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/*
* Copyright (c) 2013-2017 Richard Braun.
*
* This program 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 3 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, see <http://www.gnu.org/licenses/>.
*
*
* Locking order : mutex -> sleep queue
*/
#include <stdbool.h>
#include <stddef.h>
#include <kern/assert.h>
#include <kern/condition.h>
#include <kern/condition_types.h>
#include <kern/mutex.h>
#include <kern/sleepq.h>
#include <kern/thread.h>
static void
condition_inc_nr_sleeping_waiters(struct condition *condition)
{
condition->nr_sleeping_waiters++;
assert(condition->nr_sleeping_waiters != 0);
}
static void
condition_dec_nr_sleeping_waiters(struct condition *condition)
{
assert(condition->nr_sleeping_waiters != 0);
condition->nr_sleeping_waiters--;
}
static void
condition_inc_nr_pending_waiters(struct condition *condition)
{
condition->nr_pending_waiters++;
assert(condition->nr_pending_waiters != 0);
}
static void
condition_dec_nr_pending_waiters(struct condition *condition)
{
assert(condition->nr_pending_waiters != 0);
condition->nr_pending_waiters--;
}
static void
condition_move_waiters(struct condition *condition)
{
unsigned short old;
assert(condition->nr_sleeping_waiters != 0);
old = condition->nr_pending_waiters;
condition->nr_pending_waiters += condition->nr_sleeping_waiters;
assert(old < condition->nr_pending_waiters);
condition->nr_sleeping_waiters = 0;
}
void
condition_wait(struct condition *condition, struct mutex *mutex)
{
struct condition *last_cond;
struct sleepq *sleepq;
mutex_assert_locked(mutex);
/*
* Special case :
*
* mutex_lock(lock);
*
* for (;;) {
* while (!done) {
* condition_wait(condition, lock);
* }
*
* do_something();
* }
*
* Pull the last condition before unlocking the mutex to prevent
* mutex_unlock() from reacquiring the condition sleep queue.
*/
last_cond = thread_pull_last_cond();
sleepq = sleepq_lend(condition, true);
mutex_unlock(mutex);
if (last_cond != NULL) {
assert(last_cond == condition);
if (condition->nr_pending_waiters != 0) {
sleepq_signal(sleepq);
}
}
condition_inc_nr_sleeping_waiters(condition);
sleepq_wait(sleepq, "cond");
condition_dec_nr_pending_waiters(condition);
if (condition->nr_pending_waiters != 0) {
thread_set_last_cond(condition);
}
sleepq_return(sleepq);
mutex_lock(mutex);
}
void
condition_signal(struct condition *condition)
{
struct sleepq *sleepq;
sleepq = sleepq_acquire(condition, true);
if (sleepq == NULL) {
return;
}
if (condition->nr_sleeping_waiters == 0) {
goto out;
}
sleepq_signal(sleepq);
condition_dec_nr_sleeping_waiters(condition);
condition_inc_nr_pending_waiters(condition);
out:
sleepq_release(sleepq);
}
void
condition_broadcast(struct condition *condition)
{
struct sleepq *sleepq;
sleepq = sleepq_acquire(condition, true);
if (sleepq == NULL) {
return;
}
if (condition->nr_sleeping_waiters == 0) {
goto out;
}
sleepq_signal(sleepq);
condition_move_waiters(condition);
out:
sleepq_release(sleepq);
}
void
condition_wakeup(struct condition *condition)
{
struct sleepq *sleepq;
sleepq = sleepq_acquire(condition, true);
if (sleepq == NULL) {
return;
}
if (condition->nr_pending_waiters == 0) {
goto out;
}
/*
* Rely on the FIFO ordering of sleep queues so that signalling multiple
* times always wakes up the same thread, as long as that thread didn't
* reacquire the sleep queue.
*/
sleepq_signal(sleepq);
out:
sleepq_release(sleepq);
}
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