4 * Copyright 2001, 2004 Develer S.r.l. (http://www.develer.com/)
5 * Copyright 1999, 2000, 2001 Bernardo Innocenti <bernie@develer.com>
6 * This file is part of DevLib - See README.devlib for information.
9 * \brief Semaphore based synchronization services.
13 * \author Bernardo Innocenti <bernie@develer.com>
18 *#* Revision 1.10 2005/11/04 16:20:02 bernie
19 *#* Fix reference to README.devlib in header.
21 *#* Revision 1.9 2005/04/11 19:10:28 bernie
22 *#* Include top-level headers from cfg/ subdir.
24 *#* Revision 1.8 2005/01/22 04:20:42 bernie
25 *#* Add integrity checks.
27 *#* Revision 1.7 2004/11/28 23:20:25 bernie
28 *#* Remove obsolete INITLIST macro.
30 *#* Revision 1.6 2004/10/21 10:57:21 bernie
31 *#* Use proc_forbid()/proc_permit().
33 *#* Revision 1.5 2004/10/21 10:48:57 bernie
34 *#* sem_release(): Simplify (made by rasky on scfirm).
36 *#* Revision 1.4 2004/08/25 14:12:09 rasky
37 *#* Aggiornato il comment block dei log RCS
39 *#* Revision 1.3 2004/08/08 05:53:23 bernie
40 *#* Use DISABLE_IRQSAVE/ENABLE_IRQRESTORE; Cleanup documentation.
42 *#* Revision 1.2 2004/06/03 11:27:09 bernie
43 *#* Add dual-license information.
45 *#* Revision 1.1 2004/05/23 17:27:00 bernie
46 *#* Import kern/ subdirectory.
54 #include <cfg/debug.h>
56 INLINE void sem_verify(struct Semaphore *s)
58 LIST_ASSERT_VALID(&s->wait_queue);
59 ASSERT(s->nest_count >= 0);
60 ASSERT(s->nest_count < 128); // heuristic max
65 * \brief Initialize a Semaphore structure.
67 void sem_init(struct Semaphore *s)
69 LIST_INIT(&s->wait_queue);
76 * \brief Attempt to lock a semaphore without waiting.
78 * \return true in case of success, false if the semaphore
79 * was already locked by someone else.
81 * \note each call to sem_attempt() must be matched by a
82 * call to sem_release().
84 * \see sem_obtain() sem_release()
86 bool sem_attempt(struct Semaphore *s)
92 if ((!s->owner) || (s->owner == CurrentProcess))
94 s->owner = CurrentProcess;
105 * \brief Lock a semaphore.
107 * If the semaphore is already owned by another process, the caller
108 * process will be enqueued into the waiting list and sleep until
109 * the semaphore is available.
111 * \note Each call to sem_obtain() must be matched by a
112 * call to sem_release().
114 * \note This routine is optimized for highest speed in
115 * the most common case: the semaphore is free or locked
116 * by the calling process itself. Rearranging this code
117 * is probably a bad idea.
119 * \sa sem_release() sem_attempt()
121 void sem_obtain(struct Semaphore *s)
126 /* Is the semaphore already locked by another process? */
127 if (UNLIKELY(s->owner && (s->owner != CurrentProcess)))
129 /* Append calling process to the wait queue */
130 ADDTAIL(&s->wait_queue, (Node *)CurrentProcess);
133 * We will wake up only when the current owner calls
134 * sem_release(). Then, the semaphore will already
142 ASSERT(ISLISTEMPTY(&s->wait_queue));
144 /* The semaphore was free: lock it */
145 s->owner = CurrentProcess;
153 * \brief Release a lock on a previously locked semaphore.
155 * If the nesting count of the semaphore reaches zero,
156 * the next process waiting for it will be awaken.
158 * \note This routine is optimized for highest speed in
159 * the most common case: the semaphore has been locked just
160 * once and nobody else was waiting for it. Rearranging
161 * this code is probably a bad idea.
163 * \sa sem_obtain() sem_attempt()
165 void sem_release(struct Semaphore *s)
170 ASSERT(s->owner == CurrentProcess);
173 * Decrement nesting count and check if the semaphore
174 * has been fully unlocked.
176 if (--s->nest_count == 0)
180 /* Disown semaphore */
183 /* Give semaphore to the first applicant, if any */
184 if (UNLIKELY((proc = (Process *)REMHEAD(&s->wait_queue))))