public async Task <string> getCachedMetadataAsync(Uri target, string id, CalcMetadataCallback computer)
{
// ensure the object is up to date
var data = await getCachedObjectAsync(target);
var metafn = data.Name + ".meta." + id;
string result;
if (finished_metadata.TryGetValue(metafn, out result))
{
return(result);
}
Task <string> pending;
if (!pending_metadata.TryGetValue(metafn, out pending))
{
pending = getMetadataToMemory(data, metafn, computer);
if (!pending.IsCompleted)
{
pending_metadata.Add(metafn, pending);
}
}
return(await pending);
}
private async Task <string> getMetadataToMemory(StorageFile data, string metafn, CalcMetadataCallback computer)
{
try
{
string result;
try
{
var file = await cache_directory.GetFileAsync(metafn);
result = await FileIO.ReadTextAsync(file, Windows.Storage.Streams.UnicodeEncoding.Utf8);
return(finished_metadata[metafn] = result);
}
catch (FileNotFoundException) { }
result = finished_metadata[metafn] = await computer(data);
StorageFile newfile = await cache_directory.CreateFileAsync(metafn, CreationCollisionOption.ReplaceExisting);
await FileIO.WriteTextAsync(newfile, result, Windows.Storage.Streams.UnicodeEncoding.Utf8);
return(result);
}
finally
{
pending_metadata.Remove(metafn);
}
}