From: Tristan Partin <tristan@neon.tech>
To: Heikki Linnakangas <hlinnaka@iki.fi>
Cc: Tom Lane <tgl@sss.pgh.pa.us>
Cc: pgsql-hackers@postgresql.org
Cc: Shlok Kyal <shlok.kyal.oss@gmail.com>
Subject: Re: psql not responding to SIGINT upon db reconnection
Date: Wed, 22 Nov 2023 15:29:45 -0600
Message-ID: <CX5NSE8R07D8.9D8M8LBKP119@neon.tech> (raw)
In-Reply-To: <9b3693b7-0bc3-430a-b43f-eae44e8a39b6@iki.fi>
References: <CUAJJDVD8L61.2AH6VEEDMTXX3@gonk>
<CUAKHCX5472I.SJP0AWQRYVFA@gonk>
<CUAKIOVISECO.2S7MSQFOP1304@gonk>
<1588058.1690220636@sss.pgh.pa.us>
<CUAO24Z1Y72E.2069AD01EB4LO@gonk>
<CANhcyEVBQWoPJK+C_h1CKyN3Wr2VKHuPx=bSB4PH2LuGdut4qg@mail.gmail.com>
<CWRWDTTPP0WZ.2W75ZAVL5ND1M@neon.tech>
<5e28b89f-0033-4e42-8184-b71b731c1aa2@iki.fi>
<CX5IOLTR8MAD.1UUDEG0X673Z4@neon.tech>
<9b3693b7-0bc3-430a-b43f-eae44e8a39b6@iki.fi>
On Wed Nov 22, 2023 at 3:00 PM CST, Heikki Linnakangas wrote:
> On 22/11/2023 19:29, Tristan Partin wrote:
> > On Thu Nov 16, 2023 at 8:33 AM CST, Heikki Linnakangas wrote:
> >> On 06/11/2023 19:16, Tristan Partin wrote:
> >>>>> That sounds like a much better solution. Attached you will find a v4
> >>>>> that implements your suggestion. Please let me know if there is
> >>>>> something that I missed. I can confirm that the patch works.
> >>
> >> This patch is missing a select(). It will busy loop until the connection
> >> is established or cancelled.
> >
> > If I add a wait (select, poll, etc.), then I can't control-C during the
> > blocking call, so it doesn't really solve the problem.
>
> Hmm, they should return with EINTR on signal. At least on Linux; I'm not
> sure how portable that is. See signal(7) man page, section "Interruption
> of system calls and library functions by signal handlers". You could
> also use a timeout like 5 s to ensure that you wake up and notice that
> the signal was received eventually, even if it doesn't interrupt the
> blocking call.
Ha, you're right. I had this working yesterday, but convinced myself it
didn't. I had a do while loop wrapping the blocking call. Here is a v4,
which seems to pass the tests that were pointed out to be failing
earlier.
Noticed that I copy-pasted pqSocketPoll() into the psql code. I think
this may be controversial. Not sure what the best solution to the issue
is. I will pay attention to the buildfarm animals when they pick this
up.
--
Tristan Partin
Neon (https://neon.tech)
Attachments:v4-0001-Allow-SIGINT-to-cancel-psql-database-reconnection.patch (text/x-patch, 4.8K) download
From 1b4303df1200c561cf478f9c7037ff940f6cd741 Mon Sep 17 00:00:00 2001
From: Tristan Partin <tristan@neon.tech>
Date: Mon, 24 Jul 2023 11:12:59 -0500
Subject: [PATCH v4] Allow SIGINT to cancel psql database reconnections
After installing the SIGINT handler in psql, SIGINT can no longer cancel
database reconnections. For instance, if the user starts a reconnection
and then needs to do some form of interaction (ie psql is polling),
there is no way to cancel the reconnection process currently.
Use PQconnectStartParams() in order to insert a CancelRequested check
into the polling loop.
