1 files changed, 134 insertions, 0 deletions
diff --git a/libcr_ipc/chan.c b/libcr_ipc/chan.c
new file mode 100644
index 0000000..b7ecfc8
--- /dev/null
+++ b/libcr_ipc/chan.c
@@ -0,0 +1,134 @@
+/* libcr_ipc/chan.c - Simple channels for libcr
+ *
+ * Copyright (C) 2024-2025  Luke T. Shumaker <lukeshu@lukeshu.com>
+ * SPDX-License-Identifier: AGPL-3.0-or-later
+ */
+
+#include <string.h>  /* for memcpy() */
+
+#include <libcr/coroutine.h> /* for cid_t, cr_* */
+#include <libmisc/assert.h>
+#include <libmisc/rand.h>
+
+#define IMPLEMENTATION_FOR_LIBCR_IPC_CHAN_H YES
+#include <libcr_ipc/chan.h>
+
+struct _cr_select_waiter {
+	cid_t                            cid;
+	struct _cr_select_arg_list_node *arg_vec;
+	size_t                           arg_cnt;
+
+	size_t                           ret;
+};
+
+enum cr_select_class {
+	CR_SELECT_CLASS_DEFAULT,
+	CR_SELECT_CLASS_BLOCKING,
+	CR_SELECT_CLASS_NONBLOCK,
+};
+
+static inline enum cr_select_class cr_select_getclass(struct _cr_select_arg *arg) {
+	switch (arg->op) {
+	case _CR_SELECT_OP_RECV:
+		if (arg->ch->waiters.front && arg->ch->waiters.front->val.op == _CR_SELECT_OP_SEND)
+			return CR_SELECT_CLASS_NONBLOCK;
+		else
+			return CR_SELECT_CLASS_BLOCKING;
+	case _CR_SELECT_OP_SEND:
+		if (arg->ch->waiters.front && arg->ch->waiters.front->val.op == _CR_SELECT_OP_RECV)
+			return CR_SELECT_CLASS_NONBLOCK;
+		else
+			return CR_SELECT_CLASS_BLOCKING;
+	case _CR_SELECT_OP_DEFAULT:
+		return CR_SELECT_CLASS_DEFAULT;
+	default:
+		assert_notreached("invalid arg->op");
+	}
+}
+
+size_t cr_select_v(size_t arg_cnt, struct _cr_select_arg_list_node arg_vec[]) {
+	size_t  cnt_blocking = 0;
+	size_t  cnt_nonblock = 0;
+	size_t  cnt_default  = 0;
+
+	assert(arg_cnt);
+	assert(arg_vec);
+	cr_assert_in_coroutine();
+
+	for (size_t i = 0; i < arg_cnt; i++) {
+		switch (cr_select_getclass(&arg_vec[i].val)) {
+		case CR_SELECT_CLASS_BLOCKING:
+			cnt_blocking++;
+			break;
+		case CR_SELECT_CLASS_NONBLOCK:
+			cnt_nonblock++;
+			break;
+		case CR_SELECT_CLASS_DEFAULT:
+			cnt_default++;
+			break;
+		}
+	}
+
+	if (cnt_nonblock) {
+		size_t choice_among_nonblock = rand_uint63n(cnt_nonblock);
+		size_t choice_among_all = arg_cnt;
+		for (size_t i = 0, seen = 0; i < choice_among_all; i++) {
+			if (cr_select_getclass(&arg_vec[i].val) == CR_SELECT_CLASS_NONBLOCK) {
+				if (seen == choice_among_nonblock)
+					choice_among_all = i;
+				seen++;
+			}
+		}
+		assert(choice_among_all < arg_cnt);
+
+		struct _cr_select_arg *this = &arg_vec[choice_among_all].val;
+		assert(this->ch->waiters.front);
+		struct _cr_select_arg *other = &this->ch->waiters.front->val;
+		assert(this->val_siz == other->val_siz);
+		assert(this->ch == other->ch);
+		switch (this->op) {
+		case _CR_SELECT_OP_SEND:
+			assert(other->op == _CR_SELECT_OP_RECV);
+			memcpy(other->val_ptr, this->val_ptr, this->val_siz);
+			break;
+		case _CR_SELECT_OP_RECV:
+			assert(other->op == _CR_SELECT_OP_SEND);
+			memcpy(this->val_ptr, other->val_ptr, this->val_siz);
+			break;
+		case _CR_SELECT_OP_DEFAULT:
+			assert_notreached("_CR_SELECT_OP_DEFAULT is not CR_SELECT_CLASS_NONBLOCK");
+		}
+		struct _cr_select_waiter *waiter = other->waiter;
+		for (size_t i = 0; i < waiter->arg_cnt; i++) {
+			waiter->arg_vec[i].val.ch->nwaiters--;
+			dlist_remove(&waiter->arg_vec[i].val.ch->waiters, &waiter->arg_vec[i]);
+			if (&waiter->arg_vec[i].val == other)
+				waiter->ret = i;
+		}
+		cr_unpause(waiter->cid);
+		cr_yield();
+		return choice_among_all;
+	}
+
+	if (cnt_default) {
+		for (size_t i = 0; i < arg_cnt; i++)
+			if (cr_select_getclass(&arg_vec[i].val) == CR_SELECT_CLASS_DEFAULT)
+				return i;
+		assert_notreached("should have returned from inside for() loop");
+	}
+
+	assert(cnt_blocking && cnt_blocking == arg_cnt);
+
+	struct _cr_select_waiter waiter = {
+		.cid     = cr_getcid(),
+		.arg_vec = arg_vec,
+		.arg_cnt = arg_cnt,
+	};
+	for (size_t i = 0; i < arg_cnt; i++) {
+		arg_vec[i].val.waiter = &waiter;
+		arg_vec[i].val.ch->nwaiters++;
+		dlist_push_to_rear(&arg_vec[i].val.ch->waiters, &arg_vec[i]);
+	}
+	cr_pause_and_yield();
+	return waiter.ret;
+}