private static SuspendState SuspendImpl(ICollection<ISuspendibleRegisteredObject> allRegisteredObjects) {
            // Our behavior is:
            // - We'll call each registered object's suspend method serially.
            // - All methods have a combined 5 seconds to respond, at which
            //   point we'll forcibly return to our caller.
            // - If a Resume call comes in, we'll not call any Suspend methods
            //   we haven't yet gotten around to, and we'll execute each
            //   resume callback we got.
            // - Resume callbacks may fire in parallel, even if Suspend methods
            //   fire sequentially.
            // - Resume methods fire asynchronously, so other events (such as
            //   Stop or a new Suspend call) could happen while a Resume callback
            //   is in progress.

            CountdownEvent countdownEvent = new CountdownEvent(2);
            SuspendState suspendState = new SuspendState(allRegisteredObjects);

            // Unsafe QUWI since occurs outside the context of a request.
            // We are not concerned about impersonation, identity, etc.

            // Invoke any registered subscribers to let them know that we're about
            // to suspend. This is done in parallel with ASP.NET's own cleanup below.
            if (allRegisteredObjects.Count > 0) {
                ThreadPool.UnsafeQueueUserWorkItem(_ => {
                }, null);
            else {
                countdownEvent.Signal(); // nobody is subscribed

            // Release any unnecessary memory that we're holding on to. The GC will
            // be able to reclaim these, which means that we'll have to page in less
            // memory when the next request comes in.
            ThreadPool.UnsafeQueueUserWorkItem(_ => {
                // Release any char[] buffers we're keeping around

                // Trim expired entries from the runtime cache
                var cache = HttpRuntime.GetCacheInternal(createIfDoesNotExist: false);
                if (cache != null) {

                // Trim all pooled HttpApplication instances
                HttpApplicationFactory.TrimApplicationInstances(removeAll: true);

            }, null);

            if (Debug.IsDebuggerPresent()) {
                countdownEvent.Wait(); // to assist with debugging, don't time out if a debugger is attached
            else {
                countdownEvent.Wait(_suspendMethodTimeout); // blocking call, ok for our needs since has finite wait time
            return suspendState;
 protected override void CreateStates()
     StatePreRun = new PreRunState(this);
     StateRun = new RunState(this);
     StatePreStop = new PreStopState(this);
     StateStop = new StopState(this);
     StatePreInitialize = new PreInitializeState(this);
     StateInitialize = new InitializeState(this);
     StateRundown = new RundownState(this);
     StatePreEmergency = new PreEmergencyState(this);
     StateEmergency = new EmergencyState(this);
     StateEmergencyReset = new EmergencyResetState(this);
     StatePreAlarm = new PreAlarmState(this);
     StateAlarm = new AlarmState(this);
     StatePreWarning = new PreWarningState(this);
     StateWarning = new WarningState(this);
     StatePreSuspend = new PreSuspendState(this);
     StateSuspend = new SuspendState(this);