From 0b7bd5db8b2539d2e03b3a13b91ee6b21101460d Mon Sep 17 00:00:00 2001
From: "Luke T. Shumaker" <lukeshu@lukeshu.com>
Date: Tue, 24 Sep 2024 14:44:46 -0600
Subject: coroutine_rpc.h: Support multiple requesters

---
 coroutine_rpc.h | 53 +++++++++++++++++++++++++++++++++++------------------
 1 file changed, 35 insertions(+), 18 deletions(-)

(limited to 'coroutine_rpc.h')

diff --git a/coroutine_rpc.h b/coroutine_rpc.h
index b51445e..11d40d7 100644
--- a/coroutine_rpc.h
+++ b/coroutine_rpc.h
@@ -11,6 +11,8 @@
 #ifndef _COROUTINE_RPC_H_
 #define _COROUTINE_RPC_H_
 
+#include <assert.h>
+
 #include "coroutine.h"
 
 /**
@@ -18,15 +20,15 @@
  * rcp-channel on which the requester submits a value of type `req_t`
  * and the responder responds with a value of type `resp_t`.
  *
- * There must only ever be 1 concurrent writer and 1 concurrent
- * reader. If you need 1:n, n:1, or m:n; then you should instead use a
- * series of coroutine_chan.h.
+ * There may be multiple concurrent requesters, but only one
+ * concurrent responder.  If you need multiple concurrent responders,
+ * set up a system of coroutine_chan.h channels.
  */
-#define cr_rpc_t(req_t, resp_t) struct { \
-		cid_t   requester;       \
-		cid_t   responder;       \
-		req_t  *req_p;           \
-		resp_t *resp_p;          \
+#define cr_rpc_t(req_t, resp_t) struct {            \
+		cid_t   requester, *tail_requester; \
+		cid_t   responder;                  \
+		req_t  *req_p;                      \
+		resp_t *resp_p;                     \
 	}
 
 /* These "functions" are preprocessor macros instead of real C
@@ -40,13 +42,29 @@
  * Blocking: Always; until the responder has called both
  * cr_rpc_recv_req() and cr_rpc_send_resp().
  */
-#define cr_rpc_req(ch, _resp_p, _req) do {           \
-		(ch)->requester = cr_getcid();       \
-		(ch)->req_p = &(_req);               \
-		(ch)->resp_p = (_resp_p;             \
-		if ((ch)->responder != 0)            \
-			cr_unpause((ch)->responder); \
-		cr_pause_and_yield();                \
+#define cr_rpc_req(ch, _resp_p, _req) do {                    \
+		cid_t next = 0;                               \
+		if ((ch)->requester) {                        \
+			*((ch)->tail_requester = cr_getcid(); \
+			(ch)->tail_requester = &next;         \
+			cr_pause_and_yield();                 \
+		} else {                                      \
+			(ch)->requester = cr_getcid();        \
+			(ch)->tail_requester = &next;         \
+		}                                             \
+		assert((ch)->requester == cr_getcid());       \
+		(ch)->req_p = &(_req);                        \
+		(ch)->resp_p = (_resp_p;                      \
+		if ((ch)->responder != 0)                     \
+			cr_unpause((ch)->responder);          \
+		cr_pause_and_yield();                         \
+		if (next) {                                   \
+			(ch)->requester = next;               \
+			cr_unpause(next);                     \
+		} else {                                      \
+			(ch)->requester = 0;                  \
+			(ch)->tail_requester = NULL;          \
+		}
 	} while (0)
 
 /**
@@ -56,7 +74,7 @@
  *
  * Blocking: Never.
  */
-#define cr_rpc_have_req(ch) ((ch)->requester != 0)
+#define cr_rpc_have_req(ch) ((ch)->req_p != NULL)
 
 /**
  * cr_rpc_recv_req(cr_rpc_t(req_t, resp_t) *ch, req_t *req_p) reads
@@ -81,11 +99,10 @@
  * Blocking: Never.
  */
 #define cr_rpc_send_resp(ch, _resp) do {       \
-		cr_unpause((ch)->requester);   \
 		(ch)->responder = 0;           \
-		(ch)->requester = 0;           \
 		*((ch)->resp_p) = (_resp);     \
 		(ch)->resp_p = NULL;           \
+		cr_unpause((ch)->requester);   \
 	} while (0)
 
 #endif /* _COROUTINE_RPC_H_ */
-- 
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