/*
* Copyright (C) 2001-2004 Jakub Jermar
* All rights reserved.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions
* are met:
*
* - Redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer.
* - Redistributions in binary form must reproduce the above copyright
* notice, this list of conditions and the following disclaimer in the
* documentation and/or other materials provided with the distribution.
* - The name of the author may not be used to endorse or promote products
* derived from this software without specific prior written permission.
*
* THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
* IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
* OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
* IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
* INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
* NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
* DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
* THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
* (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
* THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
*/
#include <synch/waitq.h>
#include <synch/synch.h>
#include <synch/spinlock.h>
#include <proc/thread.h>
#include <arch/asm.h>
#include <arch/types.h>
#include <time/timeout.h>
#include <arch.h>
#include <context.h>
#include <list.h>
/** Initialize wait queue
*
* Initialize wait queue.
*
* @param wq Pointer to wait queue to be initialized.
*/
void waitq_initialize(waitq_t *wq)
{
spinlock_initialize(&wq->lock);
list_initialize(&wq->head);
wq->missed_wakeups = 0;
}
/** Handle timeout during waitq_sleep_timeout() call
*
* This routine is called when waitq_sleep_timeout() timeouts.
* Interrupts are disabled.
*
* It is supposed to try to remove 'its' thread from the wait queue;
* it can eventually fail to achieve this goal when these two events
* overlap. In that case it behaves just as though there was no
* timeout at all.
*
* @param data Pointer to the thread that called waitq_sleep_timeout().
*/
void waitq_interrupted_sleep(void *data)
{
thread_t *t = (thread_t *) data;
waitq_t *wq;
int do_wakeup = 0;
spinlock_lock(&threads_lock);
if (!list_member(&t->threads_link, &threads_head))
goto out;
grab_locks:
spinlock_lock(&t->lock);
if (wq = t->sleep_queue) {
if (!spinlock_trylock(&wq->lock)) {
spinlock_unlock(&t->lock);
goto grab_locks; /* avoid deadlock */
}
list_remove(&t->wq_link);
t->saved_context = t->sleep_timeout_context;
do_wakeup = 1;
spinlock_unlock(&wq->lock);
t->sleep_queue = NULL;
}
t->timeout_pending = 0;
spinlock_unlock(&t->lock);
if (do_wakeup) thread_ready(t);
out:
spinlock_unlock(&threads_lock);
}
/** Sleep until either wakeup or timeout occurs
*
* This is a sleep implementation which allows itself to be
* interrupted from the sleep, restoring a failover context.
*
* Sleepers are organised in FIFO fashion in a structure called wait queue.
*
* This function is really basic in that other functions as waitq_sleep()
* and all the *_timeout() functions use it.
*
* @param wq Pointer to wait queue.
* @param usec Timeout value in microseconds.
* @param nonblocking Controls whether only a conditional sleep
* (non-blocking sleep) is called for when the usec argument is 0.
*
* Relation between 'usec' and 'nonblocking' is described by this table:
*
* usec | nonblocking | what happens if there is no missed_wakeup
* -----+-------------+--------------------------------------------
* 0 | 0 | blocks without timeout until wakeup
* 0 | <> 0 | immediately returns ESYNCH_WOULD_BLOCK
* > 0 | x | blocks with timeout until timeout or wakeup
*
* @return Returns one of: ESYNCH_WOULD_BLOCK, ESYNCH_TIMEOUT,
* ESYNCH_OK_ATOMIC, ESYNCH_OK_BLOCKED.
*
* Meaning of the return values is described by the following chart:
*
* ESYNCH_WOULD_BLOCK Sleep failed because at the time of the call,
* there was no pending wakeup.
* ESYNCH_TIMEOUT Sleep timed out.
* ESYNCH_OK_ATOMIC Sleep succeeded; at the time of the call,
* where was a pending wakeup.
* ESYNCH_OK_BLOCKED Sleep succeeded; the full sleep was attempted.
