From 75363c35cc84f6411fbb73f0c380a41c5e55fdd3 Mon Sep 17 00:00:00 2001
From: Daniel Friesel <daniel.friesel@uos.de>
Date: Thu, 23 Jan 2020 17:14:01 +0100
Subject: work: Fix race condition

When a user changes their destination station or checks into a new train
while work is updating data for their in_transit entry, values for no longer
valid database entrie would be entered.
---
 lib/Travelynx/Command/work.pm | 19 +++++++++++++++++--
 1 file changed, 17 insertions(+), 2 deletions(-)

(limited to 'lib/Travelynx/Command/work.pm')

diff --git a/lib/Travelynx/Command/work.pm b/lib/Travelynx/Command/work.pm
index fbbf958..405716c 100644
--- a/lib/Travelynx/Command/work.pm
+++ b/lib/Travelynx/Command/work.pm
@@ -47,6 +47,10 @@ sub run {
 					die("could not find train $train_id at $dep\n");
 				}
 
+				# selecting on user_id and train_no avoids a race condition when
+				# a user checks into a new train while we are fetching data for
+				# their previous journey. In this case, the new train would
+				# receive data from the previous journey.
 				$db->update(
 					'in_transit',
 					{
@@ -61,7 +65,10 @@ sub run {
 							]
 						),
 					},
-					{ user_id => $uid }
+					{
+						user_id  => $uid,
+						train_no => $train->train_no
+					}
 				);
 				$self->app->add_route_timestamps( $uid, $train, 1 );
 			}
@@ -102,6 +109,10 @@ sub run {
 					return;
 				}
 
+             # selecting on user_id, train_no and checkout_station_id avoids a
+             # race condition when a user checks into a new train or changes
+             # their destination station while we are fetching times based on no
+             # longer valid database entries.
 				$db->update(
 					'in_transit',
 					{
@@ -117,7 +128,11 @@ sub run {
 							]
 						),
 					},
-					{ user_id => $uid }
+					{
+						user_id             => $uid,
+						train_no            => $train->train_no,
+						checkout_station_id => $arr
+					}
 				);
 				$self->app->add_route_timestamps( $uid, $train, 0 );
 			}
-- 
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