---
src/bin/psql/command.c | 129 ++++++++++++++++++++++++++++++++++++++++-
1 file changed, 128 insertions(+), 1 deletion(-)
diff --git a/src/bin/psql/command.c b/src/bin/psql/command.cindex 82cc091568..588eed9351 100644--- a/src/bin/psql/command.c+++ b/src/bin/psql/command.c@@ -11,6 +11,11 @@
#include <time.h>
#include <pwd.h>
#include <utime.h>
+#if HAVE_POLL+#include <poll.h>+#else+#include <sys/select.h>+#endif
#ifndef WIN32
#include <sys/stat.h> /* for stat() */
#include <sys/time.h> /* for setitimer() */
@@ -40,6 +45,7 @@
#include "large_obj.h"
#include "libpq-fe.h"
#include "libpq/pqcomm.h"
+#include "libpq/pqsignal.h"
#include "mainloop.h"
#include "portability/instr_time.h"
#include "pqexpbuffer.h"
@@ -3251,6 +3257,90 @@ copy_previous_query(PQExpBuffer query_buf, PQExpBuffer previous_buf)
return false;
}
+/*+ * Check a file descriptor for read and/or write data, possibly waiting.+ * If neither forRead nor forWrite are set, immediately return a timeout+ * condition (without waiting). Return >0 if condition is met, 0+ * if a timeout occurred, -1 if an error or interrupt occurred.+ *+ * Timeout is infinite if end_time is -1. Timeout is immediate (no blocking)+ * if end_time is 0 (or indeed, any time before now).+ */+static int+pqSocketPoll(int sock, int forRead, int forWrite, time_t end_time)+{+ /* We use poll(2) if available, otherwise select(2) */+#ifdef HAVE_POLL+ struct pollfd input_fd;+ int timeout_ms;++ if (!forRead && !forWrite)+ return 0;++ input_fd.fd = sock;+ input_fd.events = POLLERR;+ input_fd.revents = 0;++ if (forRead)+ input_fd.events |= POLLIN;+ if (forWrite)+ input_fd.events |= POLLOUT;++ /* Compute appropriate timeout interval */+ if (end_time == ((time_t) -1))+ timeout_ms = -1;+ else+ {+ time_t now = time(NULL);++ if (end_time > now)+ timeout_ms = (end_time - now) * 1000;+ else+ timeout_ms = 0;+ }++ return poll(&input_fd, 1, timeout_ms);+#else /* !HAVE_POLL */++ fd_set input_mask;+ fd_set output_mask;+ fd_set except_mask;+ struct timeval timeout;+ struct timeval *ptr_timeout;++ if (!forRead && !forWrite)+ return 0;++ FD_ZERO(&input_mask);+ FD_ZERO(&output_mask);+ FD_ZERO(&except_mask);+ if (forRead)+ FD_SET(sock, &input_mask);++ if (forWrite)+ FD_SET(sock, &output_mask);+ FD_SET(sock, &except_mask);++ /* Compute appropriate timeout interval */+ if (end_time == ((time_t) -1))+ ptr_timeout = NULL;+ else+ {+ time_t now = time(NULL);++ if (end_time > now)+ timeout.tv_sec = end_time - now;+ else+ timeout.tv_sec = 0;+ timeout.tv_usec = 0;+ ptr_timeout = &timeout;+ }++ return select(sock + 1, &input_mask, &output_mask,+ &except_mask, ptr_timeout);+#endif /* HAVE_POLL */+}+
/*
* Ask the user for a password; 'username' is the username the
* password is for, if one has been explicitly specified.
@@ -3324,6 +3414,7 @@ do_connect(enum trivalue reuse_previous_specification,
bool keep_password = true;
bool has_connection_string;
bool reuse_previous;
+ bool for_read;
has_connection_string = dbname ?
recognized_connection_string(dbname) : false;
@@ -3614,11 +3705,47 @@ do_connect(enum trivalue reuse_previous_specification,
values[paramnum] = NULL;
/* Note we do not want libpq to re-expand the dbname parameter */
- n_conn = PQconnectdbParams(keywords, values, false);+ n_conn = PQconnectStartParams(keywords, values, false);
pg_free(keywords);
pg_free(values);
+ for_read = false;+ while (true) {+ int rc;+ int sock;++ if (cancel_pressed)+ break;++ sock = PQsocket(n_conn);+ if (sock == -1)+ break;++ rc = pqSocketPoll(sock, for_read, !for_read, (time_t)-1);+ Assert(rc != 0); /* Timeout is impossible. */+ if (rc == -1)+ {+ success = false;+ break;+ }++ switch (PQconnectPoll(n_conn)) {+ case PGRES_POLLING_OK:+ case PGRES_POLLING_FAILED:+ goto finish;+ case PGRES_POLLING_READING:+ for_read = true;+ continue;+ case PGRES_POLLING_WRITING:+ for_read = false;+ continue;+ case PGRES_POLLING_ACTIVE:+ pg_unreachable();+ }+ }++ finish:
if (PQstatus(n_conn) == CONNECTION_OK)
break;
--
Tristan Partin
Neon (https://neon.tech)
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To: pgsql-hackers@postgresql.org
Cc: tristan@neon.tech, hlinnaka@iki.fi, tgl@sss.pgh.pa.us, shlok.kyal.oss@gmail.com
Subject: Re: psql not responding to SIGINT upon db reconnection
In-Reply-To: <CX5NSE8R07D8.9D8M8LBKP119@neon.tech>
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