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Diffstat (limited to 'to.do/streams.mail')
| -rw-r--r-- | to.do/streams.mail | 194 |
1 files changed, 194 insertions, 0 deletions
diff --git a/to.do/streams.mail b/to.do/streams.mail new file mode 100644 index 0000000..0e6a093 --- /dev/null +++ b/to.do/streams.mail @@ -0,0 +1,194 @@ +Received: from 204.33.249.66 by ee.lbl.gov for <vern@ee.lbl.gov> (8.8.2/1.43r) + id SAA22776; Sun, 17 Nov 1996 18:18:35 -0800 (PST) +Received: by paradigm.webvision.com (940816.SGI.8.6.9/940406.SGI) + id SAA10316; Sun, 17 Nov 1996 18:18:10 -0800 +Date: Sun, 17 Nov 1996 18:18:10 -0800 +Message-Id: <199611180218.SAA10316@paradigm.webvision.com> +From: dave madden <dhm@paradigm.webvision.com> +To: vern@ee.lbl.gov +CC: jebossom@cognos.com +In-reply-to: <199611130423.UAA10645@daffy.ee.lbl.gov> (message from Vern + Paxson on Tue, 12 Nov 1996 20:23:35 PST) +Subject: Re: flex-2.5.3: wedging streams +Status: U + + =>Date: Tue, 12 Nov 1996 20:23:35 PST + =>From: Vern Paxson <vern@ee.lbl.gov> + => +[=>>from dhm@webvision.com] + =>> After poking around in the generated scanner, it looks like I need to + =>> be able to return a new code from yy_get_next_buffer (say + =>> EOB_ACT_TRY_AGAIN) that'll cause yylex() to remember where it is + =>> and return to its caller with a "no-token-available" indication. The + =>> next call of yylex( ) should recover the saved state and consequently + =>> retry yy_get_next_buffer( ) immediately. + => + =>This would be a nice feature to have. No one is working on it as far + =>as I know. John Bossom (jebossom@Cognos.COM) is working on reentrant + =>scanners, though, which have the entire scanning state encapsulated in + =>a single struct. + =>... + =>The trick of + =>course is in getting the state reset correctly. This is already done for + =>EOB_ACT_CONTINUE_SCAN (which then also advances the state machine using + =>yy_get_previous_state()), so you should be able to follow what it does. + +Well, I got it working. I added a flag and some state in the +yy_buffer_state structure to hold yy_bp and start_state, and some code +in gen.c and flex.skl to test the flag and do [what I hope is] the +right thing. The patches are appended. I wish I had time to do a +cleaner job of it (and thoroughly test it -- I dunno if it'll work +right when faced with strange buffer switching) but I'm in a bit of a +hurry... I did try it with both C and C++, though. If you're +interested, I'll clean up my test progs and send them as well. + +To use it, just define YY_WEDGE to be the token you want returned if +the input stream blocks, and (optionally) YY_IS_WEDGED( ) to be a +function returning a boolean. If you don't define YY_IS_WEDGED, the +default is to do "(errno==EWOULDBLOCK)". Then, if YY_INPUT returns 0 +and YY_IS_WEDGED( ) is true, yylex( ) will return YY_WEDGE. If +YY_WEDGE is not defined, almost all my code gets #ifdef'd out and you +get a regular parser. + +Regards, +d. + +diff -c flex-2.5.4.orig/flex.skl flex-2.5.4/flex.skl +*** flex-2.5.4.orig/flex.skl Tue Sep 10 16:58:54 1996 +--- flex-2.5.4/flex.skl Sun Nov 17 17:44:12 1996 +*************** +*** 111,116 **** +--- 111,117 ---- + #define EOB_ACT_CONTINUE_SCAN 0 + #define EOB_ACT_END_OF_FILE 1 + #define EOB_ACT_LAST_MATCH 2 ++ #define EOB_ACT_INPUT_BLOCKED 