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 *policy,
15 struct sched_param *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 └─────────────────────────┴───────────────┴─────────┘
82 POSIX.1-2001, POSIX.1-2008.
83
85 For a description of the permissions required to, and the effect of,
86 changing a thread's scheduling policy and priority, and details of the
87 permitted ranges for priorities in each scheduling policy, see
88 sched(7).
89
91 The program below demonstrates the use of pthread_setschedparam() and
92 pthread_getschedparam(), as well as the use of a number of other sched‐
93 uling-related pthreads functions.
94 In the following run, the main thread sets its scheduling policy to
96 SCHED_FIFO with a priority of 10, and initializes a thread attributes
97 object with a scheduling policy attribute of SCHED_RR and a scheduling
98 priority attribute of 20. The program then sets (using
99 pthread_attr_setinheritsched(3)) the inherit scheduler attribute of the
100 thread attributes object to PTHREAD_EXPLICIT_SCHED, meaning that
101 threads created using this attributes object should take their schedul‐
102 ing attributes from the thread attributes object. The program then
103 creates a thread using the thread attributes object, and that thread
104 displays its scheduling policy and priority.
105 $ su # Need privilege to set real-time scheduling policies
107 Password:
108 # ./a.out -mf10 -ar20 -i e
109 Scheduler settings of main thread
110 policy=SCHED_FIFO, priority=10
111 Scheduler settings in 'attr'
113 policy=SCHED_RR, priority=20
114 inheritsched is EXPLICIT
115 Scheduler attributes of new thread
117 policy=SCHED_RR, priority=20
118 In the above output, one can see that the scheduling policy and prior‐
120 ity were taken from the values specified in the thread attributes ob‐
121 ject.
122 The next run is the same as the previous, except that the inherit
124 scheduler attribute is set to PTHREAD_INHERIT_SCHED, meaning that
125 threads created using the thread attributes object should ignore the
126 scheduling attributes specified in the attributes object and instead
127 take their scheduling attributes from the creating thread.
128 # ./a.out -mf10 -ar20 -i i
130 Scheduler settings of main thread
131 policy=SCHED_FIFO, priority=10
132 Scheduler settings in 'attr'
134 policy=SCHED_RR, priority=20
135 inheritsched is INHERIT
136 Scheduler attributes of new thread
138 policy=SCHED_FIFO, priority=10
139 In the above output, one can see that the scheduling policy and prior‐
141 ity were taken from the creating thread, rather than the thread at‐
142 tributes object.
143 Note that if we had omitted the -i i option, the output would have been
145 the same, since PTHREAD_INHERIT_SCHED is the default for the inherit
146 scheduler attribute.
147 Program source
149 /* pthreads_sched_test.c */
151 #include <pthread.h>
153 #include <stdio.h>
154 #include <stdlib.h>
155 #include <unistd.h>
156 #include <errno.h>
157 #define handle_error_en(en, msg) \
159 do { errno = en; perror(msg); exit(EXIT_FAILURE); } while (0)
160 static void
162 usage(char *prog_name, char *msg)
163 {
164 if (msg != NULL)
165 fputs(msg, stderr);
166 fprintf(stderr, "Usage: %s [options]\n", prog_name);
168 fprintf(stderr, "Options are:\n");
169 #define fpe(msg) fprintf(stderr, "\t%s", msg); /* Shorter */
170 fpe("-a<policy><prio> Set scheduling policy and priority in\n");
171 fpe(" thread attributes object\n");
172 fpe(" <policy> can be\n");
173 fpe(" f SCHED_FIFO\n");
174 fpe(" r SCHED_RR\n");
175 fpe(" o SCHED_OTHER\n");
176 fpe("-A Use default thread attributes object\n");
177 fpe("-i {e|i} Set inherit scheduler attribute to\n");
178 fpe(" 'explicit' or 'inherit'\n");
179 fpe("-m<policy><prio> Set scheduling policy and priority on\n");
180 fpe(" main thread before pthread_create() call\n");
181 exit(EXIT_FAILURE);
182 }
183 static int
185 get_policy(char p, int *policy)
186 {
187 switch (p) {
188 case 'f': *policy = SCHED_FIFO; return 1;
189 case 'r': *policy = SCHED_RR; return 1;
190 case 'o': *policy = SCHED_OTHER; return 1;
191 default: return 0;
192 }
193 }
194 static void
196 display_sched_attr(int policy, struct sched_param *param)
197 {
198 printf(" policy=%s, priority=%d\n",
199 (policy == SCHED_FIFO) ? "SCHED_FIFO" :
200 (policy == SCHED_RR) ? "SCHED_RR" :
201 (policy == SCHED_OTHER) ? "SCHED_OTHER" :
202 "???",
203 param->sched_priority);
204 }
205 static void
207 display_thread_sched_attr(char *msg)
208 {
209 int policy, s;
210 struct sched_param param;
