/// <summary>
/// This method is used to keep incoming threads cycling while the first thread retrieves the entity from
/// the persistence store.
/// </summary>
/// <param name="cacheHolder">The current cache holder.</param>
/// <param name="traceId">The resource traceid</param>
/// <param name="status">The final status.</param>
/// <returns></returns>
private void Gatekeeper(EntityCacheHolder <K, E> cacheHolder, Guid traceId, out ResourceRequestResult status, int attempts = 5)
{
int retryStart = Environment.TickCount;
while (cacheHolder.State != EntityCacheHolderState.Completed && --attempts > 0)
{
cacheHolder.Wait();
mResourceConsumer.Retry(traceId, retryStart, ResourceRetryReason.Timeout);
retryStart = Environment.TickCount;
}
if (cacheHolder.State == EntityCacheHolderState.Completed)
{
status = ResourceRequestResult.Success;
}
else if (attempts <= 0)
{
status = ResourceRequestResult.RetryExceeded;
}
else
{
status = ResourceRequestResult.TaskCancelled;
}
}
/// <summary>
/// This method retrieves the cache holder from the store. If the cache holder is not present then it
/// tries to retrieve it from the underlying store.
/// </summary>
/// <param name="key">The key to retrieve.</param>
/// <returns>The cache holder.</returns>
protected async Task <EntityCacheHolder <K, E> > TryGetCacheHolder(K key)
{
var traceId = mResourceConsumer.Start("TryGetCacheHolder", Guid.NewGuid());
ResourceRequestResult status = ResourceRequestResult.Unknown;
EntityCacheHolder <K, E> cacheHolder;
int start = StatisticsInternal.ActiveIncrement();
try
{
while (true)
{
int retryStart = Environment.TickCount;
//Get the cache holder, and if it already exists, see if you need to wait.
if (!mEntities.TryGetValue(key, out cacheHolder))
{
var temp = new EntityCacheHolder <K, E>(key, Policy.EntityDefaultTTL);
if (mEntities.TryAdd(key, temp))
{
//Ok, the entity is not in the cache, so let's go and get the entity.
cacheHolder = temp;
break;
}
}
else
{
Gatekeeper(cacheHolder, traceId, out status);
return(cacheHolder);
}
mResourceConsumer.Retry(traceId, retryStart, ResourceRetryReason.Timeout);
}
try
{
//Ok, read the entity
var result = await Read(key);
if (result != null && !result.IsFaulted && (result.ResponseCode == 200 || result.ResponseCode == 404))
{
cacheHolder.Load(result.Entity, result.ResponseCode);
status = ResourceRequestResult.Success;
}
else
{
cacheHolder.Cancel();
status = ResourceRequestResult.TaskCancelled;
}
}
catch (Exception ex)
{
cacheHolder.Cancel();
status = ResourceRequestResult.TaskCancelled;
Collector?.LogException(string.Format("Error requesting {0} - {1} ", typeof(E).Name, key.ToString()), ex);
}
finally
{
if (cacheHolder.State == EntityCacheHolderState.Cancelled)
{
mEntities.TryRemove(key, out cacheHolder);
}
//Make sure that any waiting requests are released.
cacheHolder.Release();
}
}
finally
{
StatisticsInternal.ActiveDecrement(start);
if (status != ResourceRequestResult.Success)
{
StatisticsInternal.ErrorIncrement();
}
mResourceConsumer.End(traceId, start, status);
}
return(cacheHolder);
}