1 files changed, 64 insertions, 0 deletions
diff --git a/libcr_ipc/sema.c b/libcr_ipc/sema.c
new file mode 100644
index 0000000..cb984b6
--- /dev/null
+++ b/libcr_ipc/sema.c
@@ -0,0 +1,64 @@
+/* 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);
+}