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CacheStack.cs
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CacheStack.cs
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using System;
using System.Collections.Concurrent;
using System.Collections.Generic;
using System.Linq;
using System.Runtime.CompilerServices;
using System.Threading;
using System.Threading.Tasks;
using CacheTower.Extensions;
using Microsoft.Extensions.DependencyInjection;
namespace CacheTower
{
#if NETSTANDARD2_0
public class CacheStack : ICacheStack, IDisposable
#elif NETSTANDARD2_1
public class CacheStack : ICacheStack, IAsyncDisposable
#endif
{
private bool Disposed;
private Dictionary<string, IEnumerable<TaskCompletionSource<object>>> WaitingKeyRefresh { get; }
private ICacheLayer[] CacheLayers { get; }
private ExtensionContainer Extensions { get; }
public CacheStack(ICacheLayer[] cacheLayers, ICacheExtension[] extensions)
{
if (cacheLayers == null || cacheLayers.Length == 0)
{
throw new ArgumentException("There must be at least one cache layer", nameof(cacheLayers));
}
CacheLayers = cacheLayers;
Extensions = new ExtensionContainer(extensions);
Extensions.Register(this);
WaitingKeyRefresh = new Dictionary<string, IEnumerable<TaskCompletionSource<object>>>(StringComparer.Ordinal);
}
[MethodImpl(MethodImplOptions.AggressiveInlining)]
protected void ThrowIfDisposed()
{
if (Disposed)
{
throw new ObjectDisposedException("CacheStack is disposed");
}
}
public async ValueTask CleanupAsync()
{
ThrowIfDisposed();
for (int i = 0, l = CacheLayers.Length; i < l; i++)
{
var layer = CacheLayers[i];
if (layer is ISyncCacheLayer syncLayer)
{
syncLayer.Cleanup();
}
else
{
await (layer as IAsyncCacheLayer).CleanupAsync();
}
}
}
public async ValueTask EvictAsync(string cacheKey)
{
ThrowIfDisposed();
if (cacheKey == null)
{
throw new ArgumentNullException(nameof(cacheKey));
}
for (int i = 0, l = CacheLayers.Length; i < l; i++)
{
var layer = CacheLayers[i];
if (layer is ISyncCacheLayer syncLayer)
{
syncLayer.Evict(cacheKey);
}
else
{
await (layer as IAsyncCacheLayer).EvictAsync(cacheKey);
}
}
}
public async ValueTask<CacheEntry<T>> SetAsync<T>(string cacheKey, T value, TimeSpan timeToLive)
{
ThrowIfDisposed();
var expiry = DateTime.UtcNow + timeToLive;
var cacheEntry = new CacheEntry<T>(value, expiry);
await SetAsync(cacheKey, cacheEntry);
return cacheEntry;
}
public async ValueTask SetAsync<T>(string cacheKey, CacheEntry<T> cacheEntry)
{
ThrowIfDisposed();
if (cacheKey == null)
{
throw new ArgumentNullException(nameof(cacheKey));
}
if (cacheEntry == null)
{
throw new ArgumentNullException(nameof(cacheEntry));
}
for (int i = 0, l = CacheLayers.Length; i < l; i++)
{
var layer = CacheLayers[i];
if (layer is ISyncCacheLayer syncLayerOne)
{
syncLayerOne.Set(cacheKey, cacheEntry);
}
else
{
await (layer as IAsyncCacheLayer).SetAsync(cacheKey, cacheEntry);
}
}
}
public async ValueTask<CacheEntry<T>> GetAsync<T>(string cacheKey)
{
ThrowIfDisposed();
if (cacheKey == null)
{
throw new ArgumentNullException(nameof(cacheKey));
}
for (var layerIndex = 0; layerIndex < CacheLayers.Length; layerIndex++)
{
var layer = CacheLayers[layerIndex];
if (layer is ISyncCacheLayer syncLayer)
