replication parser: pure parser and reentrant scanner

Use the flex %option reentrant and the bison option %pure-parser to
make the generated scanner and parser pure, reentrant, and
thread-safe.

Make the generated scanner use palloc() etc. instead of malloc() etc.
Previously, we only used palloc() for the buffer, but flex would still
use malloc() for its internal structures.  As a result, there could be
some small memory leaks in case of uncaught errors.  Now, all the
memory is under palloc() control, so there are no more such issues.

Simplify flex scan buffer management: Instead of constructing the
buffer from pieces and then using yy_scan_buffer(), we can just use
yy_scan_string(), which does the same thing internally.

The previous code was necessary because we allocated the buffer with
palloc() and the rest of the state was handled by malloc().  But this
is no longer the case; everything is under palloc() now.

Use flex yyextra to handle context information, instead of global
variables.  This complements the other changes to make the scanner
reentrant.

Reviewed-by: Heikki Linnakangas <hlinnaka@iki.fi>
Co-authored-by: Andreas Karlsson <andreas@proxel.se>
Reviewed-by: Andreas Karlsson <andreas@proxel.se>
Discussion: https://www.postgresql.org/message-id/flat/eb6faeac-2a8a-4b69-9189-c33c520e5b7b@eisentraut.org

1 files changed, 11 insertions, 6 deletions

diff --git a/src/include/replication/walsender_private.h b/src/include/replication/walsender_private.h
index 41ac736b953..9a9c40d6f34 100644
--- a/src/include/replication/walsender_private.h
+++ b/src/include/replication/walsender_private.h
@@ -125,12 +125,17 @@ extern void WalSndSetState(WalSndState state);
  * Internal functions for parsing the replication grammar, in repl_gram.y and
  * repl_scanner.l
  */
-extern int	replication_yyparse(void);
-extern int	replication_yylex(void);
-extern void replication_yyerror(const char *message) pg_attribute_noreturn();
-extern void replication_scanner_init(const char *str);
-extern void replication_scanner_finish(void);
-extern bool replication_scanner_is_replication_command(void);
+union YYSTYPE;
+#ifndef YY_TYPEDEF_YY_SCANNER_T
+#define YY_TYPEDEF_YY_SCANNER_T
+typedef void *yyscan_t;
+#endif
+extern int	replication_yyparse(yyscan_t yyscanner);
+extern int	replication_yylex(union YYSTYPE *yylval_param, yyscan_t yyscanner);
+extern void replication_yyerror(yyscan_t yyscanner, const char *message) pg_attribute_noreturn();
+extern void replication_scanner_init(const char *str, yyscan_t *yyscannerp);
+extern void replication_scanner_finish(yyscan_t yyscanner);
+extern bool replication_scanner_is_replication_command(yyscan_t yyscanner);
 
 extern PGDLLIMPORT Node *replication_parse_result;