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Rewrite async-connection loop in libpqwalreceiver.c, once again.

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The original coding in commit 1e8a85009 didn't use PQconnectPoll per
spec, and while the rewrite in e434ad39a is closer, it still doesn't
guarantee to wait until the socket is read-ready or write-ready (as
appropriate) before calling PQconnectPoll.  It's not clear whether
that omission is causing the continuing failures on buildfarm member
bowerbird; but given the lack of other explanations meeting the
available facts, let's tighten that up and see what happens.

An independent issue in the same loop was that it had a race condition
whereby it could clear the process's latch without having serviced an
interrupt request, causing failure to respond to a cancel while waiting
for connection (the very problem 1e8a85009 was meant to fix).

Discussion: https://postgr.es/m/7295.1489596949@sss.pgh.pa.us
This commit is contained in:
Tom Lane
2017-03-15 13:26:26 -04:00
parent 1ea60ad602
commit b5dd50f2c0
1 changed files with 30 additions and 30 deletions
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60
src/backend/replication/libpqwalreceiver/libpqwalreceiver.c
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@ -159,41 +159,41 @@ libpqrcv_connect(const char *conninfo, bool logical, const char *appname,
/*
* Poll connection until we have OK or FAILED status.
*
* Note that the initial state after PQconnectStartParams is
* PGRES_POLLING_WRITING.
* Per spec for PQconnectPoll, first wait till socket is write-ready.
*/
for (status = PGRES_POLLING_WRITING;
status != PGRES_POLLING_OK && status != PGRES_POLLING_FAILED;
status = PQconnectPoll(conn->streamConn))
status = PGRES_POLLING_WRITING;
do
{
/* Sleep a bit if waiting for socket. */
if (status == PGRES_POLLING_READING ||
status == PGRES_POLLING_WRITING)
/* Wait for socket ready and/or other events. */
int io_flag;
int rc;
io_flag = (status == PGRES_POLLING_READING
? WL_SOCKET_READABLE
: WL_SOCKET_WRITEABLE);
rc = WaitLatchOrSocket(&MyProc->procLatch,
WL_POSTMASTER_DEATH |
WL_LATCH_SET | io_flag,
PQsocket(conn->streamConn),
0,
WAIT_EVENT_LIBPQWALRECEIVER);
/* Emergency bailout? */
if (rc & WL_POSTMASTER_DEATH)
exit(1);
/* Interrupted? */
if (rc & WL_LATCH_SET)
{
int extra_flag;
int rc;
extra_flag = (status == PGRES_POLLING_READING
? WL_SOCKET_READABLE
: WL_SOCKET_WRITEABLE);
ResetLatch(&MyProc->procLatch);
rc = WaitLatchOrSocket(&MyProc->procLatch,
WL_POSTMASTER_DEATH |
WL_LATCH_SET | extra_flag,
PQsocket(conn->streamConn),
0,
WAIT_EVENT_LIBPQWALRECEIVER);
/* Emergency bailout. */
if (rc & WL_POSTMASTER_DEATH)
exit(1);
/* Interrupted. */
if (rc & WL_LATCH_SET)
CHECK_FOR_INTERRUPTS();
CHECK_FOR_INTERRUPTS();
}
}
/* If socket is ready, advance the libpq state machine */
if (rc & io_flag)
status = PQconnectPoll(conn->streamConn);
} while (status != PGRES_POLLING_OK && status != PGRES_POLLING_FAILED);
if (PQstatus(conn->streamConn) != CONNECTION_OK)
{