private static CancellationTokenHelper GetStaticDisposedHelper()
{
CancellationTokenHelper helper = new CancellationTokenHelper(false);
helper.Dispose();
return(helper);
}
private static CancellationTokenHelper GetStaticDisposedHelper() {
CancellationTokenHelper helper = new CancellationTokenHelper(false);
helper.Dispose();
return helper;
}
internal bool TryGetClientDisconnectedCancellationToken(out CancellationToken cancellationToken) {
// This API is not supported on IIS versions prior to IIS 7.5.
if (HttpRuntime.IISVersion < IIS_VERSION_75) {
cancellationToken = CancellationToken.None;
return false;
}
// The registration is done inside of the dispose lock because we don't want to
// allow registration while the native context object is being destroyed. If we
// didn't have this lock, there is a potential race condition where the
// registration could take place at the same time as a call to Dispose, at which
// point we lose our guarantees about the unmanaged code not trying to call back
// into this AppDomain.
//
// If you change the below code, be judicious with how much work is performed
// within the lock on _disposeLockObj. The p/invoke call that takes place within
// the lock will itself try to enter a critical section in the class
// MGD_CONNECTION_STORED_CONTEXT, and this could very easily lead to deadlock
// scenarios. The particular usage below is safe because the _disposeLockObj
// lock is always taken before entering the unmanaged critical section, never
// the other way around. So code that is within the unmanaged critical section
// is guaranteed to execute quickly without blocking.
if (_clientDisconnectTokenHelper == null) {
lock (_disposeLockObj) {
if (_clientDisconnectTokenHelper == null) {
if (_context == IntPtr.Zero) {
// A call to Dispose already took place, so we'll just return a pre-disposed helper.
_clientDisconnectTokenHelper = CancellationTokenHelper.StaticDisposed;
}
else {
bool isClientConnected;
int hr = IIS.MgdConfigureAsyncDisconnectNotification(_context, true /* fEnabled */, out isClientConnected);
Marshal.ThrowExceptionForHR(hr);
// Seed the helper's initial state with the known client connection status.
// Pay attention to the race condition mentioned in NotifyOfAsyncDisconnect.
LazyInitializer.EnsureInitialized(ref _clientDisconnectTokenHelper, () => new CancellationTokenHelper(canceled: !isClientConnected));
}
}
}
}
cancellationToken = _clientDisconnectTokenHelper.Token;
return true;
}
