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/*
* coroutine.h is copyright 1995, 2000 Simon Tatham.
* Modernized/improved 2023 Tyge Løvset.
*
* Permission is hereby granted, free of charge, to any person
* obtaining a copy of this software and associated documentation
* files (the "Software"), to deal in the Software without
* restriction, including without limitation the rights to use,
* copy, modify, merge, publish, distribute, sublicense, and/or
* sell copies of the Software, and to permit persons to whom the
* Software is furnished to do so, subject to the following
* conditions:
*
* The above copyright notice and this permission notice shall be
* included in all copies or substantial portions of the Software.
*
* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
* EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES
* OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
* NONINFRINGEMENT. IN NO EVENT SHALL SIMON TATHAM BE LIABLE FOR
* ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF
* CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN
* CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
* SOFTWARE.
*/
/*
* Coroutine mechanics, implemented on top of standard ANSI C. See
* https://www.chiark.greenend.org.uk/~sgtatham/coroutines.html for
* a full discussion of the theory behind this.
*
* To use these macros to define a coroutine, you need to write a
* function that looks something like this:
*
* [Re-entrant version using an explicit context structure]
*
* int ascending(ccontext* ctx) {
* cco_context(ctx,
* int idx;
* );
*
* cco_routine(c,
* for (c->idx = 0; c->idx < 10; c->idx += 1)
* cco_yield(c->idx);
*
* cco_finish:; // add this to support cco_stop!
* );
* return -1;
* }
*
* In the re-entrant version, you need to declare your persistent
* variables by the `cco_context' macro. This macro takes the base
* ccontext as first parameter.
*
* Note that the context variable is set back to zero when the
* coroutine terminates (by cco_stop, or by control reaching
* finish. This can make the re-entrant coroutines more useful
* than the static ones, because you can tell when they have
* finished.
*
* This mechanism could have been better implemented using GNU C
* and its ability to store pointers to labels, but sadly this is
* not part of the ANSI C standard and so the mechanism is done by
* case statements instead. That's why you can't put a cco_yield()
* inside a switch-statement.
*
* The re-entrant macros will malloc() the state structure on first
* call, and free() it when end is reached. If you want to
* abort in the middle, you can use, the caller should call the
* coroutine with `cco_stop(&ctx)' as parameter instead of &ctx alone.
*
* Ground rules:
* - never put `c_yield' within an explicit `switch'.
* - never put two `c_yield' statements on the same source line.
* - add `cco_finish:' label at the end of the coroutine, before
* any cleanup code. Required to support cco_stop(ctx) argument.
*
* The caller of a re-entrant coroutine must provide a context
* variable:
*
* void main(void) {
* ccontext z = 0;
* for (;;) {
* int x = ascending(&z);
* if (!z) break;
* printf("got number %d\n", x);
*
* // stop if x == 5:
* if (x == 5) ascending(cco_stop(&z));
* }
* }
*/
#ifndef COROUTINE_H
#define COROUTINE_H
#include <stdlib.h>
#include <assert.h>
/*
* `c_' macros for re-entrant coroutines.
*/
typedef struct {
int _ccoline;
} *ccontext;
#define cco_context(cref, ...) \
struct ccoContext { \
int _ccoline; \
__VA_ARGS__ \
} **_ccoparam = (struct ccoContext **)cref
#define cco_routine(ctx, ...) \
do { \
if (!*_ccoparam) { \
*_ccoparam = malloc(sizeof **_ccoparam); \
(*_ccoparam)->_ccoline = 0; \
} \
struct ccoContext *ctx = *_ccoparam; \
switch (ctx->_ccoline) { \
case 0: __VA_ARGS__ break; \
default: assert(!"cco_finish: missing"); \
} \
free(ctx), *_ccoparam = 0; \
} while (0)
#define cco_yield(ret) \
do { \
(*_ccoparam)->_ccoline = __LINE__; return ret; \
case __LINE__:; \
} while (0)
#define cco_finish case -1
#define cco_stop(ctx) \
((*(ctx))->_ccoline = -1, (ctx))
#endif /* COROUTINE_H */
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