version 1.6, 2003/02/17 22:42:09
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version 1.16, 2007/02/18 17:57:12
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\ catch, throw, etc. |
\ catch, throw, etc. |
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\ Copyright (C) 1999,2000 Free Software Foundation, Inc. |
\ Copyright (C) 1999,2000,2003,2006 Free Software Foundation, Inc. |
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\ This file is part of Gforth. |
\ This file is part of Gforth. |
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Line 20
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\ !! use a separate exception stack? anton |
\ !! use a separate exception stack? anton |
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\ user-definable rollback actions |
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Defer 'catch |
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Defer 'throw |
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' noop IS 'catch |
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' noop IS 'throw |
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\ has? backtrace [IF] |
\ has? backtrace [IF] |
Defer store-backtrace |
Defer store-backtrace |
' noop IS store-backtrace |
' noop IS store-backtrace |
\ [THEN] |
\ [THEN] |
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\ Ok, here's the story about how we get to the native code for the |
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\ recovery code in case of a THROW, and why there is all this funny |
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\ stuff being compiled by TRY and RECOVER: |
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\ Upon a THROW, we cannot just return through the ordinary return |
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\ address, but have to use a different one, for code after the |
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\ RECOVER. How do we do that, in a way portable between the various |
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\ threaded and native code engines? In particular, how does the |
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\ native code engine learn about the address of the native recovery |
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\ code? |
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\ On the Forth level, we can compile only references to threaded code. |
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\ The only thing that translates a threaded code address to a native |
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\ code address is docol, which is only called with EXECUTE and |
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\ friends. So we start the recovery code with a docol, and invoke it |
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\ with PERFORM; the recovery code then rdrops the superfluously |
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\ generated return address and continues with the proper recovery |
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\ code. |
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\ At compile time, since we cannot compile a forward reference (to the |
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\ recovery code) as a literal (backpatching does not work for |
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\ native-code literals), we produce a data cell (wrapped in AHEAD |
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\ ... THEN) that we can backpatch, and compile the address of that as |
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\ literal. |
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\ Overall, this leads to the following resulting code: |
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\ ahead |
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\ +><recovery address>-+ |
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\ | then | |
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\ +-lit | |
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\ (try) | |
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\ ... | |
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\ (recover) | |
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\ ahead | |
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\ docol: <-----------+ |
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\ rdrop |
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\ ... |
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\ then |
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\ ... |
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\ !! explain handler on-stack structure |
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Variable first-throw |
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: nothrow ( -- ) \ gforth |
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\G Use this (or the standard sequence @code{['] false catch drop}) |
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\G after a @code{catch} or @code{endtry} that does not rethrow; |
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\G this ensures that the next @code{throw} will record a |
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\G backtrace. |
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first-throw on ; |
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: (try) ( ahandler -- ) |
: (try) ( ahandler -- ) |
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first-throw on |
r> |
r> |
swap >r \ recovery address |
swap >r \ recovery address |
rp@ 'catch >r |
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sp@ >r |
sp@ >r |
fp@ >r |
fp@ >r |
lp@ >r |
lp@ >r |
handler @ >r |
handler @ >r |
rp@ handler ! |
rp@ handler ! |
backtrace-empty on |
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>r ; |
>r ; |
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: try ( compilation -- orig ; run-time -- ) \ gforth |
: try ( compilation -- orig ; run-time -- ) \ gforth |
\ !! does not work correctly for gforth-native |
\ !! does not work correctly for gforth-native |
POSTPONE lit >mark POSTPONE (try) ; immediate compile-only |
POSTPONE ahead here >r >mark 1 cs-roll POSTPONE then |
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r> POSTPONE literal POSTPONE (try) ; immediate compile-only |
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: (recover) ( -- ) |
: (recover) ( -- ) |
\ normal end of try block: restore handler, forget rest |
\ normal end of try block: restore handler, forget rest |
Line 56 Defer store-backtrace
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Line 99 Defer store-backtrace
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rdrop \ lp |
rdrop \ lp |
rdrop \ fp |
rdrop \ fp |
rdrop \ sp |
rdrop \ sp |
r> rp! |
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rdrop \ recovery address |
rdrop \ recovery address |
>r ; |
>r ; |
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: recover ( compilation orig1 -- orig2 ; run-time -- ) \ gforth |
: recover ( compilation orig1 -- orig2 ; run-time -- ) \ gforth |
\ !! check using a special tag |
\ !! check using a special tag |
POSTPONE (recover) |
POSTPONE else |
POSTPONE else ; immediate compile-only |
docol: here 0 , 0 , code-address! \ start a colon def |
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postpone rdrop \ drop the return address |
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; immediate compile-only |
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: endtry ( compilation orig -- ; run-time -- ) \ gforth |
: endtry ( compilation orig -- ; run-time -- ) \ gforth |
POSTPONE then ; immediate compile-only |
POSTPONE then |
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POSTPONE (recover) |
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; immediate compile-only |
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:noname ( x1 .. xn xt -- y1 .. ym 0 / z1 .. zn error ) \ exception |
:noname ( x1 .. xn xt -- y1 .. ym 0 / z1 .. zn error ) \ exception |
try |
try |
Line 79 is catch
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Line 125 is catch
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:noname ( y1 .. ym error/0 -- y1 .. ym / z1 .. zn error ) \ exception |
:noname ( y1 .. ym error/0 -- y1 .. ym / z1 .. zn error ) \ exception |
?DUP IF |
?DUP IF |
[ here forthstart 9 cells + ! ] |
[ here forthstart 9 cells + ! ] |
store-backtrace |
first-throw @ IF |
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store-backtrace error-stack off |
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first-throw off |
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THEN |
handler @ ?dup-0=-IF |
handler @ ?dup-0=-IF |
>stderr cr ." uncaught exception: " .error cr |
>stderr cr ." uncaught exception: " .error cr |
2 (bye) |
2 (bye) |
\ quit |
\ quit |
THEN |
THEN |
rp! |
dup rp! |
r> handler ! |
rdrop |
r> lp! |
r> lp! |
r> fp! |
r> fp! |
r> swap >r sp! drop r> |
r> -rot 2>r sp! drop 2r> |
rdrop 'throw |
r@ swap rp! perform |
THEN ; |
THEN ; |
is throw |
is throw |
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