1 | .. comment SPDX-License-Identifier: CC-BY-SA-4.0 |
---|
2 | |
---|
3 | .. COMMENT: COPYRIGHT (c) 1988-2008. |
---|
4 | .. COMMENT: On-Line Applications Research Corporation (OAR). |
---|
5 | .. COMMENT: All rights reserved. |
---|
6 | |
---|
7 | Semaphore Manager |
---|
8 | ***************** |
---|
9 | |
---|
10 | .. index:: semaphores |
---|
11 | .. index:: binary semaphores |
---|
12 | .. index:: counting semaphores |
---|
13 | .. index:: mutual exclusion |
---|
14 | |
---|
15 | Introduction |
---|
16 | ============ |
---|
17 | |
---|
18 | The semaphore manager utilizes standard Dijkstra |
---|
19 | counting semaphores to provide synchronization and mutual |
---|
20 | exclusion capabilities. The directives provided by the |
---|
21 | semaphore manager are: |
---|
22 | |
---|
23 | - rtems_semaphore_create_ - Create a semaphore |
---|
24 | |
---|
25 | - rtems_semaphore_ident_ - Get ID of a semaphore |
---|
26 | |
---|
27 | - rtems_semaphore_delete_ - Delete a semaphore |
---|
28 | |
---|
29 | - rtems_semaphore_obtain_ - Acquire a semaphore |
---|
30 | |
---|
31 | - rtems_semaphore_release_ - Release a semaphore |
---|
32 | |
---|
33 | - rtems_semaphore_flush_ - Unblock all tasks waiting on a semaphore |
---|
34 | |
---|
35 | - rtems_semaphore_set_priority_ - Set priority by scheduler for a semaphore |
---|
36 | |
---|
37 | Background |
---|
38 | ========== |
---|
39 | |
---|
40 | A semaphore can be viewed as a protected variable whose value can be modified |
---|
41 | only with the ``rtems_semaphore_create``, ``rtems_semaphore_obtain``, and |
---|
42 | ``rtems_semaphore_release`` directives. RTEMS supports both binary and |
---|
43 | counting semaphores. A binary semaphore is restricted to values of zero or one, |
---|
44 | while a counting semaphore can assume any non-negative integer value. |
---|
45 | |
---|
46 | A binary semaphore (not a simple binary semaphore) can be used to control |
---|
47 | access to a single resource. In particular, it can be used to enforce mutual |
---|
48 | exclusion for a critical section in user code (mutex). In this instance, the |
---|
49 | semaphore would be created with an initial count of one to indicate that no |
---|
50 | task is executing the critical section of code. Upon entry to the critical |
---|
51 | section, a task must issue the ``rtems_semaphore_obtain`` directive to prevent |
---|
52 | other tasks from entering the critical section. Upon exit from the critical |
---|
53 | section, the task that obtained the binary semaphore must issue the |
---|
54 | ``rtems_semaphore_release`` directive to allow another task to execute the |
---|
55 | critical section. A binary semaphore must be released by the task that |
---|
56 | obtained it. |
---|
57 | |
---|
58 | A counting semaphore can be used to control access to a pool of two or more |
---|
59 | resources. For example, access to three printers could be administered by a |
---|
60 | semaphore created with an initial count of three. When a task requires access |
---|
61 | to one of the printers, it issues the ``rtems_semaphore_obtain`` directive to |
---|
62 | obtain access to a printer. If a printer is not currently available, the task |
---|
63 | can wait for a printer to become available or return immediately. When the |
---|
64 | task has completed printing, it should issue the ``rtems_semaphore_release`` |
---|
65 | directive to allow other tasks access to the printer. |
---|
66 | |
---|
67 | Task synchronization may be achieved by creating a semaphore with an initial |
---|
68 | count of zero. One task waits for the arrival of another task by issuing a |
---|
69 | ``rtems_semaphore_obtain`` directive when it reaches a synchronization point. |
---|
70 | The other task performs a corresponding ``rtems_semaphore_release`` operation |
---|
71 | when it reaches its synchronization point, thus unblocking the pending task. |
---|
72 | |
---|
73 | .. _Nested Resource Access: |
---|
74 | |
---|
75 | Nested Resource Access |
---|
76 | ---------------------- |
---|
77 | |
---|
78 | Deadlock occurs when a task owning a binary semaphore attempts to acquire that |
---|
79 | same semaphore and blocks as result. Since the semaphore is allocated to a |
---|
80 | task, it cannot be deleted. Therefore, the task that currently holds the |
---|
81 | semaphore and is also blocked waiting for that semaphore will never execute |
---|
82 | again. |
---|
83 | |
---|
84 | RTEMS addresses this problem by allowing the task holding the binary semaphore |
---|
85 | to obtain the same binary semaphore multiple times in a nested manner. Each |
---|
86 | ``rtems_semaphore_obtain`` must be accompanied with a |
---|
87 | ``rtems_semaphore_release``. The semaphore will only be made available for |
---|
88 | acquisition by other tasks when the outermost ``rtems_semaphore_obtain`` is |
---|
89 | matched with a ``rtems_semaphore_release``. |
---|
90 | |
---|
91 | Simple binary semaphores do not allow nested access and so can be used for task |
---|
92 | synchronization. |
---|
93 | |
---|
94 | .. _Priority Inversion: |
---|
95 | |
---|
96 | Priority Inversion |
---|
97 | ------------------ |
---|
98 | |
---|
99 | Priority inversion is a form of indefinite postponement which is common in |
---|
100 | multitasking, preemptive executives with shared resources. Priority inversion |
---|
101 | occurs when a high priority tasks requests access to shared resource which is |
---|
102 | currently allocated to low priority task. The high priority task must block |
---|
103 | until the low priority task releases the resource. This problem is exacerbated |
---|
104 | when the low priority task is prevented from executing by one or more medium |
---|
105 | priority tasks. Because the low priority task is not executing, it cannot |
---|
106 | complete its interaction with the resource and release that resource. The high |
---|
107 | priority task is effectively prevented from executing by lower priority tasks. |
---|
108 | |
---|
109 | .. _Priority Inheritance: |
---|
110 | |
---|
111 | Priority Inheritance |