3 + + /* The funky do-while in the following #define is used to turn the definition + * int a single C statement (which needs a semi-colon terminator). This +*************** +*** 182,187 **** +--- 183,199 ---- + */ + int yy_is_interactive; + ++ /* ++ * Whether this input source returned EWOULDBLOCK on the last ++ * read, indicating that it's not finished, but that there are no ++ * data available now. (If this is set, the scanner will load its ++ * state from the yy_b_buf_p and yy_state rather than from ++ * its normal sources) ++ */ ++ int yy_blocked; ++ char *yy_b_buf_p; ++ void *yy_continue_state; ++ + /* Whether we're considered to be at the beginning of a line. + * If so, '^' rules will be active on the next match, otherwise + * not. +*************** +*** 634,639 **** +--- 646,660 ---- + yy_cp = yy_c_buf_p; + yy_bp = yytext_ptr + YY_MORE_ADJ; + goto yy_find_action; ++ #ifdef YY_WEDGE ++ case EOB_ACT_INPUT_BLOCKED: ++ yy_current_buffer->yy_blocked = 1; ++ yy_current_buffer->yy_continue_state = (void *)(yy_start); ++ yy_current_buffer->yy_b_buf_p = yytext_ptr + YY_MORE_ADJ; ++ yy_c_buf_p = yytext_ptr + yy_amount_of_matched_text; ++ yy_hold_char = *yy_c_buf_p; ++ return YY_WEDGE; ++ #endif /* defined(YY_WEDGE) */ + } + break; + } +*************** +*** 735,740 **** +--- 756,762 ---- + * EOB_ACT_LAST_MATCH - + * EOB_ACT_CONTINUE_SCAN - continue scanning from current position + * EOB_ACT_END_OF_FILE - end of file ++ * EOB_ACT_INPUT_BLOCKED - YY_INPUT returned 0 and errno == EWOULDBLOCK + */ + + %- +*************** +*** 844,849 **** +--- 866,880 ---- + + if ( yy_n_chars == 0 ) + { ++ #ifdef YY_WEDGE ++ #ifndef YY_IS_WEDGED ++ #include <sys/errno.h> ++ #define YY_IS_WEDGED() (errno == EWOULDBLOCK) ++ #endif /* !defined(YY_IS_WEDGED) */ ++ if (YY_IS_WEDGED( )) { ++ ret_val = EOB_ACT_INPUT_BLOCKED; ++ } else ++ #endif /* defined(YY_WEDGE) */ + if ( number_to_move == YY_MORE_ADJ ) + { + ret_val = EOB_ACT_END_OF_FILE; +*************** +*** 881,886 **** +--- 912,918 ---- + { + register yy_state_type yy_current_state; + register char *yy_cp; ++ char *yy_bp; + + %% code to get the start state into yy_current_state goes here + +*************** +*** 1215,1220 **** +--- 1247,1253 ---- + %+ + b->yy_is_interactive = 0; + %* ++ b->yy_blocked = 0; + } + + +diff -c flex-2.5.4.orig/gen.c flex-2.5.4/gen.c +*** flex-2.5.4.orig/gen.c Sat May 25 20:43:44 1996 +--- flex-2.5.4/gen.c Sun Nov 17 17:40:55 1996 +*************** +*** 750,755 **** +--- 750,770 ---- + + void gen_start_state() + { ++ outn( "#ifdef YY_WEDGE" ); ++ indent_puts( "if (yy_current_buffer->yy_blocked)" ); ++ indent_up( ); ++ indent_puts( "{" ); ++ indent_puts( "yy_current_buffer->yy_blocked = 0;" ); ++ indent_puts( ++ "yy_current_state = (yy_state_type)(yy_current_buffer->yy_continue_state);" ); ++ indent_puts( "yy_bp = yy_current_buffer->yy_b_buf_p;" ); ++ indent_puts( "}" ); ++ indent_down( ); ++ indent_puts( "else" ); ++ indent_up( ); ++ indent_puts( "{" ); ++ outn( "#endif /* defined(YY_WEDGE) */" ); ++ + if ( fullspd ) + { + if ( bol_needed ) +*************** +*** 776,781 **** +--- 791,800 ---- + indent_puts( "*yy_state_ptr++ = yy_current_state;" ); + } + } ++ outn( "#ifdef YY_WEDGE" ); ++ indent_puts( "}" ); ++ indent_down( ); ++ outn( "#endif /* defined(YY_WEDGE) */" ); + } + + |