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| 1 : | anton | 1.1 | \ catch, throw, etc. |
| 2 : | |||
| 3 : | anton | 1.20 | \ Copyright (C) 1999,2000,2003,2006,2007 Free Software Foundation, Inc. |
| 4 : | anton | 1.1 | |
| 5 : | \ This file is part of Gforth. | ||
| 6 : | |||
| 7 : | \ Gforth is free software; you can redistribute it and/or | ||
| 8 : | \ modify it under the terms of the GNU General Public License | ||
| 9 : | anton | 1.21 | \ as published by the Free Software Foundation, either version 3 |
| 10 : | anton | 1.1 | \ of the License, or (at your option) any later version. |
| 11 : | |||
| 12 : | \ This program is distributed in the hope that it will be useful, | ||
| 13 : | \ but WITHOUT ANY WARRANTY; without even the implied warranty of | ||
| 14 : | \ MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the | ||
| 15 : | \ GNU General Public License for more details. | ||
| 16 : | |||
| 17 : | \ You should have received a copy of the GNU General Public License | ||
| 18 : | anton | 1.21 | \ along with this program. If not, see http://www.gnu.org/licenses/. |
| 19 : | anton | 1.1 | |
| 20 : | \ !! use a separate exception stack? anton | ||
| 21 : | |||
| 22 : | \ has? backtrace [IF] | ||
| 23 : | Defer store-backtrace | ||
| 24 : | ' noop IS store-backtrace | ||
| 25 : | \ [THEN] | ||
| 26 : | |||
| 27 : | anton | 1.9 | \ Ok, here's the story about how we get to the native code for the |
| 28 : | \ recovery code in case of a THROW, and why there is all this funny | ||
| 29 : | \ stuff being compiled by TRY and RECOVER: | ||
| 30 : | |||
| 31 : | \ Upon a THROW, we cannot just return through the ordinary return | ||
| 32 : | \ address, but have to use a different one, for code after the | ||
| 33 : | \ RECOVER. How do we do that, in a way portable between the various | ||
| 34 : | \ threaded and native code engines? In particular, how does the | ||
| 35 : | \ native code engine learn about the address of the native recovery | ||
| 36 : | \ code? | ||
| 37 : | |||
| 38 : | \ On the Forth level, we can compile only references to threaded code. | ||
| 39 : | \ The only thing that translates a threaded code address to a native | ||
| 40 : | \ code address is docol, which is only called with EXECUTE and | ||
| 41 : | \ friends. So we start the recovery code with a docol, and invoke it | ||
| 42 : | \ with PERFORM; the recovery code then rdrops the superfluously | ||
| 43 : | \ generated return address and continues with the proper recovery | ||
| 44 : | \ code. | ||
| 45 : | |||
| 46 : | \ At compile time, since we cannot compile a forward reference (to the | ||
| 47 : | \ recovery code) as a literal (backpatching does not work for | ||
| 48 : | \ native-code literals), we produce a data cell (wrapped in AHEAD | ||
| 49 : | \ ... THEN) that we can backpatch, and compile the address of that as | ||
| 50 : | \ literal. | ||
| 51 : | |||
| 52 : | \ Overall, this leads to the following resulting code: | ||
| 53 : | |||
| 54 : | \ ahead | ||
| 55 : | \ +><recovery address>-+ | ||
| 56 : | \ | then | | ||
| 57 : | \ +-lit | | ||
| 58 : | \ (try) | | ||
| 59 : | \ ... | | ||
| 60 : | \ (recover) | | ||
| 61 : | \ ahead | | ||
| 62 : | \ docol: <-----------+ | ||
| 63 : | \ rdrop | ||
| 64 : | \ ... | ||
| 65 : | \ then | ||
| 66 : | \ ... | ||
| 67 : | |||
| 68 : | \ !! explain handler on-stack structure | ||
| 69 : | |||
| 70 : | pazsan | 1.12 | Variable first-throw |
| 71 : | anton | 1.13 | : nothrow ( -- ) \ gforth |
| 72 : | \G Use this (or the standard sequence @code{['] false catch drop}) | ||
| 73 : | \G after a @code{catch} or @code{endtry} that does not rethrow; | ||
| 74 : | \G this ensures that the next @code{throw} will record a | ||
| 75 : | \G backtrace. | ||
| 76 : | first-throw on ; | ||
| 77 : | pazsan | 1.12 | |
| 78 : | anton | 1.5 | : (try) ( ahandler -- ) |
| 79 : | pazsan | 1.12 | first-throw on |
