110 lines
2.7 KiB
C
110 lines
2.7 KiB
C
/* See the end of this file for copyright and license terms. */
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#include <arch/atom.h>
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#include <gay/clist.h>
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#include <gay/mutex.h>
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#include <gay/sched.h>
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#include <errno.h>
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void spin_init(spin_t *spin)
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{
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atom_write(&spin->lock, 0);
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}
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void spin_lock(spin_t *spin)
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{
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while (atom_write(&spin->lock, 1) != 0);
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/* nothing */
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}
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int spin_trylock(spin_t *spin)
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{
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if (atom_write(&spin->lock, 1) != 0)
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return -EAGAIN;
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return 0;
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}
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void spin_unlock(spin_t *spin)
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{
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atom_write(&spin->lock, 0);
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}
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void mtx_init(struct mtx *mtx)
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{
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atom_write(&mtx->lock, 0);
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spin_init(&mtx->wait_queue_lock);
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clist_init(&mtx->wait_queue);
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}
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void mtx_lock(struct mtx *mtx)
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{
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/*
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* acquire a lock on the wait queue before trying to claim the
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* mutex itself to make sure the mutex isn't released while we
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* are inserting ourselves into the wait queue
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*/
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spin_lock(&mtx->wait_queue_lock);
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if (atom_write(&mtx->lock, 1) == 0) {
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spin_unlock(&mtx->wait_queue_lock);
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} else {
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struct task *task = current;
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/*
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* It might not be the smartest idea to allocate this thing on
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* the stack because it's gonna blow up if the task somehow dies
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* before returning here. Let's see how this turns out.
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*/
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struct lock_waiter waiter = {
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.task = task,
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};
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clist_add(&mtx->wait_queue, &waiter.clink);
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spin_unlock(&mtx->wait_queue_lock);
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task->state = TASK_BLOCKED;
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/*
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* This is only gonna return when the task currently owning the
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* lock releases it. In that case, it doesn't unlock the mutex
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* but merely switches back to us directly and thereby implicitly
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* transfers the ownership of the mutex to us (see mtx_unlock()).
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*/
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schedule();
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}
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}
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int mtx_trylock(struct mtx *mtx)
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{
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if (atom_write(&mtx->lock, 1) != 0)
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return -EAGAIN;
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return 0;
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}
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void mtx_unlock(struct mtx *mtx)
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{
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spin_lock(&mtx->wait_queue_lock);
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if (!clist_is_empty(&mtx->wait_queue)) {
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struct lock_waiter *waiter =
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clist_first_entry(&mtx->wait_queue, typeof(*waiter), clink);
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clist_del(&waiter->clink);
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spin_unlock(&mtx->wait_queue_lock);
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waiter->task->state = TASK_READY;
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switch_to(waiter->task, current);
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} else {
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atom_write(&mtx->lock, 0);
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spin_unlock(&mtx->wait_queue_lock);
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}
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}
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/*
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* This file is part of GayBSD.
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* Copyright (c) 2021 fef <owo@fef.moe>.
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*
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* GayBSD is nonviolent software: you may only use, redistribute, and/or
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* modify it under the terms of the Cooperative Nonviolent Public License
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* (CNPL) as found in the LICENSE file in the source code root directory
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* or at <https://git.pixie.town/thufie/npl-builder>; either version 7
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* of the license, or (at your option) any later version.
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*
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* GayBSD comes with ABSOLUTELY NO WARRANTY, to the extent
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* permitted by applicable law. See the CNPL for details.
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*/
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