// This method looks up whether there's a request in progress for the given key. If there is, it returns that ongoing request's task.
// Otherwise, it triggers a new request by calling the supplied send(), tracks it in RequestsInProgress, and returns that ongoing request task.
// Once send() is done, it removes it from the list of RequestsInProgress.
private async Task <object> GroupRequestsIfNeeded(IMethodCachingSettings settings, string key, string[] metricsKeys, Func <Task <object> > send)
{
if (settings.RequestGroupingBehavior == RequestGroupingBehavior.Disabled)
{
Misses.Mark(metricsKeys);
return(await send());
}
else
{
JoinedTeam.Mark(metricsKeys);
return(await RequestsInProgress.GetOrAdd(key, _ => new Lazy <Task <object> >(async() =>
{
Misses.Mark(metricsKeys);
try { return await send(); }
finally { RequestsInProgress.TryRemove(key, out var _); }
})).Value);
}
}
private Task <object> GetOrAdd(string key, Func <Task <object> > factory, CacheItemPolicyEx policy, string[] metricsKeys, Type taskResultType)
{
Func <bool, Task <object> > wrappedFactory = async removeOnException =>
{
try
{
var result = await factory().ConfigureAwait(false);
//Can happen if item removed before task is completed
if (MemoryCache.Contains(key))
{
var revocableResult = result as IRevocable;
if (revocableResult?.RevokeKeys != null)
{
foreach (var revokeKey in revocableResult.RevokeKeys)
{
var cacheKeys = RevokeKeyToCacheKeysIndex.GetOrAdd(revokeKey, k => new HashSet <string>());
lock (cacheKeys)
{
cacheKeys.Add(key);
}
}
}
}
AwaitingResult.Decrement(metricsKeys);
return(result);
}
catch
{
if (removeOnException)
{
MemoryCache.Remove(key); // Do not cache exceptions.
}
AwaitingResult.Decrement(metricsKeys);
Failed.Mark(metricsKeys);
throw;
}
};
var newItem = new AsyncCacheItem();
Task <object> resultTask;
// Taking a lock on the newItem in case it actually becomes the item in the cache (if no item with that key
// existed). For another thread, it will be returned into the existingItem variable and will block on the
// second lock, preventing concurrent mutation of the same object.
lock (newItem.Lock)
{
if (typeof(IRevocable).IsAssignableFrom(taskResultType))
{
policy.RemovedCallback += ItemRemovedCallback;
}
// Surprisingly, when using MemoryCache.AddOrGetExisting() where the item doesn't exist in the cache,
// null is returned.
var existingItem = (AsyncCacheItem)MemoryCache.AddOrGetExisting(key, newItem, policy);
if (existingItem == null)
{
Misses.Mark(metricsKeys);
AwaitingResult.Increment(metricsKeys);
newItem.CurrentValueTask = wrappedFactory(true);
newItem.NextRefreshTime = DateTime.UtcNow + policy.RefreshTime;
resultTask = newItem.CurrentValueTask;
}
else
{
// This lock makes sure we're not mutating the same object as was added to the cache by an earlier
// thread (which was the first to add from 'newItem', for subsequent threads it will be 'existingItem').
lock (existingItem.Lock)
{
resultTask = existingItem.CurrentValueTask;
// Start refresh if an existing refresh ins't in progress and we've passed the next refresh time.
