libcr_ipc/mutex.c


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/* libcr_ipc/mutex.c - Simple mutexes for libcr
 *
 * Copyright (C) 2024-2025  Luke T. Shumaker <lukeshu@lukeshu.com>
 * SPDX-License-Identifier: AGPL-3.0-or-later
 */

#include <libcr/coroutine.h> /* for cid_t, cr_* */

#define IMPLEMENTATION_FOR_LIBCR_IPC_MUTEX_H YES
#include <libcr_ipc/mutex.h>

struct cr_mutex_waiter {
	lm_sll_node;
	cid_t                    cid;
};

void cr_mutex_lock(cr_mutex_t *mu) {
	assert(mu);
	cr_assert_in_coroutine();

	if (!mu->locked) /* non-blocking fast-path */
		mu->locked = true;
	else { /* blocking slow-path */
		struct cr_mutex_waiter self = {
			.cid     = cr_getcid(),
		};
		lm_sll_push_to_rear(&mu->waiters, &self);
		cr_pause_and_yield();
	}
	assert(mu->locked);
}

void cr_mutex_unlock(cr_mutex_t *mu) {
	assert(mu);
	cr_assert_in_coroutine();

	assert(mu->locked);
	if (mu->waiters.front) {
		cr_unpause(lm_sll_node_cast(struct cr_mutex_waiter, mu->waiters.front)->cid);
		lm_sll_pop_from_front(&mu->waiters);
	} else
		mu->locked = false;
}