osu/osu.Game/Database/DatabaseContextFactory.cs

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// Copyright (c) ppy Pty Ltd <contact@ppy.sh>. Licensed under the MIT Licence.
// See the LICENCE file in the repository root for full licence text.
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using System.Linq;
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using System.Threading;
using Microsoft.EntityFrameworkCore.Storage;
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using osu.Framework.Platform;
using osu.Framework.Statistics;
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namespace osu.Game.Database
{
public class DatabaseContextFactory : IDatabaseContextFactory
{
private readonly Storage storage;
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private const string database_name = @"client";
private ThreadLocal<OsuDbContext> threadContexts;
private readonly object writeLock = new object();
private bool currentWriteDidWrite;
private bool currentWriteDidError;
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private int currentWriteUsages;
private IDbContextTransaction currentWriteTransaction;
public DatabaseContextFactory(Storage storage)
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{
this.storage = storage;
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recycleThreadContexts();
}
private static readonly GlobalStatistic<int> reads = GlobalStatistics.Get<int>("Database", "Get (Read)");
private static readonly GlobalStatistic<int> writes = GlobalStatistics.Get<int>("Database", "Get (Write)");
private static readonly GlobalStatistic<int> commits = GlobalStatistics.Get<int>("Database", "Commits");
private static readonly GlobalStatistic<int> rollbacks = GlobalStatistics.Get<int>("Database", "Rollbacks");
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/// <summary>
/// Get a context for the current thread for read-only usage.
/// If a <see cref="DatabaseWriteUsage"/> is in progress, the existing write-safe context will be returned.
/// </summary>
public OsuDbContext Get()
{
reads.Value++;
return threadContexts.Value;
}
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/// <summary>
/// Request a context for write usage. Can be consumed in a nested fashion (and will return the same underlying context).
/// This method may block if a write is already active on a different thread.
/// </summary>
/// <param name="withTransaction">Whether to start a transaction for this write.</param>
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/// <returns>A usage containing a usable context.</returns>
public DatabaseWriteUsage GetForWrite(bool withTransaction = true)
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{
writes.Value++;
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Monitor.Enter(writeLock);
OsuDbContext context;
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try
{
if (currentWriteTransaction == null && withTransaction)
{
// this mitigates the fact that changes on tracked entities will not be rolled back with the transaction by ensuring write operations are always executed in isolated contexts.
// if this results in sub-optimal efficiency, we may need to look into removing Database-level transactions in favour of running SaveChanges where we currently commit the transaction.
if (threadContexts.IsValueCreated)
recycleThreadContexts();
context = threadContexts.Value;
currentWriteTransaction = context.Database.BeginTransaction();
}
else
{
// we want to try-catch the retrieval of the context because it could throw an error (in CreateContext).
context = threadContexts.Value;
}
}
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catch
{
// retrieval of a context could trigger a fatal error.
Monitor.Exit(writeLock);
throw;
}
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Interlocked.Increment(ref currentWriteUsages);
return new DatabaseWriteUsage(context, usageCompleted) { IsTransactionLeader = currentWriteTransaction != null && currentWriteUsages == 1 };
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}
private void usageCompleted(DatabaseWriteUsage usage)
{
int usages = Interlocked.Decrement(ref currentWriteUsages);
try
{
currentWriteDidWrite |= usage.PerformedWrite;
currentWriteDidError |= usage.Errors.Any();
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if (usages == 0)
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{
if (currentWriteDidError)
{
rollbacks.Value++;
currentWriteTransaction?.Rollback();
}
else
{
commits.Value++;
currentWriteTransaction?.Commit();
}
if (currentWriteDidWrite || currentWriteDidError)
{
// explicitly dispose to ensure any outstanding flushes happen as soon as possible (and underlying resources are purged).
usage.Context.Dispose();
// once all writes are complete, we want to refresh thread-specific contexts to make sure they don't have stale local caches.
recycleThreadContexts();
}
currentWriteTransaction = null;
currentWriteDidWrite = false;
currentWriteDidError = false;
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}
}
finally
{
Monitor.Exit(writeLock);
}
}
private void recycleThreadContexts()
{
// Contexts for other threads are not disposed as they may be in use elsewhere. Instead, fresh contexts are exposed
// for other threads to use, and we rely on the finalizer inside OsuDbContext to handle their previous contexts
threadContexts?.Value.Dispose();
threadContexts = new ThreadLocal<OsuDbContext>(CreateContext, true);
}
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protected virtual OsuDbContext CreateContext() => new OsuDbContext(storage.GetDatabaseConnectionString(database_name))
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{
Database = { AutoTransactionsEnabled = false }
};
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public void ResetDatabase()
{
lock (writeLock)
{
recycleThreadContexts();
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try
{
storage.DeleteDatabase(database_name);
}
catch
{
// for now we are not sure why file handles are kept open by EF, but this is generally only used in testing
}
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}
}
}
}