---|
112 | -------------------- |
---|
113 | |
---|
114 | Priority inheritance is an algorithm that calls for the lower priority task |
---|
115 | holding a resource to have its priority increased to that of the highest |
---|
116 | priority task blocked waiting for that resource. Each time a task blocks |
---|
117 | attempting to obtain the resource, the task holding the resource may have its |
---|
118 | priority increased. |
---|
119 | |
---|
120 | On SMP configurations, in case the task holding the resource and the task that |
---|
121 | blocks attempting to obtain the resource are in different scheduler instances, |
---|
122 | the priority of the holder is raised to the pseudo-interrupt priority (priority |
---|
123 | boosting). The pseudo-interrupt priority is the highest priority. |
---|
124 | |
---|
125 | RTEMS supports priority inheritance for local, binary semaphores that use the |
---|
126 | priority task wait queue blocking discipline. When a task of higher priority |
---|
127 | than the task holding the semaphore blocks, the priority of the task holding |
---|
128 | the semaphore is increased to that of the blocking task. When the task holding |
---|
129 | the task completely releases the binary semaphore (i.e. not for a nested |
---|
130 | release), the holder's priority is restored to the value it had before any |
---|
131 | higher priority was inherited. |
---|
132 | |
---|
133 | The RTEMS implementation of the priority inheritance algorithm takes into |
---|
134 | account the scenario in which a task holds more than one binary semaphore. The |
---|
135 | holding task will execute at the priority of the higher of the highest ceiling |
---|
136 | priority or at the priority of the highest priority task blocked waiting for |
---|
137 | any of the semaphores the task holds. Only when the task releases ALL of the |
---|
138 | binary semaphores it holds will its priority be restored to the normal value. |
---|
139 | |
---|
140 | .. _Priority Ceiling: |
---|
141 | |
---|
142 | Priority Ceiling |
---|
143 | ---------------- |
---|
144 | |
---|
145 | Priority ceiling is an algorithm that calls for the lower priority task holding |
---|
146 | a resource to have its priority increased to that of the highest priority task |
---|
147 | which will EVER block waiting for that resource. This algorithm addresses the |
---|
148 | problem of priority inversion although it avoids the possibility of changing |
---|
149 | the priority of the task holding the resource multiple times. The priority |
---|
150 | ceiling algorithm will only change the priority of the task holding the |
---|
151 | resource a maximum of one time. The ceiling priority is set at creation time |
---|
152 | and must be the priority of the highest priority task which will ever attempt |
---|
153 | to acquire that semaphore. |
---|
154 | |
---|
155 | RTEMS supports priority ceiling for local, binary semaphores that use the |
---|
156 | priority task wait queue blocking discipline. When a task of lower priority |
---|
157 | than the ceiling priority successfully obtains the semaphore, its priority is |
---|
158 | raised to the ceiling priority. When the task holding the task completely |
---|
159 | releases the binary semaphore (i.e. not for a nested release), the holder's |
---|
160 | priority is restored to the value it had before any higher priority was put |
---|
161 | into effect. |
---|
162 | |
---|
163 | The need to identify the highest priority task which will attempt to obtain a |
---|
164 | particular semaphore can be a difficult task in a large, complicated system. |
---|
165 | Although the priority ceiling algorithm is more efficient than the priority |
---|
166 | inheritance algorithm with respect to the maximum number of task priority |
---|
167 | changes which may occur while a task holds a particular semaphore, the priority |
---|
168 | inheritance algorithm is more forgiving in that it does not require this |
---|
169 | apriori information. |
---|
170 | |
---|
171 | The RTEMS implementation of the priority ceiling algorithm takes into account |
---|
172 | the scenario in which a task holds more than one binary semaphore. The holding |
---|
173 | task will execute at the priority of the higher of the highest ceiling priority |
---|
174 | or at the priority of the highest priority task blocked waiting for any of the |
---|
175 | semaphores the task holds. Only when the task releases ALL of the binary |
---|
176 | semaphores it holds will its priority be restored to the normal value. |
---|
177 | |
---|
178 | .. _Multiprocessor Resource Sharing Protocol: |
---|
179 | |
---|
180 | Multiprocessor Resource Sharing Protocol |
---|
181 | ---------------------------------------- |
---|
182 | |
---|
183 | The Multiprocessor Resource Sharing Protocol (MrsP) is defined in *A. Burns |
---|
184 | and A.J. Wellings, A Schedulability Compatible Multiprocessor Resource Sharing |
---|
185 | Protocol - MrsP, Proceedings of the 25th Euromicro Conference on Real-Time |
---|
186 | Systems (ECRTS 2013), July 2013*. It is a generalization of the Priority |
---|
187 | Ceiling Protocol to SMP systems. Each MrsP semaphore uses a ceiling priority |
---|
188 | per scheduler instance. These ceiling priorities can be specified with |
---|
189 | ``rtems_semaphore_set_priority()``. A task obtaining or owning a MrsP |
---|
190 | semaphore will execute with the ceiling priority for its scheduler instance as |
---|
191 | specified by the MrsP semaphore object. Tasks waiting to get ownership of a |
---|
192 | MrsP semaphore will not relinquish the processor voluntarily. In case the |
---|
193 | owner of a MrsP semaphore gets preempted it can ask all tasks waiting for this |
---|
194 | semaphore to help out and temporarily borrow the right to execute on one of |
---|
195 | their assigned processors. |
---|
196 | |
---|
197 | .. _Building a Semaphore Attribute Set: |
---|
198 | |
---|
199 | Building a Semaphore Attribute Set |
---|
200 | ---------------------------------- |
---|
201 | |
---|
