From 1ae924558f0ba397efb4e4b2c01b4fb80e901aa7 Mon Sep 17 00:00:00 2001
From: fr33domlover <fr33domlover@riseup.net>
Date: Tue, 18 Jun 2019 10:47:01 +0000
Subject: [PATCH] Use updateGet for atomic access to projectNextTicket

`updateGet` isn't atomic by default. In PostgreSQL the default isolation level
if committed read, and an `update` followed by a `get` doesn't guarantee you
get the same value you sent. However I'm making a patch for `persistent` to
make `updateGet` atomic for PostgreSQL.
---
 src/Vervis/Federation/Ticket.hs | 16 +++++++---------
 1 file changed, 7 insertions(+), 9 deletions(-)

diff --git a/src/Vervis/Federation/Ticket.hs b/src/Vervis/Federation/Ticket.hs
index 3fb9711..24ec549 100644
--- a/src/Vervis/Federation/Ticket.hs
+++ b/src/Vervis/Federation/Ticket.hs
@@ -179,10 +179,9 @@ projectOfferTicketF
                         findRelevantCollections hLocal $
                             activityAudience $ actbActivity body
                 mremotesHttp <- runDBExcept $ do
-                    (sid, jid, ibid, fsid, next, tids) <-
-                        getProjectAndDeps deps
+                    (sid, jid, ibid, fsid, tids) <- getProjectAndDeps deps
                     lift $ join <$> do
-                        mractid <- insertTicket jid ibid next tids
+                        mractid <- insertTicket jid ibid tids
                         for mractid $ \ ractid -> for msig $ \ sig -> do
                             remoteRecips <- deliverLocal ractid colls sid fsid
                             (sig,) <$> deliverRemoteDB (actbBL body) ractid jid sig remoteRecips
@@ -234,11 +233,8 @@ projectOfferTicketF
         tids <- for deps $ \ dep -> do
             mtid <- lift $ getKeyBy $ UniqueTicket jid dep
             fromMaybeE mtid "Local dep: No such ticket number in DB"
-        return
-            ( sid, jid, projectInbox j, projectFollowers j, projectNextTicket j
-            , tids
-            )
-    insertTicket jid ibid next deps = do
+        return (sid, jid, projectInbox j, projectFollowers j, tids)
+    insertTicket jid ibid deps = do
         let iidAuthor = remoteAuthorInstance author
             raidAuthor = remoteAuthorId author
         ractid <- either entityKey id <$> insertBy' RemoteActivity
@@ -254,7 +250,9 @@ projectOfferTicketF
                 delete ibiid
                 return Nothing
             Just _ibirid -> do
-                update jid [ProjectNextTicket +=. 1]
+                next <-
+                    ((subtract 1) . projectNextTicket) <$>
+                        updateGet jid [ProjectNextTicket +=. 1]
                 did <- insert Discussion
                 fsid <- insert FollowerSet
                 tid <- insert Ticket