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September 26, 2014 08:34
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Coroutines in C
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/* coroutine.h | |
* | |
* Coroutine mechanics, implemented on top of standard ANSI C. See | |
* http://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. | |
* | |
* [Simple version using static variables (scr macros)] | |
* int ascending (void) { | |
* static int i; | |
* | |
* scrBegin; | |
* for (i=0; i<10; i++) { | |
* scrReturn(i); | |
* } | |
* scrFinish(-1); | |
* } | |
* | |
* [Re-entrant version using an explicit context structure (ccr macros)] | |
* int ascending (ccrContParam) { | |
* ccrBeginContext; | |
* int i; | |
* ccrEndContext(foo); | |
* | |
* ccrBegin(foo); | |
* for (foo->i=0; foo->i<10; foo->i++) { | |
* ccrReturn(foo->i); | |
* } | |
* ccrFinish(-1); | |
* } | |
* | |
* In the static version, you need only surround the function body | |
* with `scrBegin' and `scrFinish', and then you can do `scrReturn' | |
* within the function and on the next call control will resume | |
* just after the scrReturn statement. Any local variables you need | |
* to be persistent across an `scrReturn' must be declared static. | |
* | |
* In the re-entrant version, you need to declare your persistent | |
* variables between `ccrBeginContext' and `ccrEndContext'. These | |
* will be members of a structure whose name you specify in the | |
* parameter to `ccrEndContext'. | |
* | |
* The re-entrant macros will malloc() the state structure on first | |
* call, and free() it when `ccrFinish' is reached. If you want to | |
* abort in the middle, you can use `ccrStop' to free the state | |
* structure immediately (equivalent to an explicit return() in a | |
* caller-type routine). | |
* | |
* A coroutine returning void type may call `ccrReturnV', | |
* `ccrFinishV' and `ccrStopV', or `scrReturnV', to avoid having to | |
* specify an empty parameter to the ordinary return macros. | |
* | |
* Ground rules: | |
* - never put `ccrReturn' or `scrReturn' within an explicit `switch'. | |
* - never put two `ccrReturn' or `scrReturn' statements on the same | |
* source line. | |
* | |
* The caller of a static coroutine calls it just as if it were an | |
* ordinary function: | |
* | |
* void main(void) { | |
* int i; | |
* do { | |
* i = ascending(); | |
* printf("got number %d\n", i); | |
* } while (i != -1); | |
* } | |
* | |
* The caller of a re-entrant coroutine must provide a context | |
* variable: | |
* | |
* void main(void) { | |
* ccrContext z = 0; | |
* do { | |
* printf("got number %d\n", ascending (&z)); | |
* } while (z); | |
* } | |
* | |
* Note that the context variable is set back to zero when the | |
* coroutine terminates (by crStop, or by control reaching | |
* crFinish). This can make the re-entrant coroutines more useful | |
* than the static ones, because you can tell when they have | |
* finished. | |
* | |
* If you need to dispose of a crContext when it is non-zero (that | |
* is, if you want to stop calling a coroutine without suffering a | |
* memory leak), the caller should call `ccrAbort(ctx)' where `ctx' | |
* is the context variable. | |
* | |
* 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 crReturn() | |
* inside a switch() statement. | |
*/ | |
/* | |
* coroutine.h is copyright 1995,2000 Simon Tatham. | |
* | |
* 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. | |
* | |
* $Id$ | |
*/ | |
#ifndef COROUTINE_H | |
#define COROUTINE_H | |
#include <stdlib.h> | |
/* | |
* `scr' macros for static coroutines. | |
*/ | |
#define scrBegin static int scrLine = 0; switch(scrLine) { case 0:; | |
#define scrFinish(z) } return (z) | |
#define scrFinishV } return | |
#define scrReturn(z) \ | |
do {\ | |
scrLine=__LINE__;\ | |
return (z); case __LINE__:;\ | |
} while (0) | |
#define scrReturnV \ | |
do {\ | |
scrLine=__LINE__;\ | |
return; case __LINE__:;\ | |
} while (0) | |
/* | |
* `ccr' macros for re-entrant coroutines. | |
*/ | |
#define ccrContParam void **ccrParam | |
#define ccrBeginContext struct ccrContextTag { int ccrLine | |
#define ccrEndContext(x) } *x = (struct ccrContextTag *)*ccrParam | |
#define ccrBegin(x) if(!x) {x= *ccrParam=malloc(sizeof(*x)); x->ccrLine=0;}\ | |
if (x) switch(x->ccrLine) { case 0:; | |
#define ccrFinish(z) } free(*ccrParam); *ccrParam=0; return (z) | |
#define ccrFinishV } free(*ccrParam); *ccrParam=0; return | |
#define ccrReturn(z) \ | |
do {\ | |
((struct ccrContextTag *)*ccrParam)->ccrLine=__LINE__;\ | |
return (z); case __LINE__:;\ | |
} while (0) | |
#define ccrReturnV \ | |
do {\ | |
((struct ccrContextTag *)*ccrParam)->ccrLine=__LINE__;\ | |
return; case __LINE__:;\ | |
} while (0) | |
#define ccrStop(z) do{ free(*ccrParam); *ccrParam=0; return (z); }while(0) | |
#define ccrStopV do{ free(*ccrParam); *ccrParam=0; return; }while(0) | |
#define ccrContext void * | |
#define ccrAbort(ctx) do { free (ctx); ctx = 0; } while (0) | |
#endif /* COROUTINE_H */ |
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