/* coroutine_chan.h - Simple request/response system for coroutine.{h,c}
 *
 * Copyright (C) 2024  Luke T. Shumaker <lukeshu@lukeshu.com>
 * SPDX-Licence-Identifier: AGPL-3.0-or-later
 */

/**
 * The cr_chan_* macros form a simple request/response channel
 * mechanism built on top of the cr_pause_and_yeild() and cr_unpause()
 * primitives.
 */
#ifndef _COROUTINE_CHAN_H_
#define _COROUTINE_CHAN_H_

#include "coroutine.h"

/**
 * cr_chan_t(req_t, resp_t) returns the type definition for a channel
 * on which the requester submits a value of type `req_t` and the
 * responder responds with a value of type `resp_t`.
 */
#define cr_chan_t(req_t, resp_t) struct { \
		cid_t requester;          \
		cid_t responder;          \
		req_t  req;               \
		resp_t resp;              \
	}

/* These are "functions" are preprocessor macros instead of real C
 * functions so that the compiler can do type-checking instead of
 * having these functions take `void*`.  */ 

/**
 * ch_chan_req(cr_chan_t(req_t, resp_t) *ch, resp_t *resp, req_t req)
 * submits the `req` request to `ch` puts the response in `*resp_p`.
 *
 * Blocks until the responder has called both cr_chan_recv_req() and
 * cr_chan_send_resp().
 */
#define cr_chan_req(ch, _resp_p, _req) do {                             \
		(ch)->requester = cr_getcid();                          \
		(ch)->req = (_req);                                     \
		if ((ch)->responder != 0)                               \
			cr_unpause((ch)->responder);                    \
		cr_pause_and_yield();                                   \
		if ((typeof(&(ch)->resp))(_resp_p))                     \
			*((typeof(&(ch)->resp))(_resp_p)) = (ch)->resp; \
	} while (0)

/**
 * cr_chan_have_req(cr_chan_t(req_t, resp_t) *ch) allows a responder
 * to check whether or not there is a request waiting to be received
 * (with cr_chan_recv_req()) without blocking if there is not.
 *
 * Never blocks.
 */
#define cr_chan_have_req(ch) ((ch)->requester != 0)

/**
 * cr_chan_recv_req(cr_chan_t(req_t, resp_t) *ch, req_t *req_p) reads
 * a request from ch into `*req_p`.
 *
 * If there is not a pending request on `ch`, blocks until there is.
 */
#define cr_chan_recv_req(ch, _req_p) do {      \
		(ch)->responder = cr_getcid(); \
		if ((ch)->requester == 0)      \
			cr_pause_and_yield();  \
		*(_req_p) = (ch)->req;         \
	} while (0)

/**
 * cr_chan_send_resp(cr_chan_t(req_t, resp_t) *ch, resp_t resp) sends
 * the reply to the most-recently-read request.
 *
 * Never blocks.
 */
#define cr_chan_send_resp(ch, _resp) do {    \
		cr_unpause((ch)->requester); \
		(ch)->responder = 0;         \
		(ch)->requester = 0;         \
		(ch)->resp = (_resp);        \
	} while (0)

#endif /* _COROUTINE_CHAN_H_ */