Make pgconn_connect_poll close the socket prior to calling

`PQconnectPoll`

Since `PQconnectPoll` can change the underlying socket and thus the file
descriptor, closing the socket after can manifest a race condition
where libpq has closed the socket and another thread has opened a socket
with the recycled file descriptor. When the original socket is closed
from Ruby, the VM will notify the new thread that the FD has closed
(erroneously) resulting in an exception.

The same for `PQresetPoll`.

ext/pg_connection.c

@@ -515,9 +515,9 @@ static VALUE
 pgconn_connect_poll(VALUE self)
 {
 	PostgresPollingStatusType status;
-	status = gvl_PQconnectPoll(pg_get_pgconn(self));
 
 	pgconn_close_socket_io(self);
+	status = gvl_PQconnectPoll(pg_get_pgconn(self));
 
 	return INT2FIX((int)status);
 }
@@ -615,9 +615,9 @@ static VALUE
 pgconn_reset_poll(VALUE self)
 {
 	PostgresPollingStatusType status;
-	status = gvl_PQresetPoll(pg_get_pgconn(self));
 
 	pgconn_close_socket_io(self);
+	status = gvl_PQresetPoll(pg_get_pgconn(self));
 
 	return INT2FIX((int)status);
 }

spec/pg/connection_spec.rb

@@ -577,6 +577,21 @@
 			conn.close
 		end
 
+		it "doesn't notify the wrong thread about closed socket (Bug #564)" do
+			10.times do
+				10.times.map do
+					Thread.new do
+						Thread.current.report_on_exception = false
+						expect do
+							threaded_conn = PG.connect( @conninfo + " sslcert=tmp_test_specs/data/ruby-pg-ca-cert" )
+							res = threaded_conn.exec("SELECT 1")
+							threaded_conn.close
+						end.not_to raise_error
+					end
+				end.each(&:join)
+			end
+		end
+
 		it "can use conn.reset_start to restart the connection" do
 			ios = IO.pipe
 			conn = described_class.connect_start( @conninfo )