| 80 : | anton | 1.1 | r> |
| 81 : | anton | 1.5 | swap >r \ recovery address |
| 82 : | anton | 1.1 | sp@ >r |
| 83 : | fp@ >r | ||
| 84 : | lp@ >r | ||
| 85 : | handler @ >r | ||
| 86 : | rp@ handler ! | ||
| 87 : | anton | 1.5 | >r ; |
| 88 : | anton | 1.1 | |
| 89 : | anton | 1.18 | : try ( compilation -- orig ; run-time -- R:sys1 ) \ gforth |
| 90 : | \G Start an exception-catching region. | ||
| 91 : | anton | 1.8 | POSTPONE ahead here >r >mark 1 cs-roll POSTPONE then |
| 92 : | anton | 1.9 | r> POSTPONE literal POSTPONE (try) ; immediate compile-only |
| 93 : | anton | 1.1 | |
| 94 : | anton | 1.17 | : (endtry) ( -- ) |
| 95 : | anton | 1.1 | \ normal end of try block: restore handler, forget rest |
| 96 : | r> | ||
| 97 : | r> handler ! | ||
| 98 : | rdrop \ lp | ||
| 99 : | rdrop \ fp | ||
| 100 : | rdrop \ sp | ||
| 101 : | rdrop \ recovery address | ||
| 102 : | >r ; | ||
| 103 : | |||
| 104 : | anton | 1.17 | : handler-intro, ( -- ) |
| 105 : | anton | 1.9 | docol: here 0 , 0 , code-address! \ start a colon def |
| 106 : | postpone rdrop \ drop the return address | ||
| 107 : | anton | 1.17 | ; |
| 108 : | |||
| 109 : | : iferror ( compilation orig1 -- orig2 ; run-time -- ) \ gforth | ||
| 110 : | anton | 1.18 | \G Starts the exception handling code (executed if there is an |
| 111 : | \G exception between @code{try} and @code{endtry}). This part has | ||
| 112 : | \G to be finished with @code{then}. | ||
| 113 : | anton | 1.17 | \ !! check using a special tag |
| 114 : | POSTPONE else handler-intro, | ||
| 115 : | ; immediate compile-only | ||
| 116 : | |||
| 117 : | : restore ( compilation orig1 -- ; run-time -- ) \ gforth | ||
| 118 : | anton | 1.18 | \G Starts restoring code, that is executed if there is an |
| 119 : | \G exception, and if there is no exception. | ||
| 120 : | anton | 1.17 | POSTPONE iferror POSTPONE then |
| 121 : | anton | 1.9 | ; immediate compile-only |
| 122 : | anton | 1.1 | |
| 123 : | anton | 1.18 | : endtry ( compilation -- ; run-time R:sys1 -- ) \ gforth |
| 124 : | \G End an exception-catching region. | ||
| 125 : | anton | 1.17 | POSTPONE (endtry) |
| 126 : | anton | 1.18 | ; immediate compile-only |
| 127 : | |||
| 128 : | : endtry-iferror ( compilation orig1 -- orig2 ; run-time R:sys1 -- ) \ gforth | ||
| 129 : | \G End an exception-catching region while starting | ||
| 130 : | \G exception-handling code outside that region (executed if there | ||
| 131 : | \G is an exception between @code{try} and @code{endtry-iferror}). | ||
| 132 : | \G This part has to be finished with @code{then} (or | ||
| 133 : | \G @code{else}...@code{then}). | ||
| 134 : | POSTPONE (endtry) POSTPONE iferror POSTPONE (endtry) | ||
| 135 : | anton | 1.16 | ; immediate compile-only |
| 136 : | anton | 1.1 | |
| 137 : | :noname ( x1 .. xn xt -- y1 .. ym 0 / z1 .. zn error ) \ exception | ||
| 138 : | try | ||
| 139 : | execute 0 | ||
| 140 : | anton | 1.17 | iferror |
| 141 : | nip | ||
| 142 : | then endtry ; | ||
| 143 : | anton | 1.1 | is catch |
| 144 : | |||
| 145 : | :noname ( y1 .. ym error/0 -- y1 .. ym / z1 .. zn error ) \ exception | ||
| 146 : | ?DUP IF | ||
| 147 : | [ here forthstart 9 cells + ! ] | ||
| 148 : | pazsan | 1.12 | first-throw @ IF |
| 149 : | store-backtrace error-stack off | ||
| 150 : | first-throw off | ||
| 151 : | THEN | ||
| 152 : | anton | 1.1 | handler @ ?dup-0=-IF |
| 153 : | anton | 1.6 | >stderr cr ." uncaught exception: " .error cr |
| 154 : | anton | 1.1 | 2 (bye) |
| 155 : | anton | 1.6 | \ quit |
| 156 : | anton | 1.1 | THEN |
| 157 : | anton | 1.19 | dup rp! ( ... ball frame ) |
| 158 : | cell+ dup @ lp! | ||
| 159 : | cell+ dup @ fp! | ||
| 160 : | cell+ dup @ ( ... ball addr sp ) -rot 2>r sp! drop 2r> | ||
| 161 : | cell+ @ perform | ||
| 162 : | anton | 1.1 | THEN ; |
| 163 : | is throw |
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