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1 | /* -*-c-*- |
2 | * |
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3 | * $Id: exc.h,v 1.4 1999/10/22 22:39:18 mdw Exp $ |
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4 | * |
5 | * Structured exception handling in C |
6 | * |
7 | * (c) 1998 Straylight/Edgeware |
8 | */ |
9 | |
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10 | /*----- Licensing notice --------------------------------------------------* |
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11 | * |
12 | * This file is part of the mLib utilities library. |
13 | * |
14 | * mLib is free software; you can redistribute it and/or modify |
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15 | * it under the terms of the GNU Library General Public License as |
16 | * published by the Free Software Foundation; either version 2 of the |
17 | * License, or (at your option) any later version. |
18 | * |
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19 | * mLib is distributed in the hope that it will be useful, |
20 | * but WITHOUT ANY WARRANTY; without even the implied warranty of |
21 | * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the |
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22 | * GNU Library General Public License for more details. |
23 | * |
24 | * You should have received a copy of the GNU Library General Public |
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25 | * License along with mLib; if not, write to the Free |
26 | * Software Foundation, Inc., 59 Temple Place - Suite 330, Boston, |
27 | * MA 02111-1307, USA. |
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28 | */ |
29 | |
30 | /*----- Revision history --------------------------------------------------* |
31 | * |
32 | * $Log: exc.h,v $ |
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33 | * Revision 1.4 1999/10/22 22:39:18 mdw |
34 | * Add an exception group for mLib. |
35 | * |
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36 | * Revision 1.3 1999/05/06 19:51:35 mdw |
37 | * Reformatted the LGPL notice a little bit. |
38 | * |
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39 | * Revision 1.2 1999/05/05 18:50:31 mdw |
40 | * Change licensing conditions to LGPL. |
41 | * |
42 | * Revision 1.1.1.1 1998/06/17 23:44:42 mdw |
43 | * Initial version of mLib |
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44 | * |
45 | */ |
46 | |
47 | #ifndef EXC_H |
48 | #define EXC_H |
49 | |
50 | #ifdef __cplusplus |
51 | extern "C" { |
52 | #endif |
53 | |
54 | #include <setjmp.h> |
55 | |
56 | /*----- Quick documentation -----------------------------------------------* |
57 | * |
58 | * This header file provides some exception handling facilities in C |
59 | * programs. It modifies the syntax of the language slightly, using the |
60 | * preprocessor. |
61 | * |
62 | * The `throw' expression returns no value. It has the syntax: |
63 | * |
64 | * THROW ( expr , expr ) |
65 | * |
66 | * The first expression must have type compatible with unsigned integer; it |
67 | * identifies an `exception type'. The second must have type compatible |
68 | * with pointer to void; it contains the `exception data'. Control is |
69 | * passed to the current exception handler. |
70 | * |
71 | * The `RETHROW' expression, valid only within an exception handler, causes |
72 | * the current exception to be thrown again. |
73 | * |
74 | * A `try' statement has the syntax: |
75 | * |
76 | * TRY stat CATCH stat END_TRY; |
77 | * |
78 | * The first statement is called the `test'; the second is the `handler'. |
79 | * During execution of the test, the handler is added to a stack of |
80 | * active exception handlers; the topmost handler on this stack is called |
81 | * the `current' handler. When execution of the test completes, the |
82 | * corresponding handler is removed from the stack. |
83 | * |
84 | * The test statement may complete in one of these ways: |
85 | * |
86 | * * Normal completion -- control reaches the end of the statement |
87 | * normally. |
88 | * |
89 | * * Throwing an exception -- an exception is thrown when the handler is |
90 | * the current exception handler. |
91 | * |
92 | * * By executing a `break' statement. |
93 | * |
94 | * * By executing the expression `EXIT_TRY' and transferring control to |
95 | * a point outside the entire `try' statement (e.g., executing a `goto' |
96 | * or `return' statement). |
97 | * |
98 | * Any other attempt to leave the test causes undefined behaviour. |
99 | * |
100 | * If an exception is thrown while the handler is the current exception |
