blob: e6df9277b31cc03855f85d8ee82bdca39321362b [file] [log] [blame]
/*
* Copyright (c) 2017 Intel Corporation
*
* SPDX-License-Identifier: Apache-2.0
*/
#include <kernel.h>
#include <pthread.h>
#include "ksched.h"
#include "wait_q.h"
void ready_one_thread(_wait_q_t *wq);
static int cond_wait(pthread_cond_t *cv, pthread_mutex_t *mut, int timeout)
{
__ASSERT(mut->sem->count == 0, "");
int ret, key = irq_lock();
mut->sem->count = 1;
ready_one_thread(&mut->sem->wait_q);
_pend_current_thread(&cv->wait_q, timeout);
ret = _Swap(key);
/* FIXME: this extra lock (and the potential context switch it
* can cause) could be optimized out. At the point of the
* signal/broadcast, it's possible to detect whether or not we
* will be swapping back to this particular thread and lock it
* (i.e. leave the lock variable unchanged) on our behalf.
* But that requires putting scheduler intelligence into this
* higher level abstraction and is probably not worth it.
*/
pthread_mutex_lock(mut);
return ret == -EAGAIN ? -ETIMEDOUT : ret;
}
/* This implements a "fair" scheduling policy: at the end of a POSIX
* thread call that might result in a change of the current maximum
* priority thread, we always check and context switch if needed.
* Note that there is significant dispute in the community over the
* "right" way to do this and different systems do it differently by
* default. Zephyr is an RTOS, so we choose latency over
* throughput. See here for a good discussion of the broad issue:
*
* https://blog.mozilla.org/nfroyd/2017/03/29/on-mutex-performance-part-1/
*/
static void swap_or_unlock(int key)
{
/* API madness: use __ not _ here. The latter checks for our
* preemption state, but we want to do a switch here even if
* we can be preempted.
*/
if (!_is_in_isr() && __must_switch_threads()) {
_Swap(key);
} else {
irq_unlock(key);
}
}
int pthread_cond_signal(pthread_cond_t *cv)
{
int key = irq_lock();
ready_one_thread(&cv->wait_q);
swap_or_unlock(key);
return 0;
}
int pthread_cond_broadcast(pthread_cond_t *cv)
{
int key = irq_lock();
while (!sys_dlist_is_empty(&cv->wait_q)) {
ready_one_thread(&cv->wait_q);
}
swap_or_unlock(key);
return 0;
}
int pthread_cond_wait(pthread_cond_t *cv, pthread_mutex_t *mut)
{
return cond_wait(cv, mut, K_FOREVER);
}
int pthread_cond_timedwait(pthread_cond_t *cv, pthread_mutex_t *mut,
const struct timespec *to)
{
return cond_wait(cv, mut, _ts_to_ms(to));
}