202 | In general, an attribute set is built by a bitwise OR of the desired attribute |
---|
203 | components. The following table lists the set of valid semaphore attributes: |
---|
204 | |
---|
205 | .. list-table:: |
---|
206 | :class: rtems-table |
---|
207 | |
---|
208 | * - ``RTEMS_FIFO`` |
---|
209 | - tasks wait by FIFO (default) |
---|
210 | * - ``RTEMS_PRIORITY`` |
---|
211 | - tasks wait by priority |
---|
212 | * - ``RTEMS_BINARY_SEMAPHORE`` |
---|
213 | - restrict values to 0 and 1 |
---|
214 | * - ``RTEMS_COUNTING_SEMAPHORE`` |
---|
215 | - no restriction on values (default) |
---|
216 | * - ``RTEMS_SIMPLE_BINARY_SEMAPHORE`` |
---|
217 | - restrict values to 0 and 1, do not allow nested access, allow deletion of |
---|
218 | locked semaphore. |
---|
219 | * - ``RTEMS_NO_INHERIT_PRIORITY`` |
---|
220 | - do not use priority inheritance (default) |
---|
221 | * - ``RTEMS_INHERIT_PRIORITY`` |
---|
222 | - use priority inheritance |
---|
223 | * - ``RTEMS_NO_PRIORITY_CEILING`` |
---|
224 | - do not use priority ceiling (default) |
---|
225 | * - ``RTEMS_PRIORITY_CEILING`` |
---|
226 | - use priority ceiling |
---|
227 | * - ``RTEMS_NO_MULTIPROCESSOR_RESOURCE_SHARING`` |
---|
228 | - do not use Multiprocessor Resource Sharing Protocol (default) |
---|
229 | * - ``RTEMS_MULTIPROCESSOR_RESOURCE_SHARING`` |
---|
230 | - use Multiprocessor Resource Sharing Protocol |
---|
231 | * - ``RTEMS_LOCAL`` |
---|
232 | - local semaphore (default) |
---|
233 | * - ``RTEMS_GLOBAL`` |
---|
234 | - global semaphore |
---|
235 | |
---|
236 | Attribute values are specifically designed to be mutually exclusive, therefore |
---|
237 | bitwise OR and addition operations are equivalent as long as each attribute |
---|
238 | appears exactly once in the component list. An attribute listed as a default |
---|
239 | is not required to appear in the attribute list, although it is a good |
---|
240 | programming practice to specify default attributes. If all defaults are |
---|
241 | desired, the attribute ``RTEMS_DEFAULT_ATTRIBUTES`` should be specified on this |
---|
242 | call. |
---|
243 | |
---|
244 | This example demonstrates the attribute_set parameter needed to create a local |
---|
245 | semaphore with the task priority waiting queue discipline. The attribute_set |
---|
246 | parameter passed to the ``rtems_semaphore_create`` directive could be either |
---|
247 | ``RTEMS_PRIORITY`` or ``RTEMS_LOCAL | RTEMS_PRIORITY``. The attribute_set |
---|
248 | parameter can be set to ``RTEMS_PRIORITY`` because ``RTEMS_LOCAL`` is the |
---|
249 | default for all created tasks. If a similar semaphore were to be known |
---|
250 | globally, then the attribute_set parameter would be ``RTEMS_GLOBAL | |
---|
251 | RTEMS_PRIORITY``. |
---|
252 | |
---|
253 | Some combinatinos of these attributes are invalid. For example, priority |
---|
254 | ordered blocking discipline must be applied to a binary semaphore in order to |
---|
255 | use either the priority inheritance or priority ceiling functionality. The |
---|
256 | following tree figure illustrates the valid combinations. |
---|
257 | |
---|
258 | .. figure:: ../images/c_user/semaphore_attributes.png |
---|
259 | :width: 90% |
---|
260 | :align: center |
---|
261 | :alt: Semaphore Attributes |
---|
262 | |
---|
263 | .. _Building a SEMAPHORE_OBTAIN Option Set: |
---|
264 | |
---|
265 | Building a SEMAPHORE_OBTAIN Option Set |
---|
266 | -------------------------------------- |
---|
267 | |
---|
268 | In general, an option is built by a bitwise OR of the desired option |
---|
269 | components. The set of valid options for the ``rtems_semaphore_obtain`` |
---|
270 | directive are listed in the following table: |
---|
271 | |
---|
272 | .. list-table:: |
---|
273 | :class: rtems-table |
---|
274 | |
---|
275 | * - ``RTEMS_WAIT`` |
---|
276 | - task will wait for semaphore (default) |
---|
277 | * - ``RTEMS_NO_WAIT`` |
---|
278 | - task should not wait |
---|
279 | |
---|
280 | Option values are specifically designed to be mutually exclusive, therefore |
---|
281 | bitwise OR and addition operations are equivalent as long as each attribute |
---|
282 | appears exactly once in the component list. An option listed as a default is |
---|
283 | not required to appear in the list, although it is a good programming practice |
---|
284 | to specify default options. If all defaults are desired, the option |
---|
285 | ``RTEMS_DEFAULT_OPTIONS`` should be specified on this call. |
---|
286 | |
---|
287 | This example demonstrates the option parameter needed to poll for a semaphore. |
---|
288 | The option parameter passed to the ``rtems_semaphore_obtain`` directive should |
---|
289 | be ``RTEMS_NO_WAIT``. |
---|
290 | |
---|
291 | Operations |
---|
292 | ========== |
---|
293 | |
---|
294 | .. _Creating a Semaphore: |
---|
295 | |
---|
296 | Creating a Semaphore |
---|
297 | -------------------- |
---|
298 | |
---|
299 | The ``rtems_semaphore_create`` directive creates a binary or counting semaphore |
---|
300 | with a user-specified name as well as an initial count. If a binary semaphore |
---|
301 | is created with a count of zero (0) to indicate that it has been allocated, |
---|
302 | then the task creating the semaphore is considered the current holder of the |
---|
303 | semaphore. At create time the method for ordering waiting tasks in the |
---|
304 | semaphore's task wait queue (by FIFO or task priority) is specified. |
---|
305 | Additionally, the priority inheritance or priority ceiling algorithm may be |
---|
306 | selected for local, binary semaphores that use the priority task wait queue |
---|
307 | blocking discipline. If the priority ceiling algorithm is selected, then the |
---|
308 | highest priority of any task which will attempt to obtain this semaphore must |
---|
309 | be specified. RTEMS allocates a Semaphore Control Block (SMCB) from the SMCB |
---|
310 | free list. This data structure is used by RTEMS to manage the newly created |
---|
311 | semaphore. Also, a unique semaphore ID is generated and returned to the |
---|
312 | calling task. |
