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| 1 : | anton | 1.1 | \ catch, throw, etc. |
| 2 : | |||
| 3 : | anton | 1.7 | \ Copyright (C) 1999,2000,2003 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 : | \ as published by the Free Software Foundation; either version 2 | ||
| 10 : | \ 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 : | \ along with this program; if not, write to the Free Software | ||
| 19 : | anton | 1.3 | \ Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111, USA. |
| 20 : | anton | 1.1 | |
| 21 : | \ !! use a separate exception stack? anton | ||
| 22 : | |||
| 23 : | \ user-definable rollback actions | ||
| 24 : | |||
| 25 : | Defer 'catch | ||
| 26 : | Defer 'throw | ||
| 27 : | |||
| 28 : | ' noop IS 'catch | ||
| 29 : | ' noop IS 'throw | ||
| 30 : | |||
| 31 : | \ has? backtrace [IF] | ||
| 32 : | Defer store-backtrace | ||
| 33 : | ' noop IS store-backtrace | ||
| 34 : | \ [THEN] | ||
| 35 : | |||
| 36 : | anton | 1.9 | \ Ok, here's the story about how we get to the native code for the |
| 37 : | \ recovery code in case of a THROW, and why there is all this funny | ||
| 38 : | \ stuff being compiled by TRY and RECOVER: | ||
| 39 : | |||
| 40 : | \ Upon a THROW, we cannot just return through the ordinary return | ||
| 41 : | \ address, but have to use a different one, for code after the | ||
| 42 : | \ RECOVER. How do we do that, in a way portable between the various | ||
| 43 : | \ threaded and native code engines? In particular, how does the | ||
| 44 : | \ native code engine learn about the address of the native recovery | ||
| 45 : | \ code? | ||
| 46 : | |||
| 47 : | \ On the Forth level, we can compile only references to threaded code. | ||
| 48 : | \ The only thing that translates a threaded code address to a native | ||
| 49 : | \ code address is docol, which is only called with EXECUTE and | ||
| 50 : | \ friends. So we start the recovery code with a docol, and invoke it | ||
| 51 : | \ with PERFORM; the recovery code then rdrops the superfluously | ||
| 52 : | \ generated return address and continues with the proper recovery | ||
| 53 : | \ code. | ||
| 54 : | |||
| 55 : | \ At compile time, since we cannot compile a forward reference (to the | ||
| 56 : | \ recovery code) as a literal (backpatching does not work for | ||
| 57 : | \ native-code literals), we produce a data cell (wrapped in AHEAD | ||
| 58 : | \ ... THEN) that we can backpatch, and compile the address of that as | ||
| 59 : | \ literal. | ||
| 60 : | |||
| 61 : | \ Overall, this leads to the following resulting code: | ||
| 62 : | |||
| 63 : | \ ahead | ||
| 64 : | \ +><recovery address>-+ | ||
| 65 : | \ | then | | ||
| 66 : | \ +-lit | | ||
| 67 : | \ (try) | | ||
| 68 : | \ ... | | ||
| 69 : | \ (recover) | | ||
| 70 : | \ ahead | | ||
| 71 : | \ docol: <-----------+ | ||
| 72 : | \ rdrop | ||
| 73 : | \ ... | ||
| 74 : | \ then | ||
| 75 : | \ ... | ||
| 76 : | |||
| 77 : | \ !! explain handler on-stack structure | ||
| 78 : | |||
| 79 : | anton | 1.5 | : (try) ( ahandler -- ) |
| 80 : | anton | 1.1 | r> |
| 81 : | anton | 1.5 | swap >r \ recovery address |
| 82 : | anton | 1.1 | rp@ 'catch >r |
| 83 : | sp@ >r | ||
| 84 : | fp@ >r | ||
| 85 : | lp@ >r | ||
| 86 : | handler @ >r | ||
| 87 : | rp@ handler ! | ||
| 88 : | backtrace-empty on | ||
| 89 : | anton | 1.5 | >r ; |
| 90 : | anton | 1.1 | |
| 91 : | : try ( compilation -- orig ; run-time -- ) \ gforth | ||
| 92 : | anton | 1.5 | \ !! does not work correctly for gforth-native |
| 93 : | anton | 1.8 | POSTPONE ahead here >r >mark 1 cs-roll POSTPONE then |
| 94 : | anton | 1.9 | r> POSTPONE literal POSTPONE (try) ; immediate compile-only |
| 95 : | anton | 1.1 | |
| 96 : | : (recover) ( -- ) | ||
| 97 : | \ normal end of try block: restore handler, forget rest | ||
| 98 : | r> | ||
| 99 : | r> handler ! | ||
| 100 : | rdrop \ lp | ||
| 101 : | rdrop \ fp | ||
| 102 : | rdrop \ sp | ||
| 103 : | r> rp! | ||
| 104 : | rdrop \ recovery address | ||
| 105 : | >r ; | ||
| 106 : | |||
| 107 : | : recover ( compilation orig1 -- orig2 ; run-time -- ) \ gforth | ||
| 108 : | \ !! check using a special tag | ||
| 109 : | POSTPONE (recover) | ||
| 110 : | anton | 1.9 | POSTPONE else |
| 111 : | docol: here 0 , 0 , code-address! \ start a colon def | ||
| 112 : | postpone rdrop \ drop the return address | ||
| 113 : | ; immediate compile-only | ||
| 114 : | anton | 1.1 | |
| 115 : | : endtry ( compilation orig -- ; run-time -- ) \ gforth | ||
| 116 : | POSTPONE then ; immediate compile-only | ||
| 117 : | |||
| 118 : | :noname ( x1 .. xn xt -- y1 .. ym 0 / z1 .. zn error ) \ exception | ||
| 119 : | try | ||
| 120 : | execute 0 | ||
| 121 : | recover | ||
| 122 : | nip | ||
| 123 : | endtry ; | ||
| 124 : | is catch | ||
| 125 : | |||
| 126 : | :noname ( y1 .. ym error/0 -- y1 .. ym / z1 .. zn error ) \ exception | ||
| 127 : | ?DUP IF | ||
| 128 : | [ here forthstart 9 cells + ! ] | ||
| 129 : | store-backtrace | ||
| 130 : | handler @ ?dup-0=-IF | ||
| 131 : | anton | 1.6 | >stderr cr ." uncaught exception: " .error cr |
| 132 : | anton | 1.1 | 2 (bye) |
| 133 : | anton | 1.6 | \ quit |
| 134 : | anton | 1.1 | THEN |
| 135 : | rp! | ||
| 136 : | r> handler ! | ||
| 137 : | r> lp! | ||
| 138 : | r> fp! | ||
| 139 : | r> swap >r sp! drop r> | ||
| 140 : | anton | 1.9 | rdrop 'throw r> perform |
| 141 : | anton | 1.1 | THEN ; |
| 142 : | is throw | ||
| 143 : |
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