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michaelpqmichaelpq
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Refactor query cancellation code into src/fe_utils/
Originally, this code was duplicated in src/bin/psql/ and src/bin/scripts/, but it can be useful for other frontend applications, like pgbench. This refactoring offers the possibility to setup a custom callback which would get called in the signal handler for SIGINT or when the interruption console events happen on Windows. Author: Fabien Coelho, with contributions from Michael Paquier Reviewed-by: Álvaro Herrera, Ibrar Ahmed Discussion: https://postgr.es/m/alpine.DEB.2.21.1910311939430.27369@lancre
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14 files changed

+294
-326
lines changed

14 files changed

+294
-326
lines changed

‎src/bin/psql/command.c

Lines changed: 1 addition & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -29,6 +29,7 @@
2929
#include "copy.h"
3030
#include "crosstabview.h"
3131
#include "describe.h"
32+
#include "fe_utils/cancel.h"
3233
#include "fe_utils/print.h"
3334
#include "fe_utils/string_utils.h"
3435
#include "help.h"

‎src/bin/psql/common.c

Lines changed: 26 additions & 161 deletions
Original file line numberDiff line numberDiff line change
@@ -23,6 +23,7 @@
2323
#include "common/logging.h"
2424
#include "copy.h"
2525
#include "crosstabview.h"
26+
#include "fe_utils/cancel.h"
2627
#include "fe_utils/mbprint.h"
2728
#include "fe_utils/string_utils.h"
2829
#include "portability/instr_time.h"
@@ -228,58 +229,28 @@ NoticeProcessor(void *arg, const char *message)
228229
* Code to support query cancellation
229230
*
230231
* Before we start a query, we enable the SIGINT signal catcher to send a
231-
* cancel request to the backend. Note that sending the cancel directly from
232-
* the signal handler is safe because PQcancel() is written to make it
233-
* so. We use write() to report to stderr because it's better to use simple
234-
* facilities in a signal handler.
235-
*
236-
* On win32, the signal canceling happens on a separate thread, because
237-
* that's how SetConsoleCtrlHandler works. The PQcancel function is safe
238-
* for this (unlike PQrequestCancel). However, a CRITICAL_SECTION is required
239-
* to protect the PGcancel structure against being changed while the signal
240-
* thread is using it.
232+
* cancel request to the backend.
241233
*
242234
* SIGINT is supposed to abort all long-running psql operations, not only
243235
* database queries. In most places, this is accomplished by checking
244-
* cancel_pressed during long-running loops. However, that won't work when
236+
* CancelRequested during long-running loops. However, that won't work when
245237
* blocked on user input (in readline() or fgets()). In those places, we
246238
* set sigint_interrupt_enabled true while blocked, instructing the signal
247239
* catcher to longjmp through sigint_interrupt_jmp. We assume readline and
248-
* fgets are coded to handle possible interruption. (XXX currently this does
249-
* not work on win32, so control-C is less useful there)
240+
* fgets are coded to handle possible interruption.
241+
*
242+
* On Windows, currently this does not work, so control-C is less useful
243+
* there, and the callback is just a no-op.
250244
*/
251245
volatile bool sigint_interrupt_enabled = false;
252246

253247
sigjmp_buf sigint_interrupt_jmp;
254248

255-
static PGcancel *volatile cancelConn = NULL;
256-
257-
#ifdef WIN32
258-
static CRITICAL_SECTION cancelConnLock;
259-
#endif
260-
261-
/*
262-
* Write a simple string to stderr --- must be safe in a signal handler.
263-
* We ignore the write() result since there's not much we could do about it.
264-
* Certain compilers make that harder than it ought to be.
265-
*/
266-
#define write_stderr(str) \
267-
do { \
268-
const char *str_ = (str); \
269-
int rc_; \
270-
rc_ = write(fileno(stderr), str_, strlen(str_)); \
271-
(void) rc_; \
272-
} while (0)
273-
274-
275249
#ifndef WIN32
276250

277251
static void
278-
handle_sigint(SIGNAL_ARGS)
252+
psql_cancel_callback(void)
279253
{
280-
int save_errno = errno;
281-
char errbuf[256];
282-
283254
/* if we are waiting for input, longjmp out of it */
284255
if (sigint_interrupt_enabled)
285256
{
@@ -288,74 +259,24 @@ handle_sigint(SIGNAL_ARGS)
288259
}
289260

290261
/* else, set cancel flag to stop any long-running loops */
291-
cancel_pressed = true;
292-
293-
/* and send QueryCancel if we are processing a database query */
294-
if (cancelConn != NULL)
295-
{
296-
if (PQcancel(cancelConn, errbuf, sizeof(errbuf)))
297-
write_stderr("Cancel request sent\n");
298-
else
299-
{
300-
write_stderr("Could not send cancel request: ");
301-
write_stderr(errbuf);
302-
}
303-
}
304-
305-
errno = save_errno; /* just in case the write changed it */
262+
CancelRequested = true;
306263
}
307264