{
if (syncLayer.IsAvailable(cacheKey))
{
var cacheEntry = syncLayer.Get<T>(cacheKey);
if (cacheEntry != default)
{
return cacheEntry;
}
}
}
else
{
var asyncLayer = layer as IAsyncCacheLayer;
if (await asyncLayer.IsAvailableAsync(cacheKey))
{
var cacheEntry = await asyncLayer.GetAsync<T>(cacheKey);
if (cacheEntry != default)
{
return cacheEntry;
}
}
}
}
return default;
}
[MethodImpl(MethodImplOptions.AggressiveInlining)]
private async ValueTask<(int LayerIndex, CacheEntry<T> CacheEntry)> GetWithLayerIndexAsync<T>(string cacheKey)
{
for (var layerIndex = 0; layerIndex < CacheLayers.Length; layerIndex++)
{
var layer = CacheLayers[layerIndex];
if (layer is ISyncCacheLayer syncLayer)
{
if (syncLayer.IsAvailable(cacheKey))
{
var cacheEntry = syncLayer.Get<T>(cacheKey);
if (cacheEntry != default)
{
return (layerIndex, cacheEntry);
}
}
}
else
{
var asyncLayer = layer as IAsyncCacheLayer;
if (await asyncLayer.IsAvailableAsync(cacheKey))
{
var cacheEntry = await asyncLayer.GetAsync<T>(cacheKey);
if (cacheEntry != default)
{
return (layerIndex, cacheEntry);
}
}
}
}
return default;
}
public async ValueTask<T> GetOrSetAsync<T>(string cacheKey, Func<T, Task<T>> getter, CacheSettings settings)
{
ThrowIfDisposed();
if (cacheKey == null)
{
throw new ArgumentNullException(nameof(cacheKey));
}
if (getter == null)
{
throw new ArgumentNullException(nameof(getter));
}
var cacheEntryPoint = await GetWithLayerIndexAsync<T>(cacheKey);
if (cacheEntryPoint != default)
{
var cacheEntry = cacheEntryPoint.CacheEntry;
var currentTime = DateTime.UtcNow;
if (cacheEntry.GetStaleDate(settings) < currentTime)
{
if (cacheEntry.Expiry < currentTime)
{
//Refresh the value in the current thread though short circuit if we're unable to establish a lock
//If the lock isn't established, it will instead use the stale cache entry (even if past the allowed stale period)
var refreshedCacheEntry = await RefreshValueAsync(cacheKey, getter, settings, waitForRefresh: false);
if (refreshedCacheEntry != default)
{
cacheEntry = refreshedCacheEntry;
}
}
else
{
//Refresh the value in the background
_ = RefreshValueAsync(cacheKey, getter, settings, waitForRefresh: false);
}
}
else if (cacheEntryPoint.LayerIndex > 0)
{
//If a lower-level cache is missing the latest data, attempt to set it in the background
_ = BackPopulateCacheAsync(cacheEntryPoint.LayerIndex, cacheKey, cacheEntry);
}
return cacheEntry.Value;
}
else
{
//Refresh the value in the current thread though because we have no old cache value, we have to lock and wait
return (await RefreshValueAsync(cacheKey, getter, settings, waitForRefresh: true)).Value;
}
}
private async ValueTask BackPopulateCacheAsync<T>(int fromIndexExclusive, string cacheKey, CacheEntry<T> cacheEntry)
{
ThrowIfDisposed();
var hasLock = false;
lock (WaitingKeyRefresh)
{
#if NETSTANDARD2_0
hasLock = !WaitingKeyRefresh.ContainsKey(cacheKey);
if (hasLock)
{
WaitingKeyRefresh[cacheKey] = Array.Empty<TaskCompletionSource<object>>();
}
#elif NETSTANDARD2_1
hasLock = WaitingKeyRefresh.TryAdd(cacheKey, Array.Empty<TaskCompletionSource<object>>());
#endif
}
if (hasLock)
{
try
{
for (; --fromIndexExclusive >= 0;)
{
var previousLayer = CacheLayers[fromIndexExclusive];
