1 .\" Copyright (c) 2008 Linux Foundation, written by Michael Kerrisk
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26 .TH PTHREAD_SETSCHEDPARAM 3 2008-11-17 "Linux" "Linux Programmer's Manual"
28 pthread_setschedparam, pthread_getschedparam \- set/get
29 scheduling policy and parameters of a thread
32 .B #include <pthread.h>
34 .BI "pthread_setschedparam(pthread_t " thread ", int " policy ,
35 .BI " const struct sched_param *" param );
36 .BI "pthread_getschedparam(pthread_t " thread ", int *" policy ,
37 .BI " struct sched_param *" param );
39 Compile and link with \fI\-pthread\fP.
43 .BR pthread_setschedparam ()
44 function sets the scheduling policy and parameters of the thread
48 specifies the new scheduling policy for
50 The supported values for
52 and their semantics, are described in
53 .BR sched_setscheduler (2).
54 .\" FIXME . pthread_setschedparam() places no restriction on the policy,
55 .\" but pthread_attr_setschedpolicy() restricts policy to RR/FIFO/OTHER
56 .\" http://sourceware.org/bugzilla/show_bug.cgi?id=7013
58 The structure pointed to by
60 specifies the new scheduling parameters for
62 Scheduling parameters are maintained in the following structure:
67 int sched_priority; /* Scheduling priority */
72 As can be seen, only one scheduling parameter is supported.
73 For details of the permitted ranges for scheduling priorities
74 in each scheduling policy, see
75 .BR sched_setscheduler (2).
78 .BR pthread_getschedparam ()
79 function returns the scheduling policy and parameters of the thread
81 in the buffers pointed to by
86 The returned priority value is that set by the most recent
87 .BR pthread_setschedparam (),
88 .BR pthread_setschedprio (3),
90 .BR pthread_create (3)
93 The returned priority does not reflect any temporary priority adjustments
94 as a result of calls to any priority inheritance or
95 priority ceiling functions (see, for example,
96 .BR pthread_mutexattr_setprioceiling (3)
98 .BR pthread_mutexattr_setprotocol (3)).
99 .\" FIXME . nptl/pthread_setschedparam.c has the following
100 .\" /* If the thread should have higher priority because of some
101 .\" PTHREAD_PRIO_PROTECT mutexes it holds, adjust the priority. */
102 .\" Eventually (perhaps after writing the mutexattr pages), we
103 .\" may want to add something on the topic to this page.
105 On success, these functions return 0;
106 on error, they return a nonzero error number.
108 .BR pthread_setschedparam ()
109 fails, the scheduling policy and parameters of
113 Both of these functions can fail with the following error:
116 No thread with the ID
120 .BR pthread_setschedparam ()
121 may additionally fail with the following errors:
125 is not a recognized policy, or
127 does not make sense for the
131 The caller does not have appropriate privileges
132 to set the specified scheduling policy and parameters.
134 POSIX.1-2001 also documents an
136 ("attempt was made to set the policy or scheduling parameters
137 to an unsupported value") error for
138 .BR pthread_setschedparam ().
140 .\" Available since glibc 2.0
144 For a description of the permissions required to, and the effect of,
145 changing a thread's scheduling policy and priority,
146 and details of the permitted ranges for priorities
147 in each scheduling policy, see
148 .BR sched_setscheduler (2).
150 The program below demonstrates the use of
151 .BR pthread_setschedparam ()
153 .BR pthread_getschedparam (),
154 as well as the use of a number of other scheduling-related
157 In the following run, the main thread sets its scheduling policy to
159 with a priority of 10,
160 and initializes a thread attributes object with
161 a scheduling policy attribute of
163 and a scheduling priority attribute of 20.
164 The program then sets (using
165 .BR pthread_attr_setinheritsched (3))
166 the inherit scheduler attribute of the thread attributes object to
167 .BR PTHREAD_EXPLICIT_SCHED ,
168 meaning that threads created using this attributes object should
169 take their scheduling attributes from the thread attributes object.
170 The program then creates a thread using the thread attributes object,
171 and that thread displays its scheduling policy and priority.