---|
313 | |
---|
314 | .. _Obtaining Semaphore IDs: |
---|
315 | |
---|
316 | Obtaining Semaphore IDs |
---|
317 | ----------------------- |
---|
318 | |
---|
319 | When a semaphore is created, RTEMS generates a unique semaphore ID and assigns |
---|
320 | it to the created semaphore until it is deleted. The semaphore ID may be |
---|
321 | obtained by either of two methods. First, as the result of an invocation of |
---|
322 | the ``rtems_semaphore_create`` directive, the semaphore ID is stored in a user |
---|
323 | provided location. Second, the semaphore ID may be obtained later using the |
---|
324 | ``rtems_semaphore_ident`` directive. The semaphore ID is used by other |
---|
325 | semaphore manager directives to access this semaphore. |
---|
326 | |
---|
327 | .. _Acquiring a Semaphore: |
---|
328 | |
---|
329 | Acquiring a Semaphore |
---|
330 | --------------------- |
---|
331 | |
---|
332 | The ``rtems_semaphore_obtain`` directive is used to acquire the |
---|
333 | specified semaphore. A simplified version of the ``rtems_semaphore_obtain`` |
---|
334 | directive can be described as follows: |
---|
335 | |
---|
336 | If the semaphore's count is greater than zero then decrement the |
---|
337 | semaphore's count else wait for release of semaphore then return |
---|
338 | SUCCESSFUL. |
---|
339 | |
---|
340 | When the semaphore cannot be immediately acquired, one of the following |
---|
341 | situations applies: |
---|
342 | |
---|
343 | - By default, the calling task will wait forever to acquire the semaphore. |
---|
344 | |
---|
345 | - Specifying ``RTEMS_NO_WAIT`` forces an immediate return with an error status |
---|
346 | code. |
---|
347 | |
---|
348 | - Specifying a timeout limits the interval the task will wait before returning |
---|
349 | with an error status code. |
---|
350 | |
---|
351 | If the task waits to acquire the semaphore, then it is placed in the |
---|
352 | semaphore's task wait queue in either FIFO or task priority order. If the task |
---|
353 | blocked waiting for a binary semaphore using priority inheritance and the |
---|
354 | task's priority is greater than that of the task currently holding the |
---|
355 | semaphore, then the holding task will inherit the priority of the blocking |
---|
356 | task. All tasks waiting on a semaphore are returned an error code when the |
---|
357 | semaphore is deleted. |
---|
358 | |
---|
359 | When a task successfully obtains a semaphore using priority ceiling and the |
---|
360 | priority ceiling for this semaphore is greater than that of the holder, then |
---|
361 | the holder's priority will be elevated. |
---|
362 | |
---|
363 | .. _Releasing a Semaphore: |
---|
364 | |
---|
365 | Releasing a Semaphore |
---|
366 | --------------------- |
---|
367 | |
---|
368 | The ``rtems_semaphore_release`` directive is used to release the specified |
---|
369 | semaphore. A simplified version of the ``rtems_semaphore_release`` directive |
---|
370 | can be described as follows: |
---|
371 | |
---|
372 | If there are no tasks are waiting on this semaphore then increment the |
---|
373 | semaphore's count else assign semaphore to a waiting task and return |
---|
374 | SUCCESSFUL. |
---|
375 | |
---|
376 | If this is the outermost release of a binary semaphore that uses priority |
---|
377 | inheritance or priority ceiling and the task does not currently hold any other |
---|
378 | binary semaphores, then the task performing the ``rtems_semaphore_release`` |
---|
379 | will have its priority restored to its normal value. |
---|
380 | |
---|
381 | .. _Deleting a Semaphore: |
---|
382 | |
---|
383 | Deleting a Semaphore |
---|
384 | -------------------- |
---|
385 | |
---|
386 | The ``rtems_semaphore_delete`` directive removes a semaphore from the system |
---|
387 | and frees its control block. A semaphore can be deleted by any local task that |
---|
388 | knows the semaphore's ID. As a result of this directive, all tasks blocked |
---|
389 | waiting to acquire the semaphore will be readied and returned a status code |
---|
390 | which indicates that the semaphore was deleted. Any subsequent references to |
---|
391 | the semaphore's name and ID are invalid. |
---|
392 | |
---|
393 | Directives |
---|
394 | ========== |
---|
395 | |
---|
396 | This section details the semaphore manager's directives. A subsection is |
---|
397 | dedicated to each of this manager's directives and describes the calling |
---|
398 | sequence, related constants, usage, and status codes. |
---|
399 | |
---|
400 | .. raw:: latex |
---|
401 | |
---|
402 | \clearpage |
---|
403 | |
---|
404 | .. _rtems_semaphore_create: |
---|
405 | |
---|
406 | SEMAPHORE_CREATE - Create a semaphore |
---|
407 | ------------------------------------- |
---|
408 | .. index:: create a semaphore |
---|
409 | .. index:: rtems_semaphore_create |
---|
410 | |
---|
411 | |
---|
412 | CALLING SEQUENCE: |
---|
413 | .. code-block:: c |
---|
414 | |
---|
415 | rtems_status_code rtems_semaphore_create( |
---|
416 | rtems_name name, |
---|
417 | uint32_t count, |
---|
418 | rtems_attribute attribute_set, |
---|
419 | rtems_task_priority priority_ceiling, |
---|
420 | rtems_id *id |
---|
421 | ); |
---|
422 | |
---|
423 | DIRECTIVE STATUS CODES: |
---|
424 | .. list-table:: |
---|
425 | :class: rtems-table |
---|
426 | |
---|
427 | * - ``RTEMS_SUCCESSFUL`` |
---|
428 | - semaphore created successfully |
---|
429 | * - ``RTEMS_INVALID_NAME`` |
---|
430 | - invalid semaphore name |
---|
431 | * - ``RTEMS_INVALID_ADDRESS`` |
---|
432 | - ``id`` is NULL |
---|
433 | * - ``RTEMS_TOO_MANY`` |
---|
434 | - too many semaphores created |
---|
435 | * - ``RTEMS_NOT_DEFINED`` |
---|
436 | - invalid attribute set |
---|
437 | * - ``RTEMS_INVALID_NUMBER`` |
---|
438 | - invalid starting count for binary semaphore |
---|
439 | * - ``RTEMS_MP_NOT_CONFIGURED`` |
---|
440 | - multiprocessing not configured |
---|
441 | * - ``RTEMS_TOO_MANY`` |
---|
442 | - too many global objects |
---|
443 | |
---|
444 | DESCRIPTION: |
---|