101 | * handler, it is given control. The variables `exc_type' and `exc_val' |
102 | * denote the exception type and value respectively -- they are passed |
103 | * unchanged from the `throw' expression which caused the exception. |
104 | * A handler is deactivated before it is invoked; if it causes an |
105 | * exception to be thrown (and does not contain a nested `try' statement) |
106 | * control will be passed to an earlier active handler. |
107 | * |
108 | * Control is passed to handlers using the `longjmp' function. |
109 | * |
110 | * Example: |
111 | * |
112 | * TRY { |
113 | * ... something dangerous ... |
114 | * } CATCH switch (exc_type) { |
115 | * case EXC_INTERESTING: |
116 | * ... handle exception ... |
117 | * break; |
118 | * default: |
119 | * ... do tidying up ... |
120 | * RETHROW; |
121 | * } END_TRY; |
122 | */ |
123 | |
124 | /*----- Exception type allocation -----------------------------------------* |
125 | * |
126 | * Nobody allocates exception types, so we'll just have to try to get along |
127 | * without too many collisions. An exception type is an unsigned long, |
128 | * which gives us four bytes. The top two bytes identify the library which |
129 | * `owns' the exception, with special values zero meaning `defined as part |
130 | * of the system' and 0xFFFF providing a shared space of types which can |
131 | * be used by anyone as long as they don't get seen by anyone else. |
132 | * |
133 | * The lower byte pair encodes a type number, and a value which defines |
134 | * the type of the value field (see below). |
135 | */ |
136 | |
137 | /* --- Type type of an exception --- */ |
138 | |
139 | typedef unsigned long exc_extype; |
140 | |
141 | /* --- Build a byte pair from two characters --- * |
142 | * |
143 | * Note the icky casting to handle signed chars. |
144 | */ |
145 | |
146 | #define EXC_PAIR(x, y) (((unsigned long)(unsigned char)(x) << 8) | \ |
147 | (unsigned long)(unsigned char)(y)) |
148 | |
149 | /* --- Allocate an exception number --- */ |
150 | |
151 | #define EXC_ALLOC(owner, type) (((unsigned long)(owner) << 16) | \ |
152 | (unsigned long)(type)) |
153 | |
154 | /* --- Special owner codes --- */ |
155 | |
156 | #define EXC_GLOBAL 0u /* The global space defined here */ |
157 | #define EXC_SHARED 0xFFFFu /* The shared space for everyone */ |
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158 | #define EXC_MLIB EXC_PAIR('m', 'L') /* Space for mLib exceptions */ |
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159 | |
160 | /*----- Exception values --------------------------------------------------* |
161 | * |
162 | * Exception values can have several different types. This is a mess, and |
163 | * C doesn't handle it too well, but we can try. I'll encode the value type |
164 | * as part of the exception type, in the top bits of the bottom byte. Messy? |
165 | * You betcha. |
166 | */ |
167 | |
168 | /* --- Encoding a value type in an extype --- */ |
169 | |
170 | #define EXC_TYPECODE(t, w) (((w) & ~0xC0u) | ((t) & 0xC0u)) |
171 | |
172 | /* --- The various value types --- */ |
173 | |
174 | #define EXC_NOVAL 0x00u /* No interesting value */ |
175 | #define EXC_INTVAL 0x40u /* Integer value */ |
176 | #define EXC_PTRVAL 0x80u /* Arbitrary pointer value */ |
177 | #define EXC_STRVAL 0xC0u /* Pointer to character string */ |
178 | |
179 | /* --- Allocating exceptions with appropriate types --- */ |
180 | |
181 | #define EXC_ALLOCN(o, t) EXC_TYPECODE(EXC_NOVAL, EXC_ALLOC(o, t)) |
182 | #define EXC_ALLOCI(o, t) EXC_TYPECODE(EXC_INTVAL, EXC_ALLOC(o, t)) |
183 | #define EXC_ALLOCP(o, t) EXC_TYPECODE(EXC_PTRVAL, EXC_ALLOC(o, t)) |
184 | #define EXC_ALLOCS(o, t) EXC_TYPECODE(EXC_STRVAL, EXC_ALLOC(o, t)) |
185 | |
186 | /* --- A union representing the type --- */ |
187 | |
188 | typedef union exc_exval { |
189 | int i; |
190 | void *p; |
191 | char *s; |
192 | } exc_exval; |
193 | |
194 | /*----- Predefined exceptions ---------------------------------------------*/ |
195 | |
196 | /* --- @EXC_NOMEM@ --- * |
197 | * |
198 | * Value: --- |
199 | * |
200 | * Meaning: An attempt to allocate memory failed. |
201 | */ |
202 | |
203 | #define EXC_NOMEM EXC_ALLOCN(EXC_GLOBAL, 0u) |
204 | |
205 | /* --- @EXC_ERRNO@ --- * |
206 | * |
207 | * Value: @int errno@ = the error raised |
208 | * |
209 | * Meaning: Some kind of OS error occurred. |
210 | */ |
211 | |
212 | #define EXC_ERRNO EXC_ALLOCI(EXC_GLOBAL, 1u) |
213 | |
214 | /* --- @EXC_OSERROR@ --- * |
215 | * |
216 | * Value: @os_error *e@ = pointer to error block |
217 | * |
