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/* libcr_ipc/select.c - Select between channels
*
* Copyright (C) 2024-2025 Luke T. Shumaker <lukeshu@lukeshu.com>
* SPDX-License-Identifier: AGPL-3.0-or-later
*/
#include <libcr_ipc/select.h>
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->waiter_typ == _CR_CHAN_SENDER)
return _CR_SELECT_CLASS_NONBLOCK;
else
return _CR_SELECT_CLASS_BLOCKING;
case _CR_SELECT_OP_SEND:
if (arg.ch->waiters.front && arg.ch->waiter_typ == _CR_CHAN_RECVER)
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");
}
}
void _cr_select_dequeue(void *_waiters, size_t idx) {
struct _cr_select_waiters *waiters = _waiters;
for (size_t i = 0; i < waiters->cnt; i++)
_cr_ipc_dll_remove(&(waiters->args[i].ch->waiters),
&(waiters->nodes[i]));
waiters->cnt = idx;
}
size_t cr_select_v(size_t arg_cnt, struct cr_select_arg 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])) {
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 = rand_uint63n(cnt_nonblock);
for (size_t i = 0, seen = 0; i < arg_cnt; i++) {
if (_cr_select_getclass(arg_vec[i]) == _CR_SELECT_CLASS_NONBLOCK) {
if (seen == choice) {
_cr_chan_xfer(arg_vec[i].op == _CR_SELECT_OP_RECV
? _CR_CHAN_RECVER
: _CR_CHAN_SENDER,
arg_vec[i].ch,
arg_vec[i].val_ptr,
arg_vec[i].val_siz);
return i;
}
seen++;
}
}
assert_notreached("should have returned from inside for() loop");
}
if (cnt_default) {
for (size_t i = 0; i < arg_cnt; i++)
if (_cr_select_getclass(arg_vec[i]) == _CR_SELECT_CLASS_DEFAULT)
return i;
assert_notreached("should have returned from inside for() loop");
}
struct _cr_select_waiters waiters = {
.cnt = arg_cnt,
.args = arg_vec,
.nodes = alloca(sizeof(struct _cr_chan_waiter) * arg_cnt),
};
for (size_t i = 0; i < arg_cnt; i++) {
waiters.nodes[i] = (struct _cr_chan_waiter){
.cid = cr_getcid(),
.val_ptr = arg_vec[i].val_ptr,
.dequeue = _cr_select_dequeue,
.dequeue_arg1 = &waiters,
.dequeue_arg2 = i,
};
_cr_ipc_dll_push_to_rear(&arg_vec[i].ch->waiters, &waiters.nodes[i]);
}
cr_pause_and_yield();
return waiters.cnt;
}
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