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Rework libpq threaded SIGPIPE handling to avoid interference with
calling applications. This is done by blocking sigpipe in the libpq thread and using sigpending/sigwait to possibily discard any sigpipe we generated.
1 parent e02ef26 commit 8408f65

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9 files changed

+115
-107
lines changed

9 files changed

+115
-107
lines changed

‎configure

Lines changed: 12 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -17431,6 +17431,18 @@ _ACEOF
1743117431
fi
1743217432
HAVE_POSIX_SIGNALS=$pgac_cv_func_posix_signals
1743317433

17434+
if test "$pgac_cv_func_posix_signals" != yes -a "$enable_thread_safety" = yes; then
17435+
{ { echo "$as_me:$LINENO: error:
17436+
*** Thread-safety requires POSIX signals, which are not supported by your
17437+
*** operating system.
17438+
" >&5
17439+
echo "$as_me: error:
17440+
*** Thread-safety requires POSIX signals, which are not supported by your
17441+
*** operating system.
17442+
" >&2;}
17443+
{ (exit 1); exit 1; }; }
17444+
fi
17445+
1743417446
if test $ac_cv_func_fseeko = yes; then
1743517447
# Check whether --enable-largefile or --disable-largefile was given.
1743617448
if test "${enable_largefile+set}" = set; then

‎configure.in

Lines changed: 8 additions & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -1,5 +1,5 @@
11
dnl Process this file with autoconf to produce a configure script.
2-
dnl $PostgreSQL: pgsql/configure.in,v 1.387 2004/11/30 06:13:04 tgl Exp $
2+
dnl $PostgreSQL: pgsql/configure.in,v 1.388 2004/12/02 15:32:50 momjian Exp $
33
dnl
44
dnl Developers, please strive to achieve this order:
55
dnl
@@ -1174,6 +1174,13 @@ AC_CHECK_TYPES(sig_atomic_t, [], [], [#include <signal.h>])
11741174

11751175

11761176
PGAC_FUNC_POSIX_SIGNALS
1177+
if test "$pgac_cv_func_posix_signals" != yes -a "$enable_thread_safety" = yes; then
1178+
AC_MSG_ERROR([
1179+
*** Thread-safety requires POSIX signals, which are not supported by your
1180+
*** operating system.
1181+
])
1182+
fi
1183+
11771184
if test $ac_cv_func_fseeko = yes; then
11781185
AC_SYS_LARGEFILE
11791186
fi

‎doc/src/sgml/libpq.sgml

Lines changed: 1 addition & 19 deletions
Original file line numberDiff line numberDiff line change
@@ -1,5 +1,5 @@
11
<!--
2-
$PostgreSQL: pgsql/doc/src/sgml/libpq.sgml,v 1.169 2004/11/27 21:56:04 petere Exp $
2+
$PostgreSQL: pgsql/doc/src/sgml/libpq.sgml,v 1.170 2004/12/02 15:32:52 momjian Exp $
33
-->
44

55
<chapter id="libpq">
@@ -3954,24 +3954,6 @@ safety</></> It is better to use the <literal>md5</literal> method,
39543954
which is thread-safe on all platforms.
39553955
</para>
39563956

3957-
<para>
3958-
<application>libpq</application> must ignore <literal>SIGPIPE</> signals
3959-
generated internally by <function>send()</> calls to backend processes.
3960-
When <productname>PostgreSQL</> is configured without
3961-
<literal>--enable-thread-safety</>, <application>libpq</> sets
3962-
<literal>SIGPIPE</> to <literal>SIG_IGN</> before each
3963-
<function>send()</> call and restores the original signal handler after
3964-
completion. When <literal>--enable-thread-safety</> is used,
3965-
<application>libpq</> installs its own <literal>SIGPIPE</> handler
3966-
before the first database connection. This handler uses thread-local
3967-
storage to determine if a <literal>SIGPIPE</> signal has been generated
3968-
by a libpq <function>send()</>. If an application wants to install
3969-
its own <literal>SIGPIPE</> signal handler, it should call
3970-
<function>PQinSend()</> to determine if it should ignore the
3971-
<literal>SIGPIPE</> signal. This function is available in both
3972-
thread-safe and non-thread-safe versions of <application>libpq</>.
3973-
</para>
3974-
39753957
<para>
39763958
If you experience problems with threaded applications, run
39773959
the program in <filename>src/tools/thread</> to see if your

‎doc/src/sgml/ref/copy.sgml

Lines changed: 2 additions & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -1,8 +1,9 @@
11
<!--
2-
$PostgreSQL: pgsql/doc/src/sgml/ref/copy.sgml,v 1.60 2004/11/27 21:56:05 petere Exp $
2+
$PostgreSQL: pgsql/doc/src/sgml/ref/copy.sgml,v 1.61 2004/12/02 15:32:53 momjian Exp $
33
PostgreSQL documentation
44
-->
55