if (previousLayer is ISyncCacheLayer prevSyncLayer)
{
if (prevSyncLayer.IsAvailable(cacheKey))
{
prevSyncLayer.Set(cacheKey, cacheEntry);
}
}
else
{
var prevAsyncLayer = previousLayer as IAsyncCacheLayer;
if (await prevAsyncLayer.IsAvailableAsync(cacheKey))
{
await prevAsyncLayer.SetAsync(cacheKey, cacheEntry);
}
}
}
}
finally
{
UnlockWaitingTasks(cacheKey, cacheEntry);
}
}
}
private async ValueTask<CacheEntry<T>> RefreshValueAsync<T>(string cacheKey, Func<T, Task<T>> getter, CacheSettings settings, bool waitForRefresh)
{
ThrowIfDisposed();
var hasLock = false;
lock (WaitingKeyRefresh)
{
#if NETSTANDARD2_0
hasLock = !WaitingKeyRefresh.ContainsKey(cacheKey);
if (hasLock)
{
WaitingKeyRefresh[cacheKey] = Array.Empty<TaskCompletionSource<object>>();
}
#elif NETSTANDARD2_1
hasLock = WaitingKeyRefresh.TryAdd(cacheKey, Array.Empty<TaskCompletionSource<object>>());
#endif
}
if (hasLock)
{
try
{
return await Extensions.RefreshValueAsync(cacheKey, async () =>
{
var previousEntry = await GetAsync<T>(cacheKey);
var oldValue = default(T);
if (previousEntry != null)
{
oldValue = previousEntry.Value;
}
var value = await getter(oldValue);
var refreshedEntry = await SetAsync(cacheKey, value, settings.TimeToLive);
_ = Extensions.OnValueRefreshAsync(cacheKey, settings.TimeToLive);
UnlockWaitingTasks(cacheKey, refreshedEntry);
return refreshedEntry;
}, settings);
}
catch
{
UnlockWaitingTasks(cacheKey, null);
throw;
}
}
else if (waitForRefresh)
{
var delayedResultSource = new TaskCompletionSource<object>();
lock (WaitingKeyRefresh)
{
var waitList = new[] { delayedResultSource };
if (WaitingKeyRefresh.TryGetValue(cacheKey, out var oldList))
{
WaitingKeyRefresh[cacheKey] = oldList.Concat(waitList);
}
else
{
WaitingKeyRefresh[cacheKey] = waitList;
}
}
//Last minute check to confirm whether waiting is required
var currentEntry = await GetAsync<T>(cacheKey);
if (currentEntry != null && currentEntry.GetStaleDate(settings) > DateTime.UtcNow)
{
UnlockWaitingTasks(cacheKey, currentEntry);
return currentEntry;
}
//Lock until we are notified to be unlocked
var result = await delayedResultSource.Task;
return result as CacheEntry<T>;
}
return default;
}
private void UnlockWaitingTasks(string cacheKey, CacheEntry cacheEntry)
{
lock (WaitingKeyRefresh)
{
if (WaitingKeyRefresh.TryGetValue(cacheKey, out var waitingTasks))
{
WaitingKeyRefresh.Remove(cacheKey);
var tasks = waitingTasks.ToArray();
for (int i = 0, l = tasks.Length; i < l; i++)
{
tasks[i].TrySetResult(cacheEntry);
}
}
}
}
#if NETSTANDARD2_0
public void Dispose()
{
Dispose(true);
GC.SuppressFinalize(this);
}
protected virtual void Dispose(bool disposing)
{
if (Disposed)
{
return;
}
if (disposing)
{
foreach (var layer in CacheLayers)
{
if (layer is IDisposable disposable)
{
disposable.Dispose();
}
}
Extensions.Dispose();
}
Disposed = true;
}
#elif NETSTANDARD2_1
public async ValueTask DisposeAsync()
{
if (Disposed)
{
return;
}
foreach (var layer in CacheLayers)
{
if (layer is IDisposable disposableLayer)
{
disposableLayer.Dispose();
}
else if (layer is IAsyncDisposable asyncDisposableLayer)
{
await asyncDisposableLayer.DisposeAsync();
}
}
await Extensions.DisposeAsync();
Disposed = true;
}
#endif
}
}