/*
* 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.
*/
/**
* @file waitq.c
* @brief Wait queue.
*
* Wait queue is the basic synchronization primitive upon which all
* other synchronization primitives build.
*
* It allows threads to wait for an event in first-come, first-served
* fashion. Conditional operation as well as timeouts and interruptions
* are supported.
*/
#include <synch/waitq.h>
#include <synch/synch.h>
#include <synch/spinlock.h>
#include <proc/thread.h>
#include <proc/scheduler.h>
#include <arch/asm.h>
#include <arch/types.h>
#include <typedefs.h>
#include <time/timeout.h>
#include <arch.h>
#include <context.h>
#include <adt/list.h>
static void waitq_timeouted_sleep(void *data);
/** 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, "waitq_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_timeouted_sleep(void *data)
{
thread_t *t = (thread_t *) data;
waitq_t *wq;
bool do_wakeup = false;
spinlock_lock(&threads_lock);
if (!thread_exists(t))
goto out;
grab_locks:
spinlock_lock(&t->lock);
if ((wq = t->sleep_queue)) { /* assignment */
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 = true;
t->sleep_queue = NULL;
spinlock_unlock(&wq->lock);
}
t->timeout_pending = false;
spinlock_unlock(&t->lock);
if (do_wakeup)
thread_ready(t);
out:
spinlock_unlock(&threads_lock);
}
/** Interrupt sleeping thread.
*
* This routine attempts to interrupt a thread from its sleep in a waitqueue.
* If the thread is not found sleeping, no action is taken.
*
* @param t Thread to be interrupted.
*/
void waitq_interrupt_sleep(thread_t *t)
{
waitq_t *wq;
bool do_wakeup = false;
ipl_t ipl;
ipl = interrupts_disable();
spinlock_lock(&threads_lock);
if (!thread_exists(t))
goto out;
grab_locks:
spinlock_lock(&t->lock);
if ((wq = t->sleep_queue)) { /* assignment */
if (!(t->sleep_interruptible)) {
/*
* The sleep cannot be interrupted.
*/
spinlock_unlock(&t->lock);
goto out;
}
if (!spinlock_trylock(&wq->lock)) {
spinlock_unlock(&t->lock);
goto grab_locks; /* avoid deadlock */
}
if (t->timeout_pending && timeout_unregister(&t->sleep_timeout))
t->timeout_pending = false;
list_remove(&t->wq_link);
t->saved_context = t->sleep_interruption_context;
do_wakeup = true;
t->sleep_queue = NULL;
spinlock_unlock(&wq->lock);
}
spinlock_unlock(&t->lock);
if (do_wakeup)
thread_ready(t);
out:
spinlock_unlock(&threads_lock);
interrupts_restore(ipl);
}
/** Sleep until either wakeup, timeout or interruption occurs
*
* This is a sleep implementation which allows itself to time out or to be
* interrupted from the sleep, restoring a failover context.
*
* Sleepers are organised in a 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 in microseconds.
* @param flags Specify mode of the sleep.
*
* The sleep can be interrupted only if the
* SYNCH_FLAGS_INTERRUPTIBLE bit is specified in flags.
* If usec is greater than zero, regardless of the value of the
* SYNCH_FLAGS_NON_BLOCKING bit in flags, the call will not return until either timeout,
* interruption or wakeup comes.
*
* If usec is zero and the SYNCH_FLAGS_NON_BLOCKING bit is not set in flags, the call
* will not return until wakeup or interruption comes.
*
* If usec is zero and the SYNCH_FLAGS_NON_BLOCKING bit is set in flags, the call will
* immediately return, reporting either success or failure.
*
* @return Returns one of: ESYNCH_WOULD_BLOCK, ESYNCH_TIMEOUT, ESYNCH_INTERRUPTED,
* ESYNCH_OK_ATOMIC, ESYNCH_OK_BLOCKED.
*
* @li ESYNCH_WOULD_BLOCK means that the sleep failed because at the time
* of the call there was no pending wakeup.
*
* @li ESYNCH_TIMEOUT means that the sleep timed out.
*
* @li ESYNCH_INTERRUPTED means that somebody interrupted the sleeping thread.
*
* @li ESYNCH_OK_ATOMIC means that the sleep succeeded and that there was
* a pending wakeup at the time of the call. The caller was not put
* asleep at all.
*
* @li ESYNCH_OK_BLOCKED means that the sleep succeeded; the full sleep was
* attempted.
*/
int waitq_sleep_timeout(waitq_t *wq, __u32 usec, int flags)
{
ipl_t ipl;
int rc;
ipl = waitq_sleep_prepare(wq);
rc = waitq_sleep_timeout_unsafe(wq, usec, flags);
waitq_sleep_finish(wq, rc, ipl);
return rc;
}
/** Prepare to sleep in a waitq.