if (existingItem.RefreshTask == null && DateTime.UtcNow >= existingItem.NextRefreshTime)
{
existingItem.RefreshTask = ((Func <Task>)(async() =>
{
try
{
var getNewValue = wrappedFactory(false);
await getNewValue.ConfigureAwait(false);
existingItem.CurrentValueTask = getNewValue;
existingItem.NextRefreshTime = DateTime.UtcNow + policy.RefreshTime;
existingItem.RefreshTask = null;
MemoryCache.Set(new CacheItem(key, existingItem), policy);
}
catch
{
existingItem.NextRefreshTime = DateTime.UtcNow + policy.FailedRefreshDelay;
existingItem.RefreshTask = null;
}
})).Invoke();
}
}
if (resultTask.GetAwaiter().IsCompleted)
{
Hits.Mark(metricsKeys);
}
else
{
JoinedTeam.Mark(metricsKeys);
}
}
}
return(resultTask);
}
private Task <object> GetOrAdd(string key, Func <Task <object> > factory, CacheItemPolicyEx policy, string groupName, string logData, string[] metricsKeys, Type taskResultType)
{
var shouldLog = ShouldLog(groupName);
async Task <object> WrappedFactory(bool removeOnException)
{
try
{
if (shouldLog)
{
Log.Info(x => x("Cache item is waiting for value to be resolved", unencryptedTags: new
{
cacheKey = key,
cacheGroup = groupName,
cacheData = logData
}));
}
var result = await factory().ConfigureAwait(false);
if (shouldLog)
{
Log.Info(x => x("Cache item value is resolved", unencryptedTags: new
{
cacheKey = key,
cacheGroup = groupName,
cacheData = logData,
value = GetValueForLogging(result)
}));
}
//Can happen if item removed before task is completed
if (MemoryCache.Contains(key))
{
var revocableResult = result as IRevocable;
if (revocableResult?.RevokeKeys != null)
{
foreach (var revokeKey in revocableResult.RevokeKeys)
{
var cacheKeys = RevokeKeyToCacheKeysIndex.GetOrAdd(revokeKey, k => new HashSet <string>());
lock (cacheKeys)
{
cacheKeys.Add(key);
}
Log.Info(x => x("RevokeKey added to reverse index", unencryptedTags: new
{
revokeKey = revokeKey,
cacheKey = key,
cacheGroup = groupName,
cacheData = logData
}));
}
}
}
AwaitingResult.Decrement(metricsKeys);
return(result);
}
catch (Exception exception)
{
Log.Info(x => x("Error resolving value for cache item", unencryptedTags: new
{
cacheKey = key,
cacheGroup = groupName,
cacheData = logData,
removeOnException,
errorMessage = exception.Message
}));
if (removeOnException)
{
MemoryCache.Remove(key); // Do not cache exceptions.
}
AwaitingResult.Decrement(metricsKeys);
Failed.Mark(metricsKeys);
throw;
}
}
var newItem = shouldLog ?
new AsyncCacheItem {
GroupName = string.Intern(groupName), LogData = logData
} :
new AsyncCacheItem(); // if log is not needed, then do not cache unnecessary details which will blow up the memory
Task <object> resultTask;
// Taking a lock on the newItem in case it actually becomes the item in the cache (if no item with that key
// existed). For another thread, it will be returned into the existingItem variable and will block on the
// second lock, preventing concurrent mutation of the same object.
lock (newItem.Lock)
{
if (typeof(IRevocable).IsAssignableFrom(taskResultType))
{
policy.RemovedCallback += ItemRemovedCallback;
}
// Surprisingly, when using MemoryCache.AddOrGetExisting() where the item doesn't exist in the cache,
// null is returned.
var existingItem = (AsyncCacheItem)MemoryCache.AddOrGetExisting(key, newItem, policy);
if (existingItem == null)
{
Misses.Mark(metricsKeys);
AwaitingResult.Increment(metricsKeys);
newItem.CurrentValueTask = WrappedFactory(true);
newItem.NextRefreshTime = DateTime.UtcNow + policy.RefreshTime;
resultTask = newItem.CurrentValueTask;
if (shouldLog)
{
Log.Info(x => x("Item added to cache", unencryptedTags: new
{
cacheKey = key,
cacheGroup = groupName,
cacheData = logData
}));
}
}
else
{
// This lock makes sure we're not mutating the same object as was added to the cache by an earlier
// thread (which was the first to add from 'newItem', for subsequent threads it will be 'existingItem').
lock (existingItem.Lock)
{
resultTask = existingItem.CurrentValueTask;
// Start refresh if an existing refresh ins't in progress and we've passed the next refresh time.
if (existingItem.RefreshTask?.IsCompleted != false && DateTime.UtcNow >= existingItem.NextRefreshTime)
{
existingItem.RefreshTask = ((Func <Task>)(async() =>
{
try
{
var getNewValue = WrappedFactory(false);
await getNewValue.ConfigureAwait(false);
existingItem.CurrentValueTask = getNewValue;
existingItem.NextRefreshTime = DateTime.UtcNow + policy.RefreshTime;
MemoryCache.Set(new CacheItem(key, existingItem), policy);
}
catch
{
existingItem.NextRefreshTime = DateTime.UtcNow + policy.FailedRefreshDelay;
}
})).Invoke();
}
}
if (resultTask.GetAwaiter().IsCompleted)
{
Hits.Mark(metricsKeys);
}
else
{
JoinedTeam.Mark(metricsKeys);
}
}
}
return(resultTask);
}