175 $ \fBsu\fP # Need privilege to set real-time scheduling policies
177 # \fB./a.out \-mf10 \-ar20 \-i e\fP
178 Scheduler settings of main thread
179 policy=SCHED_FIFO, priority=10
181 Scheduler settings in \(aqattr\(aq
182 policy=SCHED_RR, priority=20
183 inheritsched is EXPLICIT
185 Scheduler attributes of new thread
186 policy=SCHED_RR, priority=20
190 In the above output, one can see that the scheduling policy and priority
191 were taken from the values specified in the thread attributes object.
193 The next run is the same as the previous,
194 except that the inherit scheduler attribute is set to
195 .BR PTHREAD_INHERIT_SCHED ,
196 meaning that threads created using the thread attributes object should
197 ignore the scheduling attributes specified in the attributes object
198 and instead take their scheduling attributes from the creating thread.
202 # \fB./a.out \-mf10 \-ar20 \-i i\fP
203 Scheduler settings of main thread
204 policy=SCHED_FIFO, priority=10
206 Scheduler settings in \(aqattr\(aq
207 policy=SCHED_RR, priority=20
208 inheritsched is INHERIT
210 Scheduler attributes of new thread
211 policy=SCHED_FIFO, priority=10
215 In the above output, one can see that the scheduling policy and priority
216 were taken from the creating thread,
217 rather than the thread attributes object.
219 Note that if we had omitted the
221 option, the output would have been the same, since
222 .BR PTHREAD_INHERIT_SCHED
223 is the default for the inherit scheduler attribute.
227 /* pthreads_sched_test.c */
235 #define handle_error_en(en, msg) \\
236 do { errno = en; perror(msg); exit(EXIT_FAILURE); } while (0)
239 usage(char *prog_name, char *msg)
244 fprintf(stderr, "Usage: %s [options]\\n", prog_name);
245 fprintf(stderr, "Options are:\\n");
246 #define fpe(msg) fprintf(stderr, "\\t%s", msg); /* Shorter */
247 fpe("\-a<policy><prio> Set scheduling policy and priority in\\n");
248 fpe(" thread attributes object\\n");
249 fpe(" <policy> can be\\n");
250 fpe(" f SCHED_FIFO\\n");
251 fpe(" r SCHED_RR\\n");
252 fpe(" o SCHED_OTHER\\n");
253 fpe("\-A Use default thread attributes object\\n");
254 fpe("\-i {e|s} Set inherit scheduler attribute to\\n");
255 fpe(" \(aqexplicit\(aq or \(aqinherit\(aq\\n");
256 fpe("\-m<policy><prio> Set scheduling policy and priority on\\n");
257 fpe(" main thread before pthread_create() call\\n");
262 get_policy(char p, int *policy)
265 case \(aqf\(aq: *policy = SCHED_FIFO; return 1;
266 case \(aqr\(aq: *policy = SCHED_RR; return 1;
267 case \(aqo\(aq: *policy = SCHED_OTHER; return 1;
273 display_sched_attr(int policy, struct sched_param *param)
275 printf(" policy=%s, priority=%d\\n",
276 (policy == SCHED_FIFO) ? "SCHED_FIFO" :
277 (policy == SCHED_RR) ? "SCHED_RR" :
278 (policy == SCHED_OTHER) ? "SCHED_OTHER" :
280 param\->sched_priority);
284 display_thread_sched_attr(char *msg)
287 struct sched_param param;
289 s = pthread_getschedparam(pthread_self(), &policy, ¶m);
291 handle_error_en(s, "pthread_getschedparam");
293 printf("%s\\n", msg);
294 display_sched_attr(policy, ¶m);
298 thread_start(void *arg)
300 display_thread_sched_attr("Scheduler attributes of new thread");
306 main(int argc, char *argv[])
308 int s, opt, inheritsched, use_null_attrib, policy;
311 pthread_attr_t *attrp;
312 char *attr_sched_str, *main_sched_str, *inheritsched_str;
313 struct sched_param param;
315 /* Process command\-line options */
318 attr_sched_str = NULL;
319 main_sched_str = NULL;
