.Net Core 缓存方式（一）内存缓存
.Net Core 缓存方式（一）内存缓存
使用 IMemoryCache
官方文档
MemoryCache/缓存
System.Runtime.Caching/MemoryCache (NuGet 包) 可用于：
.NET Standard 2.0 或更高版本。
面向 .NET Standard 2.0 或更高版本的任何.net 实现。 例如，ASP.NET Core 2.0 或更高版本。
.NET Framework 4.5 或更高版本。
Microsoft.Extensions.Caching.Memory / IMemoryCache 建议使用 (本文中所述) ， System.Runtime.Caching / MemoryCache 因为它更好地集成到 ASP.NET Core 中。 例如， IMemoryCache 使用 ASP.NET Core依赖关系注入本身工作。
将 System.Runtime.Caching / MemoryCache ASP.NET 4.x 中的代码移植到 ASP.NET Core 时，请使用作为兼容性桥。
- 使用包
dotnet add package System.Runtime.Caching --version 4.7.0 - 使用方式
public class HomeController : Controller
{
private IMemoryCache _cache;
public HomeController(IMemoryCache memoryCache)
{
_cache = memoryCache;
}
public IActionResult CacheTryGetValueSet()
{
DateTime cacheEntry;
// Look for cache key.
if (!_cache.TryGetValue(CacheKeys.Entry, out cacheEntry))
{
// Key not in cache, so get data.
cacheEntry = DateTime.Now;
// Set cache options.
var cacheEntryOptions = new MemoryCacheEntryOptions()
// Keep in cache for this time, reset time if accessed.
.SetSlidingExpiration(TimeSpan.FromSeconds(3));
// Save data in cache.
_cache.Set(CacheKeys.Entry, cacheEntry, cacheEntryOptions);
}
return View("Cache", cacheEntry);
}
public IActionResult CacheGetOrCreate()
{
var cacheEntry = _cache.GetOrCreate(CacheKeys.Entry, entry =>
{
entry.SlidingExpiration = TimeSpan.FromSeconds(3);
return DateTime.Now;
});
return View("Cache", cacheEntry);
}
public async Task<IActionResult> CacheGetOrCreateAsynchronous()
{
var cacheEntry = await
_cache.GetOrCreateAsync(CacheKeys.Entry, entry =>
{
entry.SlidingExpiration = TimeSpan.FromSeconds(3);
return Task.FromResult(DateTime.Now);
});
return View("Cache", cacheEntry);
}
GetOrCreate 实现原理
public static TItem GetOrCreate<TItem>(this IMemoryCache cache, object key, Func<ICacheEntry, TItem> factory)
{
if (!cache.TryGetValue(key, out object result))
{
ICacheEntry entry = cache.CreateEntry(key);
result = factory(entry);
entry.SetValue(result);
// need to manually call dispose instead of having a using
// in case the factory passed in throws, in which case we
// do not want to add the entry to the cache
entry.Dispose();
}
return (TItem)result;
}
public static async Task<TItem> GetOrCreateAsync<TItem>(this IMemoryCache cache, object key, Func<ICacheEntry, Task<TItem>> factory)
{
if (!cache.TryGetValue(key, out object result))
{
ICacheEntry entry = cache.CreateEntry(key);
result = await factory(entry).ConfigureAwait(false);
entry.SetValue(result);
// need to manually call dispose instead of having a using
// in case the factory passed in throws, in which case we
// do not want to add the entry to the cache
entry.Dispose();
}
return (TItem)result;
}
// Licensed to the .NET Foundation under one or more agreements.
// The .NET Foundation licenses this file to you under the MIT license.
using System;
using System.Collections.Concurrent;
using System.Collections.Generic;
using System.Linq;
using System.Threading;
using System.Threading.Tasks;
using Microsoft.Extensions.Internal;
using Microsoft.Extensions.Logging;
using Microsoft.Extensions.Logging.Abstractions;
using Microsoft.Extensions.Options;
namespace Microsoft.Extensions.Caching.Memory
{
/// <summary>
/// An implementation of <see cref="IMemoryCache"/> using a dictionary to
/// store its entries.
/// </summary>
public class MemoryCache : IMemoryCache
{
private readonly ConcurrentDictionary<object, CacheEntry> _entries;
private long _cacheSize;
private bool _disposed;
private readonly ILogger _logger;
// We store the delegates locally to prevent allocations
// every time a new CacheEntry is created.
private readonly Action<CacheEntry> _setEntry;
private readonly Action<CacheEntry> _entryExpirationNotification;
private readonly MemoryCacheOptions _options;
private DateTimeOffset _lastExpirationScan;
/// <summary>
/// Creates a new <see cref="MemoryCache"/> instance.
