9c62cc677d
The xtensa-asm2 work included a patch that added nano_internal.h includes in lots of places that needed to have _Swap defined, because it had to break a cycle and this no longer got pulled in from the arch headers. Unfortunately those new includes created new and more amusing cycles elsewhere which led to breakage on other platforms. Break out the _Swap definition (only) into a separate header and use that instead. Cleaner. Seems not to have any more hidden gotchas. Signed-off-by: Andy Ross <andrew.j.ross@intel.com>
97 lines
2.4 KiB
C
97 lines
2.4 KiB
C
/*
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* Copyright (c) 2017 Intel Corporation
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*
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* SPDX-License-Identifier: Apache-2.0
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*/
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#include <kernel.h>
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#include <pthread.h>
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#include "ksched.h"
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#include "wait_q.h"
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#include <kswap.h>
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void ready_one_thread(_wait_q_t *wq);
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static int cond_wait(pthread_cond_t *cv, pthread_mutex_t *mut, int timeout)
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{
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__ASSERT(mut->sem->count == 0, "");
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int ret, key = irq_lock();
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mut->sem->count = 1;
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ready_one_thread(&mut->sem->wait_q);
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_pend_current_thread(&cv->wait_q, timeout);
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ret = _Swap(key);
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/* FIXME: this extra lock (and the potential context switch it
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* can cause) could be optimized out. At the point of the
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* signal/broadcast, it's possible to detect whether or not we
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* will be swapping back to this particular thread and lock it
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* (i.e. leave the lock variable unchanged) on our behalf.
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* But that requires putting scheduler intelligence into this
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* higher level abstraction and is probably not worth it.
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*/
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pthread_mutex_lock(mut);
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return ret == -EAGAIN ? -ETIMEDOUT : ret;
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}
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/* This implements a "fair" scheduling policy: at the end of a POSIX
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* thread call that might result in a change of the current maximum
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* priority thread, we always check and context switch if needed.
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* Note that there is significant dispute in the community over the
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* "right" way to do this and different systems do it differently by
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* default. Zephyr is an RTOS, so we choose latency over
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* throughput. See here for a good discussion of the broad issue:
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*
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* https://blog.mozilla.org/nfroyd/2017/03/29/on-mutex-performance-part-1/
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*/
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static void swap_or_unlock(int key)
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{
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/* API madness: use __ not _ here. The latter checks for our
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* preemption state, but we want to do a switch here even if
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* we can be preempted.
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*/
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if (!_is_in_isr() && __must_switch_threads()) {
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_Swap(key);
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} else {
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irq_unlock(key);
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}
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}
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int pthread_cond_signal(pthread_cond_t *cv)
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{
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int key = irq_lock();
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ready_one_thread(&cv->wait_q);
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swap_or_unlock(key);
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return 0;
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}
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int pthread_cond_broadcast(pthread_cond_t *cv)
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{
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int key = irq_lock();
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while (!sys_dlist_is_empty(&cv->wait_q)) {
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ready_one_thread(&cv->wait_q);
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}
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swap_or_unlock(key);
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return 0;
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}
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int pthread_cond_wait(pthread_cond_t *cv, pthread_mutex_t *mut)
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{
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return cond_wait(cv, mut, K_FOREVER);
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}
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int pthread_cond_timedwait(pthread_cond_t *cv, pthread_mutex_t *mut,
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const struct timespec *to)
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{
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return cond_wait(cv, mut, _ts_to_ms(to));
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}
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