445 | This directive creates a semaphore which resides on the local node. The |
---|
446 | created semaphore has the user-defined name specified in name and the |
---|
447 | initial count specified in count. For control and maintenance of the |
---|
448 | semaphore, RTEMS allocates and initializes a SMCB. The RTEMS-assigned |
---|
449 | semaphore id is returned in id. This semaphore id is used with other |
---|
450 | semaphore related directives to access the semaphore. |
---|
451 | |
---|
452 | Specifying PRIORITY in attribute_set causes tasks waiting for a semaphore |
---|
453 | to be serviced according to task priority. When FIFO is selected, tasks |
---|
454 | are serviced in First In-First Out order. |
---|
455 | |
---|
456 | NOTES: |
---|
457 | This directive will not cause the calling task to be preempted. |
---|
458 | |
---|
459 | The priority inheritance and priority ceiling algorithms are only supported |
---|
460 | for local, binary semaphores that use the priority task wait queue blocking |
---|
461 | discipline. |
---|
462 | |
---|
463 | The following semaphore attribute constants are defined by RTEMS: |
---|
464 | |
---|
465 | .. list-table:: |
---|
466 | :class: rtems-table |
---|
467 | |
---|
468 | * - ``RTEMS_FIFO`` |
---|
469 | - tasks wait by FIFO (default) |
---|
470 | * - ``RTEMS_PRIORITY`` |
---|
471 | - tasks wait by priority |
---|
472 | * - ``RTEMS_BINARY_SEMAPHORE`` |
---|
473 | - restrict values to 0 and 1 |
---|
474 | * - ``RTEMS_COUNTING_SEMAPHORE`` |
---|
475 | - no restriction on values (default) |
---|
476 | * - ``RTEMS_SIMPLE_BINARY_SEMAPHORE`` |
---|
477 | - restrict values to 0 and 1, block on nested access, allow deletion of locked semaphore. |
---|
478 | * - ``RTEMS_NO_INHERIT_PRIORITY`` |
---|
479 | - do not use priority inheritance (default) |
---|
480 | * - ``RTEMS_INHERIT_PRIORITY`` |
---|
481 | - use priority inheritance |
---|
482 | * - ``RTEMS_NO_PRIORITY_CEILING`` |
---|
483 | - do not use priority ceiling (default) |
---|
484 | * - ``RTEMS_PRIORITY_CEILING`` |
---|
485 | - use priority ceiling |
---|
486 | * - ``RTEMS_NO_MULTIPROCESSOR_RESOURCE_SHARING`` |
---|
487 | - do not use Multiprocessor Resource Sharing Protocol (default) |
---|
488 | * - ``RTEMS_MULTIPROCESSOR_RESOURCE_SHARING`` |
---|
489 | - use Multiprocessor Resource Sharing Protocol |
---|
490 | * - ``RTEMS_LOCAL`` |
---|
491 | - local semaphore (default) |
---|
492 | * - ``RTEMS_GLOBAL`` |
---|
493 | - global semaphore |
---|
494 | |
---|
495 | Semaphores should not be made global unless remote tasks must interact with |
---|
496 | the created semaphore. This is to avoid the system overhead incurred by |
---|
497 | the creation of a global semaphore. When a global semaphore is created, |
---|
498 | the semaphore's name and id must be transmitted to every node in the system |
---|
499 | for insertion in the local copy of the global object table. |
---|
500 | |
---|
501 | *Note*, some combinations of attributes are not valid. See the earlier |
---|
502 | discussion on this. |
---|
503 | |
---|
504 | The total number of global objects, including semaphores, is limited by the |
---|
505 | maximum_global_objects field in the Configuration Table. |
---|
506 | |
---|
507 | It is not allowed to create an initially locked MrsP semaphore and the |
---|
508 | ``RTEMS_INVALID_NUMBER`` status code will be returned on SMP configurations |
---|
509 | in this case. This prevents lock order reversal problems with the |
---|
510 | allocator mutex. |
---|
511 | |
---|
512 | .. raw:: latex |
---|
513 | |
---|
514 | \clearpage |
---|
515 | |
---|
516 | .. _rtems_semaphore_ident: |
---|
517 | |
---|
518 | SEMAPHORE_IDENT - Get ID of a semaphore |
---|
519 | --------------------------------------- |
---|
520 | .. index:: get ID of a semaphore |
---|
521 | .. index:: obtain ID of a semaphore |
---|
522 | |
---|
523 | .. index:: rtems_semaphore_ident |
---|
524 | |
---|
525 | CALLING SEQUENCE: |
---|
526 | .. code-block:: c |
---|
527 | |
---|
528 | rtems_status_code rtems_semaphore_ident( |
---|
529 | rtems_name name, |
---|
530 | uint32_t node, |
---|
531 | rtems_id *id |
---|
532 | ); |
---|
533 | |
---|
534 | DIRECTIVE STATUS CODES: |
---|
535 | .. list-table:: |
---|
536 | :class: rtems-table |
---|
537 | |
---|
538 | * - ``RTEMS_SUCCESSFUL`` |
---|
539 | - semaphore identified successfully |
---|
540 | * - ``RTEMS_INVALID_NAME`` |
---|
541 | - semaphore name not found |
---|
542 | * - ``RTEMS_INVALID_NODE`` |
---|
543 | - invalid node id |
---|
544 | |
---|
545 | DESCRIPTION: |
---|
546 | This directive obtains the semaphore id associated with the semaphore name. |
---|
547 | If the semaphore name is not unique, then the semaphore id will match one |
---|
548 | of the semaphores with that name. However, this semaphore id is not |
---|
549 | guaranteed to correspond to the desired semaphore. The semaphore id is |
---|
550 | used by other semaphore related directives to access the semaphore. |
---|
551 | |
---|
552 | NOTES: |
---|
553 | This directive will not cause the running task to be preempted. |
---|
554 | |
---|
555 | If node is ``RTEMS_SEARCH_ALL_NODES``, all nodes are searched with the |
---|
556 | local node being searched first. All other nodes are searched with the |
---|
557 | lowest numbered node searched first. |
---|
558 | |
---|
559 | If node is a valid node number which does not represent the local node, |
---|
560 | then only the semaphores exported by the designated node are searched. |
---|
561 | |
---|
562 | This directive does not generate activity on remote nodes. It accesses |
---|
563 | only the local copy of the global object table. |
---|
564 | |
---|
565 | .. raw:: latex |
---|
566 | |
---|
567 | \clearpage |
---|
568 | |
---|
569 | .. _rtems_semaphore_delete: |
---|
570 | |
---|
571 | SEMAPHORE_DELETE - Delete a semaphore |
---|
572 | ------------------------------------- |
---|
573 | .. index:: delete a semaphore |
---|
574 | .. index:: rtems_semaphore_delete |
---|
575 | |
---|
576 | CALLING SEQUENCE: |
---|
577 | .. code-block:: c |
---|
578 | |
---|