/// </summary>
/// <param name="optionsAccessor">The options of the cache.</param>
public MemoryCache(IOptions<MemoryCacheOptions> optionsAccessor)
: this(optionsAccessor, NullLoggerFactory.Instance) { }
/// <summary>
/// Creates a new <see cref="MemoryCache"/> instance.
/// </summary>
/// <param name="optionsAccessor">The options of the cache.</param>
/// <param name="loggerFactory">The factory used to create loggers.</param>
public MemoryCache(IOptions<MemoryCacheOptions> optionsAccessor, ILoggerFactory loggerFactory)
{
if (optionsAccessor == null)
{
throw new ArgumentNullException(nameof(optionsAccessor));
}
if (loggerFactory == null)
{
throw new ArgumentNullException(nameof(loggerFactory));
}
_options = optionsAccessor.Value;
_logger = loggerFactory.CreateLogger<MemoryCache>();
_entries = new ConcurrentDictionary<object, CacheEntry>();
_setEntry = SetEntry;
_entryExpirationNotification = EntryExpired;
if (_options.Clock == null)
{
_options.Clock = new SystemClock();
}
_lastExpirationScan = _options.Clock.UtcNow;
}
/// <summary>
/// Cleans up the background collection events.
/// </summary>
~MemoryCache()
{
Dispose(false);
}
/// <summary>
/// Gets the count of the current entries for diagnostic purposes.
/// </summary>
public int Count
{
get { return _entries.Count; }
}
// internal for testing
internal long Size { get => Interlocked.Read(ref _cacheSize); }
private ICollection<KeyValuePair<object, CacheEntry>> EntriesCollection => _entries;
/// <inheritdoc />
public ICacheEntry CreateEntry(object key)
{
CheckDisposed();
ValidateCacheKey(key);
return new CacheEntry(
key,
_setEntry,
_entryExpirationNotification,
_logger
);
}
private void SetEntry(CacheEntry entry)
{
if (_disposed)
{
// No-op instead of throwing since this is called during CacheEntry.Dispose
return;
}
if (_options.SizeLimit.HasValue && !entry.Size.HasValue)
{
throw new InvalidOperationException($"Cache entry must specify a value for {nameof(entry.Size)} when {nameof(_options.SizeLimit)} is set.");
}
DateTimeOffset utcNow = _options.Clock.UtcNow;
DateTimeOffset? absoluteExpiration = null;
if (entry._absoluteExpirationRelativeToNow.HasValue)
{
absoluteExpiration = utcNow + entry._absoluteExpirationRelativeToNow;
}
else if (entry._absoluteExpiration.HasValue)
{
absoluteExpiration = entry._absoluteExpiration;
}
// Applying the option's absolute expiration only if it's not already smaller.
// This can be the case if a dependent cache entry has a smaller value, and
// it was set by cascading it to its parent.
if (absoluteExpiration.HasValue)
{
if (!entry._absoluteExpiration.HasValue || absoluteExpiration.Value < entry._absoluteExpiration.Value)
{
entry._absoluteExpiration = absoluteExpiration;
}
}
// Initialize the last access timestamp at the time the entry is added
entry.LastAccessed = utcNow;
if (_entries.TryGetValue(entry.Key, out CacheEntry priorEntry))
{
priorEntry.SetExpired(EvictionReason.Replaced);
}
bool exceedsCapacity = UpdateCacheSizeExceedsCapacity(entry);
if (!entry.CheckExpired(utcNow) && !exceedsCapacity)
{
bool entryAdded = false;
if (priorEntry == null)
{
// Try to add the new entry if no previous entries exist.
entryAdded = _entries.TryAdd(entry.Key, entry);
}
else
{
// Try to update with the new entry if a previous entries exist.
entryAdded = _entries.TryUpdate(entry.Key, entry, priorEntry);
if (entryAdded)
{
if (_options.SizeLimit.HasValue)
{
// The prior entry was removed, decrease the by the prior entry's size
Interlocked.Add(ref _cacheSize, -priorEntry.Size.Value);
}
}
else
{
// The update will fail if the previous entry was removed after retrival.
// Adding the new entry will succeed only if no entry has been added since.
