System.Net.TimerThread.TimerNode.Fire C# (CSharp) Method

            internal bool Fire()
            {
                if (_timerState == TimerState.Sentinel)
                {
                    if (NetEventSource.IsEnabled) NetEventSource.Info(this, "TimerQueue tried to Fire a Sentinel.");
                }

                if (_timerState != TimerState.Ready)
                {
                    return true;
                }

                // Must get the current tick count within this method so it is guaranteed not to be before
                // StartTime, which is set in the constructor.
                int nowMilliseconds = Environment.TickCount;
                if (IsTickBetween(StartTime, Expiration, nowMilliseconds))
                {
                    if (NetEventSource.IsEnabled) NetEventSource.Info(this, $"TimerThreadTimer#{StartTime}::Fire() Not firing ({StartTime} <= {nowMilliseconds} < {Expiration})");
                    return false;
                }

                bool needCallback = false;
                lock (_queueLock)
                {
                    if (_timerState == TimerState.Ready)
                    {
                        if (NetEventSource.IsEnabled) NetEventSource.Info(this, $"TimerThreadTimer#{StartTime}::Fire() Firing ({StartTime} <= {nowMilliseconds} >= " + Expiration + ")");
                        _timerState = TimerState.Fired;

                        // Remove it from the list.
                        Next.Prev = Prev;
                        Prev.Next = Next;

                        Next = null;
                        Prev = null;
                        needCallback = _callback != null;
                    }
                }

                if (needCallback)
                {
                    try
                    {
                        Callback callback = _callback;
                        object context = _context;
                        _callback = null;
                        _context = null;
                        callback(this, nowMilliseconds, context);
                    }
                    catch (Exception exception)
                    {
                        if (ExceptionCheck.IsFatal(exception))
                            throw;

                        if (NetEventSource.IsEnabled) NetEventSource.Error(this, $"exception in callback: {exception}");

                        // This thread is not allowed to go into user code, so we should never get an exception here.
                        // So, in debug, throw it up, killing the AppDomain.  In release, we'll just ignore it.
#if DEBUG
                        throw;
#endif
                    }
                }

                return true;
            }
        }