579 | rtems_status_code rtems_semaphore_delete( |
---|
580 | rtems_id id |
---|
581 | ); |
---|
582 | |
---|
583 | DIRECTIVE STATUS CODES: |
---|
584 | .. list-table:: |
---|
585 | :class: rtems-table |
---|
586 | |
---|
587 | * - ``RTEMS_SUCCESSFUL`` |
---|
588 | - semaphore deleted successfully |
---|
589 | * - ``RTEMS_INVALID_ID`` |
---|
590 | - invalid semaphore id |
---|
591 | * - ``RTEMS_RESOURCE_IN_USE`` |
---|
592 | - binary semaphore is in use |
---|
593 | * - ``RTEMS_ILLEGAL_ON_REMOTE_OBJECT`` |
---|
594 | - cannot delete remote semaphore |
---|
595 | |
---|
596 | DESCRIPTION: |
---|
597 | This directive deletes the semaphore specified by ``id``. All tasks |
---|
598 | blocked waiting to acquire the semaphore will be readied and returned a |
---|
599 | status code which indicates that the semaphore was deleted. The SMCB for |
---|
600 | this semaphore is reclaimed by RTEMS. |
---|
601 | |
---|
602 | NOTES: |
---|
603 | The calling task will be preempted if it is enabled by the task's execution |
---|
604 | mode and a higher priority local task is waiting on the deleted semaphore. |
---|
605 | The calling task will NOT be preempted if all of the tasks that are waiting |
---|
606 | on the semaphore are remote tasks. |
---|
607 | |
---|
608 | The calling task does not have to be the task that created the semaphore. Any |
---|
609 | local task that knows the semaphore id can delete the semaphore. |
---|
610 | |
---|
611 | When a global semaphore is deleted, the semaphore id must be transmitted to |
---|
612 | every node in the system for deletion from the local copy of the global |
---|
613 | object table. |
---|
614 | |
---|
615 | The semaphore must reside on the local node, even if the semaphore was |
---|
616 | created with the ``RTEMS_GLOBAL`` option. |
---|
617 | |
---|
618 | Proxies, used to represent remote tasks, are reclaimed when the semaphore |
---|
619 | is deleted. |
---|
620 | |
---|
621 | .. raw:: latex |
---|
622 | |
---|
623 | \clearpage |
---|
624 | |
---|
625 | .. _rtems_semaphore_obtain: |
---|
626 | |
---|
627 | SEMAPHORE_OBTAIN - Acquire a semaphore |
---|
628 | -------------------------------------- |
---|
629 | .. index:: obtain a semaphore |
---|
630 | .. index:: lock a semaphore |
---|
631 | .. index:: rtems_semaphore_obtain |
---|
632 | |
---|
633 | CALLING SEQUENCE: |
---|
634 | .. code-block:: c |
---|
635 | |
---|
636 | rtems_status_code rtems_semaphore_obtain( |
---|
637 | rtems_id id, |
---|
638 | rtems_option option_set, |
---|
639 | rtems_interval timeout |
---|
640 | ); |
---|
641 | |
---|
642 | DIRECTIVE STATUS CODES: |
---|
643 | .. list-table:: |
---|
644 | :class: rtems-table |
---|
645 | |
---|
646 | * - ``RTEMS_SUCCESSFUL`` |
---|
647 | - semaphore obtained successfully |
---|
648 | * - ``RTEMS_UNSATISFIED`` |
---|
649 | - semaphore not available |
---|
650 | * - ``RTEMS_TIMEOUT`` |
---|
651 | - timed out waiting for semaphore |
---|
652 | * - ``RTEMS_OBJECT_WAS_DELETED`` |
---|
653 | - semaphore deleted while waiting |
---|
654 | * - ``RTEMS_INVALID_ID`` |
---|
655 | - invalid semaphore id |
---|
656 | |
---|
657 | DESCRIPTION: |
---|
658 | This directive acquires the semaphore specified by id. The ``RTEMS_WAIT`` |
---|
659 | and ``RTEMS_NO_WAIT`` components of the options parameter indicate whether |
---|
660 | the calling task wants to wait for the semaphore to become available or |
---|
661 | return immediately if the semaphore is not currently available. With |
---|
662 | either ``RTEMS_WAIT`` or ``RTEMS_NO_WAIT``, if the current semaphore count |
---|
663 | is positive, then it is decremented by one and the semaphore is |
---|
664 | successfully acquired by returning immediately with a successful return |
---|
665 | code. |
---|
666 | |
---|
667 | If the calling task chooses to return immediately and the current semaphore |
---|
668 | count is zero or negative, then a status code is returned indicating that |
---|
669 | the semaphore is not available. If the calling task chooses to wait for a |
---|
670 | semaphore and the current semaphore count is zero or negative, then it is |
---|
671 | decremented by one and the calling task is placed on the semaphore's wait |
---|
672 | queue and blocked. If the semaphore was created with the |
---|
673 | ``RTEMS_PRIORITY`` attribute, then the calling task is inserted into the |
---|
674 | queue according to its priority. However, if the semaphore was created |
---|
675 | with the ``RTEMS_FIFO`` attribute, then the calling task is placed at the |
---|
676 | rear of the wait queue. If the binary semaphore was created with the |
---|
677 | ``RTEMS_INHERIT_PRIORITY`` attribute, then the priority of the task |
---|
678 | currently holding the binary semaphore is guaranteed to be greater than or |
---|
679 | equal to that of the blocking task. If the binary semaphore was created |
---|
680 | with the ``RTEMS_PRIORITY_CEILING`` attribute, a task successfully obtains |
---|
681 | the semaphore, and the priority of that task is greater than the ceiling |
---|
682 | priority for this semaphore, then the priority of the task obtaining the |
---|
683 | semaphore is elevated to that of the ceiling. |
---|
684 | |
---|
685 | The timeout parameter specifies the maximum interval the calling task is |
---|
686 | willing to be blocked waiting for the semaphore. If it is set to |
---|
687 | ``RTEMS_NO_TIMEOUT``, then the calling task will wait forever. If the |
---|
688 | semaphore is available or the ``RTEMS_NO_WAIT`` option component is set, |
---|
689 | then timeout is ignored. |
---|
690 | |
---|
691 | Deadlock situations are detected for MrsP semaphores and the |
---|
692 | ``RTEMS_UNSATISFIED`` status code will be returned on SMP configurations in |
---|
693 | this case. |
---|
694 | |
---|
695 | NOTES: |
---|
696 | The following semaphore acquisition option constants are defined by RTEMS: |
---|
697 | |
---|
698 | .. list-table:: |
---|
699 | :class: rtems-table |
---|
700 | |
---|
701 | * - ``RTEMS_WAIT`` |
---|
702 | - task will wait for semaphore (default) |
---|
703 | * - ``RTEMS_NO_WAIT`` |