6+
67
<refentry id="SQL-COPY">
78
<refmeta>
89
<refentrytitle id="sql-copy-title">COPY</refentrytitle>

‎src/interfaces/libpq/fe-connect.c

Lines changed: 1 addition & 10 deletions
Original file line numberDiff line numberDiff line change
@@ -8,7 +8,7 @@
88
*
99
*
1010
* IDENTIFICATION
11-
* $PostgreSQL: pgsql/src/interfaces/libpq/fe-connect.c,v 1.290 2004/12/01 23:42:26 momjian Exp $
11+
* $PostgreSQL: pgsql/src/interfaces/libpq/fe-connect.c,v 1.291 2004/12/02 15:32:54 momjian Exp $
1212
*
1313
*-------------------------------------------------------------------------
1414
*/
@@ -866,15 +866,6 @@ connectDBStart(PGconn *conn)
866866
const char *node = NULL;
867867
int ret;
868868

869-
#ifdef ENABLE_THREAD_SAFETY
870-
#ifndef WIN32
871-
static pthread_once_t check_sigpipe_once = PTHREAD_ONCE_INIT;
872-
873-
/* Check only on first connection request */
874-
pthread_once(&check_sigpipe_once, pq_check_sigpipe_handler);
875-
#endif
876-
#endif
877-
878869
if (!conn)
879870
return 0;
880871

‎src/interfaces/libpq/fe-print.c

Lines changed: 10 additions & 4 deletions
Original file line numberDiff line numberDiff line change
@@ -10,7 +10,7 @@
1010
* didn't really belong there.
1111
*
1212
* IDENTIFICATION
13-
* $PostgreSQL: pgsql/src/interfaces/libpq/fe-print.c,v 1.55 2004/11/09 15:57:57 petere Exp $
13+
* $PostgreSQL: pgsql/src/interfaces/libpq/fe-print.c,v 1.56 2004/12/02 15:32:54 momjian Exp $
1414
*
1515
*-------------------------------------------------------------------------
1616
*/
@@ -91,7 +91,11 @@ PQprint(FILE *fout,
9191
int total_line_length = 0;
9292
int usePipe = 0;
9393
char *pagerenv;
94-
94+
#ifdef ENABLE_THREAD_SAFETY
95+
sigset_t osigset;
96+
bool sigpipe_masked = false;
97+
bool sigpipe_pending;
98+
#endif
9599
#if !defined(ENABLE_THREAD_SAFETY) && !defined(WIN32)
96100
pqsigfunc oldsigpipehandler = NULL;
97101
#endif
@@ -189,7 +193,8 @@ PQprint(FILE *fout,
189193
{
190194
usePipe = 1;
191195
#ifdef ENABLE_THREAD_SAFETY
192-
pthread_setspecific(pq_thread_in_send, "t");
196+
pq_block_sigpipe(&osigset, &sigpipe_pending);
197+
sigpipe_masked = true;
193198
#else
194199
#ifndef WIN32
195200
oldsigpipehandler = pqsignal(SIGPIPE, SIG_IGN);
@@ -311,7 +316,8 @@ PQprint(FILE *fout,
311316
pclose(fout);
312317
#endif
313318
#ifdef ENABLE_THREAD_SAFETY
314-
pthread_setspecific(pq_thread_in_send, "f");
319+
if (sigpipe_masked)
320+
pq_reset_sigpipe(&osigset, sigpipe_pending);
315321
#else
316322
#ifndef WIN32
317323
pqsignal(SIGPIPE, oldsigpipehandler);

‎src/interfaces/libpq/fe-secure.c

Lines changed: 73 additions & 59 deletions
Original file line numberDiff line numberDiff line change
@@ -11,7 +11,7 @@
1111
*
1212
*
1313
* IDENTIFICATION
14-
* $PostgreSQL: pgsql/src/interfaces/libpq/fe-secure.c,v 1.57 2004/11/20 00:35:13 tgl Exp $
14+
* $PostgreSQL: pgsql/src/interfaces/libpq/fe-secure.c,v 1.58 2004/12/02 15:32:54 momjian Exp $
1515
*
1616
* NOTES
1717
* [ Most of these notes are wrong/obsolete, but perhaps not all ]
@@ -152,12 +152,6 @@ bool pq_initssllib = true;
152152
static SSL_CTX *SSL_context = NULL;
153153
#endif
154154

