| private Register ( System.Action callback, bool useSynchronizationContext ) : System.Threading.CancellationTokenRegistration | ||
| callback | System.Action | |
| useSynchronizationContext | bool | |
| return | System.Threading.CancellationTokenRegistration | |
/// <summary>
/// Registers a callback to be invoked when this CancellationToken is cancelled.
/// </summary>
/// <param name="callback">The action to be invoked.</param>
/// <returns>A registration object that can be used to deregister the callback.</returns>
public CancellationTokenRegistration Register(Action callback)
{
if (source != null)
{
return(source.Register(callback));
}
return(default(CancellationTokenRegistration));
}
public CancellationTokenRegistration Register(Action callback, bool useSynchronizationContext)
{
if (callback == null)
{
throw new ArgumentNullException(nameof(callback));
}
return(_source?.Register(callback, useSynchronizationContext) ?? new CancellationTokenRegistration());
}
public static Task<CancellationToken> FromTimeoutAsync(int millisecondsTimeout)
{
// Note that CancellationTokenSource constructor requires input to be >= -1,
// restricting millisecondsTimeout to be >= -1 would enforce that
if (millisecondsTimeout < -1)
{
throw new ArgumentOutOfRangeException("Invalid millisecondsTimeout value " + millisecondsTimeout);
}
uint currentTime = (uint)Environment.TickCount;
long targetTime = millisecondsTimeout + currentTime;
// round the targetTime up to the next closest 15ms
targetTime = ((targetTime + (COALESCING_SPAN_MS - 1)) / COALESCING_SPAN_MS) * COALESCING_SPAN_MS;
Task<CancellationToken> tokenTask;
if (!s_tokenCache.TryGetValue(targetTime, out tokenTask))
{
var tcs = new TaskCompletionSource<CancellationToken>();
// only a single thread may succeed adding its task into the cache
if (s_tokenCache.TryAdd(targetTime, tcs.Task))
{
// Since this thread was successful reserving a spot in the cache, it would be the only thread
// that construct the CancellationTokenSource
var token = new CancellationTokenSource((int)(targetTime - currentTime)).Token;
// Clean up cache when Token is canceled
token.Register(t => {
Task<CancellationToken> ignored;
s_tokenCache.TryRemove((long)t, out ignored);
}, targetTime);
// set the result so other thread may observe the token, and return
tcs.TrySetResult(token);
tokenTask = tcs.Task;
}
else
{
// for threads that failed when calling TryAdd, there should be one already in the cache
if (!s_tokenCache.TryGetValue(targetTime, out tokenTask))
{
// In unlikely scenario the token was already cancelled and timed out, we would not find it in cache.
// In this case we would simply create a non-coalsed token
tokenTask = Task.FromResult(new CancellationTokenSource(millisecondsTimeout).Token);
}
}
}
return tokenTask;
}
