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/* ScummVM - Graphic Adventure Engine
*
* ScummVM is the legal property of its developers, whose names
* are too numerous to list here. Please refer to the COPYRIGHT
* file distributed with this source distribution.
*
* This program is free software; you can redistribute it and/or
* modify it under the terms of the GNU General Public License
* as published by the Free Software Foundation; either version 2
* of the License, or (at your option) any later version.
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details.
* You should have received a copy of the GNU General Public License
* along with this program; if not, write to the Free Software
* Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
*
* $URL$
* $Id$
*
*/
#ifndef TINSEL_COROUTINE_H
#define TINSEL_COROUTINE_H
#include "common/scummsys.h"
namespace Tinsel {
/**
* @defgroup TinselCoroutines Coroutine support for Tinsel
*
* The following is loosely based on an article by Simon Tatham:
* <http://www.chiark.greenend.org.uk/~sgtatham/coroutines.html>.
* However, many improvements and tweaks have been made, in particular
* by taking advantage of C++ features not available in C.
*
* Why is this code here? Well, the Tinsel engine apparently used
* setjmp/longjmp based coroutines as a core tool from the start, and
* so they are deeply ingrained into the whole code base. When we
* started to get Tinsel ready for ScummVM, we had to deal with that.
* It soon got clear that we could not simply rewrite the code to work
* without some form of coroutines. While possible in principle, it
* would have meant a major restructuring of the entire code base, a
* rather daunting task. Also, it would have very likely introduced
* tons of regressons.
*
* So instead of getting rid of the coroutines, we chose to implement
* them in an alternate way, using Simon Tatham's trick as described
* above. While the trick is dirty, the result seems to be clear enough,
* we hope; plus, it allowed us to stay relatively close to the
* original structure of the code, which made it easier to avoid
* regressions, and will be helpful in the future when comparing things
* against the original code base.
*/
//@{
/**
* The core of any coroutine context which captures the 'state' of a coroutine.
* Private use only.
*/
struct CoroBaseContext {
int _line;
int _sleep;
CoroBaseContext *_subctx;
CoroBaseContext() : _line(0), _sleep(0), _subctx(0) {}
~CoroBaseContext() { delete _subctx; }
};
typedef CoroBaseContext *CoroContext;
// FIXME: Document this!
extern CoroContext nullContext;
/**
* Wrapper class which holds a pointer to a pointer to a CoroBaseContext.
* The interesting part is the destructor, which kills the context being held,
* but ONLY if the _sleep val of that context is zero. This way, a coroutine
* can just 'return' w/o having to worry about freeing the allocated context
* (in Simon Tatham's original code, one had to use a special macro to
* return from a coroutine).
*/
class CoroContextHolder {
CoroContext &_ctx;
public:
CoroContextHolder(CoroContext &ctx) : _ctx(ctx) {
assert(ctx);
assert(ctx->_sleep >= 0);
ctx->_sleep = 0;
}
~CoroContextHolder() {
if (_ctx && _ctx->_sleep == 0) {
delete _ctx;
_ctx = 0;
}
}
};
#define CORO_PARAM CoroContext &coroParam
#define CORO_SUBCTX coroParam->_subctx
/**
* Begin the declaration of a coroutine context.
* This allows declaring variables which are 'persistent' during the
* lifetime of the coroutine. An example use would be:
*
* CORO_BEGIN_CONTEXT;
* int var;
* char *foo;
* CORO_END_CONTEXT(_ctx);
*
* It is not possible to initialize variables here, due to the way this
* macro is implemented. Furthermore, to use the variables declared in
* the coroutine context, you have to access them via the context variable
* name that was specified as parameter to CORO_END_CONTEXT, e.g.
* _ctx->var = 0;
*
* @see CORO_END_CONTEXT
*
* @note We always declare a variable 'DUMMY' to allow the user to specify
* an 'empty' context.
*/
#define CORO_BEGIN_CONTEXT struct CoroContextTag : CoroBaseContext { int DUMMY
/**
* End the declaration of a coroutine context.