308-
void
309-
setup_cancel_handler(void)
310-
{
311-
pqsignal(SIGINT, handle_sigint);
312-
}
313-
#else /* WIN32 */
265+
#else
314266

315-
static BOOL WINAPI
316-
consoleHandler(DWORD dwCtrlType)
267+
static void
268+
psql_cancel_callback(void)
317269
{
318-
char errbuf[256];
319-
320-
if (dwCtrlType == CTRL_C_EVENT ||
321-
dwCtrlType == CTRL_BREAK_EVENT)
322-
{
323-
/*
324-
* Can't longjmp here, because we are in wrong thread :-(
325-
*/
326-
327-
/* set cancel flag to stop any long-running loops */
328-
cancel_pressed = true;
329-
330-
/* and send QueryCancel if we are processing a database query */
331-
EnterCriticalSection(&cancelConnLock);
332-
if (cancelConn != NULL)
333-
{
334-
if (PQcancel(cancelConn, errbuf, sizeof(errbuf)))
335-
write_stderr("Cancel request sent\n");
336-
else
337-
{
338-
write_stderr("Could not send cancel request: ");
339-
write_stderr(errbuf);
340-
}
341-
}
342-
LeaveCriticalSection(&cancelConnLock);
343-
344-
return TRUE;
345-
}
346-
else
347-
/* Return FALSE for any signals not being handled */
348-
return FALSE;
270+
/* nothing to do here */
349271
}
350272

273+
#endif /* !WIN32 */
274+
351275
void
352-
setup_cancel_handler(void)
276+
psql_setup_cancel_handler(void)
353277
{
354-
InitializeCriticalSection(&cancelConnLock);
355-
356-
SetConsoleCtrlHandler(consoleHandler, TRUE);
278+
setup_cancel_handler(psql_cancel_callback);
357279
}
358-
#endif /* WIN32 */
359280

360281

361282
/* ConnectionUp
@@ -428,62 +349,6 @@ CheckConnection(void)
428349

429350

430351

431-
/*
432-
* SetCancelConn
433-
*
434-
* Set cancelConn to point to the current database connection.
435-
*/
436-
void
437-
SetCancelConn(void)
438-
{
439-
PGcancel *oldCancelConn;
440-
441-
#ifdef WIN32
442-
EnterCriticalSection(&cancelConnLock);
443-
#endif
444-
445-
/* Free the old one if we have one */
446-
oldCancelConn = cancelConn;
447-
/* be sure handle_sigint doesn't use pointer while freeing */
448-
cancelConn = NULL;
449-
450-
if (oldCancelConn != NULL)
451-
PQfreeCancel(oldCancelConn);
452-
453-
cancelConn = PQgetCancel(pset.db);
454-
455-
#ifdef WIN32
456-
LeaveCriticalSection(&cancelConnLock);
457-
#endif
458-
}
459-
460-
461-
/*
462-
* ResetCancelConn
463-
*
464-
* Free the current cancel connection, if any, and set to NULL.
465-
*/
466-
void
467-
ResetCancelConn(void)
468-
{
469-
PGcancel *oldCancelConn;
470-
471-
#ifdef WIN32
472-
EnterCriticalSection(&cancelConnLock);
473-
#endif
474-
475-
oldCancelConn = cancelConn;
476-
/* be sure handle_sigint doesn't use pointer while freeing */
477-
cancelConn = NULL;
478-
479-
if (oldCancelConn != NULL)
480-
PQfreeCancel(oldCancelConn);
481-
482-
#ifdef WIN32
483-
LeaveCriticalSection(&cancelConnLock);
484-
#endif
485-
}
486-
487352

488353
/*
489354
* AcceptResult
@@ -707,7 +572,7 @@ PSQLexec(const char *query)
707572
return NULL;
708573
}
709574

710-
SetCancelConn();
575+
SetCancelConn(pset.db);
711576

712577
res = PQexec(pset.db, query);
713578

@@ -746,7 +611,7 @@ PSQLexecWatch(const char *query, const printQueryOpt *opt)
746611
return 0;
747612
}
748613

749-
SetCancelConn();
614+
SetCancelConn(pset.db);
750615

751616
if (pset.timing)
752617
INSTR_TIME_SET_CURRENT(before);
@@ -773,7 +638,7 @@ PSQLexecWatch(const char *query, const printQueryOpt *opt)
773638
* consumed. The user's intention, though, is to cancel the entire watch
774639
* process, so detect a sent cancellation request and exit in this case.
775640
*/
776-
if (cancel_pressed)
641+
if (CancelRequested)
777642
{
778643
PQclear(res);
779644
return 0;
@@ -973,8 +838,8 @@ ExecQueryTuples(const PGresult *result)
973838
{
974839
const char *query = PQgetvalue(result, r, c);
975840

