libcr_ipc/sema.c


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/* libcr_ipc/sema.c - Simple semaphores 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_SEMA_H YES
#include <libcr_ipc/sema.h>

struct cr_sema_waiter {
	lm_sll_node;
	cid_t                    cid;
};

void cr_sema_signal(cr_sema_t *sema) {
	assert(sema);
	cr_assert_in_coroutine();

	bool saved = cr_save_and_disable_interrupts();
	sema->cnt++;
	if (sema->waiters.front && !sema->unpausing) {
		cr_unpause(
			lm_sll_node_cast(struct cr_sema_waiter, sema->waiters.front)->cid);
		sema->unpausing = true;
	}
	cr_restore_interrupts(saved);
}

void cr_sema_signal_from_intrhandler(cr_sema_t *sema) {
	assert(sema);
	cr_assert_in_intrhandler();

	sema->cnt++;
	if (sema->waiters.front && !sema->unpausing) {
		cr_unpause_from_intrhandler(
			lm_sll_node_cast(struct cr_sema_waiter, sema->waiters.front)->cid);
		sema->unpausing = true;
	}
}

void cr_sema_wait(cr_sema_t *sema) {
	assert(sema);
	cr_assert_in_coroutine();

	bool saved = cr_save_and_disable_interrupts();

	struct cr_sema_waiter self = {
		.cid    = cr_getcid(),
	};
	lm_sll_push_to_rear(&sema->waiters, &self);
	if (sema->waiters.front != &self.lm_sll_node || !sema->cnt)
		cr_pause_and_yield();
	assert(sema->waiters.front == &self.lm_sll_node && sema->cnt);
	lm_sll_pop_from_front(&sema->waiters);
	sema->cnt--;
	if (sema->cnt && sema->waiters.front)
		cr_unpause(
			lm_sll_node_cast(struct cr_sema_waiter, sema->waiters.front)->cid);
	else
		sema->unpausing = false;
	cr_restore_interrupts(saved);
}