/// <summary>
/// Read a value from the cache
/// </summary>
/// <typeparam name="T">Type to read</typeparam>
/// <param name="key">Key</param>
/// <param name="value">Value</param>
/// <param name="notFound">Create T if not found, null to not do this. Item1 = value, Item2 = expiration.</param>
public async Task <CachedItem <T> > Get <T>(string key, Func <Task <CachedItem <T> > > notFound) where T : class
{
using (var lockRead = cacheTimerLock.LockRead())
{
if (cache.TryGetValue(key, out KeyValuePair <DateTime, object> cacheValue))
{
return(new CachedItem <T>((T)cacheValue.Value, cacheValue.Key));
}
}
// most likely the callback needs to make a network request, so don't do it in a lock
// it's ok if multiple calls stack on the same cache key, the last one to finish will win
CachedItem <T> newItem = await notFound();
// don't add null values to the cache
if (newItem.Value != null)
{
using (var lockWrite = cacheTimerLock.LockWrite())
{
cache[key] = new KeyValuePair <DateTime, object>(newItem.Expiration, newItem.Value);
}
}
return(newItem);
}
