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Replace synchronous locks with async #957

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Replace synchronous locks with async #957

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83 changes: 54 additions & 29 deletions src/SQLiteAsync.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -22,6 +22,7 @@

using System;
using System.Collections;
using System.Collections.Concurrent;
using System.Collections.Generic;
using System.Linq;
using System.Linq.Expressions;
Expand Down Expand Up @@ -203,7 +204,7 @@ public SQLiteConnectionWithLock GetConnection ()
return SQLiteConnectionPool.Shared.GetConnection (_connectionString);
}

SQLiteConnectionWithLock GetConnectionAndTransactionLock (out object transactionLock)
SQLiteConnectionWithLock GetConnectionAndTransactionLock (out SemaphoreSlim transactionLock)
{
return SQLiteConnectionPool.Shared.GetConnectionAndTransactionLock (_connectionString, out transactionLock);
}
Expand All @@ -220,34 +221,38 @@ public Task CloseAsync ()

Task<T> ReadAsync<T> (Func<SQLiteConnectionWithLock, T> read)
{
return Task.Factory.StartNew (() => {
return Task.Run<T> (async () => {
var conn = GetConnection ();
using (conn.Lock ()) {
using (await conn.LockAsync ().ConfigureAwait (false)) {
return read (conn);
}
}, CancellationToken.None, TaskCreationOptions.DenyChildAttach, TaskScheduler.Default);
});
}

Task<T> WriteAsync<T> (Func<SQLiteConnectionWithLock, T> write)
{
return Task.Factory.StartNew (() => {
return Task.Run<T> (async () => {
var conn = GetConnection ();
using (conn.Lock ()) {
using (await conn.LockAsync ().ConfigureAwait (false)) {
return write (conn);
}
}, CancellationToken.None, TaskCreationOptions.DenyChildAttach, TaskScheduler.Default);
});
}

Task<T> TransactAsync<T> (Func<SQLiteConnectionWithLock, T> transact)
{
return Task.Factory.StartNew (() => {
return Task.Run<T> (async () => {
var conn = GetConnectionAndTransactionLock (out var transactionLock);
lock (transactionLock) {
using (conn.Lock ()) {
await transactionLock.WaitAsync ().ConfigureAwait (false);
try {
using (await conn.LockAsync ().ConfigureAwait (false)) {
return transact (conn);
}
}
}, CancellationToken.None, TaskCreationOptions.DenyChildAttach, TaskScheduler.Default);
finally {
transactionLock.Release ();
}
});
}

/// <summary>
Expand Down Expand Up @@ -1191,22 +1196,22 @@ public AsyncTableQuery (TableQuery<T> innerQuery)

Task<U> ReadAsync<U> (Func<SQLiteConnectionWithLock, U> read)
{
return Task.Factory.StartNew (() => {
return Task.Run<U> (async () => {
var conn = (SQLiteConnectionWithLock)_innerQuery.Connection;
using (conn.Lock ()) {
using (await conn.LockAsync ().ConfigureAwait (false)) {
return read (conn);
}
}, CancellationToken.None, TaskCreationOptions.DenyChildAttach, TaskScheduler.Default);
});
}

Task<U> WriteAsync<U> (Func<SQLiteConnectionWithLock, U> write)
{
return Task.Factory.StartNew (() => {
return Task.Run<U> (async () => {
var conn = (SQLiteConnectionWithLock)_innerQuery.Connection;
using (conn.Lock ()) {
using (await conn.LockAsync ().ConfigureAwait (false)) {
return write (conn);
}
}, CancellationToken.None, TaskCreationOptions.DenyChildAttach, TaskScheduler.Default);
});
}

/// <summary>
Expand Down Expand Up @@ -1362,7 +1367,7 @@ class Entry

public SQLiteConnectionString ConnectionString { get; }

public object TransactionLock { get; } = new object ();
public SemaphoreSlim TransactionLock { get; } = new SemaphoreSlim (1);

public Entry (SQLiteConnectionString connectionString)
{
Expand All @@ -1386,7 +1391,7 @@ public void Close ()
}

readonly Dictionary<string, Entry> _entries = new Dictionary<string, Entry> ();
readonly object _entriesLock = new object ();
readonly object _entriesLock = new object();

static readonly SQLiteConnectionPool _shared = new SQLiteConnectionPool ();

Expand All @@ -1404,11 +1409,11 @@ public SQLiteConnectionWithLock GetConnection (SQLiteConnectionString connection
return GetConnectionAndTransactionLock (connectionString, out var _);
}

public SQLiteConnectionWithLock GetConnectionAndTransactionLock (SQLiteConnectionString connectionString, out object transactionLock)
public SQLiteConnectionWithLock GetConnectionAndTransactionLock (SQLiteConnectionString connectionString, out SemaphoreSlim transactionLock)
{
var key = connectionString.UniqueKey;
Entry entry;
lock (_entriesLock) {
var key = connectionString.UniqueKey;
Entry entry;
if (!_entries.TryGetValue (key, out entry)) {
// The opens the database while we're locked
// This is to ensure another thread doesn't get an unopened database
Expand Down Expand Up @@ -1456,7 +1461,8 @@ public void Reset ()
/// </summary>
public class SQLiteConnectionWithLock : SQLiteConnection
{
readonly object _lockPoint = new object ();
readonly SemaphoreSlim _asyncLock =
new SemaphoreSlim (1);

/// <summary>
/// Initializes a new instance of the <see cref="T:SQLite.SQLiteConnectionWithLock"/> class.
Expand All @@ -1478,24 +1484,43 @@ public SQLiteConnectionWithLock (SQLiteConnectionString connectionString)
/// on the returned object.
/// </summary>
/// <returns>The lock.</returns>
[Obsolete("Please use LockAsync to prevent threadpool starvation")]
public IDisposable Lock ()
{
return SkipLock ? (IDisposable)new FakeLockWrapper() : new LockWrapper (_lockPoint);
return LockAsync ().Result;
}

/// <summary>
/// Asynchronously lock the database to serialize access to it.
/// To unlock it, call Dispose on the returned object.
/// </summary>
/// <returns>The lock.</returns>
public Task<IDisposable> LockAsync ()
{
return SkipLock ?
Task.FromResult ((IDisposable)new FakeLockWrapper ()) :
LockWrapper.CreateAsync (_asyncLock);
}

class LockWrapper : IDisposable
{
object _lockPoint;
SemaphoreSlim asyncLock;

LockWrapper (SemaphoreSlim asyncLock)
{
this.asyncLock = asyncLock;
}

public LockWrapper (object lockPoint)
public static async Task<IDisposable> CreateAsync (SemaphoreSlim asyncLock)
{
_lockPoint = lockPoint;
Monitor.Enter (_lockPoint);
var wrapper = new LockWrapper (asyncLock);
await asyncLock.WaitAsync ().ConfigureAwait (false);
return wrapper;
}

public void Dispose ()
{
Monitor.Exit (_lockPoint);
asyncLock.Release ();
}
}
class FakeLockWrapper : IDisposable
Expand Down