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replication parser: pure parser and reentrant scanner

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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
This commit is contained in:
Peter Eisentraut
2024-12-02 10:35:37 +01:00
parent 5af699066f
commit e4a8fb8fef
5 changed files with 113 additions and 77 deletions
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11
src/backend/replication/walsender.c
View File

@ -1951,6 +1951,7 @@ WalSndWaitForWal(XLogRecPtr loc)
bool
exec_replication_command(const char *cmd_string)
{
yyscan_t scanner;
int parse_rc;
Node *cmd_node;
const char *cmdtag;
@ -1990,15 +1991,15 @@ exec_replication_command(const char *cmd_string)
ALLOCSET_DEFAULT_SIZES);
old_context = MemoryContextSwitchTo(cmd_context);
replication_scanner_init(cmd_string);
replication_scanner_init(cmd_string, &scanner);
/*
* Is it a WalSender command?
*/
if (!replication_scanner_is_replication_command())
if (!replication_scanner_is_replication_command(scanner))
{
/* Nope; clean up and get out. */
replication_scanner_finish();
replication_scanner_finish(scanner);
MemoryContextSwitchTo(old_context);
MemoryContextDelete(cmd_context);
@ -2016,13 +2017,13 @@ exec_replication_command(const char *cmd_string)
/*
* Looks like a WalSender command, so parse it.
*/
parse_rc = replication_yyparse();
parse_rc = replication_yyparse(scanner);
if (parse_rc != 0)
ereport(ERROR,
(errcode(ERRCODE_SYNTAX_ERROR),
errmsg_internal("replication command parser returned %d",
parse_rc)));
replication_scanner_finish();
replication_scanner_finish(scanner);
cmd_node = replication_parse_result;