*/
int waitq_sleep_timeout(waitq_t *wq, __u32 usec, int nonblocking)
{
volatile pri_t pri; /* must be live after context_restore() */
restart:
pri = cpu_priority_high();
/*
* Busy waiting for a delayed timeout.
* This is an important fix for the race condition between
* a delayed timeout and a next call to waitq_sleep_timeout().
* Simply, the thread is not allowed to go to sleep if
* there are timeouts in progress.
*/
spinlock_lock(&THREAD->lock);
if (THREAD->timeout_pending) {
spinlock_unlock(&THREAD->lock);
cpu_priority_restore(pri);
goto restart;
}
spinlock_unlock(&THREAD->lock);
spinlock_lock(&wq->lock);
/* checks whether to go to sleep at all */
if (wq->missed_wakeups) {
wq->missed_wakeups--;
spinlock_unlock(&wq->lock);
cpu_priority_restore(pri);
return ESYNCH_OK_ATOMIC;
}
else {
if (nonblocking && (usec == 0)) {
/* return immediatelly instead of going to sleep */
spinlock_unlock(&wq->lock);
cpu_priority_restore(pri);
return ESYNCH_WOULD_BLOCK;
}
}
/*
* Now we are firmly decided to go to sleep.
*/
spinlock_lock(&THREAD->lock);
if (usec) {
/* We use the timeout variant. */
if (!context_save(&THREAD->sleep_timeout_context)) {
/*
* Short emulation of scheduler() return code.
*/
before_thread_runs();
spinlock_unlock(&THREAD->lock);
cpu_priority_restore(pri);
return ESYNCH_TIMEOUT;
}
THREAD->timeout_pending = 1;
timeout_register(&THREAD->sleep_timeout, (__u64) usec, waitq_interrupted_sleep, THREAD);
}
list_append(&THREAD->wq_link, &wq->head);
/*
* Suspend execution.
*/
THREAD->state = Sleeping;
THREAD->sleep_queue = wq;
spinlock_unlock(&THREAD->lock);
scheduler(); /* wq->lock is released in scheduler_separated_stack() */
cpu_priority_restore(pri);
return ESYNCH_OK_BLOCKED;
}
/** Wake up first thread sleeping in a wait queue
*
* Wake up first thread sleeping in a wait queue.
* This is the SMP- and IRQ-safe wrapper meant for
* general use.
*
* Besides its 'normal' wakeup operation, it attempts
* to unregister possible timeout.
*
* @param wq Pointer to wait queue.
* @param all If this is non-zero, all sleeping threads
* will be woken up and missed count will be zeroed.
*/
void waitq_wakeup(waitq_t *wq, int all)
{
pri_t pri;
pri = cpu_priority_high();
spinlock_lock(&wq->lock);
_waitq_wakeup_unsafe(wq, all);
spinlock_unlock(&wq->lock);
cpu_priority_restore(pri);
}
/** Internal SMP- and IRQ-unsafe version of waitq_wakeup()
*
* This is the internal SMP- and IRQ-unsafe version
* of waitq_wakeup(). It assumes wq->lock is already
* locked and interrupts are already disabled.
*
* @param wq Pointer to wait queue.
* @param all If this is non-zero, all sleeping threads
* will be woken up and missed count will be zeroed.
*/
void _waitq_wakeup_unsafe(waitq_t *wq, int all)
{
thread_t *t;
loop:
if (list_empty(&wq->head)) {
wq->missed_wakeups++;
if (all) wq->missed_wakeups = 0;
return;
}
t = list_get_instance(wq->head.next, thread_t, wq_link);
list_remove(&t->wq_link);
spinlock_lock(&t->lock);
if (t->timeout_pending && timeout_unregister(&t->sleep_timeout))
t->timeout_pending = 0;
t->sleep_queue = NULL;
spinlock_unlock(&t->lock);
thread_ready(t);
if (all) goto loop;
}