1PTHREAD_SETSCHEDPARAM(3) Linux Programmer's Manual PTHREAD_SETSCHEDPARAM(3)
2
6 pthread_setschedparam, pthread_getschedparam - set/get scheduling pol‐
7 icy and parameters of a thread
8
10 #include <pthread.h>
11 int pthread_setschedparam(pthread_t thread, int policy,
13 const struct sched_param *param);
14 int pthread_getschedparam(pthread_t thread, int *restrict policy,
15 struct sched_param *restrict param);
16 Compile and link with -pthread.
18
20 The pthread_setschedparam() function sets the scheduling policy and pa‐
21 rameters of the thread thread.
22 policy specifies the new scheduling policy for thread. The supported
24 values for policy, and their semantics, are described in sched(7).
25 The structure pointed to by param specifies the new scheduling parame‐
27 ters for thread. Scheduling parameters are maintained in the following
28 structure:
29 struct sched_param {
31 int sched_priority; /* Scheduling priority */
32 };
33 As can be seen, only one scheduling parameter is supported. For de‐
35 tails of the permitted ranges for scheduling priorities in each sched‐
36 uling policy, see sched(7).
37 The pthread_getschedparam() function returns the scheduling policy and
39 parameters of the thread thread, in the buffers pointed to by policy
40 and param, respectively. The returned priority value is that set by
41 the most recent pthread_setschedparam(), pthread_setschedprio(3), or
42 pthread_create(3) call that affected thread. The returned priority
43 does not reflect any temporary priority adjustments as a result of
44 calls to any priority inheritance or priority ceiling functions (see,
45 for example, pthread_mutexattr_setprioceiling(3) and pthread_mutex‐
46 attr_setprotocol(3)).
47
49 On success, these functions return 0; on error, they return a nonzero
50 error number. If pthread_setschedparam() fails, the scheduling policy
51 and parameters of thread are not changed.
52
54 Both of these functions can fail with the following error:
55 ESRCH No thread with the ID thread could be found.
57 pthread_setschedparam() may additionally fail with the following er‐
59 rors:
60 EINVAL policy is not a recognized policy, or param does not make sense
62 for the policy.
63 EPERM The caller does not have appropriate privileges to set the spec‐
65 ified scheduling policy and parameters.
66 POSIX.1 also documents an ENOTSUP ("attempt was made to set the policy
68 or scheduling parameters to an unsupported value") error for
69 pthread_setschedparam().
70
72 For an explanation of the terms used in this section, see at‐
73 tributes(7).
74 ┌────────────────────────────────────────────┬───────────────┬─────────┐
76 │Interface │ Attribute │ Value │
77 ├────────────────────────────────────────────┼───────────────┼─────────┤
78 │pthread_setschedparam(), │ Thread safety │ MT-Safe │
79 │pthread_getschedparam() │ │ │
80 └────────────────────────────────────────────┴───────────────┴─────────┘
81
83 POSIX.1-2001, POSIX.1-2008.
84
86 For a description of the permissions required to, and the effect of,
87 changing a thread's scheduling policy and priority, and details of the
88 permitted ranges for priorities in each scheduling policy, see
89 sched(7).
90
92 The program below demonstrates the use of pthread_setschedparam() and
93 pthread_getschedparam(), as well as the use of a number of other sched‐
94 uling-related pthreads functions.
95 In the following run, the main thread sets its scheduling policy to
97 SCHED_FIFO with a priority of 10, and initializes a thread attributes
98 object with a scheduling policy attribute of SCHED_RR and a scheduling
99 priority attribute of 20. The program then sets (using pthread_at‐
100 tr_setinheritsched(3)) the inherit scheduler attribute of the thread
101 attributes object to PTHREAD_EXPLICIT_SCHED, meaning that threads cre‐
102 ated using this attributes object should take their scheduling at‐
103 tributes from the thread attributes object. The program then creates a
104 thread using the thread attributes object, and that thread displays its
105 scheduling policy and priority.
106 $ su # Need privilege to set real-time scheduling policies
108 Password:
109 # ./a.out -mf10 -ar20 -i e
110 Scheduler settings of main thread
111 policy=SCHED_FIFO, priority=10
112 Scheduler settings in 'attr'
114 policy=SCHED_RR, priority=20
115 inheritsched is EXPLICIT
116 Scheduler attributes of new thread
118 policy=SCHED_RR, priority=20
119 In the above output, one can see that the scheduling policy and prior‐
121 ity were taken from the values specified in the thread attributes ob‐
122 ject.
