mirror of
https://github.com/zephyrproject-rtos/zephyr
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ec554f44d9
Just like with _Swap(), we need two variants of these utilities which can atomically release a lock and context switch. The naming shifts (for byte count reasons) to _reschedule/_pend_curr, and both have an _irqlock variant which takes the traditional locking. Just refactoring. No logic changes. Signed-off-by: Andy Ross <andrew.j.ross@intel.com>
81 lines
2.1 KiB
C
81 lines
2.1 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 <ksched.h>
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#include <wait_q.h>
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#include <posix/pthread.h>
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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->lock_count == 1, "");
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int ret, key = irq_lock();
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mut->lock_count = 0;
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mut->owner = NULL;
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_ready_one_thread(&mut->wait_q);
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ret = _pend_curr_irqlock(key, &cv->wait_q, timeout);
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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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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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_reschedule_irqlock(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 (_waitq_head(&cv->wait_q)) {
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_ready_one_thread(&cv->wait_q);
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}
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_reschedule_irqlock(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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