284 | body; | |
1285 | @} | |
1286 | @end smallexample | |
1287 | ||
1288 | becomes | |
1289 | ||
1290 | @smallexample | |
1291 | if (GOMP_single_start ()) | |
1292 | body; | |
1293 | GOMP_barrier (); | |
1294 | @end smallexample | |
1295 | ||
1296 | while | |
1297 | ||
1298 | @smallexample | |
1299 | #pragma omp single copyprivate(x) | |
1300 | body; | |
1301 | @end smallexample | |
1302 | ||
1303 | becomes | |
1304 | ||
1305 | @smallexample | |
1306 | datap = GOMP_single_copy_start (); | |
1307 | if (datap == NULL) | |
1308 | @{ | |
1309 | body; | |
1310 | data.x = x; | |
1311 | GOMP_single_copy_end (&data); | |
1312 | @} | |
1313 | else | |
1314 | x = datap->x; | |
1315 | GOMP_barrier (); | |
1316 | @end smallexample | |
1317 | ||
1318 | ||
1319 | ||
1320 | @c --------------------------------------------------------------------- | |
1321 | @c | |
1322 | @c --------------------------------------------------------------------- | |
1323 | ||
1324 | @node Reporting Bugs | |
1325 | @chapter Reporting Bugs | |
1326 | ||
1327 | Bugs in the GNU OpenMP implementation should be reported via | |
1328 | @uref{http://gcc.gnu.org/bugzilla/, bugzilla}. In all cases, please add | |
1329 | "openmp" to the keywords field in the bug report. | |
1330 | ||
1331 | ||
1332 | ||
1333 | @c --------------------------------------------------------------------- | |
1334 | @c GNU General Public License | |
1335 | @c --------------------------------------------------------------------- | |
1336 | ||
1337 | @include gpl.texi | |
1338 | ||
1339 | ||
1340 | ||
1341 | @c --------------------------------------------------------------------- | |
1342 | @c GNU Free Documentation License | |
1343 | @c --------------------------------------------------------------------- | |
1344 | ||
1345 | @include fdl.texi | |
1346 | ||
1347 | ||
1348 | ||
1349 | @c --------------------------------------------------------------------- | |
1350 | @c Funding Free Software | |
1351 | @c --------------------------------------------------------------------- | |
1352 | ||
1353 | @include funding.texi | |
1354 | ||
1355 | @c --------------------------------------------------------------------- | |
1356 | @c Index | |
1357 | @c --------------------------------------------------------------------- | |
1358 | ||
1359 | @node Index | |
1360 | @unnumbered Index | |
1361 | ||
1362 | @printindex cp | |
1363 | ||
1364 | @bye |