218 | * Meaning: For RISC OS programmers only: alternative way of propagating |
219 | * errors. |
220 | */ |
221 | |
222 | #define EXC_OSERROR EXC_ALLOCP(EXC_GLOBAL, 1u) |
223 | |
224 | /* --- @EXC_SIGNAL@ --- * |
225 | * |
226 | * Value: @int sig@ = signal number |
227 | * |
228 | * Meaning: Report the raising of a signal. |
229 | */ |
230 | |
231 | #define EXC_SIGNAL EXC_ALLOCI(EXC_GLOBAL, 2u) |
232 | |
233 | /* --- @EXC_FAIL@ --- * |
234 | * |
235 | * Value: @const char *p@ = pointer to expanatory string |
236 | * |
237 | * Meaning: Miscellaneous error. |
238 | */ |
239 | |
240 | #define EXC_FAIL EXC_ALLOCS(EXC_GLOBAL, 0xFFu) |
241 | |
242 | /*----- An exception handler block ----------------------------------------*/ |
243 | |
244 | /* --- Try to think of this as being opaque --- */ |
245 | |
246 | typedef struct __exc_hnd { |
247 | struct __exc_hnd *next; /* Pointer to next record down */ |
248 | exc_extype type; /* Type of this exception */ |
249 | exc_exval val; /* Value of this exception */ |
250 | jmp_buf buf; /* Jump buffer when exceptions hit */ |
251 | } __exc_hnd; |
252 | |
253 | /*----- Global variables --------------------------------------------------*/ |
254 | |
255 | extern __exc_hnd *__exc_list; /* List of active handlers */ |
256 | |
257 | /*----- Macros ------------------------------------------------------------*/ |
258 | |
259 | /* --- References to current exception type and value --- */ |
260 | |
261 | #define exc_type (__exc_ec.type) |
262 | #define exc_val (__exc_ec.val) |
263 | #define exc_i (__exc_ec.val.i) |
264 | #define exc_p (__exc_ec.val.p) |
265 | #define exc_s (__exc_ec.val.s) |
266 | |
267 | /* --- How it actually works --- * |
268 | * |
269 | * A `try' block is contained within a block which provides an exception |
270 | * handler buffer in automatic storage. This block is a loop, to allow |
271 | * `break' to escape from it. It adds the handler buffer to the top of a |
272 | * list, and does a `setjmp' to allow a return here following an exception. |
273 | * The `setjmp' returns zero for the `try' section, and nonzero if there's |
274 | * an exception to `catch'. It looks a little like this: |
275 | * |
276 | * do { |
277 | * __exc_hnd h; |
278 | * add_handler(&h); |
279 | * if (!setjmp(h.buf)) { |
280 | * do <try code> while (0); |
281 | * remove_handler(&h); |
282 | * } else |
283 | * <catch code> |
284 | * } while (0) |
285 | * |
286 | * Everything else is ugly hacking to make things work. |
287 | */ |
288 | |
289 | /* --- Trying things which may cause exceptions --- */ |
290 | |
291 | #define TRY do { \ |
292 | volatile __exc_hnd __exc_ec; \ |
293 | __exc_ec.next = __exc_list; \ |
294 | __exc_list = (__exc_hnd *)&__exc_ec; \ |
295 | if (!setjmp(*(jmp_buf *)&__exc_ec.buf /* very nasty! */ )) { do |
296 | |
297 | #define EXIT_TRY do __exc_list = __exc_ec.next; while (0) |
298 | #define CATCH while (0); EXIT_TRY; } else |
299 | |
300 | #define END_TRY } while (0) |
301 | |
302 | /* --- Raising exceptions --- */ |
303 | |
304 | #define THROW __exc_throw |
305 | #define RETHROW __exc_rethrow(__exc_ec.type, __exc_ec.val) |
306 | |
307 | /*----- Functions ---------------------------------------------------------*/ |
308 | |
309 | /* --- @exc_uncaught@ --- * |
310 | * |
311 | * Arguments: @void (*proc)(exc_extype type, exc_exval val) = new handler |
312 | * |
313 | * Returns: Pointer to the old handler value. |
314 | * |
315 | * Use: Sets the handler for uncaught exceptions. |
316 | */ |
317 | |
318 | typedef void (*exc__uncaught)(exc_extype /*type*/, exc_exval /*val*/); |
319 | extern exc__uncaught exc_uncaught(exc__uncaught /*proc*/); |
320 | |
321 | /* --- @__exc_throw@ --- * |
322 | * |
323 | * Arguments: @exc_extype type@ = type of exception to throw |
324 | * |
325 | * Returns: Doesn't |
326 | * |
327 | * Use: NOT FOR USER CONSUMPTION. Reads an appropriate exception |
328 | * value and throws an exception. |
329 | */ |
330 | |
331 | extern void __exc_throw(exc_extype /*type*/, ...); |
332 | |
333 | /* --- @__exc_rethrow@ --- * |
334 | * |
335 | * Arguments: @exc_extype type@ = type of exception to throw |
336 | * @exc_exval val@ = value of exception to throw |
337 | * |
338 | * Returns: Doesn't |
339 | * |
340 | * Use: NOT FOR USER CONSUMPTION. Does the donkey-work of raising |
341 | * an exception. |
342 | */ |
343 | |
344 | extern void __exc_rethrow(exc_extype /*type*/, exc_exval /*val*/); |
345 | |
346 | /*----- That's all, folks -------------------------------------------------*/ |
347 | |
348 | #ifdef __cplusplus |
349 | } |
350 | #endif |
351 | |
352 | #endif |