/// <inheritdoc />
public async Task <IHtmlContent> ProcessContentAsync(TagHelperOutput output, CacheTagKey key, DistributedCacheEntryOptions options)
{
IHtmlContent content = null;
while (content == null)
{
// Is there any request already processing the value?
if (!_workers.TryGetValue(key, out var result))
{
// There is a small race condition here between TryGetValue and TryAdd that might cause the
// content to be computed more than once. We don't care about this race as the probability of
// happening is very small and the impact is not critical.
var tcs = new TaskCompletionSource <IHtmlContent>(creationOptions: TaskCreationOptions.RunContinuationsAsynchronously);
_workers.TryAdd(key, tcs.Task);
try
{
var serializedKey = Encoding.UTF8.GetBytes(key.GenerateKey());
var storageKey = key.GenerateHashedKey();
var value = await _storage.GetAsync(storageKey);
if (value == null)
{
// The value is not cached, we need to render the tag helper output
var processedContent = await output.GetChildContentAsync();
var stringBuilder = new StringBuilder();
using (var writer = new StringWriter(stringBuilder))
{
processedContent.WriteTo(writer, _htmlEncoder);
}
var formattingContext = new DistributedCacheTagHelperFormattingContext
{
Html = new HtmlString(stringBuilder.ToString())
};
// Then cache the result
value = await _formatter.SerializeAsync(formattingContext);
var encodeValue = Encode(value, serializedKey);
await _storage.SetAsync(storageKey, encodeValue, options);
content = formattingContext.Html;
}
else
{
// The value was found in the storage, decode and ensure
// there is no cache key hash collision
byte[] decodedValue = Decode(value, serializedKey);
try
{
if (decodedValue != null)
{
content = await _formatter.DeserializeAsync(decodedValue);
}
}
catch (Exception e)
{
_logger.DistributedFormatterDeserializationException(storageKey, e);
}
finally
{
// If the deserialization fails the content is rendered
if (content == null)
{
content = await output.GetChildContentAsync();
}
}
}
}
catch
{
content = null;
throw;
}
finally
{
// Remove the worker task before setting the result.
// If the result is null, other threads would potentially
// acquire it otherwise.
_workers.TryRemove(key, out result);
// Notify all other awaiters to render the content
tcs.TrySetResult(content);
}
}
else
{
content = await result;
}
}
return(content);
}
