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