From 18d2918a02028bf649607bb9959b926d10f184f6 Mon Sep 17 00:00:00 2001
From: Vito Caputo <vcaputo@pengaru.com>
Date: Wed, 4 Nov 2020 15:47:33 -0800
Subject: thunk: introduce public variant of THUNK_DEFINE

This is necessarily split in two:

THUNK_DEFINE()
THUNK_DECLARE()

use is identical to the original THUNK_DEFINE (now THUNK_DEFINE_STATIC),
and you supply the same input to both DEFINE and DECLARE.

The THUNK_DECLARE() should go in the public header, which you also
include in the implementing .c file, not just from consumers.

The THUNK_DEFINE() goes in the implementing .c file, same as before.

Use this variant when you wish to instantiate via THUNK() from external
listings, just include the THUNK_DECLARE()-containing .h.
---
 thunk.h | 50 ++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 50 insertions(+)

diff --git a/thunk.h b/thunk.h
index ef868ab..d2ec683 100644
--- a/thunk.h
+++ b/thunk.h
@@ -418,6 +418,56 @@ struct thunk_t {
 										\
 	static int _THUNK_GEN_PROTO(_name, __VA_ARGS__)
 
+
+/* this is the public variant which is split across declare & define */
+/* put the declaration in the .h, the define in the .c, be sure to include the
+ * .h from the implementing .c - not just the consumers.
+ */
+#define THUNK_DECLARE(_name, ...)						\
+	int _THUNK_GEN_PROTO(_name, __VA_ARGS__);				\
+	typedef struct __thunk_environment_##_name {				\
+		/* struct for encapsulating the calling environment */		\
+		thunk_t			__thunk;				\
+		_THUNK_GEN_STRUCT	(__VA_ARGS__);				\
+	} __thunk_environment_##_name;						\
+										\
+	int __thunk_dispatch_##_name(thunk_t *thunk);				\
+	thunk_t * _THUNK_GEN_PROTO(__thunk_instantiate_##_name, __VA_ARGS__);
+
+
+#define THUNK_DEFINE(_name, ...)						\
+	int __thunk_dispatch_##_name(thunk_t *thunk) {				\
+		/* dispatch thunk from associated environment */		\
+		__thunk_environment_##_name *env;				\
+		int r;								\
+										\
+		/* XXX: the embedded __thunk is always at the start, otherwise	\
+		 * container_of() could be used... */				\
+		env = (__thunk_environment_##_name *)thunk;			\
+		assert(env);							\
+										\
+		r = _THUNK_GEN_DISPATCH(_name, env, __VA_ARGS__);		\
+		free(env);							\
+										\
+		return r;							\
+	}									\
+										\
+	thunk_t * _THUNK_GEN_PROTO(__thunk_instantiate_##_name, __VA_ARGS__) {	\
+		/* allocate and populate environment, return it */		\
+		__thunk_environment_##_name *env;				\
+										\
+		env = malloc(sizeof(*env));					\
+		assert(env);							\
+										\
+		_THUNK_GEN_INITIALIZE(env, __VA_ARGS__);			\
+		env->__thunk.dispatch = __thunk_dispatch_##_name;		\
+										\
+		return &env->__thunk;						\
+	}									\
+										\
+	int _THUNK_GEN_PROTO(_name, __VA_ARGS__)
+
+
 /* Call the appropriate instantiate function which returns an embedded thunk_t,
  * this is how you prepare the thunks established via THUNK_DEFINE(). */
 #define _THUNK(_call)								\
-- 
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