---|
704 | - task should not wait |
---|
705 | |
---|
706 | Attempting to obtain a global semaphore which does not reside on the local |
---|
707 | node will generate a request to the remote node to access the semaphore. |
---|
708 | If the semaphore is not available and ``RTEMS_NO_WAIT`` was not specified, |
---|
709 | then the task must be blocked until the semaphore is released. A proxy is |
---|
710 | allocated on the remote node to represent the task until the semaphore is |
---|
711 | released. |
---|
712 | |
---|
713 | A clock tick is required to support the timeout functionality of this |
---|
714 | directive. |
---|
715 | |
---|
716 | It is not allowed to obtain a MrsP semaphore more than once by one task at |
---|
717 | a time (nested access) and the ``RTEMS_UNSATISFIED`` status code will be |
---|
718 | returned on SMP configurations in this case. |
---|
719 | |
---|
720 | .. raw:: latex |
---|
721 | |
---|
722 | \clearpage |
---|
723 | |
---|
724 | .. _rtems_semaphore_release: |
---|
725 | |
---|
726 | SEMAPHORE_RELEASE - Release a semaphore |
---|
727 | --------------------------------------- |
---|
728 | .. index:: release a semaphore |
---|
729 | .. index:: unlock a semaphore |
---|
730 | .. index:: rtems_semaphore_release |
---|
731 | |
---|
732 | CALLING SEQUENCE: |
---|
733 | .. code-block:: c |
---|
734 | |
---|
735 | rtems_status_code rtems_semaphore_release( |
---|
736 | rtems_id id |
---|
737 | ); |
---|
738 | |
---|
739 | DIRECTIVE STATUS CODES: |
---|
740 | .. list-table:: |
---|
741 | :class: rtems-table |
---|
742 | |
---|
743 | * - ``RTEMS_SUCCESSFUL`` |
---|
744 | - semaphore released successfully |
---|
745 | * - ``RTEMS_INVALID_ID`` |
---|
746 | - invalid semaphore id |
---|
747 | * - ``RTEMS_NOT_OWNER_OF_RESOURCE`` |
---|
748 | - calling task does not own semaphore |
---|
749 | * - ``RTEMS_INCORRECT_STATE`` |
---|
750 | - invalid unlock order |
---|
751 | |
---|
752 | DESCRIPTION: |
---|
753 | This directive releases the semaphore specified by id. The semaphore count |
---|
754 | is incremented by one. If the count is zero or negative, then the first |
---|
755 | task on this semaphore's wait queue is removed and unblocked. The |
---|
756 | unblocked task may preempt the running task if the running task's |
---|
757 | preemption mode is enabled and the unblocked task has a higher priority |
---|
758 | than the running task. |
---|
759 | |
---|
760 | NOTES: |
---|
761 | The calling task may be preempted if it causes a higher priority task to be |
---|
762 | made ready for execution. |
---|
763 | |
---|
764 | Releasing a global semaphore which does not reside on the local node will |
---|
765 | generate a request telling the remote node to release the semaphore. |
---|
766 | |
---|
767 | If the task to be unblocked resides on a different node from the semaphore, |
---|
768 | then the semaphore allocation is forwarded to the appropriate node, the |
---|
769 | waiting task is unblocked, and the proxy used to represent the task is |
---|
770 | reclaimed. |
---|
771 | |
---|
772 | The outermost release of a local, binary, priority inheritance or priority |
---|
773 | ceiling semaphore may result in the calling task having its priority |
---|
774 | lowered. This will occur if the calling task holds no other binary |
---|
775 | semaphores and it has inherited a higher priority. |
---|
776 | |
---|
777 | The MrsP semaphores must be released in the reversed obtain order, |
---|
778 | otherwise the ``RTEMS_INCORRECT_STATE`` status code will be returned on SMP |
---|
779 | configurations in this case. |
---|
780 | |
---|
781 | .. raw:: latex |
---|
782 | |
---|
783 | \clearpage |
---|
784 | |
---|
785 | .. _rtems_semaphore_flush: |
---|
786 | |
---|
787 | SEMAPHORE_FLUSH - Unblock all tasks waiting on a semaphore |
---|
788 | ---------------------------------------------------------- |
---|
789 | .. index:: flush a semaphore |
---|
790 | .. index:: unblock all tasks waiting on a semaphore |
---|
791 | .. index:: rtems_semaphore_flush |
---|
792 | |
---|
793 | CALLING SEQUENCE: |
---|
794 | .. code-block:: c |
---|
795 | |
---|
796 | rtems_status_code rtems_semaphore_flush( |
---|
797 | rtems_id id |
---|
798 | ); |
---|
799 | |
---|
800 | DIRECTIVE STATUS CODES: |
---|
801 | .. list-table:: |
---|
802 | :class: rtems-table |
---|
803 | |
---|
804 | * - ``RTEMS_SUCCESSFUL`` |
---|
805 | - semaphore released successfully |
---|
806 | * - ``RTEMS_INVALID_ID`` |
---|
807 | - invalid semaphore id |
---|
808 | * - ``RTEMS_NOT_DEFINED`` |
---|
809 | - operation not defined for the protocol ofthe semaphore |
---|
810 | * - ``RTEMS_ILLEGAL_ON_REMOTE_OBJECT`` |
---|
811 | - not supported for remote semaphores |
---|
812 | |
---|
813 | DESCRIPTION: |
---|
814 | This directive unblocks all tasks waiting on the semaphore specified by id. |
---|
815 | Since there are tasks blocked on the semaphore, the semaphore's count is |
---|
816 | not changed by this directive and thus is zero before and after this |
---|
817 | directive is executed. Tasks which are unblocked as the result of this |
---|
818 | directive will return from the ``rtems_semaphore_obtain`` directive with a |
---|
819 | status code of ``RTEMS_UNSATISFIED`` to indicate that the semaphore was not |
---|
820 | obtained. |
---|
821 | |
---|
822 | This directive may unblock any number of tasks. Any of the unblocked tasks |
---|
823 | may preempt the running task if the running task's preemption mode is |
---|
824 | enabled and an unblocked task has a higher priority than the running task. |
---|
825 | |
---|
826 | NOTES: |
---|
827 | The calling task may be preempted if it causes a higher priority task to be |
---|
828 | made ready for execution. |
---|
829 | |
---|
830 | If the task to be unblocked resides on a different node from the semaphore, |
---|
831 | then the waiting task is unblocked, and the proxy used to represent the |
---|
832 | task is reclaimed. |
---|
833 | |
---|
834 | It is not allowed to flush a MrsP semaphore and the ``RTEMS_NOT_DEFINED`` |
---|