123 The next run is the same as the previous, except that the inherit
125 scheduler attribute is set to PTHREAD_INHERIT_SCHED, meaning that
126 threads created using the thread attributes object should ignore the
127 scheduling attributes specified in the attributes object and instead
128 take their scheduling attributes from the creating thread.
129 # ./a.out -mf10 -ar20 -i i
131 Scheduler settings of main thread
132 policy=SCHED_FIFO, priority=10
133 Scheduler settings in 'attr'
135 policy=SCHED_RR, priority=20
136 inheritsched is INHERIT
137 Scheduler attributes of new thread
139 policy=SCHED_FIFO, priority=10
140 In the above output, one can see that the scheduling policy and prior‐
142 ity were taken from the creating thread, rather than the thread at‐
143 tributes object.
144 Note that if we had omitted the -i i option, the output would have been
146 the same, since PTHREAD_INHERIT_SCHED is the default for the inherit
147 scheduler attribute.
148 Program source
150 /* pthreads_sched_test.c */
152 #include <pthread.h>
154 #include <stdio.h>
155 #include <stdlib.h>
156 #include <unistd.h>
157 #include <errno.h>
158 #define handle_error_en(en, msg) \
160 do { errno = en; perror(msg); exit(EXIT_FAILURE); } while (0)
161 static void
163 usage(char *prog_name, char *msg)
164 {
165 if (msg != NULL)
166 fputs(msg, stderr);
167 fprintf(stderr, "Usage: %s [options]\n", prog_name);
169 fprintf(stderr, "Options are:\n");
170 #define fpe(msg) fprintf(stderr, "\t%s", msg); /* Shorter */
171 fpe("-a<policy><prio> Set scheduling policy and priority in\n");
172 fpe(" thread attributes object\n");
173 fpe(" <policy> can be\n");
174 fpe(" f SCHED_FIFO\n");
175 fpe(" r SCHED_RR\n");
176 fpe(" o SCHED_OTHER\n");
177 fpe("-A Use default thread attributes object\n");
178 fpe("-i {e|i} Set inherit scheduler attribute to\n");
179 fpe(" 'explicit' or 'inherit'\n");
180 fpe("-m<policy><prio> Set scheduling policy and priority on\n");
181 fpe(" main thread before pthread_create() call\n");
182 exit(EXIT_FAILURE);
183 }
184 static int
186 get_policy(char p, int *policy)
187 {
188 switch (p) {
189 case 'f': *policy = SCHED_FIFO; return 1;
190 case 'r': *policy = SCHED_RR; return 1;
191 case 'o': *policy = SCHED_OTHER; return 1;
192 default: return 0;
193 }
194 }
195 static void
197 display_sched_attr(int policy, struct sched_param *param)
198 {
199 printf(" policy=%s, priority=%d\n",
200 (policy == SCHED_FIFO) ? "SCHED_FIFO" :
201 (policy == SCHED_RR) ? "SCHED_RR" :
202 (policy == SCHED_OTHER) ? "SCHED_OTHER" :
203 "???",
204 param->sched_priority);
205 }
206 static void
208 display_thread_sched_attr(char *msg)
209 {
210 int policy, s;
211 struct sched_param param;
212 s = pthread_getschedparam(pthread_self(), &policy, ¶m);
214 if (s != 0)
215 handle_error_en(s, "pthread_getschedparam");
216 printf("%s\n", msg);
218 display_sched_attr(policy, ¶m);
219 }
220 static void *
222 thread_start(void *arg)
223 {
224 display_thread_sched_attr("Scheduler attributes of new thread");
225 return NULL;
227 }
228 int
230 main(int argc, char *argv[])
231 {
232 int s, opt, inheritsched, use_null_attrib, policy;
233 pthread_t thread;
234 pthread_attr_t attr;
235 pthread_attr_t *attrp;
236 char *attr_sched_str, *main_sched_str, *inheritsched_str;
237 struct sched_param param;
238 /* Process command-line options. */
240 use_null_attrib = 0;
242 attr_sched_str = NULL;
243 main_sched_str = NULL;
244 inheritsched_str = NULL;
245 while ((opt = getopt(argc, argv, "a:Ai:m:")) != -1) {
247 switch (opt) {
248 case 'a': attr_sched_str = optarg; break;
249 case 'A': use_null_attrib = 1; break;
250 case 'i': inheritsched_str = optarg; break;