// This guarantees removing an old entry does not prevent adding a new entry.
entryAdded = _entries.TryAdd(entry.Key, entry);
}
}
if (entryAdded)
{
entry.AttachTokens();
}
else
{
if (_options.SizeLimit.HasValue)
{
// Entry could not be added, reset cache size
Interlocked.Add(ref _cacheSize, -entry.Size.Value);
}
entry.SetExpired(EvictionReason.Replaced);
entry.InvokeEvictionCallbacks();
}
if (priorEntry != null)
{
priorEntry.InvokeEvictionCallbacks();
}
}
else
{
if (exceedsCapacity)
{
// The entry was not added due to overcapacity
entry.SetExpired(EvictionReason.Capacity);
TriggerOvercapacityCompaction();
}
else
{
if (_options.SizeLimit.HasValue)
{
// Entry could not be added due to being expired, reset cache size
Interlocked.Add(ref _cacheSize, -entry.Size.Value);
}
}
entry.InvokeEvictionCallbacks();
if (priorEntry != null)
{
RemoveEntry(priorEntry);
}
}
StartScanForExpiredItems(utcNow);
}
/// <inheritdoc />
public bool TryGetValue(object key, out object result)
{
ValidateCacheKey(key);
CheckDisposed();
result = null;
DateTimeOffset utcNow = _options.Clock.UtcNow;
bool found = false;
if (_entries.TryGetValue(key, out CacheEntry entry))
{
// Check if expired due to expiration tokens, timers, etc. and if so, remove it.
// Allow a stale Replaced value to be returned due to concurrent calls to SetExpired during SetEntry.
if (entry.CheckExpired(utcNow) && entry.EvictionReason != EvictionReason.Replaced)
{
// TODO: For efficiency queue this up for batch removal
RemoveEntry(entry);
}
else
{
found = true;
entry.LastAccessed = utcNow;
result = entry.Value;
// When this entry is retrieved in the scope of creating another entry,
// that entry needs a copy of these expiration tokens.
entry.PropagateOptions(CacheEntryHelper.Current);
}
}
StartScanForExpiredItems(utcNow);
return found;
}
/// <inheritdoc />
public void Remove(object key)
{
if (key == null)
{
throw new ArgumentNullException(nameof(key));
}
CheckDisposed();
if (_entries.TryRemove(key, out CacheEntry entry))
{
if (_options.SizeLimit.HasValue)
{
Interlocked.Add(ref _cacheSize, -entry.Size.Value);
}
entry.SetExpired(EvictionReason.Removed);
entry.InvokeEvictionCallbacks();
}
StartScanForExpiredItems();
}
private void RemoveEntry(CacheEntry entry)
{
if (EntriesCollection.Remove(new KeyValuePair<object, CacheEntry>(entry.Key, entry)))
{
if (_options.SizeLimit.HasValue)
{
Interlocked.Add(ref _cacheSize, -entry.Size.Value);
}
entry.InvokeEvictionCallbacks();
}
}
private void EntryExpired(CacheEntry entry)
{
// TODO: For efficiency consider processing these expirations in batches.
RemoveEntry(entry);
StartScanForExpiredItems();
}
// Called by multiple actions to see how long it's been since we last checked for expired items.
// If sufficient time has elapsed then a scan is initiated on a background task.
private void StartScanForExpiredItems(DateTimeOffset? utcNow = null)
{
// Since fetching time is expensive, minimize it in the hot paths
DateTimeOffset now = utcNow ?? _options.Clock.UtcNow;
if (_options.ExpirationScanFrequency < now - _lastExpirationScan)
{
_lastExpirationScan = now;
Task.Factory.StartNew(state => ScanForExpiredItems((MemoryCache)state), this,
CancellationToken.None, TaskCreationOptions.DenyChildAttach, TaskScheduler.Default);
}
}
private static void ScanForExpiredItems(MemoryCache cache)
{
DateTimeOffset now = cache._options.Clock.UtcNow;
foreach (CacheEntry entry in cache._entries.Values)
{
if (entry.CheckExpired(now))
{
cache.RemoveEntry(entry);
}
}
}
private bool UpdateCacheSizeExceedsCapacity(CacheEntry entry)
{
if (!_options.SizeLimit.HasValue)
{
return false;
}
long newSize = 0L;
for (int i = 0; i < 100; i++)
{
long sizeRead = Interlocked.Read(ref _cacheSize);
newSize = sizeRead + entry.Size.Value;
if (newSize < 0 || newSize > _options.SizeLimit)
{
// Overflow occurred, return true without updating the cache size
return true;
}
if (sizeRead == Interlocked.CompareExchange(ref _cacheSize, newSize, sizeRead))
{
return false;
}
}
return true;
}
private void TriggerOvercapacityCompaction()
{
_logger.LogDebug("Overcapacity compaction triggered");
// Spawn background thread for compaction
ThreadPool.QueueUserWorkItem(s => OvercapacityCompaction((MemoryCache)s), this);
}
private static void OvercapacityCompaction(MemoryCache cache)
{
long currentSize = Interlocked.Read(ref cache._cacheSize);
cache._logger.LogDebug($"Overcapacity compaction executing. Current size {currentSize}");
double? lowWatermark = cache._options.SizeLimit * (1 - cache._options.CompactionPercentage);
if (currentSize > lowWatermark)
{
cache.Compact(currentSize - (long)lowWatermark, entry => entry.Size.Value);
}
cache._logger.LogDebug($"Overcapacity compaction executed. New size {Interlocked.Read(ref cache._cacheSize)}");
}
/// Remove at least the given percentage (0.10 for 10%) of the total entries (or estimated memory?), according to the following policy:
/// 1. Remove all expired items.