155-
#ifdef ENABLE_THREAD_SAFETY
156-
static void sigpipe_handler_ignore_send(int signo);
157-
pthread_key_t pq_thread_in_send = 0; /* initializer needed on Darwin */
158-
static pqsigfunc pq_pipe_handler;
159-
#endif
160-
161155
/* ------------------------------------------------------------ */
162156
/* Hardcoded values */
163157
/* ------------------------------------------------------------ */
@@ -379,9 +373,12 @@ ssize_t
379373
pqsecure_write(PGconn *conn, const void *ptr, size_t len)
380374
{
381375
ssize_t n;
382-
376+
383377
#ifdef ENABLE_THREAD_SAFETY
384-
pthread_setspecific(pq_thread_in_send, "t");
378+
sigset_t osigmask;
379+
bool sigpipe_pending;
380+
381+
pq_block_sigpipe(&osigmask, &sigpipe_pending);
385382
#else
386383
#ifndef WIN32
387384
pqsigfunc oldsighandler = pqsignal(SIGPIPE, SIG_IGN);
@@ -452,9 +449,14 @@ pqsecure_write(PGconn *conn, const void *ptr, size_t len)
452449
else
453450
#endif
454451
n = send(conn->sock, ptr, len, 0);
452+
/*
453+
* Possible optimization: if sigpending() turns out to be an
454+
* expensive operation, we can set sigpipe_pending = 'true'
455+
* here if errno != EPIPE, avoiding a sigpending call.
456+
*/
455457

456458
#ifdef ENABLE_THREAD_SAFETY
457-
pthread_setspecific(pq_thread_in_send, "f");
459+
pq_reset_sigpipe(&osigmask, sigpipe_pending);
458460
#else
459461
#ifndef WIN32
460462
pqsignal(SIGPIPE, oldsighandler);
@@ -1216,65 +1218,77 @@ PQgetssl(PGconn *conn)
12161218
}
12171219
#endif /* USE_SSL */
12181220

1219-
12201221
#ifdef ENABLE_THREAD_SAFETY
1221-
#ifndef WIN32
12221222
/*
1223-
* Check SIGPIPE handler and perhaps install our own.
1223+
* Block SIGPIPE for this thread. This prevents send()/write() from exiting
1224+
* the application.
12241225
*/
1225-
void
1226-
pq_check_sigpipe_handler(void)
1227-
{
1228-
pthread_key_create(&pq_thread_in_send, NULL);
1229-
1230-
/*
1231-
* Find current pipe handler and chain on to it.
1232-
*/
1233-
pq_pipe_handler = pqsignalinquire(SIGPIPE);
1234-
pqsignal(SIGPIPE, sigpipe_handler_ignore_send);
1235-
}
1236-
1237-
/*
1238-
* Threaded SIGPIPE signal handler
1239-
*/
1240-
void
1241-
sigpipe_handler_ignore_send(int signo)
1226+
int
1227+
pq_block_sigpipe(sigset_t *osigset, bool *sigpipe_pending)
12421228
{
1243-
/*
1244-
* If we have gotten a SIGPIPE outside send(), chain or exit if we are
1245-
* at the end of the chain. Synchronous signals are delivered to the
1246-
* thread that caused the signal.
1247-
*/
1248-
if (!PQinSend())
1229+
sigset_t sigpipe_sigset;
1230+
sigset_t sigset;
1231+
int ret;
1232+
1233+
sigemptyset(&sigpipe_sigset);
1234+
sigaddset(&sigpipe_sigset, SIGPIPE);
1235+
1236+
/* Block SIGPIPE and save previous mask for later reset */
1237+
ret = pthread_sigmask(SIG_BLOCK, &sigpipe_sigset, osigset);
1238+
1239+
/* We can have a pending SIGPIPE only if it was blocked before */
1240+
if (sigismember(osigset, SIGPIPE))
12491241
{
1250-
if (pq_pipe_handler == SIG_DFL) /* not set by application */
1251-
exit(128 + SIGPIPE); /* typical return value for SIG_DFL */
1242+
/* Is there a pending SIGPIPE? */
1243+
if (sigpending(&sigset) != 0)
1244+
return -1;
1245+
1246+
if (sigismember(&sigset, SIGPIPE))
1247+
*sigpipe_pending = true;
12521248
else
1253-
(*pq_pipe_handler) (signo); /* call original handler */
1249+
*sigpipe_pending = false;
12541250
}
1251+
else
1252+
*sigpipe_pending = false;
1253+
1254+
return ret;
12551255
}
1256-
#endif
1257-
#endif
1258-
1256+
12591257
/*
1260-
* Indicates whether the current thread is in send()
1261-
* For use by SIGPIPE signal handlers; they should
1262-
* ignore SIGPIPE when libpq is in send(). This means
1263-
* that the backend has died unexpectedly.
1258+
* Discard any pending SIGPIPE and reset the signal mask.
1259+
* We might be discarding a blocked SIGPIPE that we didn't generate,
1260+
* but we document that you can't keep blocked SIGPIPE calls across
1261+
* libpq function calls.
12641262
*/
1265-
pqbool
1266-
PQinSend(void)
1263+
int
1264+
pq_reset_sigpipe(sigset_t *osigset, bool sigpipe_pending)
12671265
{
1268-
#ifdef ENABLE_THREAD_SAFETY
1269-
return (pthread_getspecific(pq_thread_in_send) /* has it been set? */ &&
1270-
*(char *) pthread_getspecific(pq_thread_in_send) == 't') ? true : false;
1271-
#else
1266+
int signo;
1267+
sigset_t sigset;
12721268