976-
/* Abandon execution if cancel_pressed */
977-
if (cancel_pressed)
841+
/* Abandon execution if CancelRequested */
842+
if (CancelRequested)
978843
goto loop_exit;
979844

980845
/*
@@ -1091,7 +956,7 @@ ProcessResult(PGresult **results)
1091956
FILE *copystream;
1092957
PGresult *copy_result;
1093958

1094-
SetCancelConn();
959+
SetCancelConn(pset.db);
1095960
if (result_status == PGRES_COPY_OUT)
1096961
{
1097962
bool need_close = false;
@@ -1342,7 +1207,7 @@ SendQuery(const char *query)
13421207
if (fgets(buf, sizeof(buf), stdin) != NULL)
13431208
if (buf[0] == 'x')
13441209
goto sendquery_cleanup;
1345-
if (cancel_pressed)
1210+
if (CancelRequested)
13461211
goto sendquery_cleanup;
13471212
}
13481213
else if (pset.echo == PSQL_ECHO_QUERIES)
@@ -1360,7 +1225,7 @@ SendQuery(const char *query)
13601225
fflush(pset.logfile);
13611226
}
13621227

1363-
SetCancelConn();
1228+
SetCancelConn(pset.db);
13641229

13651230
transaction_status = PQtransactionStatus(pset.db);
13661231

@@ -1886,7 +1751,7 @@ ExecQueryUsingCursor(const char *query, double *elapsed_msec)
18861751
* writing things to the stream, we presume $PAGER has disappeared and
18871752
* stop bothering to pull down more data.
18881753
*/
1889-
if (ntuples < fetch_count || cancel_pressed || flush_error ||
1754+
if (ntuples < fetch_count || CancelRequested || flush_error ||
18901755
ferror(fout))
18911756
break;
18921757
}

‎src/bin/psql/common.h

Lines changed: 1 addition & 4 deletions
Original file line numberDiff line numberDiff line change
@@ -26,10 +26,7 @@ extern volatile bool sigint_interrupt_enabled;
2626

2727
extern sigjmp_buf sigint_interrupt_jmp;
2828

29-
extern void setup_cancel_handler(void);
30-
31-
extern void SetCancelConn(void);
32-
extern void ResetCancelConn(void);
29+
extern void psql_setup_cancel_handler(void);
3330

3431
extern PGresult *PSQLexec(const char *query);
3532
extern int PSQLexecWatch(const char *query, const printQueryOpt *opt);

‎src/bin/psql/large_obj.c

Lines changed: 4 additions & 3 deletions
Original file line numberDiff line numberDiff line change
@@ -9,6 +9,7 @@
99

1010
#include "common.h"
1111
#include "common/logging.h"
12+
#include "fe_utils/cancel.h"
1213
#include "large_obj.h"
1314
#include "settings.h"
1415

@@ -146,7 +147,7 @@ do_lo_export(const char *loid_arg, const char *filename_arg)
146147
if (!start_lo_xact("\\lo_export", &own_transaction))
147148
return false;
148149

149-
SetCancelConn();
150+
SetCancelConn(NULL);
150151
status = lo_export(pset.db, atooid(loid_arg), filename_arg);
151152
ResetCancelConn();
152153

@@ -182,7 +183,7 @@ do_lo_import(const char *filename_arg, const char *comment_arg)
182183
if (!start_lo_xact("\\lo_import", &own_transaction))
183184
return false;
184185

185-
SetCancelConn();
186+
SetCancelConn(NULL);
186187
loid = lo_import(pset.db, filename_arg);
187188
ResetCancelConn();
188189

@@ -244,7 +245,7 @@ do_lo_unlink(const char *loid_arg)
244245
if (!start_lo_xact("\\lo_unlink", &own_transaction))
245246
return false;
246247

247-
SetCancelConn();
248+
SetCancelConn(NULL);
248249
status = lo_unlink(pset.db, loid);
249250
ResetCancelConn();
250251

‎src/bin/psql/startup.c

Lines changed: 1 addition & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -301,7 +301,7 @@ main(int argc, char *argv[])
301301
exit(EXIT_BADCONN);
302302
}
303303

304-
setup_cancel_handler();
304+
psql_setup_cancel_handler();
305305

306306
PQsetNoticeProcessor(pset.db, NoticeProcessor, NULL);
307307

‎src/bin/scripts/clusterdb.c

Lines changed: 1 addition & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -133,7 +133,7 @@ main(int argc, char *argv[])
133133
exit(1);
134134
}
135135

136-
setup_cancel_handler();
136+
setup_cancel_handler(NULL);
137137

138138
if (alldb)
139139
{

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