/// 2. Bucket by CacheItemPriority.
/// 3. Least recently used objects.
/// ?. Items with the soonest absolute expiration.
/// ?. Items with the soonest sliding expiration.
/// ?. Larger objects - estimated by object graph size, inaccurate.
public void Compact(double percentage)
{
int removalCountTarget = (int)(_entries.Count * percentage);
Compact(removalCountTarget, _ => 1);
}
private void Compact(long removalSizeTarget, Func<CacheEntry, long> computeEntrySize)
{
var entriesToRemove = new List<CacheEntry>();
var lowPriEntries = new List<CacheEntry>();
var normalPriEntries = new List<CacheEntry>();
var highPriEntries = new List<CacheEntry>();
long removedSize = 0;
// Sort items by expired & priority status
DateTimeOffset now = _options.Clock.UtcNow;
foreach (CacheEntry entry in _entries.Values)
{
if (entry.CheckExpired(now))
{
entriesToRemove.Add(entry);
removedSize += computeEntrySize(entry);
}
else
{
switch (entry.Priority)
{
case CacheItemPriority.Low:
lowPriEntries.Add(entry);
break;
case CacheItemPriority.Normal:
normalPriEntries.Add(entry);
break;
case CacheItemPriority.High:
highPriEntries.Add(entry);
break;
case CacheItemPriority.NeverRemove:
break;
default:
throw new NotSupportedException("Not implemented: " + entry.Priority);
}
}
}
ExpirePriorityBucket(ref removedSize, removalSizeTarget, computeEntrySize, entriesToRemove, lowPriEntries);
ExpirePriorityBucket(ref removedSize, removalSizeTarget, computeEntrySize, entriesToRemove, normalPriEntries);
ExpirePriorityBucket(ref removedSize, removalSizeTarget, computeEntrySize, entriesToRemove, highPriEntries);
foreach (CacheEntry entry in entriesToRemove)
{
RemoveEntry(entry);
}
}
/// Policy:
/// 1. Least recently used objects.
/// ?. Items with the soonest absolute expiration.
/// ?. Items with the soonest sliding expiration.
/// ?. Larger objects - estimated by object graph size, inaccurate.
private void ExpirePriorityBucket(ref long removedSize, long removalSizeTarget, Func<CacheEntry, long> computeEntrySize, List<CacheEntry> entriesToRemove, List<CacheEntry> priorityEntries)
{
// Do we meet our quota by just removing expired entries?
if (removalSizeTarget <= removedSize)
{
// No-op, we've met quota
return;
}
// Expire enough entries to reach our goal
// TODO: Refine policy
// LRU
foreach (CacheEntry entry in priorityEntries.OrderBy(entry => entry.LastAccessed))
{
entry.SetExpired(EvictionReason.Capacity);
entriesToRemove.Add(entry);
removedSize += computeEntrySize(entry);
if (removalSizeTarget <= removedSize)
{
break;
}
}
}
public void Dispose()
{
Dispose(true);
}
protected virtual void Dispose(bool disposing)
{
if (!_disposed)
{
if (disposing)
{
GC.SuppressFinalize(this);
}
_disposed = true;
}
}
private void CheckDisposed()
{
if (_disposed)
{
throw new ObjectDisposedException(typeof(MemoryCache).FullName);
}
}
private static void ValidateCacheKey(object key)
{
if (key == null)
{
throw new ArgumentNullException(nameof(key));
}
}
}
}
