Improve the granularity of PQsocketPoll's timeout parameter.

Commit f5e4dedfa exposed libpq's internal function PQsocketPoll
without a lot of thought about whether that was an API we really
wanted to chisel in stone.  The main problem with it is the use of
time_t to specify the timeout.  While we do want an absolute time
so that a loop around PQsocketPoll doesn't have problems with
timeout slippage, time_t has only 1-second resolution.  That's
already problematic for libpq's own internal usage --- for example,
pqConnectDBComplete has long had a kluge to treat "connect_timeout=1"
as 2 seconds so that it doesn't accidentally round to nearly zero.
And it's even less likely to be satisfactory for external callers.
Hence, let's change this while we still can.

The best idea seems to be to use an int64 count of microseconds since
the epoch --- basically the same thing as the backend's TimestampTz,
but let's use the standard Unix epoch (1970-01-01) since that's more
likely for clients to be easy to calculate.  Millisecond resolution
would be plenty for foreseeable uses, but maybe the day will come that
we're glad we used microseconds.

Also, since time(2) isn't especially helpful for computing timeouts
defined this way, introduce a new function PQgetCurrentTimeUSec
to get the current time in this form.

Remove the hack in pqConnectDBComplete, so that "connect_timeout=1"
now means what you'd expect.

We can also remove the "#include <time.h>" that f5e4dedfa added to
libpq-fe.h, since there's no longer a need for time_t in that header.
It seems better for v17 not to enlarge libpq-fe.h's include footprint
from what it's historically been, anyway.

I also failed to resist the temptation to do some wordsmithing
on PQsocketPoll's documentation.

Patch by me, per complaint from Dominique Devienne.

Discussion: https://postgr.es/m/913559.1718055575@sss.pgh.pa.us

1 files changed, 5 insertions, 18 deletions

diff --git a/src/interfaces/libpq/fe-connect.c b/src/interfaces/libpq/fe-connect.c
index 90f259fc706..071b1b34aa1 100644
--- a/src/interfaces/libpq/fe-connect.c
+++ b/src/interfaces/libpq/fe-connect.c
@@ -2470,7 +2470,7 @@ int
 pqConnectDBComplete(PGconn *conn)
 {
 	PostgresPollingStatusType flag = PGRES_POLLING_WRITING;
-	time_t		finish_time = ((time_t) -1);
+	pg_usec_time_t end_time = -1;
 	int			timeout = 0;
 	int			last_whichhost = -2;	/* certainly different from whichhost */
 	int			last_whichaddr = -2;	/* certainly different from whichaddr */
@@ -2479,7 +2479,7 @@ pqConnectDBComplete(PGconn *conn)
 		return 0;
 
 	/*
-	 * Set up a time limit, if connect_timeout isn't zero.
+	 * Set up a time limit, if connect_timeout is greater than zero.
 	 */
 	if (conn->connect_timeout != NULL)
 	{
@@ -2490,19 +2490,6 @@ pqConnectDBComplete(PGconn *conn)
 			conn->status = CONNECTION_BAD;
 			return 0;
 		}
-
-		if (timeout > 0)
-		{
-			/*
-			 * Rounding could cause connection to fail unexpectedly quickly;
-			 * to prevent possibly waiting hardly-at-all, insist on at least
-			 * two seconds.
-			 */
-			if (timeout < 2)
-				timeout = 2;
-		}
-		else					/* negative means 0 */
-			timeout = 0;
 	}
 
 	for (;;)
@@ -2519,7 +2506,7 @@ pqConnectDBComplete(PGconn *conn)
 			(conn->whichhost != last_whichhost ||
 			 conn->whichaddr != last_whichaddr))
 		{
-			finish_time = time(NULL) + timeout;
+			end_time = PQgetCurrentTimeUSec() + (pg_usec_time_t) timeout * 1000000;
 			last_whichhost = conn->whichhost;
 			last_whichaddr = conn->whichaddr;
 		}
@@ -2534,7 +2521,7 @@ pqConnectDBComplete(PGconn *conn)
 				return 1;		/* success! */
 
 			case PGRES_POLLING_READING:
-				ret = pqWaitTimed(1, 0, conn, finish_time);
+				ret = pqWaitTimed(1, 0, conn, end_time);
 				if (ret == -1)
 				{
 					/* hard failure, eg select() problem, aborts everything */
@@ -2544,7 +2531,7 @@ pqConnectDBComplete(PGconn *conn)
 				break;
 
 			case PGRES_POLLING_WRITING:
-				ret = pqWaitTimed(0, 1, conn, finish_time);
+				ret = pqWaitTimed(0, 1, conn, end_time);
 				if (ret == -1)
 				{
 					/* hard failure, eg select() problem, aborts everything */