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 1.12 2006/07/19 12:56:27 bernie
19 *#* Convert to new Doxygen style.
21 *#* Revision 1.11 2006/02/24 01:17:05 bernie
22 *#* Update for new emulator.
24 *#* Revision 1.10 2005/11/04 16:20:02 bernie
25 *#* Fix reference to README.devlib in header.
27 *#* Revision 1.9 2005/04/11 19:10:28 bernie
28 *#* Include top-level headers from cfg/ subdir.
30 *#* Revision 1.8 2005/01/22 04:20:42 bernie
31 *#* Add integrity checks.
33 *#* Revision 1.7 2004/11/28 23:20:25 bernie
34 *#* Remove obsolete INITLIST macro.
36 *#* Revision 1.6 2004/10/21 10:57:21 bernie
37 *#* Use proc_forbid()/proc_permit().
39 *#* Revision 1.5 2004/10/21 10:48:57 bernie
40 *#* sem_release(): Simplify (made by rasky on scfirm).
42 *#* Revision 1.4 2004/08/25 14:12:09 rasky
43 *#* Aggiornato il comment block dei log RCS
45 *#* Revision 1.3 2004/08/08 05:53:23 bernie
46 *#* Use DISABLE_IRQSAVE/ENABLE_IRQRESTORE; Cleanup documentation.
48 *#* Revision 1.2 2004/06/03 11:27:09 bernie
49 *#* Add dual-license information.
51 *#* Revision 1.1 2004/05/23 17:27:00 bernie
52 *#* Import kern/ subdirectory.
56 #include <kern/proc.h>
57 #include <kern/proc_p.h>
58 #include <kern/signal.h>
59 #include <cfg/debug.h>
61 INLINE void sem_verify(struct Semaphore *s)
63 LIST_ASSERT_VALID(&s->wait_queue);
64 ASSERT(s->nest_count >= 0);
65 ASSERT(s->nest_count < 128); // heuristic max
70 * \brief Initialize a Semaphore structure.
72 void sem_init(struct Semaphore *s)
74 LIST_INIT(&s->wait_queue);
81 * \brief Attempt to lock a semaphore without waiting.
83 * \return true in case of success, false if the semaphore
84 * was already locked by someone else.
86 * \note each call to sem_attempt() must be matched by a
87 * call to sem_release().
89 * \see sem_obtain() sem_release()
91 bool sem_attempt(struct Semaphore *s)
97 if ((!s->owner) || (s->owner == CurrentProcess))
99 s->owner = CurrentProcess;
110 * \brief Lock a semaphore.
112 * If the semaphore is already owned by another process, the caller
113 * process will be enqueued into the waiting list and sleep until
114 * the semaphore is available.
116 * \note Each call to sem_obtain() must be matched by a
117 * call to sem_release().
119 * \note This routine is optimized for highest speed in
120 * the most common case: the semaphore is free or locked
121 * by the calling process itself. Rearranging this code
122 * is probably a bad idea.
124 * \sa sem_release() sem_attempt()
126 void sem_obtain(struct Semaphore *s)
131 /* Is the semaphore already locked by another process? */
132 if (UNLIKELY(s->owner && (s->owner != CurrentProcess)))
134 /* Append calling process to the wait queue */
135 ADDTAIL(&s->wait_queue, (Node *)CurrentProcess);
138 * We will wake up only when the current owner calls
139 * sem_release(). Then, the semaphore will already
147 ASSERT(LIST_EMPTY(&s->wait_queue));
149 /* The semaphore was free: lock it */
150 s->owner = CurrentProcess;
158 * \brief Release a lock on a previously locked semaphore.
160 * If the nesting count of the semaphore reaches zero,
161 * the next process waiting for it will be awaken.
163 * \note This routine is optimized for highest speed in
164 * the most common case: the semaphore has been locked just
165 * once and nobody else was waiting for it. Rearranging
166 * this code is probably a bad idea.
168 * \sa sem_obtain() sem_attempt()
170 void sem_release(struct Semaphore *s)
175 ASSERT(s->owner == CurrentProcess);
178 * Decrement nesting count and check if the semaphore
179 * has been fully unlocked.
181 if (--s->nest_count == 0)
185 /* Disown semaphore */
188 /* Give semaphore to the first applicant, if any */
189 if (UNLIKELY((proc = (Process *)list_remHead(&s->wait_queue))))