1 files changed, 44 insertions, 0 deletions
diff --git a/libcr_ipc/mutex.c b/libcr_ipc/mutex.c
new file mode 100644
index 0000000..1b4e626
--- /dev/null
+++ b/libcr_ipc/mutex.c
@@ -0,0 +1,44 @@
+/* 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_* */
+#include <libmisc/assert.h>
+
+#define IMPLEMENTATION_FOR_LIBCR_IPC_MUTEX_H YES
+#include <libcr_ipc/mutex.h>
+
+struct cr_mutex_waiter {
+	cid_t                    cid;
+};
+SLIST_DECLARE_NODE(_cr_mutex_waiter_list, struct cr_mutex_waiter);
+
+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_list_node self = { .val = {
+			.cid     = cr_getcid(),
+		}};
+		slist_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(mu->waiters.front->val.cid);
+		slist_pop_from_front(&mu->waiters);
+	} else
+		mu->locked = false;
+}