211 s = pthread_getschedparam(pthread_self(), &policy, ¶m);
213 if (s != 0)
214 handle_error_en(s, "pthread_getschedparam");
215 printf("%s\n", msg);
217 display_sched_attr(policy, ¶m);
218 }
219 static void *
221 thread_start(void *arg)
222 {
223 display_thread_sched_attr("Scheduler attributes of new thread");
224 return NULL;
226 }
227 int
229 main(int argc, char *argv[])
230 {
231 int s, opt, inheritsched, use_null_attrib, policy;
232 pthread_t thread;
233 pthread_attr_t attr;
234 pthread_attr_t *attrp;
235 char *attr_sched_str, *main_sched_str, *inheritsched_str;
236 struct sched_param param;
237 /* Process command-line options */
239 use_null_attrib = 0;
241 attr_sched_str = NULL;
242 main_sched_str = NULL;
243 inheritsched_str = NULL;
244 while ((opt = getopt(argc, argv, "a:Ai:m:")) != -1) {
246 switch (opt) {
247 case 'a': attr_sched_str = optarg; break;
248 case 'A': use_null_attrib = 1; break;
249 case 'i': inheritsched_str = optarg; break;
250 case 'm': main_sched_str = optarg; break;
251 default: usage(argv[0], "Unrecognized option\n");
252 }
253 }
254 if (use_null_attrib &&
256 (inheritsched_str != NULL || attr_sched_str != NULL))
257 usage(argv[0], "Can't specify -A with -i or -a\n");
258 /* Optionally set scheduling attributes of main thread,
260 and display the attributes */
261 if (main_sched_str != NULL) {
263 if (!get_policy(main_sched_str[0], &policy))
264 usage(argv[0], "Bad policy for main thread (-m)\n");
265 param.sched_priority = strtol(&main_sched_str[1], NULL, 0);
266 s = pthread_setschedparam(pthread_self(), policy, ¶m);
268 if (s != 0)
269 handle_error_en(s, "pthread_setschedparam");
270 }
271 display_thread_sched_attr("Scheduler settings of main thread");
273 printf("\n");
274 /* Initialize thread attributes object according to options */
276 attrp = NULL;
278 if (!use_null_attrib) {
280 s = pthread_attr_init(&attr);
281 if (s != 0)
282 handle_error_en(s, "pthread_attr_init");
283 attrp = &attr;
284 }
285 if (inheritsched_str != NULL) {
287 if (inheritsched_str[0] == 'e')
288 inheritsched = PTHREAD_EXPLICIT_SCHED;
289 else if (inheritsched_str[0] == 'i')
290 inheritsched = PTHREAD_INHERIT_SCHED;
291 else
292 usage(argv[0], "Value for -i must be 'e' or 'i'\n");
293 s = pthread_attr_setinheritsched(&attr, inheritsched);
295 if (s != 0)
296 handle_error_en(s, "pthread_attr_setinheritsched");
297 }
298 if (attr_sched_str != NULL) {
300 if (!get_policy(attr_sched_str[0], &policy))
301 usage(argv[0],
302 "Bad policy for 'attr' (-a)\n");
303 param.sched_priority = strtol(&attr_sched_str[1], NULL, 0);
304 s = pthread_attr_setschedpolicy(&attr, policy);
306 if (s != 0)
307 handle_error_en(s, "pthread_attr_setschedpolicy");
308 s = pthread_attr_setschedparam(&attr, ¶m);
309 if (s != 0)
310 handle_error_en(s, "pthread_attr_setschedparam");
311 }
312 /* If we initialized a thread attributes object, display
314 the scheduling attributes that were set in the object */
315 if (attrp != NULL) {
317 s = pthread_attr_getschedparam(&attr, ¶m);
318 if (s != 0)
319 handle_error_en(s, "pthread_attr_getschedparam");
320 s = pthread_attr_getschedpolicy(&attr, &policy);
321 if (s != 0)
322 handle_error_en(s, "pthread_attr_getschedpolicy");
323 printf("Scheduler settings in 'attr'\n");
325 display_sched_attr(policy, ¶m);
326 s = pthread_attr_getinheritsched(&attr, &inheritsched);
328 printf(" inheritsched is %s\n",
329 (inheritsched == PTHREAD_INHERIT_SCHED) ? "INHERIT" :
330 (inheritsched == PTHREAD_EXPLICIT_SCHED) ? "EXPLICIT" :
331 "???");
332 printf("\n");
333 }
334 /* Create a thread that will display its scheduling attributes */
336 s = pthread_create(&thread, attrp, &thread_start, NULL);
338 if (s != 0)
339 handle_error_en(s, "pthread_create");
340 /* Destroy unneeded thread attributes object */
342 if (!use_null_attrib) {
344 s = pthread_attr_destroy(&attr);
345 if (s != 0)
346 handle_error_en(s, "pthread_attr_destroy");
347 }
348 s = pthread_join(thread, NULL);
350 if (s != 0)
351 handle_error_en(s, "pthread_join");
352 exit(EXIT_SUCCESS);
354 }
355
357 getrlimit(2), sched_get_priority_min(2), pthread_attr_init(3),
358 pthread_attr_setinheritsched(3), pthread_attr_setschedparam(3),
359 pthread_attr_setschedpolicy(3), pthread_create(3), pthread_self(3),
360 pthread_setschedprio(3), pthreads(7), sched(7)
361
363 This page is part of release 5.10 of the Linux man-pages project. A
364 description of the project, information about reporting bugs, and the
365 latest version of this page, can be found at
366 https://www.kernel.org/doc/man-pages/.
367Linux 2020-06-09 PTHREAD_SETSCHEDPARAM(3)