-/**
- * \file
- * <!--
- * This file is part of BeRTOS.
- *
- * Bertos is free software; you can redistribute it and/or modify
- * it under the terms of the GNU General Public License as published by
- * the Free Software Foundation; either version 2 of the License, or
- * (at your option) any later version.
- *
- * This program is distributed in the hope that it will be useful,
- * but WITHOUT ANY WARRANTY; without even the implied warranty of
- * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
- * GNU General Public License for more details.
- *
- * You should have received a copy of the GNU General Public License
- * along with this program; if not, write to the Free Software
- * Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA
- *
- * As a special exception, you may use this file as part of a free software
- * library without restriction. Specifically, if other files instantiate
- * templates or use macros or inline functions from this file, or you compile
- * this file and link it with other files to produce an executable, this
- * file does not by itself cause the resulting executable to be covered by
- * the GNU General Public License. This exception does not however
- * invalidate any other reasons why the executable file might be covered by
- * the GNU General Public License.
- *
- * Copyright 2001, 2004 Develer S.r.l. (http://www.develer.com/)
- * Copyright 1999, 2000, 2001 Bernardo Innocenti <bernie@develer.com>
- *
- * -->
- *
- * \brief Semaphore based synchronization services.
- *
- * \version $Id$
- *
- * \author Bernardo Innocenti <bernie@develer.com>
- */
-
-#include "sem.h"
-#include <kern/proc.h>
-#include <kern/proc_p.h>
-#include <kern/signal.h>
-#include <cfg/debug.h>
-
-INLINE void sem_verify(struct Semaphore *s)
-{
- (void)s;
- ASSERT(s);
- LIST_ASSERT_VALID(&s->wait_queue);
- ASSERT(s->nest_count >= 0);
- ASSERT(s->nest_count < 128); // heuristic max
-}
-
-
-/**
- * \brief Initialize a Semaphore structure.
- */
-void sem_init(struct Semaphore *s)
-{
- LIST_INIT(&s->wait_queue);
- s->owner = NULL;
- s->nest_count = 0;
-}
-
-
-/**
- * \brief Attempt to lock a semaphore without waiting.
- *
- * \return true in case of success, false if the semaphore
- * was already locked by someone else.
- *
- * \note each call to sem_attempt() must be matched by a
- * call to sem_release().
- *
- * \see sem_obtain() sem_release()
- */
-bool sem_attempt(struct Semaphore *s)
-{
- bool result = false;
-
- proc_forbid();
- sem_verify(s);
- if ((!s->owner) || (s->owner == CurrentProcess))
- {
- s->owner = CurrentProcess;
- s->nest_count++;
- result = true;
- }
- proc_permit();
-
- return result;
-}
-
-
-/**
- * \brief Lock a semaphore.
- *
- * If the semaphore is already owned by another process, the caller
- * process will be enqueued into the waiting list and sleep until
- * the semaphore is available.
- *
- * \note Each call to sem_obtain() must be matched by a
- * call to sem_release().
- *
- * \note This routine is optimized for highest speed in
- * the most common case: the semaphore is free or locked
- * by the calling process itself. Rearranging this code
- * is probably a bad idea.
- *
- * \sa sem_release() sem_attempt()
- */
-void sem_obtain(struct Semaphore *s)
-{
- proc_forbid();
- sem_verify(s);
-
- /* Is the semaphore already locked by another process? */
- if (UNLIKELY(s->owner && (s->owner != CurrentProcess)))
- {
- /* Append calling process to the wait queue */
- ADDTAIL(&s->wait_queue, (Node *)CurrentProcess);
-
- /*
- * We will wake up only when the current owner calls
- * sem_release(). Then, the semaphore will already
- * be locked for us.
- */
- proc_permit();
- proc_schedule();
- }
- else
- {
- ASSERT(LIST_EMPTY(&s->wait_queue));
-
- /* The semaphore was free: lock it */
- s->owner = CurrentProcess;
- s->nest_count++;
- proc_permit();
- }
-}
-
-
-/**
- * \brief Release a lock on a previously locked semaphore.
- *
- * If the nesting count of the semaphore reaches zero,
- * the next process waiting for it will be awaken.
- *
- * \note This routine is optimized for highest speed in
- * the most common case: the semaphore has been locked just
- * once and nobody else was waiting for it. Rearranging
- * this code is probably a bad idea.
- *
- * \sa sem_obtain() sem_attempt()
- */
-void sem_release(struct Semaphore *s)
-{
- proc_forbid();
- sem_verify(s);
-
- ASSERT(s->owner == CurrentProcess);
-
- /*
- * Decrement nesting count and check if the semaphore
- * has been fully unlocked.
- */
- if (--s->nest_count == 0)
- {
- Process *proc;
-
- /* Disown semaphore */
- s->owner = NULL;
-
- /* Give semaphore to the first applicant, if any */
- if (UNLIKELY((proc = (Process *)list_remHead(&s->wait_queue))))
- {
- s->nest_count = 1;
- s->owner = proc;
- SCHED_ENQUEUE(proc);
- }
- }
-
- proc_permit();
-}