1273-
/*
1274-
* No threading: our code ignores SIGPIPE around send(). Therefore, we
1275-
* can't be in send() if we are checking from a SIGPIPE signal
1276-
* handler.
1277-
*/
1278-
return false;
1279-
#endif
1269+
/* Clear SIGPIPE only if none was pending */
1270+
if (!sigpipe_pending)
1271+
{
1272+
if (sigpending(&sigset) != 0)
1273+
return -1;
1274+
1275+
/*
1276+
* Discard pending and blocked SIGPIPE
1277+
*/
1278+
if (sigismember(&sigset, SIGPIPE))
1279+
{
1280+
sigset_t sigpipe_sigset;
1281+
1282+
sigemptyset(&sigpipe_sigset);
1283+
sigaddset(&sigpipe_sigset, SIGPIPE);
1284+
1285+
sigwait(&sigpipe_sigset, &signo);
1286+
if (signo != SIGPIPE)
1287+
return -1;
1288+
}
1289+
}
1290+
1291+
/* Restore saved block mask */
1292+
return pthread_sigmask(SIG_SETMASK, osigset, NULL);
12801293
}
1294+
#endif

‎src/interfaces/libpq/libpq-fe.h

Lines changed: 1 addition & 7 deletions
Original file line numberDiff line numberDiff line change
@@ -7,7 +7,7 @@
77
* Portions Copyright (c) 1996-2004, PostgreSQL Global Development Group
88
* Portions Copyright (c) 1994, Regents of the University of California
99
*
10-
* $PostgreSQL: pgsql/src/interfaces/libpq/libpq-fe.h,v 1.113 2004/10/30 23:11:27 tgl Exp $
10+
* $PostgreSQL: pgsql/src/interfaces/libpq/libpq-fe.h,v 1.114 2004/12/02 15:32:54 momjian Exp $
1111
*
1212
*-------------------------------------------------------------------------
1313
*/
@@ -497,12 +497,6 @@ extern int PQenv2encoding(void);
497497

498498
/* === in fe-secure.c === */
499499

500-
/*
501-
* Indicates whether the libpq thread is in send().
502-
* Used to ignore SIGPIPE if thread is in send().
503-
*/
504-
extern pqbool PQinSend(void);
505-
506500
#ifdef __cplusplus
507501
}
508502
#endif

‎src/interfaces/libpq/libpq-int.h

Lines changed: 7 additions & 6 deletions
Original file line numberDiff line numberDiff line change
@@ -12,7 +12,7 @@
1212
* Portions Copyright (c) 1996-2004, PostgreSQL Global Development Group
1313
* Portions Copyright (c) 1994, Regents of the University of California
1414
*
15-
* $PostgreSQL: pgsql/src/interfaces/libpq/libpq-int.h,v 1.96 2004/10/30 23:11:27 tgl Exp $
15+
* $PostgreSQL: pgsql/src/interfaces/libpq/libpq-int.h,v 1.97 2004/12/02 15:32:54 momjian Exp $
1616
*
1717
*-------------------------------------------------------------------------
1818
*/
@@ -31,6 +31,7 @@
3131

3232
#ifdef ENABLE_THREAD_SAFETY
3333
#include <pthread.h>
34+
#include <signal.h>
3435
#endif
3536

3637
#ifdef WIN32_CLIENT_ONLY
@@ -475,15 +476,15 @@ extern void pqsecure_close(PGconn *);
475476
extern ssize_t pqsecure_read(PGconn *, void *ptr, size_t len);
476477
extern ssize_t pqsecure_write(PGconn *, const void *ptr, size_t len);
477478

478-
#ifdef ENABLE_THREAD_SAFETY
479-
extern void pq_check_sigpipe_handler(void);
480-
extern pthread_key_t pq_thread_in_send;
481-
#endif
482-
483479
#ifdef USE_SSL
484480
extern bool pq_initssllib;
485481
#endif
486482

483+
#ifdef ENABLE_THREAD_SAFETY
484+
int pq_block_sigpipe(sigset_t *osigset, bool *sigpipe_pending);
485+
int pq_reset_sigpipe(sigset_t *osigset, bool sigpipe_pending);
486+
#endif
487+
487488
/*
488489
* this is so that we can check if a connection is non-blocking internally
489490
* without the overhead of a function call

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