* @param x name of the coroutine context
* @see CORO_BEGIN_CONTEXT
*/
#define CORO_END_CONTEXT(x) } *x = (CoroContextTag *)coroParam
/**
* Begin the code section of a coroutine.
* @param x name of the coroutine context
* @see CORO_BEGIN_CODE
*/
#define CORO_BEGIN_CODE(x) \
if (&coroParam == &nullContext) assert(!nullContext);\
if (!x) {coroParam = x = new CoroContextTag();}\
CoroContextHolder tmpHolder(coroParam);\
switch(coroParam->_line) { case 0:;
/**
* End the code section of a coroutine.
* @see CORO_END_CODE
*/
#define CORO_END_CODE \
if (&coroParam == &nullContext) nullContext = NULL; \
}
/**
* Sleep for the specified number of scheduler cycles.
*/
#define CORO_SLEEP(delay) do {\
coroParam->_line = __LINE__;\
coroParam->_sleep = delay;\
assert(&coroParam != &nullContext);\
return; case __LINE__:;\
} while (0)
#define CORO_GIVE_WAY do { g_scheduler->giveWay(); CORO_SLEEP(1); } while (0)
#define CORO_RESCHEDULE do { g_scheduler->reschedule(); CORO_SLEEP(1); } while (0)
/**
* Stop the currently running coroutine.
*/
#define CORO_KILL_SELF() \
do { if (&coroParam != &nullContext) { coroParam->_sleep = -1; } return; } while (0)
/**
* Invoke another coroutine.
*
* What makes this tricky is that the coroutine we called my yield/sleep,
* and we need to deal with this adequately.
*/
#define CORO_INVOKE_ARGS(subCoro, ARGS) \
do {\
coroParam->_line = __LINE__;\
coroParam->_subctx = 0;\
do {\
subCoro ARGS;\
if (!coroParam->_subctx) break;\
coroParam->_sleep = coroParam->_subctx->_sleep;\
assert(&coroParam != &nullContext);\
return; case __LINE__:;\
} while (1);\
} while (0)
/**
* Invoke another coroutine. Similar to CORO_INVOKE_ARGS,
* but allows specifying a return value which is returned
* if invoked coroutine yields (thus causing the current
* coroutine to yield, too).
*/
#define CORO_INVOKE_ARGS_V(subCoro, RESULT, ARGS) \
do {\
coroParam->_line = __LINE__;\
coroParam->_subctx = 0;\
do {\
subCoro ARGS;\
if (!coroParam->_subctx) break;\
coroParam->_sleep = coroParam->_subctx->_sleep;\
assert(&coroParam != &nullContext);\
return RESULT; case __LINE__:;\
} while (1);\
} while (0)
/**
* Convenience wrapper for CORO_INVOKE_ARGS for invoking a coroutine
* with no parameters.
*/
#define CORO_INVOKE_0(subCoroutine) \
CORO_INVOKE_ARGS(subCoroutine,(CORO_SUBCTX))
/**
* Convenience wrapper for CORO_INVOKE_ARGS for invoking a coroutine
* with one parameter.
*/
#define CORO_INVOKE_1(subCoroutine, a0) \
CORO_INVOKE_ARGS(subCoroutine,(CORO_SUBCTX,a0))
/**
* Convenience wrapper for CORO_INVOKE_ARGS for invoking a coroutine
* with two parameters.
*/
#define CORO_INVOKE_2(subCoroutine, a0,a1) \
CORO_INVOKE_ARGS(subCoroutine,(CORO_SUBCTX,a0,a1))
/**
* Convenience wrapper for CORO_INVOKE_ARGS for invoking a coroutine
* with three parameters.
*/
#define CORO_INVOKE_3(subCoroutine, a0,a1,a2) \
CORO_INVOKE_ARGS(subCoroutine,(CORO_SUBCTX,a0,a1,a2))
//@}
} // end of namespace Tinsel
#endif // TINSEL_COROUTINE_H
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