251 case 'm': main_sched_str = optarg; break;
252 default: usage(argv[0], "Unrecognized option\n");
253 }
254 }
255 if (use_null_attrib &&
257 (inheritsched_str != NULL || attr_sched_str != NULL))
258 usage(argv[0], "Can't specify -A with -i or -a\n");
259 /* Optionally set scheduling attributes of main thread,
261 and display the attributes. */
262 if (main_sched_str != NULL) {
264 if (!get_policy(main_sched_str[0], &policy))
265 usage(argv[0], "Bad policy for main thread (-m)\n");
266 param.sched_priority = strtol(&main_sched_str[1], NULL, 0);
267 s = pthread_setschedparam(pthread_self(), policy, ¶m);
269 if (s != 0)
270 handle_error_en(s, "pthread_setschedparam");
271 }
272 display_thread_sched_attr("Scheduler settings of main thread");
274 printf("\n");
275 /* Initialize thread attributes object according to options. */
277 attrp = NULL;
279 if (!use_null_attrib) {
281 s = pthread_attr_init(&attr);
282 if (s != 0)
283 handle_error_en(s, "pthread_attr_init");
284 attrp = &attr;
285 }
286 if (inheritsched_str != NULL) {
288 if (inheritsched_str[0] == 'e')
289 inheritsched = PTHREAD_EXPLICIT_SCHED;
290 else if (inheritsched_str[0] == 'i')
291 inheritsched = PTHREAD_INHERIT_SCHED;
292 else
293 usage(argv[0], "Value for -i must be 'e' or 'i'\n");
294 s = pthread_attr_setinheritsched(&attr, inheritsched);
296 if (s != 0)
297 handle_error_en(s, "pthread_attr_setinheritsched");
298 }
299 if (attr_sched_str != NULL) {
301 if (!get_policy(attr_sched_str[0], &policy))
302 usage(argv[0],
303 "Bad policy for 'attr' (-a)\n");
304 param.sched_priority = strtol(&attr_sched_str[1], NULL, 0);
305 s = pthread_attr_setschedpolicy(&attr, policy);
307 if (s != 0)
308 handle_error_en(s, "pthread_attr_setschedpolicy");
309 s = pthread_attr_setschedparam(&attr, ¶m);
310 if (s != 0)
311 handle_error_en(s, "pthread_attr_setschedparam");
312 }
313 /* If we initialized a thread attributes object, display
315 the scheduling attributes that were set in the object. */
316 if (attrp != NULL) {
318 s = pthread_attr_getschedparam(&attr, ¶m);
319 if (s != 0)
320 handle_error_en(s, "pthread_attr_getschedparam");
321 s = pthread_attr_getschedpolicy(&attr, &policy);
322 if (s != 0)
323 handle_error_en(s, "pthread_attr_getschedpolicy");
324 printf("Scheduler settings in 'attr'\n");
326 display_sched_attr(policy, ¶m);
327 s = pthread_attr_getinheritsched(&attr, &inheritsched);
329 printf(" inheritsched is %s\n",
330 (inheritsched == PTHREAD_INHERIT_SCHED) ? "INHERIT" :
331 (inheritsched == PTHREAD_EXPLICIT_SCHED) ? "EXPLICIT" :
332 "???");
333 printf("\n");
334 }
335 /* Create a thread that will display its scheduling attributes. */
337 s = pthread_create(&thread, attrp, &thread_start, NULL);
339 if (s != 0)
340 handle_error_en(s, "pthread_create");
341 /* Destroy unneeded thread attributes object. */
343 if (!use_null_attrib) {
345 s = pthread_attr_destroy(&attr);
346 if (s != 0)
347 handle_error_en(s, "pthread_attr_destroy");
348 }
349 s = pthread_join(thread, NULL);
351 if (s != 0)
352 handle_error_en(s, "pthread_join");
353 exit(EXIT_SUCCESS);
355 }
356
358 getrlimit(2), sched_get_priority_min(2), pthread_attr_init(3),
359 pthread_attr_setinheritsched(3), pthread_attr_setschedparam(3),
360 pthread_attr_setschedpolicy(3), pthread_create(3), pthread_self(3),
361 pthread_setschedprio(3), pthreads(7), sched(7)
362
364 This page is part of release 5.13 of the Linux man-pages project. A
365 description of the project, information about reporting bugs, and the
366 latest version of this page, can be found at
367 https://www.kernel.org/doc/man-pages/.
368Linux 2021-03-22 PTHREAD_SETSCHEDPARAM(3)