533d396761
Any number of readers may be in the critical section at a time and writers are mutually exclusive to all other threads. They are a better choice when data is rarely modified but often read and multiple threads can safely access it for reading. Priority inheritance is fully implemented along with other changes to the kernel to fully support it on multiowner objects. This also cleans up priority code in the kernel and updates some associated structures in existing objects to the cleaner form. Currently doesn't add the mrsw_lock.[ch] files since they're not yet needed by anything but the supporting improvements are still useful. This includes a typed bitarray API (bitarray.h) which is pretty basic for now. Change-Id: Idbe43dcd9170358e06d48d00f1c69728ff45b0e3 Reviewed-on: http://gerrit.rockbox.org/801 Reviewed-by: Michael Sevakis <jethead71@rockbox.org> Tested: Michael Sevakis <jethead71@rockbox.org>
138 lines
4.2 KiB
C
138 lines
4.2 KiB
C
/***************************************************************************
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* __________ __ ___.
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* Open \______ \ ____ ____ | | _\_ |__ _______ ___
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* Source | _// _ \_/ ___\| |/ /| __ \ / _ \ \/ /
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* Jukebox | | ( <_> ) \___| < | \_\ ( <_> > < <
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* Firmware |____|_ /\____/ \___ >__|_ \|___ /\____/__/\_ \
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* \/ \/ \/ \/ \/
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* $Id$
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*
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* Copyright (C) 2002 by Björn Stenberg
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*
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* This program is free software; you can redistribute it and/or
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* modify it under the terms of the GNU General Public License
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* as published by the Free Software Foundation; either version 2
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* of the License, or (at your option) any later version.
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*
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* This software is distributed on an "AS IS" basis, WITHOUT WARRANTY OF ANY
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* KIND, either express or implied.
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*
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****************************************************************************/
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/****************************************************************************
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* Simple mutex functions ;)
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****************************************************************************/
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#include <stdbool.h>
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#include "config.h"
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#include "kernel.h"
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#include "semaphore.h"
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#include "kernel-internal.h"
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#include "thread-internal.h"
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/****************************************************************************
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* Simple semaphore functions ;)
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****************************************************************************/
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/* Initialize the semaphore object.
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* max = maximum up count the semaphore may assume (max >= 1)
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* start = initial count of semaphore (0 <= count <= max) */
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void semaphore_init(struct semaphore *s, int max, int start)
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{
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KERNEL_ASSERT(max > 0 && start >= 0 && start <= max,
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"semaphore_init->inv arg\n");
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s->queue = NULL;
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s->max = max;
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s->count = start;
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corelock_init(&s->cl);
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}
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/* Down the semaphore's count or wait for 'timeout' ticks for it to go up if
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* it is already 0. 'timeout' as TIMEOUT_NOBLOCK (0) will not block and may
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* safely be used in an ISR. */
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int semaphore_wait(struct semaphore *s, int timeout)
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{
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int ret;
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int oldlevel;
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int count;
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oldlevel = disable_irq_save();
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corelock_lock(&s->cl);
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count = s->count;
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if(LIKELY(count > 0))
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{
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/* count is not zero; down it */
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s->count = count - 1;
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ret = OBJ_WAIT_SUCCEEDED;
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}
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else if(timeout == 0)
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{
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/* just polling it */
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ret = OBJ_WAIT_TIMEDOUT;
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}
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else
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{
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/* too many waits - block until count is upped... */
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struct thread_entry * current = thread_self_entry();
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IF_COP( current->obj_cl = &s->cl; )
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current->bqp = &s->queue;
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/* return value will be OBJ_WAIT_SUCCEEDED after wait if wake was
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* explicit in semaphore_release */
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current->retval = OBJ_WAIT_TIMEDOUT;
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block_thread(current, timeout);
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corelock_unlock(&s->cl);
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/* ...and turn control over to next thread */
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switch_thread();
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return current->retval;
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}
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corelock_unlock(&s->cl);
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restore_irq(oldlevel);
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return ret;
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}
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/* Up the semaphore's count and release any thread waiting at the head of the
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* queue. The count is saturated to the value of the 'max' parameter specified
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* in 'semaphore_init'. */
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void semaphore_release(struct semaphore *s)
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{
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unsigned int result = THREAD_NONE;
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int oldlevel;
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oldlevel = disable_irq_save();
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corelock_lock(&s->cl);
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if(LIKELY(s->queue != NULL))
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{
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/* a thread was queued - wake it up and keep count at 0 */
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KERNEL_ASSERT(s->count == 0,
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"semaphore_release->threads queued but count=%d!\n", s->count);
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s->queue->retval = OBJ_WAIT_SUCCEEDED; /* indicate explicit wake */
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result = wakeup_thread(&s->queue, WAKEUP_DEFAULT);
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}
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else
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{
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int count = s->count;
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if(count < s->max)
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{
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/* nothing waiting - up it */
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s->count = count + 1;
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}
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}
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corelock_unlock(&s->cl);
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restore_irq(oldlevel);
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#if defined(HAVE_PRIORITY_SCHEDULING) && defined(is_thread_context)
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/* No thread switch if not thread context */
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if((result & THREAD_SWITCH) && is_thread_context())
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switch_thread();
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#endif
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(void)result;
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}
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