/// <summary>
/// Declares the key is going to be computed.
/// It blocks the caller if there is another thread computing that key. When that other thread finishes,
/// this thread is released and returned false. the caller is expected to get the item from the cache
/// then (and caller must assume the object may be removed -unlikely but possible- by the time the caller tries to retrieve it).
/// If the method returns true, the caller to invoke "Complete" once it adds the element to the cache.
/// </summary>
/// <param name="key">The key.</param>
/// <returns><c>true</c> if true, the key doesn't have a value and is not being computed yet<c>false</c> otherwise.</returns>
public bool StartInflight(TKey key)
{
EventAndCount ev = null;
lock (this.inflight)
{
if (!this.inflight.TryGetValue(key, out ev))
{
this.inflight.Add(key, null);
}
else
{
if (ev == null)
{
ev = new EventAndCount();
this.inflight[key] = ev;
}
}
}
if (ev == null)
{
return(true);
}
ev.WaitAndReturnIfLast();
return(false);
}
/// <summary>
/// Completes the inflight operation to the specified key.
/// This method needs to be invoked right after the Add or TryAdd call if the caller invoked "Inflight".
/// </summary>
/// <param name="key">The key just added.</param>
/// <exception cref="System.InvalidOperationException">Complete was invoked without a corresponding Inflight call</exception>
public void CompleteInflight(TKey key)
{
lock (this.inflight)
{
EventAndCount ev = null;
if (!this.inflight.TryGetValue(key, out ev))
{
throw new InvalidOperationException("Complete was invoked without a corresponding Inflight call");
}
this.inflight.Remove(key);
// if anybody was waiting on this, now we tell them.
ev?.Set();
}
}