320 inheritsched_str = NULL;
322 while ((opt = getopt(argc, argv, "a:Ai:m:")) != \-1) {
324 case \(aqa\(aq: attr_sched_str = optarg; break;
325 case \(aqA\(aq: use_null_attrib = 1; break;
326 case \(aqi\(aq: inheritsched_str = optarg; break;
327 case \(aqm\(aq: main_sched_str = optarg; break;
328 default: usage(argv[0], "Unrecognized option\\n");
332 if (use_null_attrib &&
333 (inheritsched_str != NULL || attr_sched_str != NULL))
334 usage(argv[0], "Can\(aqt specify \-A with \-i or \-a\\n");
336 /* Optionally set scheduling attributes of main thread,
337 and display the attributes */
339 if (main_sched_str != NULL) {
340 if (!get_policy(main_sched_str[0], &policy))
341 usage(argv[0], "Bad policy for main thread (\-s)\\n");
342 param.sched_priority = strtol(&main_sched_str[1], NULL, 0);
344 s = pthread_setschedparam(pthread_self(), policy, ¶m);
346 handle_error_en(s, "pthread_setschedparam");
349 display_thread_sched_attr("Scheduler settings of main thread");
352 /* Initialize thread attributes object according to options */
356 if (!use_null_attrib) {
357 s = pthread_attr_init(&attr);
359 handle_error_en(s, "pthread_attr_init");
363 if (inheritsched_str != NULL) {
364 if (inheritsched_str[0] == \(aqe\(aq)
365 inheritsched = PTHREAD_EXPLICIT_SCHED;
366 else if (inheritsched_str[0] == \(aqi\(aq)
367 inheritsched = PTHREAD_INHERIT_SCHED;
369 usage(argv[0], "Value for \-i must be \(aqe\(aq or \(aqi\(aq\\n");
371 s = pthread_attr_setinheritsched(&attr, inheritsched);
373 handle_error_en(s, "pthread_attr_setinheritsched");
376 if (attr_sched_str != NULL) {
377 if (!get_policy(attr_sched_str[0], &policy))
379 "Bad policy for \(aqattr\(aq (\-a)\\n");
380 param.sched_priority = strtol(&attr_sched_str[1], NULL, 0);
382 s = pthread_attr_setschedpolicy(&attr, policy);
384 handle_error_en(s, "pthread_attr_setschedpolicy");
385 s = pthread_attr_setschedparam(&attr, ¶m);
387 handle_error_en(s, "pthread_attr_setschedparam");
390 /* If we initialized a thread attributes object, display
391 the scheduling attributes that were set in the object */
394 s = pthread_attr_getschedparam(&attr, ¶m);
396 handle_error_en(s, "pthread_attr_getschedparam");
397 s = pthread_attr_getschedpolicy(&attr, &policy);
399 handle_error_en(s, "pthread_attr_getschedpolicy");
401 printf("Scheduler settings in \(aqattr\(aq\\n");
402 display_sched_attr(policy, ¶m);
404 s = pthread_attr_getinheritsched(&attr, &inheritsched);
405 printf(" inheritsched is %s\\n",
406 (inheritsched == PTHREAD_INHERIT_SCHED) ? "INHERIT" :
407 (inheritsched == PTHREAD_EXPLICIT_SCHED) ? "EXPLICIT" :
412 /* Create a thread that will display its scheduling attributes */
414 s = pthread_create(&thread, attrp, &thread_start, NULL);
416 handle_error_en(s, "pthread_create");
418 /* Destroy unneeded thread attributes object */
420 s = pthread_attr_destroy(&attr);
422 handle_error_en(s, "pthread_attr_destroy");
424 s = pthread_join(thread, NULL);
426 handle_error_en(s, "pthread_join");
435 .BR sched_get_priority_min (2),
436 .BR sched_setscheduler (2),
437 .BR pthread_attr_init (3),
438 .BR pthread_attr_setinheritsched (3),
439 .BR pthread_attr_setschedparam (3),
440 .BR pthread_attr_setschedpolicy (3),
441 .BR pthread_create (3),
442 .BR pthread_self (3),
443 .BR pthread_setschedprio (3),
446 This page is part of release 3.65 of the Linux
449 A description of the project,
450 and information about reporting bugs,
452 \%http://www.kernel.org/doc/man\-pages/.