-/*!
- * \file
- * <!--
- * Copyright 2001,2004 Develer S.r.l. (http://www.develer.com/)
- * Copyright 1999,2000,2001 Bernardo Innocenti <bernie@develer.com>
- * This file is part of DevLib - See devlib/README for information.
- * -->
- *
- * \brief Semaphore based synchronization services.
- *
- * \version $Id$
- *
- * \author Bernardo Innocenti <bernie@develer.com>
- */
-
-/*
- * $Log$
- * Revision 1.2 2004/06/03 11:27:09 bernie
- * Add dual-license information.
- *
- * Revision 1.1 2004/05/23 17:27:00 bernie
- * Import kern/ subdirectory.
- *
- */
-
-#include "sem.h"
-#include "proc.h"
-#include "proc_p.h"
-#include "signal.h"
-#include "hw.h"
-
-
-/*!
- * \brief Initialize a Semaphore structure
- */
-void sem_init(struct Semaphore *s)
-{
- INITLIST(&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().
- */
-bool sem_attempt(struct Semaphore *s)
-{
- DISABLE_INTS;
- if ((!s->owner) || (s->owner == CurrentProcess))
- {
- s->owner = CurrentProcess;
- s->nest_count++;
- ENABLE_INTS;
- return true;
- }
- ENABLE_INTS;
- return false;
-}
-
-
-/*!
- * \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.
- */
-void sem_obtain(struct Semaphore *s)
-{
- DISABLE_INTS;
-
- /* Is the semaphore already locked by another process? */
- if (s->owner && (s->owner != CurrentProcess))
- {
- /* Append calling process to the wait queue */
- ADDTAIL(&s->wait_queue, (Node *)CurrentProcess);
- ENABLE_INTS;
-
- /* We will awake only when the current owner calls
- * ReleaseSemaphore(). Then, the semaphore will already
- * be locked for us.
- */
- proc_schedule();
- }
- else
- {
- /* The semaphore is free: lock it */
- s->owner = CurrentProcess;
- s->nest_count++;
- ENABLE_INTS;
- }
-}
-
-
-/*!
- * \brief Releases 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.
- */
-void sem_release(struct Semaphore *s)
-{
- DISABLE_INTS;
-
- /* Decremement nesting count and check if the semaphore
- * has been fully unlocked
- */
- if (--s->nest_count == 0)
- {
- /* Disown semaphore */
- s->owner = NULL;
-
- /* Anybody still waiting for this semaphore? */
- if (!ISLISTEMPTY(&s->wait_queue))
- {
- /* Give semaphore to the first applicant */
- Process *proc = (Process *)s->wait_queue.head;
- REMOVE((Node *)proc);
- s->nest_count = 1;
- s->owner = proc;
- SCHED_ENQUEUE(proc);
- }
- }
-
- ENABLE_INTS;
-}
-