/// <summary>
/// Disposes of the registration and unregisters the target callback from the associated
/// <see cref="T:System.Threading.CancellationToken">CancellationToken</see>.
/// If the target callback is currently executing this method will wait until it completes, except
/// in the degenerate cases where a callback method deregisters itself.
/// </summary>
public void Dispose()
{
// If the token source has been disposed, we must throw.
if (m_tokenSource != null)
{
m_tokenSource.ThrowIfDisposed();
}
// Remove the entry from the array.
// This call includes a full memory fence which prevents potential reorderings of the reads below
bool deregisterOccured = TryDeregister();
// We guarantee that we will not return if the callback is being executed (assuming we are not currently called by the callback itself)
// We achieve this by the following rules:
// 1. if we are called in the context of an executing callback, no need to wait (determined by tracking callback-executor threadID)
// - if the currently executing callback is this CTR, then waiting would deadlock. (We choose to return rather than deadlock)
// - if not, then this CTR cannot be the one executing, hence no need to wait
//
// 2. if deregistration failed, and we are on a different thread, then the callback may be running under control of cts.Cancel()
// => poll until cts.ExecutingCallback is not the one we are trying to deregister.
if (m_tokenSource != null &&
m_tokenSource.IsCancellationRequested && //running callbacks has commenced.
!m_tokenSource.IsCancellationCompleted && //running callbacks hasn't finished
!deregisterOccured && //deregistration failed (ie the callback is missing from the list)
m_tokenSource.ThreadIDExecutingCallbacks != Thread.CurrentThread.ManagedThreadId) //the executingThreadID is not this threadID.
{
// Callback execution is in progress, the executing thread is different to us and has taken the callback for execution
// so observe and wait until this target callback is no longer the executing callback.
m_tokenSource.WaitForCallbackToComplete(m_callbackInfo);
}
}