835 | status code will be returned on SMP configurations in this case. |
---|
836 | |
---|
837 | .. raw:: latex |
---|
838 | |
---|
839 | \clearpage |
---|
840 | |
---|
841 | .. _rtems_semaphore_set_priority: |
---|
842 | |
---|
843 | SEMAPHORE_SET_PRIORITY - Set priority by scheduler for a semaphore |
---|
844 | ------------------------------------------------------------------ |
---|
845 | .. index:: set priority by scheduler for a semaphore |
---|
846 | .. index:: rtems_semaphore_set_priority |
---|
847 | |
---|
848 | CALLING SEQUENCE: |
---|
849 | .. code-block:: c |
---|
850 | |
---|
851 | rtems_status_code rtems_semaphore_set_priority( |
---|
852 | rtems_id semaphore_id, |
---|
853 | rtems_id scheduler_id, |
---|
854 | rtems_task_priority new_priority, |
---|
855 | rtems_task_priority *old_priority |
---|
856 | ); |
---|
857 | |
---|
858 | DIRECTIVE STATUS CODES: |
---|
859 | .. list-table:: |
---|
860 | :class: rtems-table |
---|
861 | |
---|
862 | * - ``RTEMS_SUCCESSFUL`` |
---|
863 | - successful operation |
---|
864 | * - ``RTEMS_INVALID_ID`` |
---|
865 | - invalid semaphore or scheduler id |
---|
866 | * - ``RTEMS_INVALID_ADDRESS`` |
---|
867 | - ``old_priority`` is NULL |
---|
868 | * - ``RTEMS_INVALID_PRIORITY`` |
---|
869 | - invalid new priority value |
---|
870 | * - ``RTEMS_NOT_DEFINED`` |
---|
871 | - operation not defined for the protocol ofthe semaphore |
---|
872 | * - ``RTEMS_ILLEGAL_ON_REMOTE_OBJECT`` |
---|
873 | - not supported for remote semaphores |
---|
874 | |
---|
875 | DESCRIPTION: |
---|
876 | This directive sets the priority value with respect to the specified |
---|
877 | scheduler of a semaphore. |
---|
878 | |
---|
879 | The special priority value ``RTEMS_CURRENT_PRIORITY`` can be used to get |
---|
880 | the current priority value without changing it. |
---|
881 | |
---|
882 | The interpretation of the priority value depends on the protocol of the |
---|
883 | semaphore object. |
---|
884 | |
---|
885 | - The Multiprocessor Resource Sharing Protocol needs a ceiling priority per |
---|
886 | scheduler instance. This operation can be used to specify these priority |
---|
887 | values. |
---|
888 | |
---|
889 | - For the Priority Ceiling Protocol the ceiling priority is used with this |
---|
890 | operation. |
---|
891 | |
---|
892 | - For other protocols this operation is not defined. |
---|
893 | |
---|
894 | EXAMPLE: |
---|
895 | .. code-block:: c |
---|
896 | :linenos: |
---|
897 | |
---|
898 | #include <assert.h> |
---|
899 | #include <stdlib.h> |
---|
900 | #include <rtems.h> |
---|
901 | |
---|
902 | #define SCHED_A rtems_build_name(' ', ' ', ' ', 'A') |
---|
903 | #define SCHED_B rtems_build_name(' ', ' ', ' ', 'B') |
---|
904 | |
---|
905 | static void Init(rtems_task_argument arg) |
---|
906 | { |
---|
907 | rtems_status_code sc; |
---|
908 | rtems_id semaphore_id; |
---|
909 | rtems_id scheduler_a_id; |
---|
910 | rtems_id scheduler_b_id; |
---|
911 | rtems_task_priority prio; |
---|
912 | |
---|
913 | /* Get the scheduler identifiers */ |
---|
914 | sc = rtems_scheduler_ident(SCHED_A, &scheduler_a_id); |
---|
915 | assert(sc == RTEMS_SUCCESSFUL); |
---|
916 | sc = rtems_scheduler_ident(SCHED_B, &scheduler_b_id); |
---|
917 | assert(sc == RTEMS_SUCCESSFUL); |
---|
918 | |
---|
919 | /* Create a MrsP semaphore object */ |
---|
920 | sc = rtems_semaphore_create( |
---|
921 | rtems_build_name('M', 'R', 'S', 'P'), |
---|
922 | 1, |
---|
923 | RTEMS_MULTIPROCESSOR_RESOURCE_SHARING | RTEMS_BINARY_SEMAPHORE, |
---|
924 | 1, |
---|
925 | &semaphore_id |
---|
926 | ); |
---|
927 | assert(sc == RTEMS_SUCCESSFUL); |
---|
928 | |
---|
929 | /* |
---|
930 | * The ceiling priority values per scheduler are equal to the value specified |
---|
931 | * for object creation. |
---|
932 | */ |
---|
933 | prio = RTEMS_CURRENT_PRIORITY; |
---|
934 | sc = rtems_semaphore_set_priority(semaphore_id, scheduler_a_id, prio, &prio); |
---|
935 | assert(sc == RTEMS_SUCCESSFUL); |
---|
936 | assert(prio == 1); |
---|
937 | |
---|
938 | /* Check the old value and set a new ceiling priority for scheduler B */ |
---|
939 | prio = 2; |
---|
940 | sc = rtems_semaphore_set_priority(semaphore_id, scheduler_b_id, prio, &prio); |
---|
941 | assert(sc == RTEMS_SUCCESSFUL); |
---|
942 | assert(prio == 1); |
---|
943 | |
---|
944 | /* Check the ceiling priority values */ |
---|
945 | prio = RTEMS_CURRENT_PRIORITY; |
---|
946 | sc = rtems_semaphore_set_priority(semaphore_id, scheduler_a_id, prio, &prio); |
---|
947 | assert(sc == RTEMS_SUCCESSFUL); |
---|
948 | assert(prio == 1); |
---|
949 | prio = RTEMS_CURRENT_PRIORITY; |
---|
950 | sc = rtems_semaphore_set_priority(semaphore_id, scheduler_b_id, prio, &prio); |
---|
951 | assert(sc == RTEMS_SUCCESSFUL); |
---|
952 | assert(prio == 2); |
---|
953 | sc = rtems_semaphore_delete(semaphore_id); |
---|
954 | assert(sc == RTEMS_SUCCESSFUL); |
---|
955 | exit(0); |
---|
956 | } |
---|
957 | |
---|
958 | #define CONFIGURE_SMP_APPLICATION |
---|
959 | #define CONFIGURE_APPLICATION_NEEDS_CLOCK_DRIVER |
---|
960 | #define CONFIGURE_APPLICATION_NEEDS_CONSOLE_DRIVER |
---|
961 | #define CONFIGURE_MAXIMUM_TASKS 1 |
---|
962 | #define CONFIGURE_MAXIMUM_SEMAPHORES 1 |
---|
963 | #define CONFIGURE_MAXIMUM_MRSP_SEMAPHORES 1 |
---|
964 | #define CONFIGURE_SMP_MAXIMUM_PROCESSORS 2 |
---|
965 | #define CONFIGURE_SCHEDULER_SIMPLE_SMP |
---|
966 | |
---|
967 | #include <rtems/scheduler.h> |
---|
968 | |
---|
969 | RTEMS_SCHEDULER_CONTEXT_SIMPLE_SMP(a); |
---|
970 | RTEMS_SCHEDULER_CONTEXT_SIMPLE_SMP(b); |
---|
971 | |
---|
972 | #define CONFIGURE_SCHEDULER_CONTROLS \ |
---|
973 | RTEMS_SCHEDULER_CONTROL_SIMPLE_SMP(a, SCHED_A), \ |
---|
974 | RTEMS_SCHEDULER_CONTROL_SIMPLE_SMP(b, SCHED_B) |
---|
975 | #define CONFIGURE_SMP_SCHEDULER_ASSIGNMENTS \ |
---|
976 | RTEMS_SCHEDULER_ASSIGN(0, RTEMS_SCHEDULER_ASSIGN_PROCESSOR_MANDATORY), \ |
---|
977 | RTEMS_SCHEDULER_ASSIGN(1, RTEMS_SCHEDULER_ASSIGN_PROCESSOR_MANDATORY) |
---|
978 | #define CONFIGURE_RTEMS_INIT_TASKS_TABLE |
---|
979 | #define CONFIGURE_INIT |
---|
980 | #include <rtems/confdefs.h> |
---|