*
* This function will return holding the lock of the wait queue
* and interrupts disabled.
*
* @param wq Wait queue.
*
* @return Interrupt level as it existed on entry to this function.
*/
ipl_t waitq_sleep_prepare(waitq_t *wq)
{
ipl_t ipl;
restart:
ipl = interrupts_disable();
if (THREAD) { /* needed during system initiailzation */
/*
* 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);
interrupts_restore(ipl);
goto restart;
}
spinlock_unlock(&THREAD->lock);
}
spinlock_lock(&wq->lock);
return ipl;
}
/** Finish waiting in a wait queue.
*
* This function restores interrupts to the state that existed prior
* to the call to waitq_sleep_prepare(). If necessary, the wait queue
* lock is released.
*
* @param wq Wait queue.
* @param rc Return code of waitq_sleep_timeout_unsafe().
* @param ipl Interrupt level returned by waitq_sleep_prepare().
*/
void waitq_sleep_finish(waitq_t *wq, int rc, ipl_t ipl)
{
switch (rc) {
case ESYNCH_WOULD_BLOCK:
case ESYNCH_OK_ATOMIC:
spinlock_unlock(&wq->lock);
break;
default:
break;
}
interrupts_restore(ipl);
}
/** Internal implementation of waitq_sleep_timeout().
*
* This function implements logic of sleeping in a wait queue.
* This call must be preceeded by a call to waitq_sleep_prepare()
* and followed by a call to waitq_slee_finish().
*
* @param wq See waitq_sleep_timeout().
* @param usec See waitq_sleep_timeout().
* @param flags See waitq_sleep_timeout().
*
* @return See waitq_sleep_timeout().
*/
int waitq_sleep_timeout_unsafe(waitq_t *wq, __u32 usec, int flags)
{
/* checks whether to go to sleep at all */
if (wq->missed_wakeups) {
wq->missed_wakeups--;
return ESYNCH_OK_ATOMIC;
}
else {
if ((flags & SYNCH_FLAGS_NON_BLOCKING) && (usec == 0)) {
/* return immediatelly instead of going to sleep */
return ESYNCH_WOULD_BLOCK;
}
}
/*
* Now we are firmly decided to go to sleep.
*/
spinlock_lock(&THREAD->lock);
if (flags & SYNCH_FLAGS_INTERRUPTIBLE) {
/*
* If the thread was already interrupted,
* don't go to sleep at all.
*/
if (THREAD->interrupted) {
spinlock_unlock(&THREAD->lock);
spinlock_unlock(&wq->lock);
return ESYNCH_INTERRUPTED;
}
/*
* Set context that will be restored if the sleep
* of this thread is ever interrupted.
*/
THREAD->sleep_interruptible = true;
if (!context_save(&THREAD->sleep_interruption_context)) {
/* Short emulation of scheduler() return code. */
spinlock_unlock(&THREAD->lock);
return ESYNCH_INTERRUPTED;
}
} else {
THREAD->sleep_interruptible = false;
}
if (usec) {
/* We use the timeout variant. */
if (!context_save(&THREAD->sleep_timeout_context)) {
/* Short emulation of scheduler() return code. */
spinlock_unlock(&THREAD->lock);
return ESYNCH_TIMEOUT;
}
THREAD->timeout_pending = true;
timeout_register(&THREAD->sleep_timeout, (__u64) usec, waitq_timeouted_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() */
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, bool all)
{
ipl_t ipl;
ipl = interrupts_disable();
spinlock_lock(&wq->lock);
_waitq_wakeup_unsafe(wq, all);
spinlock_unlock(&wq->lock);
interrupts_restore(ipl);
}
/** 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, bool 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);
/*
* Lock the thread prior to removing it from the wq.
* This is not necessary because of mutual exclusion
* (the link belongs to the wait queue), but because
* of synchronization with waitq_timeouted_sleep()
* and waitq_interrupt_sleep().
*
* In order for these two functions to work, the following
* invariant must hold:
*
* t->sleep_queue != NULL <=> t sleeps in a wait queue
*
* For an observer who locks the thread, the invariant
* holds only when the lock is held prior to removing
* it from the wait queue.
*/
spinlock_lock(&t->lock);
list_remove(&t->wq_link);
if (t->timeout_pending && timeout_unregister(&t->sleep_timeout))
t->timeout_pending = false;
t->sleep_queue = NULL;
spinlock_unlock(&t->lock);
thread_ready(t);
if (all)
goto loop;
}