private Task OnRevoke(string revokeKey)
{
if (revokeKey == null)
{
throw new ArgumentNullException();
}
RecentRevokesCache.RegisterRevokeKey(revokeKey, DateTime.UtcNow);
var revokeApplied = false;
if (RevokeKeyToCacheItemsIndex.TryGetValue(revokeKey, out var _))
{
lock (RevokeKeyToCacheItemsIndex)
if (RevokeKeyToCacheItemsIndex.TryGetValue(revokeKey, out var hash))
{
foreach (var item in hash)
{
item.IsRevoked = true;
}
revokeApplied = true;
}
}
if (revokeApplied)
{
Revokes.Meter("Succeeded", Unit.Events).Mark();
Log.Debug(x => x("Revoke applied", unencryptedTags: new { revokeKey }));
}
else
{
Revokes.Meter("Discarded", Unit.Events).Mark();
}
return(Task.CompletedTask);
}
private void CacheResponse(string cacheKey, DateTime requestSendTime, Task <object> responseTask, IMethodCachingSettings settings)
{
var cacheItem = new AsyncCacheItem
{
NextRefreshTime = DateTime.UtcNow + settings.RefreshTime.Value,
Value = responseTask,
};
// Register each revoke key in the response with the reverse index, if the response is not an exception and is a Revocable<>.
// Starting from now, the IsRevoked property in cacheItem might be set to true by another thread in OnRevoked().
var revokeKeys = ExtarctRevokeKeys(responseTask);
if (revokeKeys.Any())
{
lock (RevokeKeyToCacheItemsIndex)
foreach (var revokeKey in revokeKeys)
{
RevokeKeyToCacheItemsIndex.GetOrAdd(revokeKey, _ => new HashSet <AsyncCacheItem>()).Add(cacheItem);
}
}
// Check if we got a revoke message from one of the revoke keys in the response while the request was in progress.
// Do this AFTER the above, so there's no point in time that we don't monitor cache revokes
var recentlyRevokedKey = revokeKeys.FirstOrDefault(rk => RecentRevokesCache.TryGetRecentlyRevokedTime(rk, requestSendTime) != null);
if (recentlyRevokedKey != null)
{
Items.Meter("RevokeRaceCondition", Unit.Items).Mark();
Log.Warn(x => x("Got revoke during request, marking as stale", unencryptedTags: new
{
revokeKey = recentlyRevokedKey,
requestSendTime,
cacheKey,
revokeTime = RecentRevokesCache.TryGetRecentlyRevokedTime(recentlyRevokedKey, requestSendTime)
}));
cacheItem.IsRevoked = true;
}
// Set the MemoryCache policy based on our caching settings. If the response has no revoke keys, no need to receive a callback
// event when it's removed from the cache since we don't need to remove it from the reverse index.
var cacheItemPolicy = new CacheItemPolicy {
};
if (settings.ExpirationBehavior == ExpirationBehavior.ExtendExpirationWhenReadFromCache)
{
cacheItemPolicy.SlidingExpiration = settings.ExpirationTime.Value;
}
else
{
cacheItemPolicy.AbsoluteExpiration = DateTime.UtcNow + settings.ExpirationTime.Value;
}
if (revokeKeys.Any())
{
cacheItemPolicy.RemovedCallback += ItemRemovedCallback;
}
// Store the response in the main cache. Note that this will trigger a removal of a currently-cached value, if any,
// i.e. call ItemRemovedCallback() with Reason=Removed.
MemoryCache.Set(new CacheItem(cacheKey, cacheItem), cacheItemPolicy);
}
// This method has one of 5 possible outcomes:
//
// 1. We got a response from the service (null, not null or an exception) and the caching settings dictate that we should cache it:
// We cache it with the default RefreshTime. This extends the ExpirationTime as well.
//
// 2. The caching settings dictate that the response shouldn't be cached, and should be ignored, and currentValue != null :
// We return the currentValue and set its next refresh time to be now + FailedRefreshDelay so we don't "attack" the target service
//
// 3. The caching settings dictate that the response should not be cached, and should be ignored, and currentValue == null :
// We return the response anyway, since we don't have a previously-good value
//
// 4. The caching settings dictate that the response shouldn't be cached, nor ignored and removed from cache:
// We return the response and remove the previously-cached response from the cache
//
// 5. The caching settings dictate that the response shouldn't be cached, nor ignored and remain in cache:
// We return the response
private async Task <object> TryFetchNewValue(string cacheKey, Func <Task <object> > serviceMethod,
IMethodCachingSettings settings, string[] metricsKeys, CallReason callReason, AsyncCacheItem currentValue = null)
{
// We use the RecentRevokesCache to keep track of recent revoke messages that arrived, to detect if the response we're about
// to receive was revoked while in transit. It will track revoke messages as long as the task is not completed.
var requestSendTime = DateTime.UtcNow;
var tcs = new TaskCompletionSource <bool>();
RecentRevokesCache.RegisterOutgoingRequest(tcs.Task, requestSendTime);
// We capture the response from the service here, including if it was an exception
var(response, responseKind) = await CallService(serviceMethod, metricsKeys);
string outcome = null;
// Outcome #1: Cache the response
if (settings.ResponseKindsToCache.HasFlag(responseKind))
{
outcome = "cached";
CacheResponse(cacheKey, requestSendTime, response, settings);
}
else if (settings.ResponseKindsToIgnore.HasFlag(responseKind))
{
// Outcome #2: Leave old response cached and return it, and set its refresh time to the (short) FailedRefreshDelay
if (currentValue != null)
{
outcome = "ignored_cachedValueExist";
currentValue.NextRefreshTime = DateTime.UtcNow + settings.FailedRefreshDelay.Value;
response = currentValue.Value;
}
// Outcome #3: We don't have currentValue, so we cant ignore response and we return it
else
{
outcome = "ignored_cachedValueDoesNotExist";
}
}
else //Dont cache and dont ignore (i.e. return it)
{
outcome = "notCachedNotIgnored";
// Outcome #4: Do not cache response and return it; remove previously-cached value (if exist)
if (settings.NotIgnoredResponseBehavior == NotIgnoredResponseBehavior.RemoveCachedResponse)
{
if (MemoryCache.Remove(cacheKey) != null)
{
outcome = "notCachedNotIgnored_cachedValueRemoved";
}
}
// Outcome #5: Do not cache response and return it; leave old response cached
// If old response is not null, set its refresh time to the (short) FailedRefreshDelay
else if (currentValue != null)
{
currentValue.NextRefreshTime = DateTime.UtcNow + settings.FailedRefreshDelay.Value;
}
}
Log.Debug(x => x("Service call", unencryptedTags: new { cacheKey, callReason, responseKind, outcome }));
tcs.SetResult(true); // RecentRevokesCache can stop tracking revoke keys
return(await response); // Might throw stored exception
}
