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Fix thread safety of realm Refresh operation

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Due to the lack of locking, there was a chance the the update thread
`context` was retrieved just before the `flushContexts` call, followed
by `.Refresh()` being run while the blocking behaviour was invoked.

This can be seen in test failures such as
https://ci.appveyor.com/project/peppy/osu/builds/39859786/tests.

As an aside, I tried multiple different methods to avoid `lock()` on the
update thread but they felt flaky. The overhead of lock when there's no
contention is reportedly around 30-50ns, so likely not of concern. We
can address it at a later point if it becomes one.
This commit is contained in:
Dean Herbert 2021-07-04 16:24:39 +09:00
parent 49090a0d1b
commit 567e9f33a9
1 changed files with 10 additions and 3 deletions
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13
osu.Game/Database/RealmContextFactory.cs
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@ -38,6 +38,8 @@ namespace osu.Game.Database
private static readonly GlobalStatistic<int> pending_writes = GlobalStatistics.Get<int>("Realm", "Pending writes"); private static readonly GlobalStatistic<int> pending_writes = GlobalStatistics.Get<int>("Realm", "Pending writes");
private static readonly GlobalStatistic<int> active_usages = GlobalStatistics.Get<int>("Realm", "Active usages"); private static readonly GlobalStatistic<int> active_usages = GlobalStatistics.Get<int>("Realm", "Active usages");
private readonly object updateContextLock = new object();
private Realm context; private Realm context;
public Realm Context public Realm Context
@ -107,8 +109,11 @@ namespace osu.Game.Database
{ {
base.Update(); base.Update();
if (context?.Refresh() == true) lock (updateContextLock)
refreshes.Value++; {
if (context?.Refresh() == true)
refreshes.Value++;
}
} }
private Realm createContext() private Realm createContext()
@ -156,7 +161,9 @@ namespace osu.Game.Database
Logger.Log(@"Flushing realm contexts...", LoggingTarget.Database); Logger.Log(@"Flushing realm contexts...", LoggingTarget.Database);
var previousContext = context; var previousContext = context;
context = null;
lock (updateContextLock)
context = null;
// wait for all threaded usages to finish // wait for all threaded usages to finish
while (active_usages.Value > 0) while (active_usages.Value > 0)